WO1998059380A1

WO1998059380A1 - Dry-etching of thin film layers

Info

Publication number: WO1998059380A1
Application number: PCT/US1998/013225
Authority: WO
Inventors: Jie Chen; Haruhiro Goto; Marc Michael Kollrack; Carl Sorensen; John White; Tzy-Chung Wu; Yuen-Kui Wong
Original assignee: Applied Komatsu Technology, Inc.
Priority date: 1997-06-25
Filing date: 1998-06-23
Publication date: 1998-12-30

Abstract

A reactive ion etch (RIE) technique includes providing a material layer to be etched and supplying a reactive gas to a vicinity of the material layer. A single electric field is supplied to react the reactive gas with the material layer so as to form volatile byproducts of reactive gas and the material layer. The electric field has a frequency in the range from approximately 1 megahertz (MHz) to approximately 11 megahertz (MHz), for example, approximately 2 MHz. Indium and tin oxides, as well as aluminum and aluminum alloys, are suitable as the material layer.

Description

DRY-ETCHING OF THIN FILM LAYERS

Related Applications This application is related to the applications listed below which are being filed on the same date and assigned to the same assignee as the present invention. The applications listed below are incorporated herein by reference in their entirety: (1) U.S. Serial No. 08/881,323, entitled "DRY-ETCHING OF INDIUM AND TIN OXIDES," by Jie Chen, Haruhiro Goto, Marc Michael Kollrack, Kai-An Wang, Yuen-Kui Wong and Tzy-Chung Wu; and (2) U.S. Serial No. 08/881,950, entitled "DRY-ETCHING OF INDIUM AND TIN OXIDES," by Jie Chen and Yuen-Kui Wong. Background of the Invention

The invention relates generally to dry etching of thin film layers, including the etching of film layers formed on insulative substrates such as glass substrates, to selectively remove portions of the thin film. For example, the manufacture of a flat glass panel display typically begins with a clean glass substrate. Transistors are formed on the flat panel using film deposition and selective etching techniques. Sequential deposition, photo-lithography and selective etching of film layers on the substrate create individual transistors on the substrate. These devices, as well as metallic interconnections, liquid crystal cells and other devices formed on the substrate are then used to create active matrix display screens on the substrate to create a flat panel display in which display states are electrically created in the individual pixels.

Aluminum or an aluminum alloy can be used for the metallic interconnections, such as gate source and drain electrodes . Opto-electronic devices such as liquid crystal displays (LCD's), charge coupled sensor devices (CCD's) and the like often include thin film transparent electrodes disposed over a light transmitting or light receiving element. The transparent electrodes are typically composed of an oxide of indium (InO) or an oxide of tin (SnO) or a mixture of these oxides or a compound having the general formulation: In_xSn_yO_z, where the z factor is greater than zero but less than 100% and where the sum x+y fills the remainder of the 100%. The formulation, In_xSn_yO_z is commonly known in the art as ITO.

It is generally desirable in mass-production situations to etch the transparent-electrode thin film in such a way that the etching does not significantly damage any underlying structures. It is also generally desirable to perform the etch as quickly as possible and with as few steps as necessary in order to reduce mass- production complexity and costs. However, as the size of the substrate increases, it becomes increasingly difficult to achieve a uniform etch across the surface of the thin film layer, and under etching or over etching of the thin film layer can occur. Under etching refers to the condition where the thin film is not etched through thoroughly and undesired shorts appear in the resultant conductor pattern. Over etching refers to the condition where the thin film is etched through thoroughly and undesired etching of the underlying substrate begins and/or time and resources are wasted in trying to etch to a depth beyond that needed. In addition, a single defect in a flat panel substrate can render the entire display defective. Yet, individual defective devices in a flat panel display cannot generally be removed. Thus, the elimination of defects during the manufacturing process of flat panel displays is particularly important. According to one known etching technique, disclosed in U.S. Application Serial No. 08/273,382, filed July 7, 1994 by Wong et al . , an etch chamber is provided for plasma etching the surface of a flat panel display substrate. The chamber can be configured as a reactive ion etch chamber in which the substrate is received on a support member which can be maintained at a negative self-biasing voltage with a radio frequency (RF) voltage source at approximately 13.5 megahertz (MHz) . The chamber is maintained at a vacuum pressure, and an etching gas species is charged into the chamber and sparked into a plasma by the RF voltage source . The present invention is directed to improvements to this and similar techniques. Summary of the Invention

