WO2007067604A2 - Method of making undoped, alloyed and doped chalcogenide films by mocvd processes - Google Patents

Method of making undoped, alloyed and doped chalcogenide films by mocvd processes Download PDF

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WO2007067604A2
WO2007067604A2 PCT/US2006/046524 US2006046524W WO2007067604A2 WO 2007067604 A2 WO2007067604 A2 WO 2007067604A2 US 2006046524 W US2006046524 W US 2006046524W WO 2007067604 A2 WO2007067604 A2 WO 2007067604A2
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precursor
vapors
gas
substrate
doping
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WO2007067604A3 (en
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Edwin M. Dons
Gary S. Tompa
Catherine E. Rice
Joseph D. Cuchiaro
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Structured Materials Inc.
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/305—Sulfides, selenides, or tellurides
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
    • C23C16/45523—Pulsed gas flow or change of composition over time
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/011—Manufacture or treatment of multistable switching devices
    • H10N70/021—Formation of the switching material, e.g. layer deposition
    • H10N70/023—Formation of the switching material, e.g. layer deposition by chemical vapor deposition, e.g. MOCVD, ALD
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/20—Multistable switching devices, e.g. memristors
    • H10N70/231—Multistable switching devices, e.g. memristors based on solid-state phase change, e.g. between amorphous and crystalline phases, Ovshinsky effect
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/801—Constructional details of multistable switching devices
    • H10N70/881—Switching materials
    • H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
    • H10N70/8828—Tellurides, e.g. GeSbTe
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312

Definitions

  • This invention relates to a Method of Making Undoped, Alloyed and Doped
  • Flash memory chips are Flash memory chips, so-called because of the ability to write them individually while erasing them in chunks. This type of device is ubiquitous in today's cell phones, digital cameras, media cards etc.
  • Flash memory suffers from several shortcomings that limit their market potential. Primarily, writing data to a Flash memory is too slow for Flash to rival its DRAM cousins.
  • Flash memories can only be reprogrammed a limited number of times without incurring wear-out, typically on the order of a million re-programming cycles. While this may be enough for certain applications, it makes Flash memory ill-suited for general computing applications.
  • FRAM Ferroelectric RAM
  • MRAM Magnetoresistive RAM
  • C-RAM Chalcogenide RAM
  • OFUM Ovonic Unified Memory
  • PRAM Phase-Change RAM
  • C-RAM apart from having a small cell size and large endurance, is a low-power memory. Since the binary information is represented by two different phases of the material it is inherently nonvolatile, requiring no energy to keep the material in either of its two stable binary structural states. In addition, since the data in a chalcogenide memory element is stored as a structural phase rather than an electrical charge or state, it is expected to be impervious to ionizing radiation effects. This makes C-RAM ideally suited for space-based and military applications.
  • Nonvolatile memory devices are found in the majority of military as well as commercial systems.
  • the type of nonvolatile memory of this program, C-RAM is especially relevant to Military Device Applications (MDA) for its radiation hardness.
  • MDA Military Device Applications
  • C-RAM is inherently resistant to radiation, making this device an attractive option for military and aerospace applications.
  • C-RAM memory devices can be operated at low voltages and offer fast write/erase speeds.
  • the ease with which C-RAM memory can be scaled to smaller sizes offers the opportunity to develop high density memories that are radiation hardened.
  • phase-change nonvolatile memories are focused on the chalcogenide material Ge 2 Sb 2 Te 5 used for rewriteable optical media (CD-RW and DVD-RW).
  • chalcogen refers to the Group VI elements of the periodic table (among them sulfur (S), selenium (Se) and tellurium (Te)).
  • Chalcogenide refers to compounds or alloys, hereafter referred to as alloys, containing at least one of these elements such as the alloy of germanium, antimony, and tellurium discussed here. This phase-change technology uses a thermally activated, rapid, reversible change in the structure of the alloy to store data.
  • the two structural states of the chalcogenide alloy are an amorphous state and a polycrystalline state. Relative to the amorphous state, the polycrystalline state shows a dramatic increase in free electron density, similar to a metal. This difference in free electron density gives rise to a difference in reflectivity and resistivity.
  • a laser is used to heat the material to change states. The state of the memory is read by directing a low-power laser at the material and detecting the difference in reflectivity between the two phases.
  • a memory cell consists of a top electrode, a layer of chalcogenide and a bottom electrode that at the base is connected to a transistor (see Figure 1 which is a simplified diagram of a chalcogenide memory cell taken from J. Maimon, K. Hunt, L. Burcin, J. Rodgers, K. Knowles, "Integration And Circuit Demonstration of
  • Chalcogenide Memory Elements with a Radiation Hardened CMOS Technology Proceedings 2002 Non-Volatile Memory Technology Symposium, paper no. 23, Nov. 2002. Reading the cell is done by measuring the resistance. Resistive heating is used to change the phase of the chalcogenide layer. To write data into the cell, the chalcogenide is heated past its melting point (Tm) and then rapidly cooled to make it amorphous. To make it crystalline, it is heated just below its melting point and held there for approximately 50 ns, giving the atoms time to position themselves in their crystal locations.
  • Tm melting point
  • C-RAM Complementary Metal-organic chemical vapor deposition
  • Single cells have been studied in detail with reported cycling endurance up to one trillion and write/erase speeds in the tens of nanoseconds. Cycling endurance is observed to be dependent on the magnitude of the reset current. Overheating the cell with a large programming current causes failed cells to get stuck at low resistance states.
  • Programming currents are typically on the order of 1 mA, but for practical reasons are desirable to be reduced to 0.2 mA to 0.4 m A.
  • One way to achieve this is to dope the chalcogenide material with nitrogen. Nitrogen-doped chalcogenides such as Ge 2 Sb 2 Te S have a higher resistance and therefore a lower programming current. Similarly, alloying the chalcogenide with Sn or Se may have the same effect on programming current.
