JPH04337702A - Formation of diffraction grating - Google Patents

Abstract

PURPOSE:To obtain a rectangular resist diffraction grating and to improve the dimensional accuracy of patterns as well as to shorten stages by executing a two luminous flux interference exposing stage using an assigned photoresist and a UV laser, etc., and a developing stage using an assigned developer. CONSTITUTION:Polyvinyl phenol or a copolymer with suitable different monomers is used for a base resin and a photoresist 2 which is quinonediazides is used for a photosensitive agent. An assigned photoresist layer 2 is irradiated with two luminous fluxes at the incident angle theta corresponding to a desired period by the two luminous flux exposing method using a He-Cd laser which is the UV laser and is thereby exposed. The assigned photoresist layer 2 is in succession developed with the alkaline developer, by which the rectanglar diffraction grating pattern 3 of the photoresist meeting the degree of the photosensitivity by the intensity distribution of the interference fringes generated by the interference exposing is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a diffraction grating, and more particularly to a method for producing an etching mask for producing a diffraction grating.

0002

2. Description of the Related Art Diffraction gratings are used in various optical circuit elements such as filters, optical couplers, distributed feedback lasers, and distributed Bragg reflection lasers in optical ICs. Diffraction gratings used in optical integrated circuits have a period of approximately 0.1 μm ~
It has a thickness of 1.0 μm and is mainly made using a holographic method.

The principle of the holographic exposure method is that a coherent light beam emitted from a single light source is made into a uniform parallel beam, split into two beams with equal amplitude intensity by a beam splitter, and the split beams are photographed at an intersection angle of 2θ. incident on the resist surface. The two beams generate interference fringes on the photoresist surface and sensitize the photoresist according to the light intensity distribution of the interference fringes. Next, an etching mask is formed by developing the photoresist.

[0004] In recent years, etching of submicron patterns has become the mainstream dry process, and resist patterns must be able to withstand this etching process. Among these, anisotropic etching methods such as sputter etching, ion beam etching, and ion milling can faithfully realize a pattern shape. The pattern shape obtained by this method is
It is determined by the etching selectivity of the mask material and the sample, and this is 3
If the difference in etching speed is small, the resist will also be etched at the same time, resulting in a sinusoidal etched shape. Therefore, a resist with sufficient resist thickness and a vertical cross-sectional shape is required.

A conventional method for creating an etching mask will be explained with reference to the drawings.

In the first method, as shown in FIG. 3, a photoresist is coated on a substrate 9, and after prebaking, a photoresist layer 10 is obtained (FIG. 3(b)). Next, He-Cd
Exposure is performed by two-beam interferometry using a laser (λ = 325 nm) (FIG. 3(c)), and development is performed to form the desired photoresist diffraction grating pattern 11 (FIG. 3(d)).
).

In the second method, as shown in FIG. 2, a second etching mask layer 5 (organic or metal) is formed on the substrate 4 by coating or vapor deposition (FIG. 2(a)). Next, a photoresist is applied, and after prebaking, a photoresist layer 6 is obtained (FIG. 2(b)). Next, exposure is performed by two-beam interferometry using a He-Cd laser (λ = 325 nm) (Fig. 2(c)), followed by development to form a desired photoresist diffraction grating pattern 7 (Fig. 2(c)). 2(d)
). Further, wet etching is performed using the photoresist diffraction grating pattern 7 as a mask to etch the second etching mask layer 5 (FIG. 2(e)). In this way, a multilayer diffraction grating pattern 8 is formed.

[0008]

The method for forming an etching mask for a diffraction grating described above has the following problems. That is, in the first method, the layer thickness of the single-layer resist, which is related to pattern uniformity and resist cross-sectional shape, cannot be made thicker than the pattern line width. Furthermore, since the light intensity during interference exposure exhibits a sinusoidal distribution, the cross-sectional shape of the resist follows this and may be sinusoidal or S-shaped. For this reason,
The cross-sectional shape of the pattern etched using this resist as a mask has a tapered shape. Furthermore, if the pattern line width is, for example, 0.2 μm, the resist layer thickness is also limited to 0.2 μm, so dry etching also progresses etching of the photoresist mask, making it impossible to form deep grooves. First, it has been impossible to form a thick square wave pattern that is desirable for highly accurate pattern transfer by dry etching.

In the second method, the thickness and shape of the first etching mask layer are improved, but after patterning the photoresist layer 6 in patterning the second etching mask layer 5, When forming the pattern of the second etching mask layer 5 using the diffraction grating pattern 7 as a mask, a dedicated etching process is required, which increases the pattern forming process and reduces dimensional accuracy.
It may not be possible to create a good diffraction grating. In particular, in the production of fine diffraction gratings with a period of 0.1 μm to 1.0 μm, the yield was low and this was a big problem.

Other methods for producing a diffraction grating include linear drawing using an electron beam exposure method and maskless processing using a focused ion beam. Since these are charged beams, it is possible to converge the beam diameter to 0.1 μm or less, and fine patterns can be drawn directly with high precision, but on the other hand, due to proximity effects and back scattering, ,0
．． It is difficult to draw a diffraction grating with a period of 3 μm or less on a thick resist and a thick substrate. Furthermore, there is a problem that throughput and yield decrease as patterns become finer.

The present invention was made to solve the problems of the prior art described above, and its purpose is to provide a method for creating a square wave etching mask for creating a diffraction grating with a fine period. That's true.

