JPH06244149A - Pattern etching method for SiC - Google Patents

Abstract

(57) [Abstract] [Purpose] A SiC substrate is etched into a desired shape at high speed by a simple process, and a smooth finished surface is obtained. [Structure] A pattern mask is formed of a resist material on a SiC substrate, and [Ar / (CBrF ₃ + Ar)] = 5
Reactive ion beam etching is performed using a mixed gas of 0 to 95% of CBrF ₃ and Ar. [Effect] Since the etching rate of the SiC substrate is approximately the same as that of the resist, direct pattern etching can be performed on the resist without performing lift-off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, SiC or SiC as a blue semiconductor laser material or an environment-resistant semiconductor material.
SiC that can be used when creating a diffraction grating
The present invention relates to a highly efficient etching method for (silicon carbide).

[0002]

2. Description of the Related Art As a diffraction grating for synchrotron radiation (SR light) and short wavelength, high power lasers, it is stable up to a relatively high temperature even when the temperature rises due to these high energy radiation, and the thermal conductivity is high. Due to its high rate, a SiC diffraction grating with good cooling efficiency is ideal. However, even if an attempt is made to engrave the diffraction grating pattern directly on the SiC substrate by dry etching such as the ion beam method, the resist is etched faster than the SiC substrate, so that the diffraction grating pattern is formed directly on the SiC substrate. It was difficult to do. Therefore, conventionally, the following method has been devised.

First, as shown in FIG. 5, a resist pattern 55 (5
3 is the original resist layer), and after lift-off, A
l The reverse pattern 56 is formed.

CF using this Al pattern 56 as a mask
₄ and CF ₄ + O ₂ ion beam 57 to carry out reactive ion etching (RIE) to obtain a desired pattern 58 on SiC (JW Palmour et al., "
Dry Etching of β-SiC inCF4 and CF4 + 02 mixtures ",
J. Vac. Sci. Technol. A4 (3), May / Jun 1986, p.590-5
93).

In another method, as shown in FIG. 6, SiC is used.
A PMMA diffraction grating pattern 64 is created by applying PMMA 63 on the substrate 62 and irradiating it with an electron beam 65 so as to form a diffraction grating pattern (electron beam lithography). Similarly, a reverse Cr pattern 66 is formed from this resist pattern 64 by lift-off.
Reactive ion beam etching (RIBE) with the reactive ion beam 67 of CF ₄ + O ₂ is performed to obtain SiC6.
2. Obtain the diffraction grating pattern on (Shinji Matsui et a
l., "Reactive Ion-Beam Etching of Silicon Carbid
e ", Japanese Journal of Applied Physics, Vol. 20, No.
1, January, 1981, pp.L38-L40).

[0006]

According to the method of FIG.
Since the etching of C is performed by RIE, the SiC 51 is exposed to the plasma during the etching, and the etching surface becomes very rough. Therefore, when it is used as a diffraction grating, there is a problem that it is impossible to perform high-precision spectroscopy.

In the method of FIG. 6, the resist pattern 64 is formed by electron beam lithography, so that it takes a long time to draw the pattern. In particular, since a diffraction grating for SR (synchronized light) needs to have a large area, it is difficult to use the electron beam lithography in terms of production efficiency. Also, in FIG.
In both methods of FIG. 6, in order to increase the etching selectivity ratio of the SiC substrate to the mask ([SiC substrate etching rate] / [mask etching rate]), lift-off is performed from the photoresists 55 and 64 to mask the Al or Cr mask 56. , 66, and has a drawback that an additional lift-off process is required.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a SiC pattern capable of rapidly etching a SiC substrate into a desired pattern by a simple process. An object is to provide an etching method.

[0009]

A method for etching a pattern of SiC according to the present invention, which has been made to solve the above-mentioned problems, forms a pattern mask of a resist material on a substrate of SiC, and (CBrF ₃ + Ar) Etching of a SiC substrate is performed by irradiating anisotropic plasma etching such as reactive ion beam generated from a mixed gas of CBrF ₃ and Ar with a partial pressure ratio of Ar of 50 to 95% from vertically above the substrate. It is to do.