  • C-RAM devices are currently produced using sputtering.
  • sputtering limits further device improvements because of difficulties in meeting device architecture / conformality requirements for increased endurance, reliability and higher density components.
  • sputtering has limited flexibility in varying the composition of the chalcogenide alloy. MOCVD overcomes these and other sputter related limitations.
  • C-RAM is a phase change memory that stores its digital information as either a crystalline or amorphous structural phase identified through distinctly different resistive paths to conductive charge in a thin, chalcogenide layer. This mechanism of data storage offers an important advantage over other types of memory, such as
  • the active, chalcogenide layer is fabricated by sputtering. This process has several characteristics that limit device performance and its technological advancement as implemented in nonvolatile device structures. Specifically, practical endurance (the number of programming cycles before failure) of sputter-made C-RAMs is ⁇ 10 8 . Furthermore, improved conformality will lead to higher speeds and lower operating voltage through increased density scaling.
  • MOCVD Metalorganic Chemical Vapor Deposition is a well-established manufacturing technology that has a demonstrated capability of uniformly fabricating thin films of high quality and excellent conformality integrated circuit device layers at a high throughput rate.
  • MOCVD also offers the opportunity to easily vary the alloy composition of the chalcogenide layer which should further improve endurance and other device characteristics.
  • MOCVD has an advantage over sputtering for alloy/dopant tuning in that it offers run-to-run tuning of composition through flow control as compared to the need to purchase new targets and to re-setup and qualify the tool for sputtering; thus greatly speeding the process and reducing the cost.
  • the present invention is directed to an improved production technology for chalcogenide-based nonvolatile memories (C-RAM) based on Metal-Organic Chemical Vapor Deposition (MOCVD).
  • C-RAM chalcogenide-based nonvolatile memories
  • MOCVD Metal-Organic Chemical Vapor Deposition
  • Figure 4 shows a microscopic image of a representative GeSbTe thin film fabricated by MOCVD as part of this work.
  • the film was fabricated in accordance with processes described herein.
  • the film was conclusively verified to contain all three elements by both X-Ray Fluorescence (XRF) and Auger Electron Spectroscopy (AES).
  • XRF X-Ray Fluorescence
  • AES Auger Electron Spectroscopy
  • GeSbTe-based thin films were fabricated by MOCVD in both single layer fashion, i.e. simultaneous feeding of all precursors into the chamber, and multilayer fashion, i.e. alternately, germanium (Ge) and antimony/tellurium
  • the fabricated films were characterized by X-Ray Fluorescence (XRF) and Auger Electron Spectroscopy (AES) and were conclusively found to contain all three constituent elements.
  • XRF X-Ray Fluorescence
  • AES Auger Electron Spectroscopy
  • Germane (GeH 4 ) gas was used as the germanium precursor.
  • metalorganic germanium sources such as tetraethylgermane (C 2 Hs) 4 Ge, diethylgermane (C 2 Hs) 2 GeH 2 , and trimethylgermane (CHs) 3 GeH can be used in the present process, they were found to be more or less effective than
  • TMSb Trimethylantimony
  • C 2 Hs Triethylantimony
  • TESb Triethylantimony
  • C 3 H 7 Diisopropyltelluride
  • Te Triethylantimony
  • the temperature at which deposition takes place ranges from 450 0 C to 500 0 C.
  • the chamber pressure at which deposition takes places ranges from 5 Torr to 10 Torr (although other chamber pressures may be utilized).
  • Figure 1 depicts a chalcogenide-based memory cell
  • Figure 2 schematic representation of a CVD deposition system suitable for carrying out the present invention
  • Figure 3 shows the XRF spectrum for a representative GeSbTe deposition done in accordance with the present invention.
  • Figure 4 is a photomicrograph of a GeSbTe film deposited done in accordance with the present invention.
  • Figure 2 depicts the first of two CVD chambers that were used in this work. Gases are fed into a vacuum reactor chamber 20 through a showerhead located inside chamber 20 which contains gas inlets 22 for precursor vapors and a carrier gas 24, which in this case is hydrogen. Heating of chamber 20 is achieved through resistive heating of SiC-coated graphite filaments. The chamber pressure is recorded through a baratron. The temperature of chamber 20 is recorded via thermocouples that are positioned in close proximity to the substrate platter. Wafers are mounted on a substrate platter that is equipped with a ferrofluidic rotation assembly rotated by an external motor 26. During deposition the entire wafer assembly rotates at a predetermined speed, typically 750 revolutions per minute.
  • Chamber 20 is equipped with hardware for 6" wafer processing through an automated wafer transfer robot and load lock chamber (not shown).
  • Figure 2 also depicts a schematic of the gas panel used for depositing GeSbTe- based films.
  • a germane gas bottle 28 and hydrogen gas bottle 24 are shown that tie into the main gas panel.
  • Three bubbler sources 3Oa 5 30b and 30c are depicted in the center of the drawing, one for the antimony precursor, one for the tellurium precursor and a spare one that can be used for metalorganic germanium, or doping/alloying precursors if so desired.
  • Bubbler sources 3Oa 5 30b and 30c are each surrounded by liquid baths 32a, 32b and 32c to maintain the precursors at the desired temperatures
  • the precursor vapors are transported to the showerhead by the carrier gas bubbled therethrough, from where they are fed into the chamber through needle valves 34.
  • the lower right portion of the drawing represents the vaccum pumping manifold 36.
  • the reactor is comprised of a vertically mounted IV2" diameter quartz tube.
  • the top flange was equipped with a gas feedthrough. Precursor and carrier gas mix immediately before entering the reactor.
  • a baratron was mounted on the top flange for pressure control.
  • a small graphite cylinder is used as a sample holder. Heating of the small reactor is achieved through 500 W quartz halogen light bulbs. This type of light bulb provides a rapid heating up and cooling down cycle of the chamber, thereby considerably reducing the time needed per process run.