0012

[Means for Solving the Problems] The present invention provides a pattern forming method for forming a diffraction grating on a substrate, in which a designated photoresist is used, and a two-beam interference exposure step using an ultraviolet laser or the like and a developing step using a designated developer are performed. A method for producing a diffraction grating characterized by the following characteristics.

[0013] For the photoresist, it is desirable to use a base resin that is as transparent (with low absorption) to the exposure wavelength as possible, and is made of polyvinylphenol or a resin copolymerized with a suitable different monomer, such as styrene, It is desirable to use other styrene derivatives such as para-methylstyrene and α-methylstyrene.

The photosensitizer is a quinone diazide, such as 1,2 naphthoquinone diazide 5-sulfonyl chloride or 1,2 naphthoquinone diazide 4-sulfonyl chloride, and a carbonyl group such as bisphenol A which has no absorption at the exposure wavelength. It is desirable to use a compound bound to a compound that does not have it.

The main solvent used is, for example, ethyl lactate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, ethyl lactate, diacetone alcohol, cyclohexanone, etc., and the photoresist film thickness used is 3000 Å or less. The laser for two-beam interference exposure in the exposure process is an ultraviolet laser whose oscillation wavelength is in the ultraviolet region, and the developer in the development process is
For example, it is desirable to use an alkaline aqueous solution such as trimethylhydroxyethyl, ammonium hydroxide, sodium hydroxide, potassium hydroxide, tetramethylammonium, or hydroxide aqueous solution.

[0016]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing the steps of one embodiment of the method for producing a diffraction grating based on the present invention. First, the semiconductor substrate 1 is wiped and cleaned with a surfactant, then ultrasonic cleaning with an organic solvent is repeated 2 to 3 times, dried with N2 blow, and heat treated at 200°C for 30 minutes (Fig. 1(a)). Subsequently, hexamethyldisilazane (trade name: HMDS: manufactured by Chisso Corporation), which is an adhesion promoter, was spin coated, and 150
Heat treatment is performed at °C for 10 minutes.

Next, a photoresist for two-beam interference exposure diluted as desired is applied to the entire surface of the substrate 1 to form a photoresist layer 2, and a photoresist layer 2 is formed using a hot plate at 115°.
C. Soft bake for 45 seconds. In this example, the resist composition used was polyvinylphenol (trade name: Maruka Linker, average molecular weight 15,000, manufactured by Maruzen Petrochemical Co., Ltd.).
: polystyrene equivalent) and naphthoquinone diazide-5-
Sulfonyl chloride and 2,3,4 trihydroxybenzophenone ester compound (sensitizer) in a weight ratio of 3:1
Dissolve the mixture in ethyl cellosolve acetate,
The sample was filtered with a 0.2 μm Teflon membrane filter. The thickness of photoresist layer 2 is 1000
Approximately Å to 1200 Å is suitable. (Figure 1(b)).

Next, for example, a He-
Using a two-beam interference exposure method using a Cd laser (wavelength λ = 325 nm), the specified photoresist layer 2 is exposed by irradiating two light beams at an incident angle θ corresponding to a desired period (see FIG. 1).
c)).

Subsequently, by developing the specified photoresist layer 2 with an alkaline developer, a rectangular diffraction grating pattern 3 of the photoresist is formed according to the degree of exposure due to the intensity distribution of interference fringes generated by interference exposure. It is formed(
Figure 1(d)). Then, using this rectangular diffraction grating resist pattern 3 as an etching mask, the semiconductor substrate 1 is
For wet etching, for example, H3PO4 or NH4
A diffraction grating can be obtained by performing etching using an OH-based etching solution or, in the case of dry etching, using a Cl2-based gas, etc., and then removing the etching mask layer; however, the present invention is limited only to the above embodiments. For example, any type of ultraviolet laser for interference exposure may be used as long as the wavelength is in the ultraviolet region. Further, in the above embodiments, a semiconductor substrate is used, but glass or optical glass may also be used.

[0020]

[Effect of the invention] As explained above, according to the present invention, (1
) A rectangular resist grating pattern is obtained. (2) Pattern dimensional accuracy can be improved. (3) The process can be shortened. (4) Yield can be improved. Effects such as these are brought about.

[Brief explanation of drawings]

FIG. 1 is a process sectional view showing the process of one embodiment of the present invention.

FIG. 2 is a process cross-sectional view of a conventional method for producing a diffraction grating.

FIG. 3 is a process cross-sectional view of a conventional method for producing a diffraction grating.

[Explanation of symbols]

1 Substrate 2 Specified photoresist layer 3 Specified photoresist rectangular grating pattern 4 Substrate 5 Second etching mask layer 6 Photoresist layer 7 Photoresist grating pattern 8 Multilayer diffraction grating pattern 9 Substrate

Claims (2)

[Claims] Claim 1: In a pattern forming method for forming a diffraction grating on a substrate, the base resin is polyvinyl phenol or a copolymer with a suitable different type of monomer, and the photosensitive agent is a photoresist of quinonediazides, Two-beam interference exposure process using an interference exposure laser,
A method for creating a diffraction grating characterized by performing a development process using an alkaline aqueous solution. 2. The film thickness of the photoresist is 3000.
2. The method of forming a diffraction grating according to claim 1, wherein the interference exposure laser is an ultraviolet laser.