In general, in one aspect, the invention features an etch method which includes providing a material layer to be etched and supplying a reactive gas to a vicinity of the material layer. A single electric field is supplied to react the reactive gas with the material layer so as to form volatile byproducts of reactive gas and the material layer. The electric field has a frequency in the range from approximately 1 MHz to approximately 11 MHz. In another aspect, the invention features an apparatus for dry-etching a thin film material. The apparatus includes a chamber for supporting the thin film material and a flow passageway associated with the chamber for supplying a reactive gas to the chamber in a vicinity of the thin film material. The apparatus also includes a single electric field generator for developing an oscillating electric field within the chamber to react the reactive gas with the thin film material and thereby form volatile by-products of the reactive gas and the thin film material. The electric field has a frequency in the range from approximately 1 megahertz (MHz) to approximately 11 megahertz (MHz) .

In various implementations, the invention includes one or more the following features. The frequency of the electric field can be in the range of approximately 1.8 to 2.2 MHz, for example, approximately 2 MHz. In general, the frequency of the electric field can be selected to provide a more uniform etch across a surface of the material layer. The frequency of the electric field can also be selected to reduce residue on the etched surface.

In one implementation, the material layer consists essentially of a group member selected from the group consisting of an indium oxide (InO) , a tin oxide (SnO) , a mixture of indium and tin oxides, a compound of indium and of tin and of oxygen having the general formulation In_xSn_yO_z where z is substantially greater than zero but less than 100% and where the sum x+y fills the remainder of the 100%, and a mixture of the preceding ones of said group members. The reactive gas can include a halogen- containing compound.

In yet another implementation, the material layer consists essentially of a metal or metal alloy, such as aluminum or an aluminum alloy. In various implementations, the material layer can be incorporated into a flat panel display.

A mask layer can be provided over the material layer, with the mask layer having one or more apertures defined through the mask layer for exposing corresponding one or more surface portions of the material to products of the reactive gas and the applied electric field. The frequency of the electric field can be selected to reduce damage to the mask layer.

A substrate can be provided below the material layer, and a determination can be made as to when the etch process etches through the material layer to the substrate. The etch process can be halted at or about the time it is determined that the etch process has etched through the material layer to the substrate . In various implementations, the invention features one or more of the following advantages. By using an electric field having a relatively low frequency, a more uniform etch of the thin film layer can be obtained. Similarly a cleaner etch with less residue and less damage to photoresist layers can be obtained. Such advantages can be particularly important in the manufacture of relatively large devices such as flat panel displays. Moreover, these advantages can be obtained through the use of a single RF generator which provides a single RF electric field as a pedestal RF in the vicinity of a substrate-supporting cathode and also provides a plasma RF in the vicinity of a plasma above the material layer.

Brief Description of the Drawing FIG. 1 is a cross-sectional schematic of a reactive ion etch (RIE) system for carrying out a dry etch process in accordance with the invention.

FIGS. 2 and 3 are scanning electron microscope (SEM) micrographs showing the surface of etched Mo/Al-Nd samples.

Description of the Preferred Embodiments Fig. 1 schematically shows in cross-section an RIE system 100. A more detailed mechanical description of the basic etching apparatus may be found in the previously mentioned U.S. Application Serial No.