  • Germanium film was deposited on a 6" silicon wafer using the large MOCVD reactor shown in Fig. 2.
  • the film was grown at a temperature of 540 0 C for 30 minutes at a 3 Torr chamber pressure.
  • the average thickness of the film was found to be 640 A.
  • the deposition of Germanium was routinely achieved in both the large reactor as well as the small quartz reactor.
  • the source of the germanium was germane gas, hydrogen was the carrier gas and Diisopropyltelluride (C 3 H- Z ) 2 Te [DiPTe] was used as the tellurium precursor.
  • the XRF spectrum for a representative GeTe deposition indicates that both germanium and tellurium are present in the film, albeit at a low tellurium concentration. The film appeared polycrystalline upon deposition.
  • the source of the germanium was germane gas, hydrogen was the carrier gas and Trimethylantimony (CHa) 3 Sb [TMSb] was used as the antimony precursor XRF analysis showed the presence of germanium and antimony in the deposited film.
  • the XRF spectrum of the antimony-tellurium film (SbTe) shows the presence of tellurium in the film.
  • Auger Electron Spectroscopy (AES) was performed on the sample.
  • Sputter depth profiles were acquired from the sample. Carbon, oxygen, antimony, and tellurium were monitored as a function of sputter depth. The profiles were quantified using elemental sensitivity factors.
  • the depth scale was calibrated using a thermal oxide of silicon of known thickness and assuming that these materials sputter at the same rate as SiO 2 -
  • both antimony and tellurium were recorded as well as atomic oxygen and carbon.
  • the profile obtained from the described sample shows that the coating is of uniform composition to the final sputter depth.
  • the atomic concentrations of Sb (40%) and Te (60%) prove the film to be a compositionally correct Sb 2 Te 3 chalcogenide.
  • Initial GeSbTe films were grown in a single layer fashion, i.e. all precursors were simultaneously fed into the chamber. Exemplary fabrication details are listed in Table E.
  • the starting precursor concentration By varying the starting precursor concentration, the resulting film composition can be controlled.
  • additional precursors such as Tin (Sn), selenium (Se), Silicon (Si), nitrogen (N) and gallium (Ga)
  • the GeSbTe- based thin film composition can be alloyed/doped.
  • Example precursors for Sn, Se 5 Si, N, and Ga are tetraethyltin ((C 2 Hs) 4 Sn) 3 di-isopropyl selenium ((C 3 H- ⁇ ) 2 Se), silane (SiH 4 ), ammonia (NH 3 ), and trimethyl gallium ((CH 3 ) 3 Ga), respectively.
  • Auger Electron Spectroscopy was also performed on a representative GeSbTe film. Again a sputter depth profiles was acquired from the sample. Carbon, oxygen, germanium, antimony, and tellurium were monitored as a function of sputter depth. The profiles were quantified using elemental sensitivity factors. The depth scale was calibrated using a thermal oxide of silicon of known thickness and assuming that these materials sputter at the same rate as SiO 2 . The profile for the sample was acquired from a relatively smooth area of the sample. The depth profile shows the presence of a germanium-rich oxide followed by a layer containing Ge, Sb 3 Te, and O. Silicon was detected after sputtering ⁇ 8O ⁇ A.
  • the secondary electron images showed that much of the wafer still contained coating material after the completion of the profile. Therefore a second profile was started on one of these remaining regions.
  • the second profile showed the coating in this area had a uniform composition of Sb (30%), Ge (10%), and Te (60%) to a depth of ⁇ l,500A .
  • the films were generally found to have a large surface roughness. Further efforts were made to reduce the roughness of the deposited films through process improvements. One improvement in particular, was the use of diethylgermane as a germanium precursor which was found to improve the surface roughness significantly compared to films prepared using germane, when growing in one step. The result of this effort is depicted in Figure 4 This figure shows a microscopic image (magnification 150Ox) of a GeSbTe film. Upon visual inspection, the film was found to be smooth. Microscopy revealed that the film is of a polycrystalline nature with large grains (several microns in diameter) as evidenced by the grain boundaries. In addition, the XRF spectrum is shown, indicating that all three elements are present. Other films appeared amorphous and yet others very rough depending upon process parameters.
  • the present process is not in any way limited to the direct deposition of the material directly onto a substrate.
  • the deposition of the material is not in any way limited to the direct deposition of the material directly onto a substrate.
  • chalcogenide material may be part of a multiple step process for forming an integrated circuit, such as the memory chip shown in Fig. 1 herein.
  • the chalcogenide film can be located in between a top and a bottom layer, either of which may consist of a metal, carbon, highly doped semiconductor, among others.
  • the properties of the deposited film can be controlled by varying the process parameters such as precursor composition, temperature, time, pressure, and flow rate of the precursors and carrier gases.
  • Additional precursors may also be added to the deposition process so as to add a doping/alloying element to the deposited film suitable doping/alloying elements include: N, Ga, Si, Ni 5 V, Se, S, and Sn, among others. Whether the element is a dopant or an alloy depends on the nature of the added element and the amount added.
  • dopant refers to a substitution of an element by a small amount of an element of a different valence (or group in the periodic table), for example substituting N (group V, nominal valence -3) for Se (group VI, nominal valence -2), whereas alloy refers to an addition of any proportion of an element generally of the same valence or group in the periodic table, for example Si (group IV) substituted for Ge (group IV), or in reference to a solid solution of metals. .
  • the present process may also be used to manufacture other
  • chalcogenide films such as AgInSbTe (which also has phase- properties), InSe, SbSe, SbTe, InSbSe, InSbTe, GeSbSe, and GeSbTeSe.
  • GeSbTe-based thin films were fabricated by MOCVD in both single layer fashion, i.e. simultaneous feeding of all precursors into the chamber, and multilayer fashion, i.e. alternately, germanium (Ge) and antimony/tellurium
  • the fabricated films were characterized by X-Ray Fluorescence (XRF) and Auger Electron Spectroscopy (AES) (surface and depth profile) and were conclusively found to contain all three constituent elements.
