JPH0361901A - Production of lambda/4 shift diffraction grating - Google Patents

Abstract

PURPOSE:To simplify process and to improve the accuracy of the diffraction grating by using an image reversal resist and subjecting the resist to interference exposing, then developing the image reversal resist on a 1st region on a substrate without subjecting this resist to reversal processing and subjecting the resist on the remaining regions to the reversal processing, then developing the resist and etching the substrate with the pattern as a mask. CONSTITUTION:The image reversal resist 2 is applied on the substrate 1 and is subjected to the interference exposing 3. The image reversal resist 2 on the 1st region of the substrate 1 is developed to form the 1st pattern which is the pattern of the interference exposing; thereafter, the reversal processing of the image reversal resist 2 is executed. The image reversal resist 2 on the 2nd regions exclusive of the 1st region of the substrate 1 is thereafter developed to form the 2nd pattern reversed from the pattern of the interference exposing. The substrate 1 is etched with the 1st and 2nd patterns as the mask. The reversal patterns are formable by the single resist in this way, by which the processes are simplified and the increase in the region of the transition region generating in the case of pattern formation by using two kinds of the resists is prevented. The accuracy of the diffraction grating is thus improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a λ/4 shift diffraction grating,
In particular, the present invention relates to a method for manufacturing a λ/4 shift diffraction grating that can simplify the process.

[Conventional technology]

In order to make the distributed feedback laser oscillate in the longitudinal fundamental mode,
A method of providing a λ/4 shift region in the central portion of a diffraction grating is generally known.

FIGS. 2(a) to 2(e) are process diagrams showing a conventional method for manufacturing a phase shift type diffraction grating, in which l represents a semiconductor substrate and 12 represents a negative resist. Reference numeral 13 denotes an intermediate layer for preventing mixing of the upper and lower resists, and here OBC, which is the same material as the negative resist and does not have a photosensitive group, is used. 14 is a first positive resist, 15 is a second positive resist, and 16 is an oxygen barrier film for preventing the resist from chemically reacting with oxygen during exposure. It uses PVA, which does not have the same properties.

Next, the steps of the prior art will be explained.

First, as shown in FIG. 2(a), a negative resist 12. Middle layer 13. First positive resist 14
A part of the first positive resist 14 is removed as shown in FIG. 2(b) using a normal photolithography technique. Then, using the pattern of this first positive resist 14 as a mask, the intermediate layer 13 is formed using a nitric acid solution.
．． The negative resist 12 is etched as shown in FIG. 2(C). After removing the first positive resist 14, the second positive resist 14 is removed.
As shown in Figure (d), the second positive resist 15. An oxygen barrier film 16 is formed. In this state, interference exposure is performed as shown in 2E(e), and then development and rinsing are performed to form a negative resist 12. With the second positive resist 15, as shown in FIG.
), the group vi1 is etched using this as a mask, and the negative resist 12 and the second positive resist 15 are removed to obtain the phase shift type diffraction grating shown in FIG. It will be done.

[Problem to be solved by the invention]

The conventional method for manufacturing a λ/4 shift diffraction grating is as described above, but there are problems in that different types of resist must be applied, which complicates the work in the development process, etc. There is a problem in that the transition region becomes wider due to the boundary between different resists.

This invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a λ/4 shift diffraction grating, which can produce a λ/4 shift diffraction grating with high precision through a simple process. With the goal.

[Means to solve the problem]

A method for manufacturing a λ/4 shift diffraction grating according to the present invention includes applying an image reversal resist on a substrate, performing interference exposure,
After developing the image reversal resist on the first region of the substrate to form a first pattern that is the interference exposure pattern, the image reversal resist is subjected to reversal processing, and then the image reversal resist is developed on the first region of the substrate other than the first region. developing the image reversal resist on the second area of the first area to form a second pattern that is an inversion of the pattern of the interference exposure; The substrate is etched using the second pattern as a mask.

[Effect]

In this invention, an image reversal resist is used, and after the image reversal resist is subjected to interference exposure, the image reversal resist on the first area of the substrate is developed without performing reversal processing, and the image reversal resist on the remaining area is developed. After the reversal process, it is developed to form a pattern, and the substrate is etched using this pattern as a mask.This allows the reversal pattern to be formed using a single resist, which simplifies the process and allows for the formation of a diffraction grating. Accuracy can be improved.

(Example〕 An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1(a) to (el) show λ/ according to an embodiment of the present invention.
1 is a cross-sectional process diagram showing a method for manufacturing a four-phase shift diffraction grating; in the figure, 1 is a semiconductor substrate, 2 is an image reversal resist, and 3 is an exposure light source that forms interference fringes. Reference numeral 4 denotes a resist salt penetration prevention film, and OBC can be used as the resist salt penetration prevention film 4 as in the conventional case. 5 is a cover resist.

As the cover resist 5, either a positive resist or a negative resist may be used.