08/273,382, filed July 7, 1994 by Wong et al . , entitled "METHOD AND APPARATUS FOR ETCHING FILM LAYERS ON LARGE SUBSTRATE, " assigned to the assignee of the present invention, and incorporated herein by reference in its entirety. System 100 includes a substrate-supporting cathode 110 that is spaced-apart from an opposed anode 180 within a low-pressure chamber 105. The anode 180 may be a discrete element as shown or it may be defined by one or more of the inner walls of the etch chamber 105 rather than being a separate element. In one implementation, the inner walls of the chamber define the anode, and the cathode is placed centrally within the chamber so that multiple faces of the cathode oppose corresponding inner walls of the chamber. The latter implementation allows for the simultaneous etch of two or more workpieces in one chamber .

A single RF generator 190 is coupled electrically to the cathode 110 and anode 180 for producing an RF field between the opposed faces of the cathode and anode. The RF field consists essentially of a single frequency.

The frequency (f) of the generated RF field can be in the range of approximately 1 MHz to approximately 11 MHz. The single frequency field generated by the RF generator 190 is used for both plasma creation and ion acceleration. The single frequency field is, therefore, developed as a pedestal RF in the vicinity of the substrate-supporting cathode 110 as well as a plasma RF in the vicinity of the plasma above the workpiece 115. The frequency of the electric field produced by the RF generator 190 can be selected to reduce residue on the etched surface 135 of the workpiece 115.

In certain implementations, a single variable frequency generator is used to apply an RF frequency of about 2 MHz in the vicinity of the plasma above the workpiece 115. When a 2 MHz plasma RF is applied using currently available variable frequency generators, an approximately fifteen percent variation in frequency can occur such that the resulting plasma RF is in the range of about 1.8 to 2.2 MHz. A gas supply 150, which can include a gas container or gas tank, is operatively coupled to the low- pressure chamber 105 for supplying a reactive gas 155 into the chamber 105. When the material to be etched is ITO, the reactive gas 155 can include, for example, one or more halogen-containing compounds such as hydrogen bromide (HBr) , hydrogen iodide (HI) and hydrogen chloride (HC1) . When the material to be etched is aluminum or an aluminum alloy, the reactive gas 155 can include, for example, chlorine (Cl₂) or boron tri-chloride (BC1₃) . The flow rate of the supplied reactive gas 155 is typically approximately 100 to 200 standard cubic centimeters (seem) , although higher or lower flow rates may be desirable in certain implementations. A flow-rate control device 153, such as a valve, is provided for regulating the inflow rate of the reactive gas 155 so as to maintain a desired level of inflow (e.g., 100 seem which is the flow of gas which fills up per minute a volume of 100 cc to a pressure of 1 atmosphere at 0oc) . Usually there is no inert carrier gas such as argon, helium or nitrogen in the input gas stream because more work is needed to exhaust this additional material to maintain low pressure. However, one may use one or more such inert gases as a carrier for the reactive gas 155 if desired.

A pressure regulator 177 is provided along the exhaust path of vacuum pump 170 for maintaining a desired pressure level within chamber 105.

A workpiece 115, which has a material layer 130 to be etched, is mounted on the cathode 110. In certain implementations, the material layer 130 is a transparent- electrode layer. The workpiece 115 can include a substrate 120 onto which the material layer 130 is deposited. The substrate 120 may be composed of, for example, one or more layers of materials such as glass (Si0₂) , silicon nitride (Si₃N₄) , amorphous silicon (a-Si) , poly or mono-crystalline silicon (p-Si or Si) , or other materials as may be suitable for a specific optoelectronic application. The transparent-electrode material layer 130 can be a thin film having a thickness of 1500 angstroms or less and comprising ITO, an indium oxide, a tin oxide or a mixture of these oxides. In other implementations, the material layer 130 is aluminum or an aluminum alloy. A pre-patterned mask 140 that has been formed by photolithography or other suitable techniques is provided about the material layer 130 which is to be etched. The mask 140 has one or more apertures 145 defined therethrough for exposing a surface portion 135 of the material layer 130. Unexposed portions of material layer 130 are protected from etching by the material of the mask 140. The mask 140 can be composed of materials such as photoresist deposited to a thickness of 1.5 μm. The frequency of the electric field produced by the RF generator 190 can be selected to reduce damage to the mask layer 140.

