US20100183818A1

US20100183818A1 - Apparatus and method of depositing films using bias and charging behavior of nanoparticles formed during chemical vapor deposition

Info

Publication number: US20100183818A1
Application number: US12/440,304
Authority: US
Inventors: Nong-Moon Hwang; Chan-soo Kim; Jae-Ik Lee; Yung-Bin Chung; Woong-kyu Youn
Original assignee: Seoul National University Industry Foundation
Current assignee: Seoul National University Industry Foundation
Priority date: 2006-09-06
Filing date: 2007-09-06
Publication date: 2010-07-22
Also published as: WO2008030047A1

Abstract

Provided are an apparatus and a method of depositing films capable of controlling deposition rate and film properties using the charging behavior of nanoparticles formed in gas phase. The apparatus includes a chamber in which a substrate is loaded, a gas supply system configured to introduce a reaction gas into the chamber, a filament configured to emit heat for dissociating the introduced reaction gas, a power supply configured to apply a constant alternate current or direct current voltage, and a bias supply unit configured to apply a bias to at least one of a top, a side and a bottom of the substrate using a voltage applied from the power supply while a film is deposited on the substrate from the dissociated reaction gas, the bias supply unit being separated from the substrate.

Description

TECHNICAL FIELD

The present disclosure relates to a method of depositing films using the charging behavior of nanoparticles formed during chemical vapor deposition, and more particularly, to an apparatus and a method of depositing films capable of increasing deposition rate and controlling film properties using the charging behavior of nanoparticles formed in gas phase.

BACKGROUND ART

Film deposition using chemical vapor deposition (CVD) has a limitation in that it is difficult to effectively satisfy demands for increasing deposition rate and improving film properties at the same time in spite of the increase in energy applied to a reaction material.
It was difficult to simultaneously achieve the increase of film deposition rate and the improvement of film properties by varying reaction conditions in CVD process, causing difficulties in satisfying both price and quality. The reason is that it was short of a definitive understanding of a film deposition mechanism by CVD. For instance, it was insufficient to understand the reason why film deposition rates and properties of deposited films are different according to kinds of substrates, that is to say, according to an electrical conductive substrate such as a stainless substrate or an electrical insulation substrate such as a glass substrate and a silicon wafer, even under the same process conditions.
Of many theories for facilitating to understand the deposition mechanism of CVD process, it is possible to explain the deposition behavior of films by understanding nanoparticles formed in gas phase as deposition units and their characteristics, which differs from a typical theory that deposition units are thought to be either an atom or a molecule.
In particular, if characteristics of the nanoparticles can change by a new method of applying a bias during deposition of generated nanoparticles, the new method is capable of controlling the film properties as well as the film deposition rate.
Accordingly, it is necessary to develop a new technology of forming films, which can increase a film deposition rate and control film properties by controlling the deposition behavior of nanoparticles generated in CVD and the generation behavior using characteristics of the nanoparticles.

DISCLOSURE

Technical Problem

To satisfy both demands for increase in film deposition rate and improvement in film properties at a time, there is required a method capable of separating a generation step of nanoparticles in gas phase and a deposition step of the generated nanoparticles and separately controlling each step. In addition, there is also required an apparatus of depositing films, which can be used in implementing this method.

Technical Solution

A step-by-step control technology for film deposition is realizable from the understanding about characteristics of nanoparticles formed in gas phase. It has been regarded that a conventional film deposition was performed with a deposition material in units of an atom formed in gas phase. Therefore, a technology where a generation step of deposition units for a deposition film and a deposition step of the deposition units can be separately controlled has not been considered yet.
Accordingly, the present disclosure suggests a technology capable of controlling film deposition by separating a generation step of nanoparticles, i.e., deposition unit of the films, and a deposition step of the generated deposition units based on a new paradigm for the deposition units.
The present disclosure provides a technology of forming films by respectively controlling a generation step of nanoparticles and a deposition step of the generated nanoparticles using the charged behavior of nanoparticles formed in gas phase, and thus provides a method and an apparatus of depositing films, which can improve deposition rate and control film properties.
The present disclosure also provides a technology of controlling the charged behavior of nanoparticles, which are deposition units of films, formed in gas phase.
The present disclosure also provides a technology of controlling the deposition behavior by application of an electrical bias affecting the charged behavior of nanoparticles, deposition units, formed in gas phase.
The present disclosure also provides a method capable of improving deposition rate and controlling film properties.
According to an exemplary embodiment, an apparatus of depositing films, includes: a chamber in which a substrate is loaded; a gas supply system configured to introduce a reaction gas into the chamber; a filament configured to emit heat for dissociating the introduced reaction gas; a power supply configured to apply a constant alternate current (AC) or direct current (DC) voltage; and a bias supply unit configured to apply a bias to at least one of a top, a side and a bottom of the substrate using a voltage applied from the power supply while a film is deposited on the substrate from the dissociated reaction gas, the bias supply unit being separated from the substrate.
According to another exemplary embodiment, an apparatus of depositing films, includes: a chamber in which a substrate is loaded and a pressure is maintained at an atmospheric pressure, a low pressure or a high pressure; a gas supply system configured to introduce a reaction gas into the chamber; a heating element configured to emit heat for dissociating the introduced reaction gas; and a bias supply device configured to apply an electric field to the substrate.
According to yet another exemplary embodiment, a method of depositing films, includes: loading a substrate in the chamber and introducing a reaction gas; dissociating the reaction gas; triggering nucleation in the dissociated reaction gas; forming a charged nanoparticle through growth of a nanoparticle generated from the nucleation; and applying a bias to the substrate to deposit a film by drawing the charged nanoparticle toward the substrate.
The method of depositing films may be performed using a film deposition apparatus according to exemplary embodiments, and alternatively the method may be performed using another film deposition apparatus modified from a typical chemical vapor deposition (CVD) apparatus, a hot-filament chemical vapor deposition (HFCVD) apparatus, a plasma CVD apparatus, a metal-organic chemical vapor deposition (MOCVD) apparatus, or other apparatuses of forming films where charged nanoparticles are generated.
The charged nanoparticle may be formed in gas phase by adjusting a dissociation degree of the reaction gas, and an electrical polarity ratio between positively and negatively charged nanoparticles may be controlled.
A mixed gas of silane and hydrogen may be used as the reaction gas, and at least one of a fraction and a size of the nanoparticle charged in gas phase may change by increasing at least one selected from a dissociation temperature of the reaction gas, a fraction of the silane in the mixed gas and a pressure of the mixed gas.
The bias may be applied to a top of the substrate to thereby change an electrical polarity ratio of the nanoparticle to be deposited, by changing the charge amount of the nanoparticle before the nanoparticles are deposited on the substrate.
A film deposition may be divided into a nucleation and a growth, and an electrical polarity ratio of nanoparticles to be deposited may change by changing at least one of a fraction and a size of the nanoparticle charged in gas phase in each of the nucleation and the growth and changing the charge amount of the nanoparticles before the nanoparticles are deposited on the substrate.
There is provided a film deposition technology associated with the charged behavior of nanoparticles, i.e., deposition units of films, formed in gas phase, or to the control of the charged behavior.