  • XRF X-Ray Fluorescence
  • AES Auger Electron Spectroscopy
  • Germane (GeHU) gas was used as the germanium precursor.
  • metalorganic germanium sources such as tetraethylgermane (C 2 Hs) 4 Ge, diethylgermane (C 2 Hs) 2 GeH 2 , and trimethylgermane (CHj) 3 GeH can be used in the present process as they were found to be more or less effective than Germane and can impede deposition under certain circumstances.
  • Diisopropyltelluride (C 3 Hv) 2 Te was used as the tellurium precursor.
  • the temperature at which deposition takes place ranges from 450 0 C to 500 0 C.
  • the chamber pressure at which deposition takes places ranges from 5 Torr to 10 Torr.

Abstract

A method of making Undoped, Alloyed and Doped Chalcogenide Films by CVD and particularly a film of GeSbTe which is a phase change material. These films are useful in electronic memory devices and other applications. In the method gas or vapor phase precursors of the elements are transported to a reaction chamber where they are deposited on a heated substrate under controlled conditions.

Description

Method of Making Undoped, Alloyed and Doped Chalcogenide Films by MOCVD Processes
REFERENCE TO RELATED APPLICATIONS
This application claims priority of U.S. Provisional Patent application S.N
60/742,691 on December 6, 2005 and titled "Undoped, Alloyed and Doped GeSbTe- based Chalcogenide Films".
STATEMENT OF GOVERNMENT SUPPORT OF THE INVENTION
The work leading to this invention was supported by the US Missile Defense
Agency under contact No. HQ0006-05-C-7182
BACKGROUND OF THE INVENTION This invention relates to a Method of Making Undoped, Alloyed and Doped
Chalcogenide Films by Metalorganic Chemical Vapor Deposition (MOCVD) Processes. The Chalcogenide Films produced thereby have particular applicability to non-volatile memory cells for electronic and integrated circuit applications. Nonvolatility, the ability to retain data in a memory cell for years when un- powered, is crucial for most electronic systems. Most nonvolatile memory devices are Flash memory chips, so-called because of the ability to write them individually while erasing them in chunks. This type of device is ubiquitous in today's cell phones, digital cameras, media cards etc. But Flash memory suffers from several shortcomings that limit their market potential. Primarily, writing data to a Flash memory is too slow for Flash to rival its DRAM cousins. Secondly, Flash memories can only be reprogrammed a limited number of times without incurring wear-out, typically on the order of a million re-programming cycles. While this may be enough for certain applications, it makes Flash memory ill-suited for general computing applications.
As a consequence a number of different nonvolatile memory technologies are emerging as a viable alternative to replace Flash, most prominently Ferroelectric RAM (FRAM or FeRAM), Magnetoresistive RAM (MRAM) and Chalcogenide RAM (C-RAM, but also called Ovonic Unified Memory (OUM), or Phase-Change RAM (PRAM)). These devices have little in common, except that they can be reprogrammed a near unlimited number of times and be programmed in nanoseconds rather than microseconds. Table A below summarizes the different nonvolatile memory technologies:
TABLE A: Comparison of commercially available memories, (values are approximate)
SRAM FLASH FRAM MRAM C-RAM
Nonvolatile No Yes Yes Yes Yes
Cell size factor 8 8 18 10-20 6
Endurance, cycles Infinite 106 1016 1014 >108
Read/write Voltage Low High Low Moderate Low
Read/write Speed (ns) 25/25 20/1000 40/40 20/30 <50/<50
Radiation Hardened Yes No No No Yes
From Table A it is clear that C-RAM, apart from having a small cell size and large endurance, is a low-power memory. Since the binary information is represented by two different phases of the material it is inherently nonvolatile, requiring no energy to keep the material in either of its two stable binary structural states. In addition, since the data in a chalcogenide memory element is stored as a structural phase rather than an electrical charge or state, it is expected to be impervious to ionizing radiation effects. This makes C-RAM ideally suited for space-based and military applications.
Nonvolatile memory devices are found in the majority of military as well as commercial systems. The type of nonvolatile memory of this program, C-RAM, is especially relevant to Military Device Applications (MDA) for its radiation hardness. Unlike state-of-the-art electronic tunneling nonvolatile memory, as compared in Table A, C-RAM is inherently resistant to radiation, making this device an attractive option for military and aerospace applications. In addition, C-RAM memory devices can be operated at low voltages and offer fast write/erase speeds. Furthermore, the ease with which C-RAM memory can be scaled to smaller sizes offers the opportunity to develop high density memories that are radiation hardened.
Most commercial research on phase-change nonvolatile memories is focused on the chalcogenide material Ge2Sb2Te5 used for rewriteable optical media (CD-RW and DVD-RW). The term "chalcogen" refers to the Group VI elements of the periodic table (among them sulfur (S), selenium (Se) and tellurium (Te)). "Chalcogenide" refers to compounds or alloys, hereafter referred to as alloys, containing at least one of these elements such as the alloy of germanium, antimony, and tellurium discussed here. This phase-change technology uses a thermally activated, rapid, reversible change in the structure of the alloy to store data. The two structural states of the chalcogenide alloy are an amorphous state and a polycrystalline state. Relative to the amorphous state, the polycrystalline state shows a dramatic increase in free electron density, similar to a metal. This difference in free electron density gives rise to a difference in reflectivity and resistivity. In the case of the re-writeable CD and DVD disk technology, a laser is used to heat the material to change states. The state of the memory is read by directing a low-power laser at the material and detecting the difference in reflectivity between the two phases. A memory cell consists of a top electrode, a layer of chalcogenide and a bottom electrode that at the base is connected to a transistor (see Figure 1 which is a simplified diagram of a chalcogenide memory cell taken from J. Maimon, K. Hunt, L. Burcin, J. Rodgers, K. Knowles, "Integration And Circuit Demonstration of
Chalcogenide Memory Elements with a Radiation Hardened CMOS Technology," Proceedings 2002 Non-Volatile Memory Technology Symposium, paper no. 23, Nov. 2002. Reading the cell is done by measuring the resistance. Resistive heating is used to change the phase of the chalcogenide layer. To write data into the cell, the chalcogenide is heated past its melting point (Tm) and then rapidly cooled to make it amorphous. To make it crystalline, it is heated just below its melting point and held there for approximately 50 ns, giving the atoms time to position themselves in their crystal locations.
