JPH11335874A - Working of zinc oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the working precision, to accelerate etching rate and to solve the problems of corrosiveness and toxicity by using a process gas contg. methane at the time of dry etching treatment of a film formed on a substrate. SOLUTION: An SiO2 layer 2 is formed on the surface of a silicon substrate 1 by a thermal oxidation method, and a ZnO film 3 is formed on the SiO2 layer by a magnetron sputtering method. Al is vapor-deposited on the ZnO film 3 to form Al electrically conductive film 5, a resist 6 is applied on the surface, and the resist 6 is patterned by an electron beam plotting method. Then, an electrically conductive film 5 is etched, the resist 6 is peeled, and the ZnO film 3 is dry-etched by using a reactive ion etching device. As a process gas for the dry etching, a gaseous mixture of methane and argon is used. The mixing ratio of methane is controlled in the range of 2 to 8 mol.%. The etching rate of ZnO is about 100 Angstron/min, and the etching rate of Al is about 0 Angstron/min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a zinc oxide film, and more particularly to a dry etching process for a zinc oxide film formed on a substrate.

[0002]

2. Description of the Related Art Zinc oxide (ZnO) has been widely used as a piezoelectric material for surface acoustic wave filters. ZnO has the advantage that the material is inexpensive and good quality crystals with high piezoelectric effect can be obtained. Also, ZnO
Is optically transparent and has been studied variously as a waveguide layer of an active optical integrated device. Further, in recent years, demand for a transparent electrode has been increasing due to a reduction in resistance.

In order to use ZnO for the above-mentioned various uses, it is necessary to process ZnO, and various etching methods have been studied to obtain a desired shape. The etching method is roughly classified into wet etching in which a sample is immersed in a chemical and dry etching using a gas phase etching medium. H ₃ PO ₄ : CH ₃ COO for wet etching
Although H: H ₂ O (1: 1: 30) is used, there is no anisotropy and a high aspect ratio cannot be achieved. That is, Z
When the nO film is processed into an uneven shape (assuming that a grating is formed on the ZnO film), if anisotropic etching is possible, the aspect ratio b / a can be obtained as shown in FIG. And a desired rectangular shape with a high value can be obtained.
However, wet etching progresses isotropically, so that an undercut occurs, and as shown in FIG. 3B, there is a problem that processing accuracy is deteriorated.

On the other hand, in the conventional dry etching, a mixed gas of CF ₂ Cl ₂ and Ar is used as an etching medium, but the etching rate for ZnO is as low as 21 angstroms / min, which is disadvantageous for mass production. In addition, the reaction product may be corrosive or toxic due to containing chlorine, and handling is difficult. In addition, it is subject to CFC regulations.

It is an object of the present invention to provide a method for processing a zinc oxide film which has high processing accuracy and etching rate and does not cause problems of corrosiveness and toxicity.

[0006]

In order to achieve the above objects, a method for processing a zinc oxide film according to the present invention provides a method for dry etching of a zinc oxide film formed on a substrate using methane (CH ₄ ). The process gas contained was used.

By performing dry etching using a process gas containing methane, ZnO reacts with CH ₄ to form volatile Zn (CH ₃ ) ₂ and is etched. Oxygen is volatilized as CO ₂ and H ₂ O. This etching proceeds anisotropically, can be processed into an accurate rectangular shape, can achieve an etching rate of 100 Å / min depending on the etching conditions, and can be mass-produced. In addition, it can be freely implemented out of the scope of the regulation of CFCs, and there is no problem of corrosion and toxicity due to chlorine.

Further, in the present invention, a mixture of methane and a diluent gas is used as the process gas, and as the diluent gas, it is preferable to use a rare gas, H _2, or the like, particularly, argon (Ar). These diluting gases have an effect of preventing C and the like from being polymerized and deposited.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a method for processing a zinc oxide film according to the present invention will be described with reference to the accompanying drawings.

One embodiment described here is shown in FIG.
As shown in FIG.
An O ₂ layer 2 is formed, a ZnO film 3 is formed on the SiO ₂ layer 2, and a grating 4 having a rectangular cross section is formed on the surface of the ZnO film 3. The ZnO film 3 functions as an optical waveguide having an acousto-optic effect, and the grating 4 functions as a light input / output coupling unit.