ADVANTAGEOUS EFFECTS

According to exemplary embodiments, the generation behavior of nanoparticles, which are charged neutrally, negatively or positively by reaction gas, can be controlled by varying reaction conditions of the reaction gas. At the same time, the deposition behavior can also be separately controlled by applying a bias to a substrate in consideration of the charged behavior of the charged nanoparticles, independently of the generation behavior. Accordingly, it is possible to control film deposition rate and improve structural properties of films. That is, it is possible to control properties of a film texture as well as a film deposition rate by controlling nanoparticles to selectively participate in the film deposition according to the charged behavior of the nanoparticles, through the control of electrostatic properties of deposition sources charged in gas phase, the control of attractive or repulsive force between the charged deposition sources according to a bias applied to a periphery of the substrate, and the control of deposition behavior according to a difference in electrical conductivity of a substrate.
In addition, it is possible to control the deposition behavior of thin films and thick films upon an electrically insulating substrate such as ceramic substrate through which an electrical bias does not pass and a plastic substrate requiring a low reaction temperature as well as an electrically conductive substrate, by separating a bias supply unit from the substrate and applying the electrical bias to the substrate from a detached position. As such, the deposition behavior of thin films can be effectively controlled by virtue of the improvement of the bias application.
Furthermore, the control of the deposition behavior can make it possible to deposit films having uniform texture, thus contributing to reduction in haze of the thin films, reduction in formation of voids, improvement in surface roughness, and improvement in degree of crystallinity.
Particularly, contrary to a related art film deposition process where film deposition is performed without a secondary process upon deposition units formed in gas phase, exemplary embodiments can provide such an advantageous merit that a variety of materials can be used as a substrate by selectively depositing some deposition units, i.e., nanoparticles, of which charged behavior differs than that of other deposition units. Further, according to exemplary embodiment, it is possible to control film properties and film deposition rate depending on the charged behavior of various materials generated in gas phase.

DESCRIPTION OF DRAWINGS

Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating an apparatus of measuring charged nanoparticles formed in gas phase and controlling the generation of the nanoparticles, which is available in implementing embodiments;

FIG. 2 is a schematic view illustrating an apparatus of depositing films according to an exemplary embodiment;

FIGS. 3A and 3B are views of a bias supply unit configured to apply an electrical bias to a substrate during film deposition according to the exemplary embodiment;

FIG. 4 is a schematic view illustrating the case that the bias is applied to a top of the substrate during the deposition process according to the exemplary embodiment;

FIG. 5 is a flowchart illustrating a method of depositing films according to exemplary embodiments;

FIGS. 6( a) through 6(c) are schematic views illustrating deposition behaviors caused by interactions between a polarity of a bias applied to the substrate and polarities of charged nanoparticles in the method of depositing films according to the exemplary embodiments;

FIG. 7 is a schematic view of an apparatus of depositing films according to another exemplary embodiment;

FIGS. 8( a) through 8(c) are photographs illustrating a bias supply device of experimental examples, which is included in the deposition apparatus of FIG. 7;

FIG. 9 is a schematic view illustrating a bias supply device having an alternative structure included in the deposition apparatus of FIG. 7;

FIG. 10 is a schematic view of an apparatus of depositing films according to still another exemplary embodiment;

FIGS. 11A and 11B are graphs illustrating number concentration of charged nanoparticles versus particle size, which are measured under various reaction conditions;

FIG. 12 is a graph illustrating deposition behaviors according to a concentration of reaction gas and a bias applied to a bottom of a substrate in a method of depositing films using the deposition apparatus of FIG. 2, where the substrate is an electrical conductor;

FIG. 13 is a graph illustrating deposition behaviors according to a concentration of reaction gas and a bias applied to a bottom of a substrate in a method of depositing films using the deposition apparatus of FIG. 2, where the substrate is an electrical insulator;

FIG. 14 is a graph illustrating film properties obtained by the different deposition behaviors of the samples in FIG. 13, which are measured by Raman spectroscopy;

FIG. 15 is a graph illustrating deposition behaviors according to a concentration of reaction gas and a bias applied to a top of a substrate in a method of depositing films using the deposition apparatus of FIG. 2, where the substrate is an electrical insulator;

FIGS. 16A through 16C are schematic views illustrating a method of applying a bias in experimental examples of a method of depositing films using the deposition apparatus of FIG. 7;

FIG. 17 illustrates field emission-scanning electron microscope (FE-SEM) images comparing thicknesses of the experimental examples of FIGS. 16A through 16C with that of a comparative example in the case where the substrate is an electrical insulator;

FIG. 18 is a graph illustrating a deposition thickness and a deposition rate per second for each of the samples of FIG. 17 in the case where the substrate is an electrical insulator; and

FIG. 19 is a graph illustrating film properties obtained by the comparative example and the experimental examples of FIGS. 16A through 16C, which are measured by Raman spectroscopy.

MODE FOR INVENTION

Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, shapes of elements are exaggerated for emphasizing definite explanation. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. FIG. 1 illustrates an example of an apparatus of measuring nanoparticles, which is adapted to measure charged nanoparticles formed in gas phase and control the generation of the nanoparticles under reaction conditions of embodiments, which is available in implementing embodiments.
Referring to FIG. 1, an apparatus 1 of measuring nanoparticles includes a gas supply system 4, an atmospheric pressure chemical vapor deposition (APCVD) chamber 5, a heating element 6, a differential mobility analyzer (DMA) 8 and a Faraday cup electrometer (FCE) 9.
The chamber 5 of FIG. 1 is a horizontal furnace type chamber. Reaction gas flows into the chamber 5 and thermally decomposed. A pressure inside the chamber is maintained at an atmospheric pressure. The chamber 5 is an insulator made of quartz and may have a tubular shape. Examples of a material that used for the heating element 6 may include graphite, silicon carbide (SiC), etc. The heating element 6 may have the shape of a bar, a plate, a coil, and so forth, and the heating element 6 may be provided singularly or in plurality.
The gas supply system 4 for introducing source gas such as reaction gas and carrier gas into the chamber 5 includes a gas pipe 2 and a flow controller 3.
Referring to FIG. 1, the DMA 8 classifies charged particles according to electrical mobility when particles nucleated in gas phase after thermally decomposed in the chamber 5 are charged while they colliding against chamber walls, i.e., surface-ionized. The DMA 8 cannot classify uncharged particles so that it cannot determine a size and a concentration of the uncharged particles. The charged nanoparticles existing in gas phase under an atmospheric pressure or a low pressure inside the chamber 5 are measured from the atmospheric pressure DMA and the low pressure DMA. The classified charged particles move to the FCE 9 so that the charged particles corresponding a voltage intentionally applied from the outside are measured as a current. The applied voltage determines a size of the charged nanoparticle, and the charged current value is converted into a concentration of the charged nanoparticle.
As described above, the apparatus 1 of measuring nanoparticles can control the amount of the neutrally, negatively or positively charged nanoparticles which are formed in gas phase during film deposition by changing reaction conditions. Therefore, the apparatus 1 of measuring nanoparticles is available in controlling the generation of nanoparticles in gas phase suitable for deposition purpose according to kinds of deposition material and substrate.

