JP2936187B2 - Method of forming resist pattern - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming (producing) a resist pattern having a high aspect ratio, a photoresist used therefor, and a method for producing a diffraction grating from the resist pattern formed by the method.

[0002]

2. Description of the Related Art A diffraction grating is, for example, a distributed feedback type (Dist.
ributed FeedBack) used for lasers. Distributed feedback lasers are more excellent in monochromaticity than Fabry-Perot lasers, and are used in various fields such as light sources for communication. FIG. 6 is a sectional view showing the configuration of a distributed feedback laser. A waveguide layer 42 is provided adjacent to the laser active layer 41, and the waveguide layer 42
A grating (diffraction grating) 43 is engraved on the top. The above two layers are called a core part. Cladding layers 44 are formed above and below the core. The photons generated in the active layer 41 propagate along the laser axis direction and are scattered by the diffraction grating 43 on the waveguide layer 42, so that laser oscillation is performed. Unlike a Fabry-Perot type, a distributed feedback type laser does not require mirror surfaces at both ends, so that the laser and the waveguide can be formed on the same substrate and are suitable for integration.

In general, the pitch of a diffraction grating required for a distributed feedback laser is 0.36 μm or less. Opt. Lett., Vo.
As reported in l.13, No.7 (1988), it is generally made as follows. First, a photoresist is uniformly applied on a substrate by, for example, a spin coating method. Next, a diffraction grating pattern is formed by interference fringes produced by the two-beam interference exposure method. Thereafter, by developing, a resist pattern having the same pattern as the diffraction grating pattern is formed.

Since the substrate is exposed from a portion of the resist pattern where the resist is not placed, the exposed substrate portion is removed by etching thereafter, and a groove is dug. At this time, since the resist is also thinned by the etching, the thickness of the resist pattern is preferably about 1000 ° or more. Finally, the resist pattern is removed by a solvent or other means. Thus, a predetermined interval (pitch) on the substrate
Thus, a diffraction grating in which grooves are arranged can be obtained.

[0005]

The conventional resist pattern has a problem that the aspect ratio (aspect ratio) is low. When the two-beam interference exposure method is used, the aspect ratio generally decreases as the thickness of the resist increases. When the aspect ratio is low, for example, a groove of a diffraction grating to be formed becomes shallow, so that the performance of the diffraction grating decreases.

Accordingly, an object of the present invention is to form a resist pattern having a high aspect ratio.

[0007]

Means for Solving the Problems Conventionally used photoresists have an A-parameter at G-line (wavelength 438 nm).
And the B parameter is 0.10 (referred to as resist Z). The inventors of the present invention have studied and studied various resists focusing on the A and B parameters. As a result, when a photoresist having an A parameter of 0.6 or more and a B parameter of 0.2 or more is used, a high aspect ratio is obtained. It has been found that a resist pattern can be obtained, and the present invention has been accomplished.

Therefore, the present invention firstly provides a method for forming a resist pattern by exposing a photoresist to a diffraction grating pattern having a pitch of 0.36 μm or less by a two-beam interference exposure method and developing the photoresist. A method of forming a resist pattern, wherein a photoresist having an A parameter of 0.6 or more and a B parameter of 0.2 or more at G line is used.

Further, according to the present invention, there is provided a method of forming a photoresist having a pitch of 0.36, wherein the A parameter in the G line is 0.6 or more and the B parameter is 0.2 or more.
Photoresist for forming diffraction grating pattern of less than μm ”
I will provide a. Furthermore, the present invention provides a first step of applying a photoresist having an A parameter of 0.6 or more on a substrate and a B parameter of 0.2 or more on a substrate; A second step of forming a resist pattern by exposing and developing a diffraction grating pattern having a pitch of 0.36 μm or less, and a third step of removing a portion of the substrate on which the resist is not placed. When,
And a fourth step of removing the resist. "

[0010]

The diffraction grating pattern can be formed by a two-beam interference exposure method, an electron beam drawing method, a mask pattern exposure method, or the like. The electron beam drawing method has poor throughput, and the mask pattern exposure method makes it difficult to form a diffraction grating having a pitch of 0.36 μm or less unless X-rays are used as a light source. When X-rays are used, there are restrictions on the apparatus, such as the size of the apparatus. Therefore, in the present invention, the two-beam interference exposure method is used from the viewpoint of ease of preparation, pattern precision, throughput, and the like.

