Patent Application
20100133233
The present invention relates to a dry etching method.
In conventional dry etching apparatuses, electrostatic chucks and mechanical chucks have been used as mechanisms for fixing a substrate. One example of electrostatic chucks is a bipolar electrostatic chuck that includes an electrostatic chuck electrode. The electrostatic chuck electrode includes a circular first electrode and second electrodes. The second electrodes include a central electrode on the central side of the first electrode, corresponding to the central portion of a wafer, and a surrounding electrode outside the first electrode. A wafer is chucked on the top surface of the electrostatic chuck electrode by electrostatic forces generated between the first electrode and the second electrodes (see, for example, Patent Document 1). In this bipolar electrostatic chuck, helium gas is supplied to a narrow space between the wafer and the electrostatic chuck electrode to cool a substrate to be processed.
To meet recent demands for miniaturization of electronic devices and communication devices, in quartz oscillators (crystal oscillators) serving as key devices, ultrasmall quartz oscillators having a quartz element size of approximately 1.2 mm have been manufactured by photolithography and practically used. However, there is a demand for still finer quartz oscillators on the order of micrometers. It is known that quartz oscillators of such an order are formed by micromachining a quartz substrate by a dry etching method because quartz oscillators of such an order cannot be processed mechanically (see, for example, Patent Document 2). In this case, a substrate is etched on both sides or etched very deeply on one side to form a quartz oscillator.
Patent Document 1: Japanese Patent Application Publication No. 10-125769 (paragraph 0018 and FIG. 6)
However, when a substrate is continuously etched on both sides or etched very deeply on one side with an etching apparatus having an electrostatic chuck as described above, as the thickness of the substrate to be processed decreases, the substrate has a decreased strength and is susceptible to temperature changes. Thus, a crack may form in the substrate. Furthermore, cooling helium gas present between the substrate and an electrostatic chuck electrode may leak from the crack.
It is an object of the present invention to solve the problems of the prior art and to provide a dry etching method for micromachining a substrate while the substrate is fixed so as not to form a crack even when the substrate is etched on both sides or etched very deeply on one side.
A dry etching method according to the present invention comprises: introducing an etching gas including a fluorocarbon gas and a rare gas into a vacuum chamber; generating plasma in the vacuum chamber having a predetermined pressure; and etching a substrate adhered on an adhesive surface of a heat-conductive sheet disposed on a substrate table. Fixing a substrate on a heat-conductive sheet allows the entire substrate to be uniformly supported and promotes heat conduction to the substrate, which facilitates control of the temperature of the substrate. The substrate can therefore be etched as desired without causing a crack.
A dry etching method according to the present invention comprises: introducing an etching gas including a fluorocarbon gas and a rare gas into a vacuum chamber; generating plasma in the vacuum chamber having a predetermined pressure; etching one side of a substrate to be processed adhered on an adhesive surface of a heat-conductive sheet disposed on a substrate table; detaching the substrate from the heat-conductive sheet and reversing the substrate; adhering the one side on the adhesive surface of the heat-conductive sheet; and etching the other side of the substrate under substantially same conditions as conditions for the one side. Fixing a substrate on a heat-conductive sheet allows the entire substrate to be uniformly supported and promotes heat conduction to the substrate, which facilitates control of the temperature of the substrate. Both sides of the substrate can therefore be etched.
In this case, the substrate is preferably detached from the heat-conductive sheet by heating or UV irradiation. Damage for the substrate can be reduced by detaching the substrate through such a process. Preferably, the substrate is a quartz substrate. Preferably, the heat-conductive sheet has a slit. The slit facilitates the detachment of the substrate from the heat-conductive sheet and decreases air bubbles under the heat-conductive sheet.
In etching, the flow rate of the rare gas preferably ranges from 80% to 95% of the total flow rate of the etching gas, and the rare gas is preferably at least one of Ar, Kr, and Xe. The flow rate of the rare gas below 80% of the total flow rate results in an excessively large number of active species, and etching cannot be performed as desired. The flow rate of the rare gas above 95% results in an excessively small number of active species, and etching cannot be performed sufficiently.
Preferably, the dry etching method is performed in a low-pressure process at 1 Pa or less. At a pressure above 1 Pa, radical reactions are difficult to prevent, making micromachining difficult.