Embodiment 1

FIG. 2 illustrates an apparatus of depositing films according to an exemplary embodiment.
Referring to FIG. 2, a hot-filament or hot-wire CVD (HFCVD or HWCVD) apparatus 10, an apparatus of depositing films, includes a gas supply system 20, a filament 30, a substrate 40 on which a thin film is formed, a cooler 50 configured to cool the substrate 40, a substrate holder 60, a power supply 70, and a bias supply unit 80. The gas supply system 20 is configured with a gas pipe and a gas flowmeter, and supplies source gas such as reaction gas into a chamber 15 of the HFCVD apparatus 10. The filament 30 is configured to emit heat so as to dissociate the reaction gas introduced into the chamber 15. The substrate holder 60 is capable of adjusting a distance between the substrate 40 and the filament 30 using, for example, an adjustment screw. The power supply 70 is capable of applying a constant alternative current (AC) voltage or a constant direct current (DC) voltage. The bias supply unit 80 is configured to apply a bias to a top, a side or a bottom of the substrate 40. The bias supply unit 80 is separated from the substrate 40, and applies an electrical bias to a periphery of the substrate 40 during deposition process. For instance, FIG. 2 illustrates the bias supply unit 80 designed to apply the bias to the bottom of the substrate 40.
By using the HFCVD apparatus 10, it is possible to deposit one of a silicon film, a carbon nanotube and a nanowire in the method of depositing films according to the exemplary embodiment. Particularly, in the case of the silicon film, it is possible to deposit one of a single crystalline silicon film, an amorphous silicon film and a poly crystalline silicon film through epitaxial growth or another kind of growth mechanism.
In the HFCVD apparatus 10, a graphite heating element or a metal heating element is used as the filament 30 for dissociating the reaction gas at a high temperature. Specifically, the filament 30 may be formed of tungsten (W), rhenium (Re), molybdenum (Mo), rhodium (Rh), platinum (Pt), tantalum (Ta), iridium (Ir) or a combination thereof. In addition, the filament may be realized with other heating elements of various materials. The filament 30 may have the shape of a single wire, a twisted wire or other shapes. The filament 30 may be provided singularly or in plurality.
The introduced reaction gas, which is dissociated by the high temperature filament 30, includes silane compound expressed as Si_nH_2n+2(n is a positive integer) as major gas in the case of depositing a silicon film. Specifically, the silane compound for the reaction gas may include monosilane, disilane, trisilane, tetrasilane, etc. For easy handling, the silane compound for use in the reaction gas may be monosilane, disilane, trisilane or a combination thereof. However, the reaction gas is not limited the above-listed one. Thus, the reaction gas may include fluorosilane, chlorosilane, organic silane, germane, germanium fluoride, hydrocarbon gas, or other hydrocarbon compounds. In detail, examples of the fluorosilane expressed as SiH_2n+2−mF_m(n is a natural number and m is an integer of 0 or more, where m<2n+2) may be SiH₃Cl, SiH₂Cl₂, SiHCl₃, SiCl₄, Si₂Cl₆, Si₂HCl₅or Si₃Cl₈. Examples of the chlorosilane expressed Si_nH_2n+2−mCl_m(n is a natural number and m is an integer of 0 or more, where m<2n+2) may be SiH₃Cl, SiH₂Cl₂or SiHCl₃, SiCl₄, Si₂Cl₆, Si₂HCl₅, or Si₃Cl₈. Examples of the organic silane expressed as Si_nR_2n+2−mH_mmay be Si(CH₃)H₃, Si(CH₃)₂H₂or Si(CH₃)₃H. Examples of the germane expressed as Ge_nH_2n+2may be GeH₄or Ge₂H₆in the case of deposing a germanium film. Examples of the germanium fluoride expressed as Ge_nH_2n+2−mF_mmay be GeF₄and the like. Examples of the hydrocarbon gas may be methane (CH₄), ethane (C₂H₆), propane (C₃H₈), ethylene (C₂H₄), acetylene (C₂H₂), and so forth.
Although such reaction gas may be used by itself, silane compound gas may be used as being diluted by adding supporting gas. Herein, the supporting gas may include: a reactive gas such as hydrogen, fluorine and chlorine gas; a gas containing a Group Iii element as a dopant, for example, diborane (B₂H₆) gas and trimethylboron (B(CH₃)₃) gas, or a gas containing a Group V element as a dopant, for example, phosphine (PH₃) gas; and an inert gas such as helium, argon and neon; nitrogen gas. A dilution ratio of the silane compound to the added gas may be in the range of approximately 0.1% to approximately 100% by volume percent. Taking into account of an actual semiconductor film-forming rate, the dilution ratio may be approximately 1% or more.
Though a flow rate of the reaction gas may be in the range of approximately 1 sccm to approximately 1,000 sccm, and an internal pressure of the chamber 15 may be in the range of approximately 5 mTorr to approximately 760 Torr, the flow rate and the internal pressure of the chamber may be appropriately selected depending on the film-forming rate.
In performing a method of depositing films using the HFCVD apparatus 10 according to the exemplary embodiment, the bias supply unit 80 may be formed of a conductive material, particularly metal, of which electrical conductivity may be in the range of approximately 1,000 to approximately 10⁷(Ω·cm)⁻¹. The substrate 40 and the bias supply unit 80 may have an area ranging from approximately 1 to approximately 120,000 cm². The bias supply unit 80 may have a larger size than the substrate 40, but may change its size depending on deposition purposes.
The bias supply unit 80 may be shaped as a plate structure illustrated in FIG. 3A or a mesh structure illustrated in FIG. 3B. Alternatively, the bias supply unit 80 may have a tubular shape. As illustrated in FIG. 2, the bias supply unit 80 may be designed to have the shape of the plate structure of FIG. 3A for applying the bias to the bottom of the substrate 40 on which film deposition is performed. Alternatively, the bias may be applied to the top of the substrate 40, as illustrated in FIG. 4. In this case, the bias supply unit 80 is shaped as the mesh structure of FIG. 3B, and it is positioned on the top of the substrate 40. The mesh type bias supply unit 80 may change its aperture size, shape and installation position depending on deposition purposes. As such, in the apparatus and method of depositing films according to the exemplary embodiment, the bias supply unit 80 applying an electrical bias is separated from the substrate 40, and thus it may positioned over or under the substrate 40. Furthermore, the bias may be applied to the side of the substrate 40 according to circumstances. During the deposition, a polarity of the bias may not be changed, or the polarity of the bias may be alternated periodically or arbitrarily. The method of depositing films according to the embodiment using the HFCVD apparatus 10 will be described with reference to FIGS. 5 and 6.
First, in operation S1, the substrate 40 is loaded into the chamber 15, and reaction gas is introduced.
A temperature of the substrate 40 may be in the range of approximately 293 to 1,200 K. A temperature of the substrate may be in the range of approximately 293 to 773 K in consideration of the heat resistance of the substrate 40 and film properties.
The substrate 40 may include one of a conductive material, a nonconductive material and a plastic. A transparent substrate may include a transparent polymer film substrate as well as a typical glass substrate. Herein, examples of the transparent polymer film substrate may be polyethylene terephthalate (PET), polycarbonate, polyimide (PI) or polyethylenenaphthalate. Examples of the typical glass substrate may be blue plate glass, borosilicate glass, and quartz glass. In addition to a substrate of metal having electrical conductivity and a ceramic substrate, a polymer resin such as cloth and texture are also available. This is ascribed to the fact that it is possible to control the deposition behavior of films upon an electrically insulating substrate such as ceramic substrate through which an electrical bias does not pass and a plastic substrate requiring a low reaction temperature as well as an electrically conductive substrate, by separating the bias supply unit 80 from the substrate 40 and applying the electrical bias to the substrate 40 from a detached position.
Specifically, the substrate 40 may also be provided by forming a metal film such as stainless steel, molybdenum, titanium, silver and aluminum, upon a surface of a metal substrate such as stainless steel, molybdenum, titanium, silver and aluminum, a surface of a glass substrate such as borosilicate glass, blue plate glass and quartz glass, or a surface of a polymer film. A substrate obtained by forming a transparent electrode on the glass substrate, the polymer film and the metal substrate may also be available. Here, the transparent electrode may include, for example, a transparent metal or a metal oxide such as tin oxide, indium oxide and zinc oxide.
As for a thickness of the substrate 40, a glass substrate may have a thickness ranging from approximately 0.5 to approximately 10 mm, a polymer film may have a thickness ranging from approximately 10 to approximately 500 μm, and a metal film or a substrate of metal element may have a thickness ranging from approximately 50 to approximately 50,000 Å. Moreover, when an amorphous semiconductor thin film is deposited on the substrate 40, the film may be formed to a thickness ranging from approximately 10 Å to approximately 10 μm (i.e., 100,000 Å), a film-forming rate may be in the range of approximately 0.1 to approximately 1,000 Å/sec, desirably in the range of approximately 5 to approximately 30 Å/sec.
A mixed gas of silane and helium may be used as the reaction gas for silicon film deposition. Nitrogen gas may be added to the mixed gas of silane and helium and the mixed gas with nitrogen gas added is then introduced into the chamber 15.
Thereafter, in operation S2, the reaction gas is dissociated using the filament 30. The exemplary embodiments described herein are based on the present inventors' new theory for the film deposition. So far, it has been believed that film growth was mainly carried out in units of either an atom or a molecule, and most of developments for thin film processes are advanced on the basis of such a belief. Therefore, a condition of causing a gas-phase nucleation has become a limitation in increasing a deposition rate. To over come such a limitation, it is necessary to establish appropriate conditions where thin films with good quality can grow even under the condition that the nucleation occurs in gas phase. To this end, it has been announced that it is possible to deposit the thin film with good quality at a high deposition rate by making charged clusters, e.g., charged nuclei or nanoparticles (Nong-Moon Hwang, Doh-Yeon Kim, J. Appl. Phys, 79 234. 2003).