Development of C-RAM is taking place in three areas: device physics, programming current reduction and manufacturing. Single cells have been studied in detail with reported cycling endurance up to one trillion and write/erase speeds in the tens of nanoseconds. Cycling endurance is observed to be dependent on the magnitude of the reset current. Overheating the cell with a large programming current causes failed cells to get stuck at low resistance states. Programming currents are typically on the order of 1 mA, but for practical reasons are desirable to be reduced to 0.2 mA to 0.4 m A. One way to achieve this is to dope the chalcogenide material with nitrogen. Nitrogen-doped chalcogenides such as Ge2Sb2TeS have a higher resistance and therefore a lower programming current. Similarly, alloying the chalcogenide with Sn or Se may have the same effect on programming current.
C-RAM devices are currently produced using sputtering. However, sputtering limits further device improvements because of difficulties in meeting device architecture / conformality requirements for increased endurance, reliability and higher density components. Furthermore, sputtering has limited flexibility in varying the composition of the chalcogenide alloy. MOCVD overcomes these and other sputter related limitations.
C-RAM is a phase change memory that stores its digital information as either a crystalline or amorphous structural phase identified through distinctly different resistive paths to conductive charge in a thin, chalcogenide layer. This mechanism of data storage offers an important advantage over other types of memory, such as
FLASH or SRAM because it results in the memory being inherently resistant to radiation damage as the macroscopic layer resistance does not change due to ionizing radiation strikes. As stated above, currently, the active, chalcogenide layer is fabricated by sputtering. This process has several characteristics that limit device performance and its technological advancement as implemented in nonvolatile device structures. Specifically, practical endurance (the number of programming cycles before failure) of sputter-made C-RAMs is ~ 108. Furthermore, improved conformality will lead to higher speeds and lower operating voltage through increased density scaling.
MOCVD Metalorganic Chemical Vapor Deposition is a well-established manufacturing technology that has a demonstrated capability of uniformly fabricating thin films of high quality and excellent conformality integrated circuit device layers at a high throughput rate. However, until now MOCVD has not been applied successfully to C-RAM fabrication. Importantly, MOCVD also offers the opportunity to easily vary the alloy composition of the chalcogenide layer which should further improve endurance and other device characteristics. In addition, MOCVD has an advantage over sputtering for alloy/dopant tuning in that it offers run-to-run tuning of composition through flow control as compared to the need to purchase new targets and to re-setup and qualify the tool for sputtering; thus greatly speeding the process and reducing the cost.
SUMMARY OF THE INVENTION
The present invention is directed to an improved production technology for chalcogenide-based nonvolatile memories (C-RAM) based on Metal-Organic Chemical Vapor Deposition (MOCVD). The overall objective of this work was twofold: 1) the fabrication of chalcogenide Ge2Sb2Tes test structures grown by MOCVD and 2) the development of an improved manufacturing process over current state-of-the-art sputtering technology. CMOS-compatible, MOCVD-produced Ge2Sb2Te5-based nonvolatile memory technology exceeds the best features of current state-of-the-art sputter-produced technology without the inherent degradation and endurance limitations. In addition, the use of MOCVD to grow the active chalcogenide layer affords sub-nm growth control and a proven production capability that promises to lead to improved device properties and thus, improved products for the military and aerospace markets.
The outcome of this work is that we have achieved the main objective of developing an MOCVD process for the deposition of GeSbTe thin films. During the course of the work, we fabricated various samples of GeSb, GeTe5 SbTe and GeSbTe thin films and conclusively verified the presence of all three elements (germanium, antimony and tellurium) in the film, effectively varying the composition of GexSbyTez over the range x5 y, and z between 0 and 1. (Hereafter we will use the term "GeSbTe" to collectively represent any of these compositions). To the best of our knowledge, it is the first time that this has been achieved.
Figure 4 shows a microscopic image of a representative GeSbTe thin film fabricated by MOCVD as part of this work. The film was fabricated in accordance with processes described herein. The film was conclusively verified to contain all three elements by both X-Ray Fluorescence (XRF) and Auger Electron Spectroscopy (AES).
A number of important aspects of MOCVD technology of GeSbTe-based thin films were established:
• GeSbTe-based thin films were fabricated by MOCVD in both single layer fashion, i.e. simultaneous feeding of all precursors into the chamber, and multilayer fashion, i.e. alternately, germanium (Ge) and antimony/tellurium
(Sb/Te) are fed into the chamber.
. The fabricated films were characterized by X-Ray Fluorescence (XRF) and Auger Electron Spectroscopy (AES) and were conclusively found to contain all three constituent elements.
• Germane (GeH4) gas was used as the germanium precursor.
. While metalorganic germanium sources such as tetraethylgermane (C2Hs)4Ge, diethylgermane (C2Hs)2GeH2, and trimethylgermane (CHs)3GeH can be used in the present process, they were found to be more or less effective than
Germane and can impede deposition under certain circumstances.
• Either Trimethylantimony (CHa)3Sb [abbreviated herein as "TMSb"] or Triethylantimony (C2Hs)3Sb ["TESb"] was used as the antimony precursor. Diisopropyltelluride (C3H7)2Te ["DiPTe"] was used as the tellurium precursor. • The temperature at which deposition takes place ranges from 450 0C to 500 0C.