[0010]

[Function] FIG. 1 shows various composition ratios (CBrF ₃ + A).
r) The Ar content in the mixed gas and the photoresist standardized by the ion current density when reactive ion beam etching is performed using the mixed gas (here, OFPR5000 manufactured by Tokyo Ohka Co., Ltd.) and The relationship with the etching rate of SiC is shown. As shown in FIG. 1, CBr
For F ₃ only ([Ar / (CBrF ₃ + Ar)] = 0
%) Or only Ar ([Ar / (CBrF ₃ +
Ar)] = 100%), the etching rate of the resist is more than double that of SiC. That is, under such a condition, SiC, which is the object of etching, is hardly etched, while the resist is etched at a rate more than twice that rate. Therefore, conventionally, as described above, an extra step of forming a mask of Al or Cr by lift-off has been included. Such a phenomenon also occurs when other photoresist materials are used when reactive ion beam etching is performed on SiC.

On the other hand, [Ar / (CBrF ₃ + A
r)] is in the range of 50 to 95%, the etching rate of SiC is specifically increased, and is almost the same as the etching rate of resist. Therefore, as shown in FIG. 2, the selection ratio ([SiC etching rate] / [resist etching rate]) is also 0.5 or less in other ranges, but is close to 1 in this range. Becomes Therefore, by performing the reactive ion beam etching under such a condition, the pattern etching of the SiC substrate can be performed at a high speed with only the photoresist without requiring an extra step of lift-off.

[0012]

EXAMPLE As a first example of the present invention, a laminar type Si
A method of manufacturing the C diffraction grating will be described with reference to FIG. First, a sintered SiC substrate 31 is prepared (a), and a β-SiC single crystal layer 32 is deposited on the surface thereof by CVD. This surface is optically polished to reveal a (2,2,0) oriented surface on the surface (b). Further, a photoresist (here, OFPR5000 manufactured by Tokyo Ohka Co., Ltd.) layer 33 having a thickness of 300 nm is formed on this surface by spin coating (c). After coating, the substrate is placed in a 90 ° C. fresh air oven and baked for 30 minutes.
The CVD-SiC layer 32 is not β-SiC but α-.
SiC may be used, and the orientation plane is not limited to (2,2,0), but (1,1,1) or a mixed orientation film may be used. Furthermore, amorphous SiC may be used. The material of the photoresist is not limited to the OFPR5000, and other photoresists may be used.

Next, holographic exposure is performed to form a pattern of the laminar diffraction grating. That is, by irradiating the plane wave 34 from two directions and forming interference fringes on the resist 33, a parallel line-shaped latent image having a sinusoidal cross-sectional exposure density is formed in the resist layer 33 (d). Here, He-Cd laser light (wavelength λ = 441.6 nm) is used as the exposure light, and 1200 lines / n are used.
Create a parallel line pattern of m. After the exposure, the resist mask 35 having a parallel line shape and a half-sine cross section is left on the substrate 32 by processing with a dedicated developer (e). Here, by appropriately adjusting the exposure time and the phenomenon time, the ratio of the portion covered with the resist 35 and the portion not covered with the resist 35 (that is, the portion where the SiC substrate 32 is exposed) on the substrate 32 ( L & S ratio) can be set arbitrarily. Here, the L & S ratio is 1: 1. In the method of this embodiment, since the diffraction grating pattern is created by holographic exposure, the periodic error, which is the most important characteristic of the diffraction grating, is unlikely to occur (this easily occurs in the electron beam lithography performed by the method of FIG. 6). A high-precision diffraction grating can be manufactured.

The exposure wavefront of the holographic exposure method is a two-beam spherical wave with a concave diffraction grating, and at least one of the two beams is an aspherical wave when manufacturing an aberration-correcting diffraction grating.