Meanwhile, a technique, entitled “Ionized Cluster Beam Deposition (IOCVD)” where charged clusters are intentionally generated, they are accelerated, and they are thus deposited on a deposition target has been developed by Yamada, Tagaki et al. In this technique, however, an adiabatic expansion should be performed to form the clusters and an electron gun should be used for ionizing the clusters. Therefore, a deposition apparatus for realizing this technique must have a complicated structure and further an ionization efficiency of the generated cluster is too low, that is, 30% or lower. In addition, since the clusters were accelerated and deposited according to this technique, a high vacuum level lower than 0.000001 Torr should be maintained.
On the contrary, according to the exemplary embodiment, it is possible to spontaneously generate charged deposition units, i.e., charged nanoparticles or nanoclusters, by dissociating the reaction gas simply using the filament 30, without the use of an additional apparatus for generating the nanoparticles or the nanoclusters.
Afterwards, in operation S3, nucleation occurs in a state of the dissociated reaction gas. Subsequently, in operation S4, the nanoparticles generated during the nucleation are charged due to different work function from the inside of the chamber 115 while the nanoparticles are growing.
In the exemplary embodiments, characteristics of positive or negative charges can also be controlled by adjusting a dissociation degree of the reaction gas. That is, it is possible to control the charge amount and the polarity ratio of the charged nanoparticles according to circumstances. As a relative ratio between the positively and negatively charged nanoparticles changes, a correlation with the charged behavior of the charged nanoparticles affected by the relative ratio can be controlled, thus adjusting deposition rate and film properties.
Specifically, a mixed gas of silane and hydrogen is used as the reaction gas. In this case, it is possible to change at least one of a fraction and sizes of silicon nanoparticles charged in gas phase by increasing at least one selected from a dissociation temperature of the reaction gas (i.e., temperature of the filament 30), a fraction of silane in the mixed gas and a pressure of the chamber 15 caused by the mixed gas.
For example, the dissociation degree of the reaction gas depends on the temperature of the filament 30. As the temperature of the filament 30 increases, the dissociation degree of the reaction gas increases. Such an increase in the temperature of the filament 30 changes the dissociation degree of the reaction gas, which changes electrostatic properties of deposition unit particles based on the present inventors'⊚ new deposition theory. In the case of depositing a silicon thin film, the relative ratio of the negatively charged particles becomes higher than that of the positively charged particles as the temperature of the filament 30 increases. The increase in the dissociation degree of the reaction gas according to the temperature control of the filament 30 and the related improvement of the thin film properties differ from the dissociation degree of the reaction gas in a related art method of using plasma.
In other words, the method of depositing films according to the exemplary embodiment includes controlling the generation behavior associated with charged characteristics such as size, number concentration, charge amount and charge ratio of the charged nanoparticles formed in gas phase by adjusting process parameters, e.g., reaction temperature, the amount of reaction gas, reaction pressure, in CVD process.
The electrostatic characteristic caused by the charge amount of the charged nanoparticles is removed at or accumulated on the surface of the substrate 40 according to the electrical conductivity of the substrate 40, which changes an interaction behavior between the substrate 40 and the charged nanoparticles depending on the polarities of the charged nanoparticles successively deposited. Since the electrostatic characteristic caused by the charge amount of the charged nanoparticles is removed at the surface of the substrate 40 if the substrate 40 has a high electrical conductivity, the nanoparticles deposited on the substrate 40 do not have an effect on nanoparticles to be deposited later. However, an attractive force or a repulsive force is exerted on nanoparticles to be deposited later because the electrostatic characteristic caused by the charge amount of the charged nanoparticles is accumulated on the surface of the substrate 40 if the substrate has a low electrical conductivity or is an insulator. Change in deposition behaviors according to the electrical conductivity of the substrate 40 will be more fully described in experimental examples later.
In operation S5, the bias supply unit 80 applies a bias to the substrate 40 to draw the charged nanoparticles toward the substrate 40, thus depositing a film. The deposition behavior is controlled by continuously or alternately applying a positive or negative bias. That is, the deposition rate of the charged nanoparticles and the related structural characteristics of thin films are controlled by selectively taking positively or negatively charged nanoparticles through bias application during deposition process. The method of depositing films according to the exemplary embodiments may be performed under the condition that a voltage of the power supply 70 is in the range of approximately +1,000 V to approximately −1,000 V, and DC or AC with a frequency ranging from approximately 0.01 Hz to approximately 10 kHz may be applied.
The method of depositing films according to the exemplary embodiments includes controlling the deposition behavior of the charged nanoparticles using electric field intensity and a polarity change through a bias unit (e.g., the bias supply unit 80 in this embodiment).
For example, by applying a bias to the top of the substrate 40, an electrical polarity ratio of nanoparticles to be deposited may be changed before the nanoparticles are deposited on the substrate 40. A method of controlling deposition behaviors of charged nanoparticles according to a position of the bias supply unit 80 will be more fully described in experimental examples below. The thin film deposition is divided into two steps, i.e., nucleation and growth. The electrical polarity ratio of the nanoparticles to be deposited may be changed by varying at least one of a fraction and sizes of the charged nanoparticles in each step, and varying the charge amount of the nanoparticle before the nanoparticles are deposited on the substrate 40. For example, it is possible to decrease the fraction and the sizes of the nanoparticles in an initial step of the film deposition, i.e., in the nucleation step, and to increase the fraction and the size of the nanoparticle in the growth step, and vice versa. The positively charged nanoparticles to be deposited may be dominant in the nucleation step and the negatively charged nanoparticles to be deposited may be dominant in the growth step, and vice versa.
FIGS. 6( a) through 6(c) are schematic views illustrating deposition behaviors caused by interactions between a polarity of a bias applied to the substrate and polarities of charged nanoparticles in the method of depositing films according to the exemplary embodiments.
Referring to FIG. 6( a), when a positive bias, e.g., +150 V, is applied to the conductive substrate 40 in the case that the charged nanoparticles 90 have negative polarities, the deposition rate increases because the nanoparticles 90 are drawn toward the substrate 40 due to an attractive force. Referring to FIG. 6( b), when a bias is not applied to the conductive substrate 40, the deposition rate is equal to that of the related art irrespective of whether the charged nanoparticles have positive or negative polarities. Referring to FIG. 6( c), however, when a negative bias, e.g., −150 V, is applied to the conductive substrate 40 in the case that the charged nanoparticles 90 have negative polarities, the deposition rate is too low because the nanoparticles 90 are repulsed from the substrate 40 due to a repulsive force. As such, the deposition rate can be controlled by applying the bias to the substrate 40, making it possible to control the structural characteristics of the deposited thin film.
In the method of depositing films according to the exemplary embodiments, the generation behavior of nanoparticles charged by reaction gas can be controlled by varying reaction conditions of the reaction gas. At the same time, the deposition behavior can also be separately controlled by applying a bias to a substrate in consideration of the charged behavior of the charged nanoparticles, independently of the generation behavior. Since the bias supply unit 80 applying the electrical bias is separated from the substrate 4, the bias supply unit 80 can be disposed on the top or the side of the substrate 40 as well as the bottom of the substrate 40 so that it is possible to effectively control the deposition behavior. This separation of the bias supply unit 80 from the substrate 40 makes it possible to control the deposition behavior of thin films and thick films upon an electrically insulating substrate such as ceramic substrate through which an electrical bias does not pass and a plastic substrate requiring a low reaction temperature as well as an electrically conductive substrate. Furthermore, the control of the deposition behavior can make it possible to deposit films having uniform texture, thus contributing to reduction in haze of the thin films, reduction in formation of voids, improvement in surface roughness, and improvement in degree of crystallinity.
The deposition rate of the charged nanoparticles and the related structural characteristics of thin films are controlled by selectively taking positively or negatively charged nanoparticles through bias application during deposition process. For example, when depositing silicon films, because the charged crystalline silicon nanoparticles move to a region under the effect of the bias at a high flow rate, it is possible to obtain a crystalline silicon film with low impurity content, high degree of crystallinity and high deposition rate as well.
Besides the HFCVD apparatus 10, the method of depositing films as described above may be implemented using another apparatus of depositing films that falls within a scope of the present invention, in which a unit of dissociating the reaction gas and a unit of applying a bias to the substrate are employed. The apparatus of depositing films, which is available in realizing the method, may include an HFCVD apparatus, a plasma CVD apparatus, and an atmospheric pressure CVD (APCVD) apparatus.