The image reversal resist 2 is generally commercially available and has the following properties. That is, if it is developed directly after exposure, it exhibits properties similar to those of a positive resist, and the exposed portions are removed by development. on the other hand,
If a reversal bake (reversal beta) is performed before development and then development is performed, the opposite properties to those described above will be exhibited, and AZ5206E is a specific product of a 0-image reversal resist in which the areas exposed to light remain after development. be.

Next, the manufacturing process will be explained.

First, as shown in FIG. 1(a), an image reversal resist 2 is coated on a semiconductor substrate 1 to a thickness of several hundred to several hundred people.
Interference exposure is performed using beam interferometry 3.

After the interference exposure, the resist salt penetration prevention film 4 and the cover resist 5 are removed as shown in FIG. 1(b) without development.
6 Next, as shown in FIG. 1(C), a part of the cover resist 5 is removed by exposure and development, and the remaining part is used as a mask to remove the resist salt penetration prevention film 4. The image reversal resist 2 in the area where the cover resist 5 has been removed is developed, and then a reversal bake is performed to reverse the properties of the image reversal resist. Then, the cover resist 5 and the resist mixing prevention film 4 are removed, and the first
As shown in Figure (d), the remaining image reversal resist 2 is developed. Here, in order to increase the etching rate of the image reversal resist 2 to be removed in this part with respect to the developer, the cover resist 5 and the resist mixing prevention film 4 are prepared.
After removing the pattern, the image reversal resist 2 is exposed (flood exposure) only in the areas where no pattern is formed, and then the resist is developed.After this, the substrate 1 is etched using the pattern formed by the resist as a mask. The pattern is transferred onto the semiconductor substrate 1, and the resist is removed as shown in FIG. 1(e) to complete the process.

The diffraction grating obtained in the above process has λ/4 in its central part.
Schiff) II region is formed, and if a distributed feedback semiconductor laser is manufactured using a semiconductor substrate on which this diffraction grating is formed, one that oscillates in a single mode at the Bragg wavelength can be obtained.

In this way, in this example, using an image reversal resist,
After this is subjected to interference exposure, the image reversal resist on the first area of the substrate is developed without performing reversal processing, and the image reversal resist on the remaining areas is developed after performing reversal processing to form a pattern. However, since the substrate is etched using this pattern as a mask, it is possible to form an inverted pattern using a single resist, simplifying the process, and eliminating the transition region that occurs when forming a pattern using two types of resist. It is possible to prevent the area from becoming wide and improve the accuracy of the diffraction grating.

In the above implementation, baking is performed after FIG. 1(C), and the cover resist 5. The pattern shown in FIG. 1 (dl) was obtained by removing the resist mixing prevention film 4, exposing only the portions of the image reversal resist 2 where no pattern was formed, and developing the resist. After the process shown in FIG.
．． The resist mixing prevention film 4 may be removed, the entire surface exposed again, and developed to obtain the pattern shown in FIG. 1(d). In this case, the pattern shown in FIG.
The pattern formed in step C) is baked and tightened,
Pattern distortion can be prevented from occurring in the process shown in FIG. 1(d).

Furthermore, in the above embodiment, the λ/4 shift diffraction grating is formed directly on the semiconductor substrate, but the diffraction grating may also be formed on another film, such as an insulating film, formed on the semiconductor substrate. Alternatively, the diffraction grating may be formed on a semiconductor substrate in which one or more semiconductor layers having a composition different from that of the substrate are formed.

〔Effect of the invention〕

As described above, according to the present invention, an image reversal resist is applied onto a substrate, interference exposure is performed, and the image reversal resist on a region of the substrate is developed to form a first pattern that is the pattern of the interference exposure. After forming the pattern, a reversal process is performed on the image reversal resist, and then the image reversal resist on the remaining area of the substrate is developed to form a second pattern that is an inversion of the interference exposure pattern. 1. Since the substrate is etched using the second pattern as a mask, it is possible to easily form a λ/4 shift diffraction grating with fewer transition regions.

[Brief explanation of drawings]

FIG. 1(a) to (el is λ/ according to an embodiment of the present invention)
A cross-sectional process diagram showing a method for manufacturing a 4-phase shift diffraction grating. FIGS. 2A to 2E are cross-sectional process diagrams showing a method for manufacturing a conventional λ/4 phase shift diffraction grating. 1... Semiconductor substrate , 2... Image inversion resist, 3.
... Interference exposure light source, 4... Resist mixing prevention film, 5... Cover resist, 12... Negative resist,
13... Intermediate layer, 14... First positive resist, 1
5... Second positive resist, 16... PVA film. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A step of applying an image reversal resist on a substrate forming a diffraction grating and performing interference exposure, and a step of developing the resist on a region of the substrate to form a first pattern of the interference exposure. and after performing a reversal process on the image reversal resist, developing the resist on the remaining area of the substrate to form a second pattern that is an inversion of the pattern of the interference exposure; . A method for manufacturing a λ/4 shift diffraction grating, comprising the steps of: transferring a second resist pattern onto a semiconductor substrate.