• The chamber pressure at which deposition takes places ranges from 5 Torr to 10 Torr (although other chamber pressures may be utilized).
• Films were fabricated using either hydrogen or argon as the carrier gas, other inert carrier gases may also be used.
• The stated ranges are by way of example only and can be varied by those of ordinary skill in the art
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference is made to the following drawings which are to be taken in conjunction with the detailed description to follow in which:
Figure 1 depicts a chalcogenide-based memory cell; Figure 2 schematic representation of a CVD deposition system suitable for carrying out the present invention;
Figure 3 shows the XRF spectrum for a representative GeSbTe deposition done in accordance with the present invention; and.
Figure 4 is a photomicrograph of a GeSbTe film deposited done in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS MOCVD Equipment
Figure 2 depicts the first of two CVD chambers that were used in this work. Gases are fed into a vacuum reactor chamber 20 through a showerhead located inside chamber 20 which contains gas inlets 22 for precursor vapors and a carrier gas 24, which in this case is hydrogen. Heating of chamber 20 is achieved through resistive heating of SiC-coated graphite filaments. The chamber pressure is recorded through a baratron. The temperature of chamber 20 is recorded via thermocouples that are positioned in close proximity to the substrate platter. Wafers are mounted on a substrate platter that is equipped with a ferrofluidic rotation assembly rotated by an external motor 26. During deposition the entire wafer assembly rotates at a predetermined speed, typically 750 revolutions per minute. Chamber 20 is equipped with hardware for 6" wafer processing through an automated wafer transfer robot and load lock chamber (not shown). Figure 2 also depicts a schematic of the gas panel used for depositing GeSbTe- based films. On the left, a germane gas bottle 28 and hydrogen gas bottle 24 are shown that tie into the main gas panel. Three bubbler sources 3Oa5 30b and 30c are depicted in the center of the drawing, one for the antimony precursor, one for the tellurium precursor and a spare one that can be used for metalorganic germanium, or doping/alloying precursors if so desired. Bubbler sources 3Oa5 30b and 30c are each surrounded by liquid baths 32a, 32b and 32c to maintain the precursors at the desired temperatures The precursor vapors are transported to the showerhead by the carrier gas bubbled therethrough, from where they are fed into the chamber through needle valves 34. The lower right portion of the drawing represents the vaccum pumping manifold 36.
Initial process development was performed in this large scale reactor. However, during the course of the program it was decided to continue GeSbTe process development efforts in a small scale quartz reactor tube, heated by lamps and without rotation. The use of such a tube has a number of advantages: it allows us to visibly monitor the deposition process, it provides a relatively quick way to obtain basic process parameters for a new material such as the one under development in this work, it increases sample throughput and it reduces the amount of consumables. The reactor is comprised of a vertically mounted IV2" diameter quartz tube. The top flange was equipped with a gas feedthrough. Precursor and carrier gas mix immediately before entering the reactor. In addition, a baratron was mounted on the top flange for pressure control. A small graphite cylinder is used as a sample holder. Heating of the small reactor is achieved through 500 W quartz halogen light bulbs. This type of light bulb provides a rapid heating up and cooling down cycle of the chamber, thereby considerably reducing the time needed per process run.
Ge Deposition
As a demonstration of the capability to grow elemental Germanium films in the above described equipment, a germanium film was deposited on a 6" silicon wafer using the large MOCVD reactor shown in Fig. 2. The film was grown at a temperature of 540 0C for 30 minutes at a 3 Torr chamber pressure. The average thickness of the film was found to be 640 A. The deposition of Germanium was routinely achieved in both the large reactor as well as the small quartz reactor.
Further characterization of the film by X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) revealed a crystalline structure for the germanium film.
GeTe, GeSb and SbTe Deposition
From the previous section it is clear that single layers of germanium can be routinely deposited using the above-described methodology. Subsequently, a concerted effort was made to, first, establish a GeTe process, a GeSb process and a SbTe process. We anticipated that development of these processes would provide us with an additional tool from which process windows to integrate them in order to form a compositionally correct GeSbTe film could be derived. In this section, results for germanium-tellurium, germanium-antimony and antimony-tellurium film growth are presented. Both germanium and tellurium precursor are added to the chamber with hydrogen used as carrier gas. The details of the GeTe deposition are listed in Table B below :
Figure imgf000010_0001
As shown in Table B, the source of the germanium was germane gas, hydrogen was the carrier gas and Diisopropyltelluride (C3H-Z)2Te [DiPTe] was used as the tellurium precursor. The XRF spectrum for a representative GeTe deposition indicates that both germanium and tellurium are present in the film, albeit at a low tellurium concentration. The film appeared polycrystalline upon deposition.
This result has provided us with a process window for both germanium and tellurium deposition. The next focus of our efforts was the deposition of germanium and antimony films (GeSb). The fabrication details are listed in Table C Below.
Figure imgf000010_0002
As shown in Table C5 the source of the germanium was germane gas, hydrogen was the carrier gas and Trimethylantimony (CHa)3Sb [TMSb] was used as the antimony precursor XRF analysis showed the presence of germanium and antimony in the deposited film.
Next an antimony-tellurium film (SbTe) without germanium was deposited, The fabrication details are listed in Table D Below:
Figure imgf000011_0001
As shown in Table D, hydrogen was the carrier gas and Trimethylantimony (CHa)3Sb [TMSb] was used as the antimony precursor and Diisopropyltelluride (C3H7)2Te [DiPTe] was used as the tellurium precursor
The XRF spectrum of the antimony-tellurium film (SbTe) shows the presence of tellurium in the film. In addition, Auger Electron Spectroscopy (AES) was performed on the sample. Sputter depth profiles were acquired from the sample. Carbon, oxygen, antimony, and tellurium were monitored as a function of sputter depth. The profiles were quantified using elemental sensitivity factors. The depth scale was calibrated using a thermal oxide of silicon of known thickness and assuming that these materials sputter at the same rate as SiO2- On the surface of the sample, both antimony and tellurium were recorded as well as atomic oxygen and carbon. The profile obtained from the described sample shows that the coating is of uniform composition to the final sputter depth. Importantly, the atomic concentrations of Sb (40%) and Te (60%) prove the film to be a compositionally correct Sb2Te3 chalcogenide.