Embodiment 2

FIG. 7 illustrates an apparatus of depositing films according to another exemplary embodiment.
Referring to FIG. 7, an APCVD apparatus 110, an apparatus of depositing films, according to this exemplary embodiment includes a chamber 115, a gas supply system 120, a heating element 130 and a bias supply device 190.
The APCVD apparatus 110 of FIG. 7 is a horizontal furnace type apparatus. In the chamber 115 of the APCVD apparatus 110, reaction gas is horizontally supplied and exhausted, and a substrate 140 is loaded. The internal pressure of the chamber 115 is maintained at an atmospheric pressure. The chamber 115 may be formed of quartz and shaped as a tube.
The gas supply system 120 introduces source gas such as reaction gas and carrier gas into the chamber 115, and includes a gas pipe and a gas flowmeter. The heating element 130 is configured to emit heat so as to dissociate the reaction gas introduced into the chamber 115. Examples of a material that may be used for the heating element may be graphite, SiC, etc. The heating element 130 may have the shape of a bar, a plate, a coil, and so on. The heating element 130 may be provided singularly or in plurality. The heating element 130 shown in FIG. 7 is a bar-shaped SiC heating element. For instance, six bar-shaped SiC heating elements may be radially disposed around the chamber 115.
The bias supply device 190 of the APCVD apparatus 110 according to this exemplary embodiment is disposed over or under the substrate 140 and applies a bias to the substrate 140 from a detached position. Specifically, the bias supply device 190 includes a first plate 170 disposed over the substrate 140, a second plate 175 disposed under the substrate 140 and facing the first plate 170, a ground unit 180 connected to the first plate 170 through a line 171, and a power supply connected to the second plate 175 through a line 176.
The ground unit 180 and the power supply 185 are disposed outside the chamber 115. The substrate 140 is placed on a surface of the second plate 175, which is opposite to the first plate 170. A recess R is provided in the second plate 175 to settle the substrate 140. The first plate 170 is grounded because it is connected to the ground unit 180. The power supply 185 applies a constant AC or DC voltage to the second plate 175, and applies a bias to the substrate 140 from a detached position thereunder.
A voltage of the power supply 185 is in the range of approximately +1,000 V to approximately −1,000 V, and a DC or an AC having a frequency ranging from approximately 0.01 Hz to approximately 10 kHz may be applied. The first and second plates 170 and 175 may be formed of a conductive material, particularly metallic material. The first and second plates 170 and 175 may have larger sizes than the substrate 140, and may change their sizes depending on deposition purpose.
FIGS. 8( a) through 8(c) are photographs of a bias supply device used in following experimental examples, showing the first plate 170, the second plate 175 and lines 171 and 176 for connecting the first and second plates 170 and 175 to the ground unit and the power supply. The first and second plates 170 and 175 were prepared to have a plate structure of SUS material. In particular, FIG. 8( c) illustrates a top surface of the second plate 175 where a recess R is provided for settling the substrate 140.
FIG. 9 is a schematic view of a bias supply device having alternative structure included in the deposition apparatus of FIG. 7. Referring to FIG. 9, a recess R⊚ for settling the substrate 140 is provided in a surface of the first plate 170, which is opposite to the second plate 175. The substrate 140 is received in the recess R⊚ The power supply 185 and the ground unit 180 are connected to the first plate 170 and the second plate 175, respectively. In the bias supply device 190, a bias is applied to the substrate 140 from a detached position thereabove. The bias supply device may apply the bias to the substrate 140 from a detached position thereabove or thereunder. One of the first and second plates 170 and 175 is connected to the ground unit 180, and the other is connected to the power supply 185.
In the APCVD apparatus 110, nucleated and grown nanoparticles may be positively or negatively charged due to a different work function from the inside of the chamber through bipolar charging mechanism. The bias supply device 190 draws the charged nanoparticles toward the substrate 140. The carrier gas, e.g., nitrogen gas, introduced by the gas supply system 120 facilitates the charged nanoparticles to move toward the bias supply device 190. The movement rate of the charged nanoparticles can be controlled by adjusting a flow rate of the carrier gas through a gas flowmeter. The charged nanoparticles arriving at the bias supply device 190 are forced to move toward the substrate 140 so that the nanoparticles are deposited on the substrate 140.
As described above, since the apparatus of depositing films according to this exemplary embodiment can apply a bias to the substrate during film deposition, the crystallized and charged nanoparticles are drawn toward the substrate and then deposited on the substrate, which makes it possible to improve the deposition rate and control the degree of crystallinity as well. Accordingly, it is possible to obtain a crystalline silicon film in as-depo state, which is a peculiar effect resulted from the aforementioned method of depositing films where the deposition of the crystalline silicon film is accomplished without additional recrystallization step unlike the related art.

Embodiment 3

FIG. 10 illustrates an apparatus of depositing films according to still another exemplary embodiment.
Referring to FIG. 10, an APCVD apparatus 210, an apparatus of depositing films, according to this exemplary embodiment includes a chamber 215, a gas supply system 120, a heating element 130 and a bias supply device 190′. Like reference numerals in FIG. 10 denote like elements of FIG. 7, and thus their description will be omitted herein.
The APCVD apparatus 210 of FIG. 10 is a vertical furnace type apparatus in which the reaction gas is vertically supplied and exhausted.
The bias supply device 190′ is configured to apply a bias to the substrate from a detached position thereunder. Specifically, the bias supply device 190′ includes a first plate 170′ disposed over the substrate 140, a second plate 175 disposed under the substrate 140 and facing the first plate 170′ a ground unit 180 connected to the first plate 170′ through a line 171, and a power supply 185 connected to the second plate 175 through a line 176.
While the charged nanoparticles move downward along the flow direction of carrier gas, they may encounter the first plate 170′. Therefore, the first plate 170′ may have a mesh shape such that the charged nanoparticles can pass therethrough. Depending on the deposition purpose, it is possible to use the first plate 170′ by varying an aperture size, shape and installation position of the mesh.
Although FIG. 10 exemplarily illustrates that the ground unit 180 and the power supply 185 are provided below the chamber 215, the ground unit 180 and the power supply may be provided on the side of the chamber. Furthermore, although FIG. 10 exemplarily illustrates that the substrate 140 is disposed in a direction perpendicular to an extension direction of the chamber 215, the substrate 140 is disposed in a direction parallel with an extension direction of the chamber 215.
The method of depositing films as described in FIG. 5 may also be performed using the APCVD apparatuses of FIGS. 7 and 10. The foregoing description for the method of depositing films using the HFCVD apparatus with reference to FIGS. 2 and 5 is also available for the method of depositing films using the APCVD apparatuses of FIGS. 7 and 10 except that the heating element 130 and the bias supply device 190 and 190′ are used instead of the filament 30 and the bias supply unit 80, respectively.