The A and B parameters are parameters relating to the properties of the resist. The A parameter indicates the absorbance of the photosensitive component, and the B parameter indicates the absorbance of the non-photosensitive component (resin and photosensitive agent skeleton compound). A = (1 / D) × (T (∞) / T (0)) B = (1 / D) × ln (T (∞)) where T (∞): after exposure Resist transmittance T (0): transmittance of unexposed resist D: resist thickness

In the present invention, the A parameter at the G line of the photoresist is preferably 0.7 or less. Also, B
It is preferable that the parameter is 0.5 or less. Further, the thickness of the photoresist in the present invention is preferably from 1,000 to 10,000.

[0013]

FIG. 1 is a diagram showing a configuration example of a two-beam interference exposure apparatus. In FIG. 1, a He-Cd laser (wavelength 325 nm) 1
The laser light emitted from the laser beam is split in two directions by the beam splitter 2. The separated laser beams pass through the apertures 3a and 3b and are reflected by the mirrors 4a and 4b.
The light is collimated by the collimating lenses 6a and 6b via the spatial filters 5a and 5b. In this way, the light passing through the collimating lenses 6a and 6b
The light beam is caused to interfere, and the photoresist 7 applied on the substrate 8 is exposed to a diffraction grating pattern.

In the two-beam interference exposure performed as described above, assuming that the direction of intersection between the photoresist surface and the incident surface is the Z direction, the complex amplitude of the optical electric field of the two beams is expressed by the following equation. E ₁ = Aexp Thus [-ik (Zsinθ-Xcosθ)] E ₂ = CAexp [-ik (-Zsinθ-Xcosθ) -iφ], photosensitivity of the photoresist surface is expressed by the following equation. | E ₁ + E ₂ | ² _{x = 0} = | A | ² [1 + C ² + 2C · cos 2 (kZ sin θ−φ)] As can be seen from this equation, the light intensity is spatially modulated in the Z direction into a sinusoidal wave, and the two light fluxes When the electric field intensity ratio C = 1, the degree of modulation becomes maximum.

On the other hand, the period (pitch) of the diffraction grating pattern
Is represented by the following equation. Λ = 2π / 2k · sin θ = λ ₀ / (2n · sin θ) where λ _{0 is} the laser light wavelength of the light source (in vacuum) n is the refractive index of the spatial medium (〜1). The forming procedure will be described.
First, a photoresist is prepared to have an appropriate viscosity, and coated on a substrate to a film thickness of about 1000 ° by a spin coating method. Thereafter, a predetermined baking (firing) is added. Spin co
The resist is 2cp and the spin speed is 4000rpm
It is preferable to set the degree. Thereafter, a diffraction grating pattern having a pitch of 0.255 nm was formed by the two-beam exposure apparatus described above. In this case, it is needless to say that a spatial filter or the like is appropriately provided on the optical axis while paying attention to the profile of the optical wavefront. The exposure energy of the total is about 30 mJ / cm ² .
Further, development is performed with a predetermined developing solution while confirming interference fringes.

As the photoresist, the resists X (Example), Y (Comparative Example) and Z (Comparative Example) shown in Table 1 were used. Table 1 shows the values of the A and B parameters of the resists X, Y and Z.