A dry etching method according to the present invention comprises: fixing a heat-conductive sheet on a base; adhering a quartz substrate on an adhesive surface of the heat-conductive sheet; placing the base on a substrate table in a vacuum chamber; introducing an etching gas including a fluorocarbon gas and a rare gas into the vacuum chamber; forming a magnetic neutral line while maintaining the internal pressure of the vacuum chamber at 1 Pa or less; applying an electric field to generate plasma in the vacuum chamber; etching one side of the quartz substrate; detaching the quartz substrate from the heat-conductive sheet and reversing the substrate; adhering the one side of the quartz substrate on the adhesive surface of the heat-conductive sheet; and etching the other side of the quartz substrate under substantially same conditions as conditions for the one side. In etching of a quartz substrate fixed on a heat-conductive sheet using a dry etching apparatus that forms a magnetic neutral line and generates plasma, both sides of the substrate can be etched as desired with high-efficiency plasma while the entire substrate is uniformly supported.
In this case, preferably, the flow rate of the rare gas ranges from 80% to 95% of the total flow rate of the etching gas, the rare gas is at least one of Ar, Kr, and Xe, the heat-conductive sheet has a slit, and the substrate is detached from the heat-conductive sheet by heating or UV irradiation.
A dry etching method according to the present invention allows a substrate to be etched simply as desired without causing a crack in the substrate.
The vacuum chamber 11 includes a lower substrate processing chamber 13 and an upper plasma generation chamber 14. A substrate table 2 is disposed at the center of the bottom of the substrate processing chamber 13. The substrate table 2 includes a substrate electrode 21, an electrostatic chuck electrode 22 disposed on the substrate electrode 21, and a support 23 for supporting the substrate electrode 21 and the electrostatic chuck electrode 22. The substrate electrode 21 is connected to a first high-frequency power source 25 via a blocking capacitor 24, acts as a floating electrode in terms of electric potential, and has negative bias potential. The electrostatic chuck electrode 22 may be a known electrostatic chuck electrode.
In the present invention, a base 27 on which a heat-conductive sheet 26 is placed is fixed with an electrostatic chuck electrode 22, and a substrate S to be processed is adhered on an adhesive surface of the heat-conductive sheet. Fixing the substrate S on the adhesive surface obviates the necessity of fixing the substrate S with an electrostatic chuck electrode, allowing the entire substrate S to be held stably and preventing the occurrence of a crack in the substrate. With such a structure, helium gas (not shown) in the electrostatic chuck electrode 22 has a cooling effect on the substrate S through the heat-conductive sheet 26, allowing the temperature of the substrate S to be controlled and preventing the occurrence of a crack in the substrate S.
Examples of the material of an adhesive layer in the heat-conductive sheet 26 include heat-conductive resins, for example, rubber, such as acrylic or isoprene isobutylene, or resins, such as silicone. The material of an adhesive layer may be any material provided that the adhesive layer can be detached by heating or UV irradiation. The heat-conductive sheet 26 has at least one heat-conductive adhesive surface.
A heat-conductive sheet 26 having a slit may be attached on the base 27. The slit facilitates the detachment of the heat-conductive sheet, and, in some cases, the slit prevents present the occurrence of a crack in the substrate due to the gas, such as air or an etching gas incorporated by evacuation, present between the heat-conductive sheet and the base (i.e., generation of gas bubbles). The shape of the slit may be not only linear, but also polygonal, circular, or a combination thereof. For example, in etching with a striped mask, preferably, a first slit is formed on a diagonal line of a substrate, and a second slit is formed in the direction of the stripes of the striped mask. After a heat-conductive sheet is fixed on the base, the heat-conductive sheet is preferably pressed with a rubber roller, a paddle, or a press machine to prevent such gas from being incorporated between the heat-conductive sheet and the base.
The substrate table 2 faces a top plate 15, which is disposed at the top of the plasma generation chamber 14 and is fixed to the sidewall of the plasma generation chamber 14. The top plate 15 is connected to a gas-inlet line 31 of gas-inlet means 3, which introduce an etching gas into the vacuum chamber 11. The gas-inlet line 31 has two branches, which lead to a rare gas source 33 and a fluorocarbon gas source 34 via gas-flow control means 32.
The top plate 15 may include a shower plate connected to the gas-inlet means 3.
The plasma generation chamber 14 has a cylindrical dielectric sidewall. A magnetic field coil 41 is disposed outside the sidewall as means for generating a magnetic field. The magnetic field coil 41 forms a magnetic neutral loop (not shown) in the plasma generation chamber 14.