Experimental Example 1

In this experimental example, the apparatus of measuring charged nanoparticles illustrated in FIG. 1 was used.
The temperature of the chamber 5 was in the range of 773 K to 1,273 K for dissociating reaction gas. A mixed gas of silane (SiH₄) and nitrogen (N₂) was used as the reaction gas in which the concentration of silane is approximately 10%. The results of number concentrations versus sizes of nanoparticles in gas phase are illustrated in FIGS. 11A and 11B, while changing the temperature of the chamber 5 from 773 K to 1,273 K using a power supply. FIG. 11A illustrates a concentration distribution of negatively charged nanoparticles in the chamber 5, and FIG. 11B illustrates a concentration distribution of positively charged nanoparticles in the chamber 5. As the temperature of the chamber 5 increases, the concentration of the negatively charged nanoparticles increases but that of the positively charged nanoparticles decreases, as illustrated in FIGS. 11A and 11B.
As such, it is possible to control the deposition behavior of films by changing the generation behavior of the charged nanoparticles generated in the chamber.

Experimental Example 2

In this experimental example, the HFCVD apparatus 10 of FIG. 2 was used as the apparatus of depositing nanoparticles.
The temperature of the filament 30 was set to 1,833 K for dissociating reaction gas. The substrate 40 was formed of stainless steel with an area of 2 cm×2 cm and a thickness of 1 mm. The temperature of the substrate 40 is set to 393 K. A mixed gas of silane (SiH₄) and nitrogen (N₂) was used as the reaction gas in which the concentration of silane was set to 20% and 10%, respectively. A DC bias of +150 V and −150 V was respectively applied using the power supply 70. A copper plate was used as the bias supply unit 80, and disposed below the substrate 40, as illustrated in FIG. 2. The pressure of the chamber 15 was set to 0.7 Torr, and deposition was performed for 30 minutes. The mass of the substrate 40 was measured before and after the reaction so that the deposition amount per unit area according to the bias application was estimated by a mass difference between the comparison substrates prepared under the same conditions except the condition of bias application (the increased mass of the deposited substrate with the bias applied−the increased mass of the deposited substrate without the bias applied=the deposition amount according to the bias application).
FIG. 12 is a graph illustrating deposition behaviors according to a concentration of reaction gas and a bias applied to a bottom of a substrate in the method of depositing films according to the exemplary embodiments, where the substrate is an electrical conductor (stainless steel).
Referring to FIG. 12, the sample (a) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 20% and the bias is set to +150 V. The sample (b) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 20% and the bias is set to −150 V. The sample (c) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 10% and the bias is set to +150 V. The sample (d) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 10% and the bias is set to −150 V. Here, heights of bars in FIG. 12 denote increments in the mass of the silicon thin films of the samples (a), (b), (c) and (d), respectively.
As illustrated in FIG. 12, from the results of mass increase in silicon thin films obtained by applying the bias to the conductive substrate, it can be appreciated that the deposition rate of the silicon thin film increases in order by the samples (a), (b), (c) and (d). In the sample (d), it is observed that the deposition rate is lower than the case of no bias application, which may be construed that the charged nanoparticles generated under the silane concentration of 20% and 10%, respectively, may exhibit different generation behaviors.
In the samples (a) and (b) prepared under the silane concentration of 20%, negatively charged nanoparticles are mainly generated, and also small amount of positively charged nanoparticles are generated so that the deposition rate increases by the positive bias. In the samples (c) and (d) prepared under the silane concentration of 10%, negatively charged nanoparticles are more generated than the samples (a) and (b), and thus the negatively charged nanoparticles, majority of the generated nanoparticles, are repulsed from the substrate when the bias of −150 V is applied, which makes it difficult to deposit the nanoparticles on the substrate. In this case, the amount of the positively charged nanoparticles which can be easily deposited is extremely small so that they hardly contributes to the increase in deposition rate.
Resultantly, in the case where the substrate is formed of stainless steel with high electrical conductivity, it is possible to increase the deposition rate by applying a bias of which a polarity is opposite to a polarity of the nanoparticles dominantly existing in the charged nanoparticles according to variations in charged behaviors of the charged nanoparticles generated depending on the dissociation condition (i.e., concentration of silane) of the reaction gas. In addition, a relative ratio of the positively or negatively charged nanoparticles increases as the concentration of the reaction gas increases.

Experimental Example 3

In this experimental example, the HFCVD apparatus 10 of FIG. 2 was used as an apparatus of depositing nanoparticles.
The temperature of the filament 30 was set to 1,833 K for dissociating reaction gas. The substrate 40 was formed of polyethylene terephthalate (PET) with an area of 3 cm×6 cm and a thickness of 0.5 mm. The temperature of the substrate 40 is set to 353 K.
A mixed gas of hydrogen (H₂) and silane (SiH₄) was used as the reaction gas in which the concentration of silane was set to 20% and 10%, respectively. A DC bias of +150 V and −150 V was respectively applied using the power supply 70. A copper plate was used as the bias supply unit 80, and disposed below the substrate 40, as illustrated in FIG. 2. The pressure of the chamber 15 was set to 0.7 Torr, and deposition was performed for 30 minutes. The mass of the substrate 40 was measured before and after the reaction so that the deposition amount per unit area according to the bias application was estimated by a mass difference between the comparison substrates prepared under the same conditions except the condition of bias application (the increased mass of the deposited substrate with the bias applied−the increased mass of the deposited substrate without the bias applied=the deposition amount according to the bias application).
FIG. 13 is a graph illustrating deposition behaviors according to a concentration of reaction gas and a bias applied to a bottom of a substrate in a method of depositing films using the deposition apparatus of FIG. 2, where the substrate is an electrical insulator (e.g., PET).
Referring to FIG. 13, the sample (a) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 20% and the bias is set to +150 V. The sample (b) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 20% and the bias is set to −150 V. The sample (c) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 10% and the bias is set to +150 V. The sample (d) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 10% and the bias is set to −150 V. Here, heights of bars in FIG. 13 denote increments in the mass of the silicon thin films of the samples (a), (b), (c) and (d), respectively.
As illustrated in FIG. 13, from the results of mass increase in the silicon thin film obtained by applying the bias to the nonconductive substrate, it can be appreciated that the deposition rate of the silicon thin film increases in order by the samples (b), (d), (a) and (c). In the samples (a) and (c), it is observed that the deposition rate is lower than the case of no bias application.
This result is caused by that the PET with low electrical conductivity is used as the substrate unlike the experimental example 2. The charges of the deposited nanoparticles do not escape from the PET substrate 40, electrical insulator, and accumulated on the substrate 40. Thus, the deposition rate is reduced due to a repulsive force between the previously deposited nanoparticles and nanoparticles to be deposited later. Accordingly, the deposition rate is lowest in the sample (c) in which the negatively charged nanoparticles dominantly exist. The deposition rate of the sample (a) where positively charged nanoparticles increase is also lower than the case of no bias application. In the case where the bias of −150 V is applied, i.e., in the samples (b) and (d), the application of a negative bias increases the deposition rate because the deposition of positively charged nanoparticles, of which the amount is relatively smaller than that of negatively charged nanoparticles, becomes a rate determining step of the deposition rate.
Particularly, the deposition rate is higher in the sample (b) than the sample (d) because a relative generation ratio of the positive charged nanoparticle to the negatively charged nanoparticle is higher and the dissociated amount is greater in the sample (b) than the sample (d).
FIG. 14 is a graph illustrating film properties resulted from the difference of deposition behaviors in the samples of FIG. 13, which are measured by Raman spectroscopy.
Referring to FIG. 14, the degree of the crystallinity is highest in the ample (d) because a repulsive force between the charged nanoparticles with the same polarity is strongest during the deposition of the thin film. That is, the reason is that a ratio of negatively charged nanoparticles to positively charged nanoparticles is higher in the samples (c) and (d) obtained under the condition of the silane concentration of 10% than the samples (a) and (b) obtained under the condition of the silane concentration of 20%.
Resultantly, in the case where the substrate is formed of PET, i.e., an electrical insulator, it is possible to increase the deposition rate by applying a bias of which a polarity is the same as a polarity of the nanoparticles dominantly existing in the charged nanoparticles according to variations in charged behaviors of the charged nanoparticles generated depending on the dissociation condition (i.e., concentration of silane) of the reaction gas. It is apparent that it is possible to increase the degree of crystallinity of a thin film when a generation ratio between the positively and negatively charged nanoparticles increases due to a high dissociation degree of the reaction gas under the same condition.