[0017]

[Table 1]

FIGS. 2 to 4 show cross sections of resist patterns in which a diffraction grating pattern is formed by using these photoresists as described above. FIG. 2 shows a resist pattern obtained using a photoresist X, FIG. 3 shows a pattern using a photoresist Y, and FIG. 4 shows a pattern using a photoresist Z. Each had a thickness of 1000 mm. As shown in FIG. 2, in the case of the resist X, a rectangular pattern is formed, and there is no residual film at a portion where the resist should not be left. Even if there is some residual film, since it is etched when dry etching is performed thereafter, it does not matter, but in the present embodiment, since there is no residual film,
The etching may be performed by wet etching.
On the other hand, as shown in FIGS. 3 and 4, in the case of the resists Y and Z, the resists are sinusoidal, have small steps, and have many residual films.

The cross-sectional shape of the resist pattern is as follows.
Naturally, it is preferable to have a rectangular shape as shown in FIG. Whether the shape is preferable or not can be represented by the aspect ratio (aspect ratio) of the cross-sectional shape of the resist pattern. FIG. 5 (cross-sectional view of the resist pattern) is a diagram for explaining how to determine the aspect ratio. The aspect ratio is obtained by the formula: aspect ratio = b / a, where a is the length of the valley and b is the height of the peak.

Referring to the resist patterns shown in FIGS.
The results of determining the aspect ratio are also shown in Table 1. It can be seen that the one formed by the resist X has a large aspect ratio. It is preferable that the aspect ratio is large in the etching in the subsequent step. Also, resist X
In the case where is used, the allowable value of the developing time is 2-3 times higher than that of the others, and the reproducibility of pattern formation is good.

As described above, a diffraction grating is formed on the substrate 8 from the resist pattern formed using the resist X. Since the substrate surface is exposed in the portion of the resist pattern where the resist is not placed, the exposed substrate surface is removed by dry etching to dig a groove. By removing the resist pattern with a solvent or other means, a diffraction grating can be formed on the substrate 8.

In this embodiment, the He-Cd laser is used as the light source in the two-beam interference exposure.
A laser or the like may be used.

[0023]

As described above, according to the present invention, a resist pattern having a large aspect ratio can be obtained even if the thickness of the resist is increased. Further, according to the present invention, it is possible to easily obtain a resist pattern having a large allowable value of the process and a large aspect ratio.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a two-beam interference exposure apparatus used in an embodiment of the present invention.

FIG. 2 is a sectional view of a resist pattern formed using a resist X shown in Table 1.

FIG. 3 is a sectional view of a resist pattern formed using a resist Y shown in Table 1.

FIG. 4 is a sectional view of a resist pattern formed using a resist Z shown in Table 1.

FIG. 5 is a diagram for explaining how to determine an aspect ratio of a resist pattern.

FIG. 6 is a sectional view showing a configuration of a distributed feedback laser.

[Explanation of symbols]

 Reference Signs List 1 He-Cd laser 2 Beam splitter 3a, 3b Aperture 4a, 4b Mirror 5a, 5b Spatial filter 6a, 6b Collimating lens 7 Photoresist 8 Substrate

Claims (3)

(57) [Claims] 1. A method of forming a resist pattern by exposing a photoresist to a diffraction grating pattern having a pitch of 0.36 .mu.m or less by a two-beam interference exposure method and developing the photoresist, wherein the photoresist is an A-parameter in G-line. −
Parameter (absorbance of photosensitive component) is 0.6 or more and B parameter
A method for forming a resist pattern, wherein a resist having a (non-photosensitive component absorbance) of 0.2 or more is used. 2. An A-parameter for G-line (absorption of photosensitive component).
The B parameter (absorption of non-photosensitive components ) is 0.6 or more.
0.36 pitch of photoresist with a yield of 0.2 or more
A photoresist for forming a diffraction grating pattern of μm or less. 3. An A-parameter for G-line (photosensitive)
( Absorbance of component) is 0.6 or more and B parameter (non-photosensitive)
A first step of applying a photoresist having a component absorbance of 0.2 or more, and a pitch of 0.36 on the photoresist by a two-beam interference exposure method.
a second step of forming a resist pattern by exposing and developing a diffraction grating pattern of μm or less; a third step of removing a portion of the substrate on which the resist is not placed; And a fourth step of removing the resist.