In order to manufacture the above surface acoustic wave device, first, a ZnO film 3 is formed on the SiO ₂ layer 2 by a magnetron sputtering method. Next, on the ZnO film 3, A
1 is deposited to form a conductive film, and a resist is applied thereon, and the resist is patterned by an electron beam lithography method. FIG. 1A shows a patterned state, 5 shows an Al conductive film, and 6 shows a patterned resist.

Next, the Al conductive film 5 is etched to remove the resist 6 (see FIG. 1B). Next, the ZnO film 3 is dry-etched using a reactive ion etching apparatus. In this etching apparatus, as shown in FIG. 2, an anode electrode 12 and a cathode electrode 13 are arranged in parallel at a predetermined interval in an airtightly maintained etching chamber 11. The anode electrode 12 is grounded, the wafer 13 (the substrate 1 in the state shown in FIG. 1B) is attached to the cathode electrode 13, and the high-frequency power source 1
4 applies a high frequency. Further, a process gas is sent into the chamber 11. This process gas is a mixed gas of methane and argon, and the mixing ratio of methane is 2
It is adjusted in the range of ８8 mol%.

Further, the chamber 11 is provided with a turbo molecular pump 16 and an oil rotary pump 1 through a variable exhaust valve 15.
7 is connected. In addition, a load lock chamber 21 is installed adjacent to the chamber 11, and the load lock chamber 2
1 is connected to a turbo molecular pump 22 and an oil rotary pump 23.

Here, various conditions of dry etching will be described. Electrodes (anode, cathode): 160 mm in diameter High frequency power supply: 13.56 MHz, MAX 300 W Gas flow rate: CH ₄ / Ar = 1/24 SCCM Process pressure: 20 mTorr RF power: 70 W Etching time: 20 min

As a result of performing dry etching under the above conditions, the etching rate of ZnO was 100 Å / min, and the etching rate of Al was almost 0 Å / min. In the etching process, ZnO reacts with CH ₄ to form volatile Zn (CH ₃ ) ₂
And proceed. Oxygen is volatilized as CO ₂ and H ₂ O. Ar has an effect of preventing C and the like from being polymerized and deposited on the ZnO film.

In dry etching using a process gas containing CH ₄ , the etching rate is changed from 21 Å / min to 100 Å / mi.
n, and mass productivity can be ensured. In addition, etching has anisotropy, and accurate rectangular unevenness can be formed with a high aspect ratio as shown in FIG. In addition, there is an advantage that the process gas does not contain Freon or chlorine, and legal regulations and handling restrictions are eliminated.

The method for processing a zinc oxide film according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In particular, the CH ₄ dilution gas may be a rare gas such as He or Ne, H _2, or the like in addition to Ar. The ZnO film to be processed is used not only as an optical waveguide but also as a piezoelectric or transparent material for various uses.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing one embodiment of a method for processing a zinc oxide film according to the present invention.

FIG. 2 is a schematic configuration diagram showing a reactive ion etching apparatus used in the present invention.

FIG. 3 shows an uneven shape formed by etching;
(A) shows processing by anisotropic etching, and (B) shows processing by isotropic etching.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 silicon substrate 2 SiO ₂ layer 3 ZnO film 5 Al conductive film 6 resist

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01L 41/22 H01L 41/22 Z (72) Inventor Masatoshi Kitamon 36 Takedawaraya-cho, Fushimi-ku, Kyoto-shi, Kyoto Prefecture Samco International Co., Ltd. Inside the research institute (72) Inventor Noritake Kobuya Inside Samco International Research Institute, 36, Takedawaraya-cho, Fushimi-ku, Kyoto-shi, Kyoto

Claims (3)

[Claims] 1. A method for processing a zinc oxide film, wherein a process gas containing methane is used for dry etching of a zinc oxide film formed on a substrate. 2. The method according to claim 1, wherein the process gas is a mixed gas of methane and argon. 3. The processing method according to claim 2, wherein the mixing ratio of methane in the mixed gas of methane and argon is 2 to 8 mol%.