Experimental Example 4

Like the experimental example 3, the HFCVD apparatus 10 of FIG. 2 was used. The temperature of the filament 30 was set to 1,833 K for dissociating reaction gas. The substrate 40 was formed of polyethylene terephthalate (PET) with an area of 3 cm×6 cm and a thickness of 0.5 mm. The temperature of the substrate 40 is set to 353 K. A mixed gas of hydrogen (H₂) and silane (SiH₄) was used as the reaction gas in which the concentration of silane was set to 20% and 10%, respectively. A DC bias of +150 V and ⊚50 V was respectively applied using the power supply 70. Hitherto, the conditions are the same as those of the experimental example 3.
Instead, a copper mesh was used as the bias supply unit 80 and disposed over the PET substrate 40. A wire of the copper mesh had a diameter of 0.4 mm, and an aperture between wires per square centimeter was 64. The pressure of the chamber 15 was set to 0.7 Torr, and deposition was performed for 30 minutes. The mass of the substrate 40 was measured before and after the reaction so that the deposition amount per unit area according to the bias application was estimated by a mass difference between the comparison substrates prepared under the same conditions except the condition of bias application (the increased mass of the deposited substrate with the bias applied−the increased mass of the deposited substrate without the bias applied=the deposition amount according to the bias application).
FIG. 15 is a graph illustrating deposition behaviors according to a concentration of reaction gas and a bias applied to a top of a substrate in a method of depositing films using the deposition apparatus of FIG. 2, where the substrate is an electrical insulator.
Referring to FIG. 15, the sample (a) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 20% and the bias is set to +150 V. The sample (b) is prepared by depositing nanoparticles under the condition that the concentration of silane is set to 20% and the bias is set to −150 V. Here, heights of bars in FIG. 15 denote increments in the mass of the silicon thin films of the samples (a) and (b), respectively.
As illustrated in FIG. 15, in both the samples (a) and (b), it is observed that the deposition rate is lower than the case of no bias application. The deposition rate is much lower in the case of applying a positive bias, i.e., the sample (a), than the case of applying a negative bias, i.e., the sample (b). The reason is that most of the charged nanoparticles, i.e., basic units of silicon thin film deposition, are captured by the copper mesh to which the bias is applied, before they are deposited on the substrate. It is apparent that it is possible to control the deposition rate using such a method of applying the bias.

Experimental Example 5

Like the experimental example 2, the HFCVD apparatus 10 of FIG. 2 was used as an apparatus of depositing nanoparticles.
The temperature of the filament 30 was set to 2,173 K for dissociating reaction gas. The substrate 40 was formed of stainless steel with an area of 2 cm×2 cm and a thickness of 1 mm. The temperature of the substrate 40 is set to 523 K.
A mixed gas of hydrogen (H₂) and methane (CH₄) was used as the reaction gas in which the concentration of methane was set to 20%. A DC bias of +25V, +0 V and ⊚00 V was respectively applied using the power supply 70. A copper plate was used as the bias supply unit 80, and disposed below the substrate 40, as illustrated in FIG. 2. The pressure of the chamber 15 was set to 170 Torr, and deposition was performed for 30 minutes.
As a result, the growth of carbon nanotubes is actively performed in the case of applying +25 V rather than the case of applying ⊚00 V. It is construed that this is resulted from the fact the nanoparticles formed in gas phase are negatively charged.