The chamber 105 is sealed to maintain pressures at a desired level in the vicinity of the workpiece 115. The vacuum pump 170 is operated to exhaust gases from the chamber 105 and to create the desired pressure within the chamber .

The RF generator 190 is activated by the etch- controller 176 to provide an oscillating electric field between the cathode 110 and anode 180 for etching through the exposed portion of material layer 130 in a single step and stopping after etch-through has been achieved. The power density (W) of the applied RF field is typically in the vicinity of approximately 0.5 watt per centimeter squared (0.5 W/cm²) as measured relative to the exposed surface area 135 of material layer 130. However, higher or lower power densities can be used depending on the particular application. In general, the etch rate tends to increase at higher power densities. However, at higher power densities, photoresist can become more difficult to remove following the dry etch.

The intensity (volts/cm) of the RF field is sufficiently large to disassociate the reactive gas 155 into atomic constituents (free radicals) . In one embodiment, a field intensity in the range of 300 to 800 volts/cm is created in the vicinity of the exposed surface portion 135 of material layer 130.

A temperature controller 109, such as a fluid- cooled heat exchanger, is coupled to the cathode 110 to maintain the temperature of the cathode in the range of approximately 5 to 80oc. The temperature of the substrate 120 should be maintained at approximately 120oc or less, and preferably at lOOoc or less to prevent damage to the films on the substrate 120. The temperature of the substrate 120 is determined by thermal transfer through the cathode 110 to the temperature controller 109. The temperature of the plasma 160 that forms in the vicinity of the surface portion 135 can be significantly higher and tends to be sporadic as the plasma fluctuates . The applied RF electric field causes the reactive gas 155 to react with the material layer 130 so as to form volatile byproducts of reactive gas and the material layer. The material layer 130 is thereby etched.

A spectroscopic analyzer 175 is provided along the exhaust path of the vacuum pump 170 for optically scanning the exhaust gases 165, analyzing the results and thereby determining the chemical composition of the exhaust gases 165.

The spectroscopic analyzer 175 is coupled to an etch-controller 176 that turns off the RF generator 190 and thereby halts the etch process when the analyzer 175 indicates that effective etch-through has been achieved. A second spectroscopic detector, referred to as an OES (Optical Emission Spectroscope) 108, can also be installed approximately in line with the workpiece surface. The OES 108 is coupled to the etch-controller 176 so as to turn off the RF generator 190 and thereby halt the etch process when effective etch-through is indicated to have been reached according to empirically- determined criteria.

The term 'effective etch-through' is used here to mean the condition when etching has progressed sufficiently far into the material layer 130 so that a useable wiring pattern is created in the material layer 130 without leaving behind undesired shorts or low resistance paths between conductors of that layer that are to be electrically isolated from one another.

TABLE- 1 shows some experimental results obtained for the case where the material layer 130 consists essentially of ITO on a substrate 120 of SiN. The sample size was approximately 550 mm by 650 mm. The flow of the various reactive gases was in the range of approximately 100-300 seem, and the pressure in the chamber was approximately 5-50 milliTorr (mTorr) . In addition, the flow of argon gas was in the range of approximately 0-300 seem. The plasma RF frequency was varied from approximately 13.56 MHz to approximately 2 MHz as indicated by TABLE-1.