A high-frequency antenna coil 42 for generating plasma is disposed between the magnetic field coil 41 and the outside of the sidewall of the plasma generation chamber 14. The high-frequency antenna coil 42 has a parallel antenna structure and constructed such that a voltage can be applied to the high-frequency antenna coil 42 by a second high-frequency power source 43. After a magnetic neutral line is formed by the magnetic field coil 41, an alternating electric field is applied along the magnetic neutral line to generate discharge plasma along the magnetic neutral line.
A mechanism for adjusting the voltage applied to the antenna coil to a predetermined voltage may be disposed.
An etching apparatus thus constituted has a simple structure and can form high-efficiency plasma without mutual interference of applied high-frequency electric fields.
An etching apparatus for performing a dry etching method according to the present invention may include a Faraday shield-like (or electrostatic field shield-like) floating electrode (not shown) inside the high-frequency antenna coil 42. The Faraday shield is a known Faraday shield and is, for example, a metal plate that has a plurality of parallel slits and an antenna coil intersecting the slits at right angles at the longitudinal midpoints of the slits. A metallic frame for equalizing the electric potential of a strip of metal plate is disposed at each longitudinal end of the slits. The metal plate can shield against an electrostatic field of the antenna coil 42 but cannot shield against an induction magnetic field. The induction magnetic field enters plasma and forms an induction electric field. The width of the slit can be appropriately determined for each purpose and ranges from 0.5 to 10 mm, preferably 1 to 2 mm. An excessively wide slit unfavorably causes the penetration of an electrostatic field. The slits may have a thickness of approximately 2 mm.
A method for etching a substrate S to be processed on both sides with the above-described etching apparatus 1 will be described below with reference to
An object to be etched with the etching apparatus 1 is preferably a quartz substrate. A quartz substrate itself can be processed to manufacture, for example, a crystal oscillator on the order of micrometers, which has not been manufactured by conventional machining. A generally-used substrate on which a SiO2 film, a film of a compound containing SiO2, or a film formed of a material for optical elements is formed may be processed.
Examples of the compound containing SiO2 include TEOS—SiO2, phosphosilicate glass, borophosphosilicate glass, rare-earth-doped glass, and low-expansion crystallized-glass. Examples of the material for optical elements include lithium niobate, lithium tantalate, titanium oxide, tantalum oxide, and bismuth oxide.
The substrate may include a SiOCH material film formed by spin coating, such as HSQ or MSQ, a Low-k material film, which is formed of a SiOC material and is formed by CVD and has a relative dielectric constant in the range of 2.0 to 3.2, or a porous material film.
Examples of the SiOCH material include LKD5109r5 (trade name) manufactured by JSR Co., HSG-7000 (trade name) manufactured by Hitachi Chemical Co., Ltd., HOSP (trade name) manufactured by Honeywell Electric Materials, Nanoglass (trade name) manufactured by Honeywell Electric Materials, OCD T-12 (trade name) manufactured by Tokyo Ohka Kogyo Co., Ltd., OCD T-32 (trade name) manufactured by Tokyo Ohka Kogyo Co., Ltd., IPS2.4 (trade name) manufactured by Catalysts & Chemicals Industries Co., Ltd., IPS2.2 (trade name) manufactured by Catalysts & Chemicals Industries Co., Ltd., ALCAP-S5100 (trade name) manufactured by Asahi Kasei Co., and ISM (trade name) manufactured by ULVAC, Inc.
Examples of the SiOC material include Aurola2.7 (trade name) manufactured by ASM Japan K.K., Aurola2.4 (trade name) manufactured by ASM Japan K.K., Orion2.2 (trade name) manufactured by Fastgate Co. and Trikon Technologies Inc., Coral (trade name) manufactured by Novellus Systems Inc., Black Diamond (trade name) manufactured by Applied Materials, Inc. (AMAT), and NCS (trade name) manufactured by Fujitsu Ltd. Examples of the SiOC material also include SiLK (trade name) manufactured by The Dow Chemical Company, Porous-SiLK (trade name) manufactured by The Dow Chemical Company, FLARE (trade name) manufactured by Honeywell Electric Materials, Porous FLARE (trade name) manufactured by Honeywell Electric Materials, and GX-3P (trade name) manufactured by Honeywell Electric Materials.