GeSbTe Deposition
In order to establish a basic set of process parameters for the deposition of compositionally correct GeSbTe films, we performed a series of deposition runs with all three precursors present. Depositions were carried out on both quartz substrates and silicon substrates. Films were generally found to be polycrystalline upon deposition and adhering to both silicon and quartz. The most important observation that can be made from this work is that all three elements were conclusively identified in a single thin film form. For the first time, we achieved MOCVD deposition of GeSbTe thin films and verified the presence of all elements within the deposited film.
Initial GeSbTe films were grown in a single layer fashion, i.e. all precursors were simultaneously fed into the chamber. Exemplary fabrication details are listed in Table E. By varying the starting precursor concentration, the resulting film composition can be controlled. Furthermore, by adding additional precursors, such as Tin (Sn), selenium (Se), Silicon (Si), nitrogen (N) and gallium (Ga), the GeSbTe- based thin film composition can be alloyed/doped. Example precursors for Sn, Se5 Si, N, and Ga are tetraethyltin ((C2Hs)4Sn)3 di-isopropyl selenium ((C3H-^)2Se), silane (SiH4), ammonia (NH3), and trimethyl gallium ((CH3)3Ga), respectively.
Figure imgf000013_0001
The significance of this result is that all three elements are verifiably present in thin film form. However, both the tellurium and antimony content were found to be significantly reduced with respect to those found in the process of Table D (SbTe without germanium), indicating that germanium could have an etching or equivalent effect on antimony/tellurium deposition. To circumvent the etching effect, further processing was performed in a multilayer fashion. Typically a total of between 10 and 20 layers of— alternately— germanium (Ge) and antimony/tellurium (SbTe) films were deposited. The layers were of 5 to 15 nm thickness. To this extent, germanium precursor was first fed into the chamber. At a specified time the germane gas was turned off, after which both antimony and tellurium precursor vapors were fed into the chamber. Subsequently, both antimony and tellurium precursors were turned off and germanium precursor was again fed into the chamber. This cycle was repeated a specified number of times. It was found that this multilayer fabrication approach was advantageous to deposition of GeSbTe-thin films.
Tables F and G list the fabrication details for the fabricated films
Figure imgf000013_0002
Figure imgf000014_0001
Figure imgf000014_0002
Auger Electron Spectroscopy was also performed on a representative GeSbTe film. Again a sputter depth profiles was acquired from the sample. Carbon, oxygen, germanium, antimony, and tellurium were monitored as a function of sputter depth. The profiles were quantified using elemental sensitivity factors. The depth scale was calibrated using a thermal oxide of silicon of known thickness and assuming that these materials sputter at the same rate as SiO2. The profile for the sample was acquired from a relatively smooth area of the sample. The depth profile shows the presence of a germanium-rich oxide followed by a layer containing Ge, Sb3 Te, and O. Silicon was detected after sputtering ~8OθA. The secondary electron images showed that much of the wafer still contained coating material after the completion of the profile. Therefore a second profile was started on one of these remaining regions. The second profile showed the coating in this area had a uniform composition of Sb (30%), Ge (10%), and Te (60%) to a depth of ~l,500A .
The films were generally found to have a large surface roughness. Further efforts were made to reduce the roughness of the deposited films through process improvements. One improvement in particular, was the use of diethylgermane as a germanium precursor which was found to improve the surface roughness significantly compared to films prepared using germane, when growing in one step. The result of this effort is depicted in Figure 4 This figure shows a microscopic image (magnification 150Ox) of a GeSbTe film. Upon visual inspection, the film was found to be smooth. Microscopy revealed that the film is of a polycrystalline nature with large grains (several microns in diameter) as evidenced by the grain boundaries. In addition, the XRF spectrum is shown, indicating that all three elements are present. Other films appeared amorphous and yet others very rough depending upon process parameters.
Applications/Enhancements
It is to be noted that the present process is not in any way limited to the direct deposition of the material directly onto a substrate. The deposition of the
chalcogenide material may be part of a multiple step process for forming an integrated circuit, such as the memory chip shown in Fig. 1 herein. As such the chalcogenide film can be located in between a top and a bottom layer, either of which may consist of a metal, carbon, highly doped semiconductor, among others. The properties of the deposited film can be controlled by varying the process parameters such as precursor composition, temperature, time, pressure, and flow rate of the precursors and carrier gases.
Additional precursors may also be added to the deposition process so as to add a doping/alloying element to the deposited film suitable doping/alloying elements include: N, Ga, Si, Ni5 V, Se, S, and Sn, among others. Whether the element is a dopant or an alloy depends on the nature of the added element and the amount added. Typically the term "dopant" refers to a substitution of an element by a small amount of an element of a different valence (or group in the periodic table), for example substituting N (group V, nominal valence -3) for Se (group VI, nominal valence -2), whereas alloy refers to an addition of any proportion of an element generally of the same valence or group in the periodic table, for example Si (group IV) substituted for Ge (group IV), or in reference to a solid solution of metals. . In addition to GeSbTe- based thin films, the present process may also be used to manufacture other
chalcogenide films such as AgInSbTe (which also has phase- properties), InSe, SbSe, SbTe, InSbSe, InSbTe, GeSbSe, and GeSbTeSe.
Summary
A number of important aspects of MOCVD technology of GeSbTe-based thin films were established:
• GeSbTe-based thin films were fabricated by MOCVD in both single layer fashion, i.e. simultaneous feeding of all precursors into the chamber, and multilayer fashion, i.e. alternately, germanium (Ge) and antimony/tellurium
(Sb/Te) are fed into the chamber.