In TABLE-1, the uniformity was determined as follows. The depth of the ITO etch was measured at multiple points across the workpiece 115, and the maximum and minimum depths were noted. The uniformity was set equal to one-hundred times the ratio of the difference between the maximum and minimum depths and the sum of the maximum and minimum depths. In other words, (maximum depth) - (minimum depth) uniformity x 100 (maximum depth) + (minimum depth)

TABLE-1

As can be seen from the data in TABLE-1, a reduction in the RF frequency from approximately 13.56 MHz to approximately 2 MHz resulted in a more uniform etch of the ITO layer across the surface of the workpiece

115. For example, using HBr as the reactive gas with a power density of about 0.56 W/cm², the uniformity was only approximately 35% when the plasma RF was 13.56 MHz, whereas the uniformity dropped to about 17% when a plasma RF of about 2 MHz was used. Similarly, using HI as the reactive gas with a power density of about 0.49 W/cm², the uniformity was only approximately 39% when the plasma RF was 13.56 MHz, whereas the uniformity dropped to about 12% when a plasma RF of about 2 MHz was used. Moreover, using a lower plasma RF, the resulting uniformity did not significantly change even when other parameters, such as the power density, were varied. FIGS. 2 and 3 are scanning electron microscope (SEM) micrographs showing etched molybdenum (Mo) aluminum-neodymium (Al-Nd) samples 201, 202. The magnification of the micrographs is approximately twenty and thirty thousand times, respectively. The RF frequency used to etch the sample 201 shown in FIG. 2 was approximately 13.56 MHz, whereas the RF frequency used to etch the sample shown 202 in FIG. 3 was approximately 2 MHz. Using a RF frequency of approximately 2 MHz to etch the surface of the sample 202 resulted in a cleaner etch with less residue and less damage to the photoresist layer. Further details of the etch processes performed with respect to the samples shown in FIGS. 2 and 3 are described below. The samples 201, 202, shown in FIGS. 2 and 3, respectively, included an Al-Nd layer 203 approximately 2500 angstroms thick on an oxide layer (not shown) . The samples 201, 202 also included an Mo layer 205, approximately 750 angstroms thick, on the Al-Nd layer 203. A layer of photoresist 207 was deposited on the Mo layer 205 prior to carrying out the etch process.

The etch process for the sample 201 (FIG. 2) was as follows. First, the Mo layer 205 was etched for about eighty seconds using a reactive gas including SF₆ (approximately 400 seem) and 0₂ (approximately 20 seem) . The chamber pressure was about 60 mTorr, and the total power was approximately 1020 Watts.

Next, the Al-Nd layer 203 was etched for about sixty seconds using a reactive gas containing Ar (approximately 100 seem) and Cl₂ (approximately 10 seem) . The pressure was about 9 mTorr, and the total power was about 2500 Watts. The Al-Nd layer 203 was then etched for about four minutes using a reactive gas including Ar (approximately 80 seem) , Cl₂ (approximately 40 seem) and BC1₃ (approximately 10 seem) . The pressure was about 7.3 mTorr, and the total power was about 2000 Watts.

The etch process for the sample 202 (FIG. 3) was as follows. First, the Mo layer 205 was etched for about three minutes using a reactive gas including SF₆

(approximately 280 seem) and 0₂ (approximately 20 seem) . The chamber pressure was about 60 mTorr, and the total power was approximately 700 Watts.

Next, the Al-Nd layer 203 was etched for about one minute and forty-five seconds using a reactive gas containing BC1₃ (approximately 100 seem) . The pressure was about 15 mTorr, and the total power was about 1500 Watts. The Al-Nd layer 203 was then etched for about one minute using a reactive gas including Cl₂ (approximately 100 seem) and BC1₃ (approximately 15 seem) . The pressure was about 9 mTorr, and the total power was about 1500 Watts.

Next, the Al-Nd layer 203 was etched for about seven minutes using a reactive gas containing Ar (approximately 100 seem) , and Cl₂ (approximately 100 seem) and BC1₃ (approximately 15 seem) . The pressure was about 10 mTorr, and the total power was about 1500 Watts. The Al-Nd layer 203 was then etched for about two minutes using a reactive gas including Ar (approximately 100 seem) , Cl₂ (approxi-mately 50 seem) and BC1₃

(approximately 15 seem) . The pressure was about 8 mTorr, and the total power was about 1500 Watts.