As illustrated in
The substrate S on which the mask M is formed is fixed on the adhesive surface of the heat-conductive sheet 26 disposed on the base 27 with a surface S1 facing upward (see
To detach a heat-conductive sheet by heating, the temperature may be increased with a hot plate, an air-heating furnace, or near-infrared rays to, for example, approximately 170° C. at which the heat-conductive sheet can be detached.
Examples of the etching gas include gases that contain a fluorocarbon gas and at least one gas selected from rare gases, such as Ar, Xe, and Kr. Examples of the fluorocarbon gas include CF4, C2F6, C4F8, and C3F8. In particular, C4F8 and C3F8 are preferred. In this case, the rare gas is introduced by the gas-flow control means 32 such that the rare gas constitutes 80% to 95% of the total flow rate of the etching gas. The etching gas is introduced in a plasma atmosphere into a vacuum chamber 11 at an operating pressure of 1.0 Pa or less and a flow rate of 100 to 300 sccm, and etching is performed.
According to a dry etching method using such a dry etching apparatus 1, a quartz substrate can be etched to a thickness of 10 μm. For example, a substrate having a thickness in the range of 50 to 150 μm can be etched on both sides at a high aspect ratio, such as a width of 1 μm and a depth in the range of 20 to 70 μm.
In the present example, a quartz substrate was etched on both sides with an etching apparatus 1 illustrated in
A thermal release sheet (Revalpha (trade name), thermal release temperature 170° C.) having an adhesive layer on both sides manufactured by Nitto Denko Co. was prepared as a heat-conductive sheet 26. Slits having shapes illustrated in
The quartz substrate was etched by approximately 45 μm while the etching gas was introduced for 50 minutes. The silicon base was then removed from the etching apparatus 1. The substrate S was detached from the heat-conductive sheet on a hot plate at 120° C. The substrate S was then reversed and was fixed on the heat-conductive sheet with an unetched surface facing upward. The substrate S was etched again by approximately 45 μm under the substantially same conditions while the etching gas was introduced for 50 minutes.
a) and 4(b) show that surfaces S1 and S2 of the substrate S were etched and that the substrate S was etched on both sides without a crack, leaving only a very thin central portion (approximately 10 μm).
Etching was performed under the same conditions as in Example 1, except that the substrate was placed on the silicon base directly rather than through the heat-conductive sheet. After etching of a surface, the silicon base was removed, and a crack was observed in the substrate. The direct installation of the substrate on the base probably resulted in low thermal conductivity and insufficient cooling. The substrate was therefore subjected to high temperature to form a crack.
Etching was performed under the same conditions as in Example 1, except that the substrate S was fixed on a heat-conductive paste applied to the silicon base without providing the heat-conductive sheet. After etching of the backside, the silicon base was removed, and a crack was observed in the substrate S. Gas bubbles in the paste were probably thermally expanded and caused a crack in the substrate S. Removal of the heat-conductive paste required ultrasonic cleaning in alcohol. After the ultrasonic cleaning, additional fine cracks formed in the substrate.
Etching was performed under the same conditions as in Example 1, except that the heat-conductive sheet had slits having the shapes illustrated in
Etching was performed under the same conditions as in Example 1, except that the heat-conductive sheet had a slit having the shape illustrated in
Etching was performed under the same conditions as in Example 1, except that the heat-conductive sheet had slits having the shapes illustrated in
Etching was performed under the same conditions as in Example 1, except that the heat-conductive sheet had a slit having the shape illustrated in
According to the above-described results demonstrate that only when the heat-conductive sheet having the slits in the shapes described in Example 1 is used, the quartz substrate can be etched on both sides with the etching apparatus 1.
According to a dry etching method of the present invention, a substrate can be stably etched on both sides. Thus, the present invention can be utilized in the semiconductor technical field.
a) to 2(c) are schematic views illustrating a double-sided dry etching method according to the present invention.
a) and 4(b) are SEM photographs indicating the results of Example 1: 4(a) is a cross-sectional SEM photograph of a substrate, and 4(b) is an SEM photograph of the substrate viewed from obliquely above.
a) to 5(d) are schematic views illustrating the shapes of slits in heat-conductive sheets used in Comparative Examples 3 to 6: 5(a) for Comparative Example 3, 5(b) for Comparative Example 4, 5(c) for Comparative Example 5, and 5(d) for Comparative Example 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-127789 | May 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/058534 | 5/8/2008 | WO | 00 | 12/8/2009 |