Dry etching is performed by irradiating the reactive ion beam 36 using a mixed gas of CBrF ₃ and Ar from a direction perpendicular to the substrate 32 with the resist 35 having the diffraction grating pattern thus formed as a mask. (F). The composition of this mixed gas is [Ar / (CBrF ₃
+ Ar)] = 75%. This ion beam etching is performed until the etching groove has a predetermined depth (10 nm) (the relationship between the etching time and the groove depth is experimentally obtained in advance). Finally, the photoresist 35 remaining on the surface is removed by ashing with O ₂ plasma (a resist stripping solution or a solvent may be used) to obtain the intended laminar diffraction grating 37.

Laminar type diffraction grating 37 produced in this way
Can be used as it is in the wavelength region where the reflectance of SiC is sufficiently high. Further, in a wavelength region where the reflectance of SiC is low, the reflectance is increased by using a coating of gold (Au), platinum (Pt) or the like, or by coating an X-ray multilayer film.

The method according to the present invention can be used not only for producing a laminar diffraction grating but also for producing an arbitrary pattern. For example, as shown in FIG.
Si with a resist film formed in the step (c) of the above embodiment
Pattern exposure is performed on the C substrate 32 (FIG. 4A) with a photomask 41 having an arbitrary pattern to form a resist 44 having a desired pattern (c). And likewise,
(CBrF ₃ + Ar) reactive ion beam 45 ([Ar
/ (CBrF ₃ + Ar)] = 50 to 95%), it is possible to easily and efficiently form the pattern 46 on the SiC substrate 32, which has been difficult in the past.

[0018]

In the SiC pattern etching method according to the present invention, since the etching rate of SiC is about the same as the etching rate of the resist, the SiC substrate is directly etched by the resist mask without the extra step of lift-off. Pattern etching becomes possible. Moreover, since the SiC substrate is not exposed to plasma, a smooth surface can be obtained. Therefore, a desired pattern can be etched on SiC by a simple and short process, and for example, it has excellent heat resistance and
It is possible to manufacture a laminar type diffraction grating formed of only SiC with good cooling efficiency. Ar contained in the mixed gas also has a function of removing impurities sputtered from the chamber during etching and cleaning the inside of the apparatus. Therefore, the maintenance interval of the etching apparatus becomes long and the maintenance becomes easy.

[Brief description of drawings]

FIG. 1 is a photoresist and S standardized by Ar content in a mixed gas and ion current density in reactive ion etching using a (CBrF ₃ + Ar) mixed gas.
The graph of the relationship with the etching rate of iC.

FIG. 2 is a graph in which the selection ratio is plotted again on the vertical axis of the data of FIG.

FIG. 3 is a laminar type SiC that is a first embodiment of the present invention.
Explanatory drawing of the process of creating a diffraction grating.

FIG. 4 is an explanatory view of a process of forming an arbitrary pattern on a SiC substrate which is a second embodiment of the present invention.

FIG. 5 is an explanatory view of a step of performing pattern etching on a SiC substrate by a conventional method.

FIG. 6 is an explanatory view of a step of performing pattern etching on a SiC substrate by another conventional method.

[Explanation of symbols]

31 ... SiC substrate 32 ... β-SiC
Single crystal layers 33, 35 ... Photoresist 34 ... Holographic exposure plane wave 36 ... (CBrF ₃ + Ar) reactive ion beam 37 ... Laminar diffraction grating 41 ... Photomask 44 ... Photoresist pattern 46 ... Pattern on SiC substrate

Claims (1)

[Claims] 1. A pattern mask is formed of a resist material on a SiC substrate, and A for (CBrF ₃ + Ar) is formed.
Etching of a SiC substrate is performed by irradiating anisotropic plasma etching such as a reactive ion beam generated from a mixed gas of CBrF ₃ and Ar with a partial pressure ratio of r of 50 to 95% from vertically above the substrate. A pattern etching method of SiC, which is performed.