• The fabricated films were characterized by X-Ray Fluorescence (XRF) and Auger Electron Spectroscopy (AES) (surface and depth profile) and were conclusively found to contain all three constituent elements.
• Germane (GeHU) gas was used as the germanium precursor.
While metalorganic germanium sources such as tetraethylgermane (C2Hs)4Ge, diethylgermane (C2Hs)2GeH2, and trimethylgermane (CHj)3GeH can be used in the present process as they were found to be more or less effective than Germane and can impede deposition under certain circumstances.
• Either Trimethylantimony (CHs)3Sb or Triethylantimony (C2Hs)3Sb was used as the antimony precursor.
Diisopropyltelluride (C3Hv)2Te was used as the tellurium precursor.
• The temperature at which deposition takes place ranges from 450 0C to 500 0C.
The chamber pressure at which deposition takes places ranges from 5 Torr to 10 Torr.
• Films were fabricated using either hydrogen or argon as the carrier gas. Other inert carrier gases may also be used. • The stated ranges are by way of example only and can be varied by those of ordinary skill in the art
The present invention has been described with respect to exemplary embodiments. However, as those skilled in the art will recognize, modifications and variations in the specific details which have been described and illustrated may be resorted to without departing from the spirit and scope of the invention as defined in the claims to follow.

Claims

What is claimed is:
1. A method of depositing a GexSbyTez where X = O - I5 Y = O -I and Z = O - I on a substrate comprising the steps of:
a) placing the substrate in a reactor chamber;
b) providing a gas precursor of Ge;
c) providing a vapor source of Sb;
d) providing a vapor source of Te;
e) transporting the gas precursor of Ge, the Sb vapors, and the Te vapors to the reactor chamber;
f) heating the substrate so as to cause the gas precursor of Ge3 the Sb vapors, and the Te vapors to deposit Ge, Sb and Te on the surface of the substrate; and
g) modulating the flow of the gas precursor of Ge, the Sb precursor vapors, and the Te precursor vapors so as to form the desired GeSbTe film.
2. The method of claim 1 further including the step of rotating the substrate during deposition.
3. The method of claim 1 wherein the GeSbTe film comprises Ge2Sb2TeS.
4. The method of claim 1 wherein the gas precursor of Ge comprises germane gas (GeH4)
5. The method of claim 1 wherein the vapor source of at least one of Sb and Te comprise liquid precursors of Sb and Te through which a carrier gas is bubbled so as to capture the vapors from the liquid precursors.
6. The method of claim 5 wherein the carrier gas comprises hydrogen.
7. The method of claim 1 wherein the liquid precursor of Sb comprises either Trimethylantimony (CH3)3Sb or Triethylantimony (C2Hs)3S.
8. The method of claim 1 wherein the liquid precursor of Te comprises Diisopropyltelluride (C3H7)2Te.
9. The method of claim 1 wherein the germane gas, the Sb precursor vapors, and the Te precursor vapors deposit Ge, Sb and Te simultaneously on the surface of the substrate.
10. The method of claim 1 wherein the germane gas, the Sb precursor vapors, and the Te precursor vapors are operated in an alternating manner so as to deposit Ge, Sb and Te in alternating layers on the surface of the substrate.
11. The method of claim 1 wherein the germane gas, the Sb precursor vapors, and the Te precursor vapors are operated in an functionally varying manner so as to deposit Ge, Sb and Te in layers of varying or oscillating composition on the surface of the substrate.
12. The method of claim 1 further including the steps of providing a precursor of a doping/alloying element, transporting the precursor of the doping/alloying element to the reactor chamber, and depositing the doping/alloying element along with the other constituents of the GeSbTe film.
13. The method of claim 12 wherein the doping/alloying element is selected from the group consisting of: N, Ga, Si, Ni, Se, S,and Sn.
14. A GeSbTe film produced by the process of claim 1.
15. The GeSbTe film of claim 14 comprising alternating layers of Ge, Sb and Te .
16. A method of depositing a germanium based chalcogenide film on a substrate comprising the steps of:
a) placing the substrate in a reactor chamber;
b) providing a precursor of Ge;
c) providing a vapor source of a chalcogen element;
d) transporting the gas precursor of Ge and the chalcogen element vapor to the reactor chamber; e) heating the substrate so as to cause the precursor of Ge, and the chalcogen element vapor to deposit Ge, and the chalcogen on the surface of the substrate; and f) modulating the flow of the precursor of Ge, and the and the chalcogen element vapor so as to form the desired GeSbTe film.
17. The method of claim 16 further including the steps of providing a precursor of a doping/alloying element and transporting the doping/alloying precursor to the reactor chamber and modulating tbe flow of the precursor of Ge, and the chalcogen element vapor and the doping/alloy ing element so as to form the desired film.
18. The method of claim 11 wherein the doping/alloying element is selected from the group consisting of: N, Ga, Si, Ni, V, Se, Sb, S,and Sn.
19. The method of claim 16 wherein the chalcogen element comprises at least one of sulfur (S), selenium (Se) and tellurium (Te).
20. The method of claim 16 wherein the vapor source of the chalcogen element comprises a liquid precursor through which a carrier gas is bubbled so as to capture the vapors from the liquid precursors.
21 The method of claim 20 wherein the carrier gas comprises hydrogen.
21. The method of claim 15 wherein the precursor of Ge comprises germane gas (GeH4 )
22.The method of claim 15 wherein the precursor of Ge comprises a liquid precursor.
23. The method of claim 22 wherein the liquid precursor of Ge is selected from the group of: tetraethylgermane (C2Hs)4Ge, diethylgermane (C2Hs)2GeH2, and trimethylgermane (CH3)3GeH through which a carrier gas is bubbled so as to capture the vapors from the liquid precursors.
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