Experimental Example 6

In this experimental example, the APCVD apparatus 110 of FIG. 7 was used as an apparatus of depositing films.
The highest temperature at a center C of the chamber 115 was set to 1.073 K, and the temperature decreases as far away from the center C. The substrate 140 was loaded in a left position with respect to the center C of the chamber 115. The position where the substrate 140 was loaded was set to a temperature of 933 K. A mixed gas of 90%-heliumn (He) and 10%-silane (SiH₄) was used as the reaction gas. The first and second plates 170 and 175 were formed of SUS material. The substrate 140 was placed on the second plate 175, as illustrated in FIG. 7. The pressure of the chamber 115 was set to 760 Torr, and deposition was performed for 30 minutes. The experiment was performed under the condition that the flow rate of carrier gas, e.g., nitrogen gas, was 1,000 sccm and the flow rate of the reaction gas was 10 sccm. Three kinds of voltages were applied by the power supply 185, as illustrated in FIGS. 16A through 16C.
FIG. 16A illustrates the case that the power supply 185 applies +50 V DC bias. Since a positive polarity is applied to the second plate 175, a negative polarity is relatively applied to the first plate 170. The negatively charged nanoparticles 192 are drawn toward the second plate 175 so that the negatively charged nanoparticles 192 are mainly deposited on the substrate 140 placed on the second plate 175. On the contrary, the positively charged nanoparticles 193 are drawn toward the first plate 170 so that positively charged nanoparticles 193 are difficult to be deposited on the substrate 140.
FIG. 16B illustrates the case that the power supply 185 applies −50 V DC bias. Since a negative polarity is applied to the second plate 175, a positive polarity is relatively applied to the second plate 175. The positively charged nanoparticles 193 are drawn toward the second plate 175 so that positively charged nanoparticles 193 are mainly deposited on the substrate 140 placed on the second plate 175. On the contrary, the negatively charged nanoparticles 192 are drawn toward the first plate 170 so that the negatively charged nanoparticles 192 are difficult to be deposited on the substrate 140.
FIG. 16C illustrates the case that DC voltages of +50 V and −50 V are alternately applied at every 5 seconds. When the DC bias of +50 V is applied, the negatively charged nanoparticles are mainly deposited on the substrate 140. In contrast, when the DC bias of −50 V is applied, the positively charged nanoparticles are mainly deposited on the substrate 140. Therefore, the polarity of the nanoparticle deposited on the substrate depends on the polarity of the bias.
To analyze the deposition rate of each deposition sample, a section of the sample was observed with a field emission scanning electron microscope (FE-SEM). The degree of crystallinity was measured with a Raman spectroscopy.
FIG. 17 illustrates FE-SEM images comparing thicknesses of the experimental examples of FIGS. 16A through 16C with that of a comparative example in the case where the substrate is an electrical insulator. FIG. 18 is a graph illustrating a deposition thickness and a deposition rate per second for each of the samples of FIG. 17 in the case where the substrate is an electrical insulator.
In this case, the substrate is an insulator of quartz glass.
In FIGS. 17 and 18, from the result of change in a thickness of the silicon thin film obtained by applying the bias to the insulating substrate, it can be observed that the deposition rate of the silicon thin film increases in order by the sample (c), the sample (b), the sample of the comparative example, and the sample (a). In the sample of the comparative example, it is observed that the deposition rate is higher than the sample (a) where the bias of +50 V is applied.
Such a result is caused by that the quartz glass with low electrical conductivity was used as the substrate and the positively charged particles existed more than the negatively charged particles in the chamber, which were observed from DMA experimental results. In general, the deposition rate decreases due to a repulsive force when the deposited nanoparticles and the nanoparticles to be deposited have the same polarities. In the samples (a) and (b), the deposition is performed in this manner. The nanoparticles having a polarity opposite to that of the deposited nanoparticle are deposited on the substrate due to an attractive force so that the substrate is neutralized again. The particles having the polarity responsive to the applied bias are deposited on the substrate again. The reason why the deposition rate of the sample (a) is lower than that of the sample (b) is that the negatively charged particles are fewer than the positively charged particles and the fewer particles determine the deposition rate. The sample (c) exhibits excellent the deposition rate because all the positively and negatively charged particles existing in the chamber are used as deposition sources due to the alternative application of voltages. In the sample of the comparative example, the particles are randomly deposited on the substrate according to Brownian motion.
FIG. 19 illustrates measurement results of Raman spectroscopy showing film properties of the samples of FIG. 17 according to deposition behaviors.
Referring to FIG. 19, it is observed that amorphous silicon is deposited in the case where the bias is not applied, i.e., in the case of the comparative example. In contrast, the crystallinity can be observed when the bias is applied according to the embodiments. When the bias voltage is applied, it is observed that the degree of crystallinity increases in order by the case of depositing negatively charged particles as deposition sources, the case of depositing positively charged particles as deposition sources, and the case of alternately depositing positively and negatively charged particles as deposition sources.
As described above, a film deposition is performed by drawing charged silicon particles, which have been crystallized already in a chamber, toward a substrate by applying a bias. Therefore, it is apparent that it is possible to obtain a crystallized silicon film for a short time at a low temperature through one-step, which was impossible in the related art.
Although the apparatus and method of depositing films using a bias and a charging behavior of nanoparticles formed during a chemical vapor deposition have been described with reference to the specific embodiments, they are not limited thereto. Therefore, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the present invention defined by the appended claims.

Claims

1-20. (canceled)

21. A method of depositing films, the method comprising:

controlling a generation behavior associated with a charged behavior including a size, a number concentration, a charge amount and a charge ratio of a charged nanoparticle formed in gas phase by adjusting a process parameter including a reaction temperature, an amount of a reaction gas and a reaction pressure in a chemical vapor deposition (CVD) process; and

controlling a deposition behavior of the charged nanoparticle using variations in an electric field intensity and a polarity through a bias unit.

22. An apparatus of depositing films, the apparatus comprising:

a chamber in which a substrate is loaded and a pressure is maintained at an atmospheric pressure, a low pressure or a high pressure;

a gas supply system configured to introduce a reaction gas into the chamber;

a heating element configured to emit heat for dissociating the introduced reaction gas; and

a bias supply device configured to apply an electric field to the substrate,

wherein the bias supply device comprises:

a first plate disposed over the substrate;

a second plate disposed under the substrate, and facing the first plate:

a power supply configured to apply a constant AC or DC voltage to one of the first and second plates; and

a ground unit configured to ground the other of the first and second plates.

23. An apparatus of depositing films, the apparatus comprising:

a gas supply system configured to introduce a reaction gas into the chamber;

a bias supply device configured to apply an electric field to the substrate,

wherein the substrate is disposed on a surface of the second plate opposite to the first plate,

the first plate being connected to the ground unit, and the second plate being connected to the power supply.

24. An apparatus of depositing films, the apparatus comprising:

a gas supply system configured to introduce a reaction gas into the chamber;

a bias supply device configured to apply an electric field to the substrate,

wherein the bias supply device draws a charged nanoparticles, which is nucleated and grown from the dissociated reaction gas, toward the substrate.

25. The apparatus of claim 4, wherein the gas supply system additionally introduces a carrier gas facilitating the movement of the charged nanoparticle into the chamber,

the gas supply system comprising a gas flowmeter configured to control a movement rate of the charged nanoparticle by controlling a flow rate of the carrier gas.

26. A method of depositing films, the method comprising:

loading a substrate in the chamber and introducing a reaction gas;

dissociating the reaction gas;

triggering nucleation in the dissociated reaction gas;

forming a charged nanoparticle through growth of a nanoparticle generated from the nucleation; and

applying a bias to the substrate to deposit a film by drawing the charged nanoparticle toward the substrate.

27. The method of claim 6, wherein the depositing of the film is performed using a hot-filament or hot-wire chemical vapor deposition (HFCVD or HWCVD) apparatus, a plasma CVD apparatus or an atmospheric pressure CVD (APCVD) apparatus.

28. The method of claim 6, wherein the charged nanoparticle is formed in gas phase by adjusting a dissociation degree of the reaction gas, and an electrical polarity ratio between positively and negatively charged nanoparticles is controlled.

29. The method of claim 6, wherein the substrate is formed of a conductive material, and a deposition rate increases by applying a bias of which a polarity is opposite to a polarity of the charged nanoparticle dominantly existing in the nanoparticles formed in gas phase.

30. The method of claim 6, wherein the substrate is formed of one of a nonconductive material and a plastic, and a deposition rate increases by applying a bias, of which a polarity is the same as a polarity of the charged nanoparticle dominantly existing in the nanoparticles formed in gas phase, to a periphery of the substrate.

31. The method of claim 6, wherein the substrate is formed of one of a nonconductive material and a plastic, and a degree of crystallinity of a film increases by increasing an electrical polarity ration of the nanoparticles.

32. The method of claim 6, wherein a mixed gas of silane and hydrogen is used as the reaction gas, and at least one of a fraction and a size of the nanoparticle charged in gas phase changes by increasing at least one selected from a dissociation temperature of the reaction gas, a fraction of the silane in the mixed gas and a pressure of the mixed gas.

33. The method of claim 6, wherein the bias is applied to a top of the substrate to thereby change an electrical polarity ratio of the nanoparticle to be deposited, by changing the charge amount of the nanoparticle before the nanoparticles are deposited on the substrate.

34. The method of claim 13, wherein a film deposition is divided into a nucleation and a growth, and an electrical polarity ratio of nanoparticles to be deposited changes by changing at least one of a fraction and a size of the nanoparticle charged in gas phase in each of the nucleation and the growth and changing the charge amount of the nanoparticles before the nanoparticles are deposited on the substrate.

35. The method of claim 6, wherein one of a silicon film, a carbon nanotube and a nanowire is deposited using the method, and the silicon film comprises one of a single crystalline silicon film, an amorphous silicon film and a poly crystalline silicon film.

36. The method of claim 6, wherein a voltage for applying the bias is in the range of approximately +1,000 V to approximately −1,000 V, and a DC or an AC having a frequency ranging from approximately 0.01 Hz to approximately 10 kHz is applied.

37. The method of claim 6, wherein the bias is applied such that its polarity is periodically or arbitrarily alternated.