JPH0534512A - Formation of grating pattern - Google Patents

Abstract

PURPOSE:To obtain a grating pattern having excellent smoothness and accuracy by coating a substrate with a positive type novolak resist and carrying out exposure with converged ion beams and development. CONSTITUTION:An Si substrate 1 is spin-coated with a positive type novolak resist 2 and this resist 2 is baked and exposed with converged Be ion beams 3 obtd. from an Au-Si-Be alloy ion source with a prescribed repeating period. The exposed resist is developed with a satd. aq. potassium hydroxide soln. mixed with water in 1:4 ratio as an aq. alkali developer and the developed resist is rinsed with pure water to form a resist pattern 2. Pattern transfer is then carried out by reactive ion etching with CF4 as anisotropic dry etching through the resist pattern 2 as a mask to form a grating pattern in the substrate 1. The taper angle of the grating pattern can be arbitrarily controlled in accordance with the concn. of the aq. alkali developer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a grating pattern used in a manufacturing process of a semiconductor device or a diffraction grating, and more particularly to a method of forming a grating pattern using a focused ion beam.

[0002]

2. Description of the Related Art A grating pattern is used for a light or X-ray diffraction grating, a solid-state laser, or the like, and its diffraction efficiency depends on the smoothness of the pattern wall of the grating pattern, the repetition period, and the angle accuracy.

A conventional grating pattern forming method will be described with reference to FIGS. 3 (a) to 3 (d).

First, as shown in FIG. 3A, the substrate 1
A novolac-based positive resist 2 is applied on top.

Next, as shown in FIG. 3B, the mask 4
Through the ultraviolet light 5 through the novolak positive resist 2
To expose. At this time, the exposure amount is made shorter than in the normal pattern formation.

Next, as shown in FIG. 3C, a corrugated resist pattern 2 is formed by developing in a potassium hydroxide aqueous solution developer.

Depending on the application, the resist pattern 2 can be used as it is.

Usually, as shown in FIG. 3D, the pattern is transferred to the substrate by anisotropic dry etching such as CF ₄ reactive ion etching using the resist pattern 2 as an etching mask to form the grating pattern 1. ..

[0009]

DISCLOSURE OF THE INVENTION In the prior art,
A corrugated resist pattern or a substrate on which it is transferred is used.

In any case, there is a problem in that a wavy grating pattern is formed, the smoothness and accuracy of the pattern side wall are poor, and high diffraction efficiency cannot be obtained.

An object of the present invention is to provide a method of forming a grating pattern, which is superior in smoothness and accuracy of pattern side walls and has high diffraction efficiency as compared with the prior art.

[0012]

A method for forming a grating pattern according to the present invention comprises a step of applying a novolac-type positive resist on a substrate, a step of exposing the resist with a focused ion beam, and a step of developing the resist. It includes and.

[0013]

The resist exposure using the focused ion beam is less susceptible to the proximity effect due to the forward and backscattering compared to the resist exposure using the electron beam which is generally used as a fine pattern forming means at present, and thus the electron beam is used. A fine pattern that cannot be formed by exposure can be formed.

FIG. 2 shows the dissolution characteristics of a typical novolac-type positive resist (MP2400; trade name) manufactured by Shipley Co., Ltd. in a photosensitive aqueous solution and an unexposed photosensitive solution in an alkaline aqueous solution by a focused ion beam.

As the alkaline aqueous solution developer, a saturated aqueous solution of potassium hydroxide (MP2401 manufactured by Shipley): H ₂ O
= 1: 4 is used.

Although the dissolution characteristics of the exposed portion and the unexposed portion are almost linear, when the remaining film ratio of the exposed portion becomes 0%, the remaining film ratio of the unexposed portion also decreases to 65%. The pattern shows a tendency to cause a reduction in the residual film rate and a side wall taper shape due to erosion in the vertical and lateral directions of the pattern.

Therefore, it is possible to form a grating pattern of a constant cycle by exposing the line pattern by the focused ion beam exposure at a constant cycle and then developing it.