As can be seen from FIGS. 2 and 3, using a RF field of approximately 2 MHz to etch the surface of the sample 202 resulted in a cleaner etch with less residue and less damage to the photoresist layer than the results obtained using a 13.56 MHz field.

The experimental tests and results discussed above are intended to be exemplary only. Other implementations are contemplated within the scope of the following claims .

Claims

What is claimed is:

1. An etch method comprising: providing a material layer to be etched; supplying a reactive gas to a vicinity of the material layer; and supplying a single electric field to react the supplied reactive gas with the material layer so as to form volatile byproducts of reactive gas and the material layer, wherein the electric field has a frequency in the range from approximately 1 megahertz (MHz) to approximately 11 megahertz (MHz) .

2. The etch method of claim 1 wherein the frequency of the electric field is approximately 2 MHz.

3. The etch method of claim 1 wherein the frequency of the electric field is in the range of 1.8

MHz to 2.2 MHz.

4. The etch method of claim 1 wherein the material layer consists essentially of a group member selected from the group consisting of an indium oxide (InO) , a tin oxide (SnO) , a mixture of indium and tin oxides, a compound of indium and of tin and of oxygen having the general formulation In_xSn_yO_z where z is substantially greater than zero but less than 100% and where the sum x+y fills the remainder of the 100%, and a mixture of the preceding ones of said group members.

5. The etch method of claim 4 wherein the reactive gas includes a halogen-containing compound.

6. The etch method of claim 1 wherein the material layer consists essentially of a metal or a metal alloy.

7. The etch method of claim 1 wherein the material layer consists essentially of aluminum.

8. The etch method of claim 1 wherein the material layer consists essentially of an aluminum alloy.

9. The etch method of claim 1 further comprising incorporating the material layer into a flat panel display.

10. The etch method of claim 1 wherein the frequency of the electric field is selected to provide a more uniform etch across a surface of the material layer.

11. The etch method of claim 1 wherein the frequency of the electric field is selected to reduce residue on the etched surface.

12. The etch method of claim 1 further comprising : providing a mask layer over the material layer, the mask layer having one or more apertures defined through the mask layer for exposing corresponding one or more surface portions of the material to products of the reactive gas and the applied electric field.

13. The etch method of claim 12 wherein the frequency of the electric field is selected to reduce damage to the mask layer.

14. The etch method of claim 1 further comprising: providing a substrate below the material layer; determining when the etch process etches through the material layer to the substrate; and halting the etch process at or about the time it is determined that the etch process has etched through the material layer to the substrate.

15. An apparatus for dry-etching a thin film material comprising: a chamber for supporting the thin film material ; a container operatively coupled to the chamber for supplying a reactive gas into the chamber in a vicinity of the thin film material; and a single electric field generator for developing an oscillating electric field within the chamber to react the reactive gas with the thin film material and thereby form volatile by-products of the reactive gas and the thin film material, wherein the electric field has a frequency in the range from approximately 1 megahertz (MHz) to approximately 11 megahertz (MHz) .

16. The apparatus of claim 15 wherein the electric field has a frequency of approximately 2 MHz.

17. The apparatus of claim 15 wherein the electric field has a frequency of in the range of approximately 1.8 to 2.2 MHz.

18. The apparatus of claim 17 further comprising a thin film material supported in the chamber, wherein the thin film material consists essentially of a metal or metal alloy.

19. The apparatus of claim 17 further comprising a thin film material supported in the chamber, wherein the thin film material consists essentially of aluminum or an aluminum alloy.

20. The apparatus of claim 17 further comprising a thin film material supported in the chamber, wherein the thin film material consists essentially of a group member selected from the group consisting of an indium oxide (InO), a tin oxide (SnO) , a mixture of indium and tin oxides, a compound of indium and of tin and of oxygen having the general formulation In_xSn_yO_z where z is substantially greater than zero but less than 100% and where the sum x+y fills the remainder of the 100%, and a mixture of the preceding ones of said group members .