Since the difference in dissolution rate between the exposed portion and the unexposed portion of the resist by the focused ion beam depends on the concentration of the alkaline aqueous solution, the taper angle of the grating pattern can be arbitrarily controlled by the concentration of the alkaline aqueous solution. You can

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to (d).

First, as shown in FIG. 1A, a novolac-based positive resist 2 having a thickness of about 1.0 μm is spin-coated on a Si substrate 1 and baked at 80 ° C. for 30 minutes.

Next, as shown in FIG. 1B, Au-S
Acceleration energy 2 obtained from i-Be alloy ion source
The resist is exposed using a Be focused ion beam 3 of 60 keV. Here, the beam diameter and drawing line width of the Be focused ion beam 3 were both 50 nm, and the repetition period was 1.0 μm. The exposure amount is 4.0 × 10 ¹² ions /
It was set to cm ² .

Next, as shown in FIG. 1 (c), a saturated aqueous solution of potassium hydroxide: H ₂ O is used as an alkaline aqueous solution developer.
The resist pattern 2 was formed by developing for 2 minutes at = 1: 4 and rinsing with pure water for 1 minute.

Next, as shown in FIG. 1D, CF _{4 is used} as anisotropic dry etching by using the resist 2 as a mask.
Pattern transfer was performed by reactive ion etching. Here, the flow rate of CF ₄ is 10 sccm, and the high frequency power is 2
50 W and etching time was 20 minutes. As a result, it was possible to form a grating pattern on the substrate 1 with a repetition period of 1.0 μm and a taper angle of about 70 °, which was superior in smoothness and accuracy of the pattern side surface to the conventional method.

In this example, a Be focused ion beam with an acceleration energy of 260 keV obtained from an Au-Si-Be alloy ion source was used in the focused ion beam exposure process.
Other acceleration energies and other sources of elemental metal ions such as Li, Ga, Au, Au-Si, Pt-Sb, Pb-N
Alloy ion source such as i-B, or He, H ₂ , O
It is also possible to use a focused ion beam composed of ions obtained from a gas ion source such as ₂ or F ₂ .

The exposure amount of the focused ion beam is 1.5 × 10.
_{Although it is set to 13} ions / cm ₂ , this can be set to an arbitrary exposure amount within the range in which the latent image forming reaction is caused in the resist used and the film reduction of the resist film due to ion bombardment does not occur.

Although MP2400 manufactured by Shipley Co., Ltd. was used as the novolac-based positive resist in this embodiment, other novolac-based positive resist can be used.

Although a potassium hydroxide saturated aqueous solution (MP2401 manufactured by Shipley Co.): H ₂ O = 1: 4 was used as the developing solution, other alkaline aqueous solution developing solutions such as tetramethylammonium hydroxide (TMAH) may also be used. it can. The concentration can be freely set within the range where the desired taper angle is obtained.

Further, in the present embodiment, the pattern was transferred onto the Si substrate by CF ₄ reactive ion etching to form a grating pattern.
s, quartz, etc. can be used, and Au on the resist pattern can be used instead of anisotropic dry etching depending on the application.
It is also possible to deposit a metal thin film such as Al and use it as a grating pattern.

[0029]

EFFECTS OF THE INVENTION By coating a novolac-type positive resist on a substrate, exposing it with a focused ion beam, and then developing it, a grating pattern with excellent smoothness and precision, which could not be obtained by the prior art, is formed. We were able to.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention in the order of steps.

FIG. 2 is a graph showing dissolution characteristics of a resist in a developing solution.

FIG. 3 is a cross-sectional view showing a method of forming a grating pattern according to a conventional technique in order of steps.

[Explanation of symbols]

 1 Si substrate 2 Novolac positive resist 3 Be focused ion beam 4 Mask 5 Ultraviolet light

Claims (1)

Claim: What is claimed is: 1. In forming a grating pattern on a substrate by focused ion beam exposure, a step of applying a novolac positive resist on the substrate, and a step of exposing the resist by a focused ion beam. And a step of developing the resist, the method for forming a grating pattern.