JPS6141147A - Etching method - Google Patents

Abstract

PURPOSE:To enable a pattern having exact periodicity, such as diffraction grating, to be formed through etching even by using a negative type photoresist, by attaching a solvent having affinity to a hydrophobic photoresist to said hydrophobic photoresist. CONSTITUTION:A relieved OMR2' is formed on a substrate 1 by using OMR as a negative resist, and immersed into a solvent having affinity to the substrate 1, such as methyl alcohol 6 to attach it to the surface. Then, it is immersed into an etching solution mixture 7 of a nitric acid type etching soln. and the affinitive solvent to etch it by using the OMR2' as a mask, thus permitting a pattern having exact periodicity, such as diffraction grating, to be formed by etching even when a negative type photoresist is used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an etching method for etching semiconductor substrates, dielectric substrates, and the like.

(Prior art) Diffraction gratings are used in distributed feedback semiconductor lasers, which are attracting attention due to their single-wavelength oscillation, or in wavelength-selective multiplexers and demultiplexers. It has become indispensable for various devices that construct long-distance, high-capacity optical 7-IPA communications.

In particular, since the period of a diffraction grating directly affects the oscillation wavelength of a semiconductor laser or the selected wavelength of a demultiplexer/multiplexer, a method for manufacturing a diffraction grating with good periodicity and good reproducibility is desired. There is.

Conventionally, the method for manufacturing diffraction gratings that has been widely used is to use H
This is a method in which exposure and development is performed by three-beam interference exposure using near-ultraviolet oscillation light from an e-Cd laser or the like, and the image is further transferred onto a substrate by chemical etching.

In addition, the inventor of the present invention has proposed a method for manufacturing a diffraction grating that effectively utilizes a negative photoresist in which the exposed pattern remains as a film (Japanese Patent Application No. 59-5210
No. 0). This negative photoresist is particularly effective in manufacturing a diffraction grating whose phase is partially reversed, and it is expected that diffraction gratings using the negative photoresist will be manufactured in the future.

However, conventional techniques have the disadvantage that fine patterns cannot be precisely manufactured.

(Object of the Invention) An object of the present invention is to provide an etching method that can form a precise pattern such as a diffraction grating having accurate periodicity by etching even when using a negative photoresist film.

(Principle, structure and operation of the invention) The present invention will be explained in detail below with reference to the drawings.

First, the results of an investigation into the reason why a conventional negative photoresist film cannot form a precise pattern by etching will be explained.

FIG. 1 shows a conventional etching process using a negative photoresist (hereinafter referred to as "N resist") made of non-hydrophilic cyclized rubber. The figure (a) shows a region A, which is etched on the substrate 1 after a process such as mask exposure. : It is in a state where it is divided into a region B which is masked by the N resist film 2. FIG. 2B shows a state in which the above-described substrate 1 is immersed in an etching solution 3 and the region A is etched. Here, the commonly used cyclized rubber-based N resist has a property of being very difficult to be mixed with water. Therefore, it is difficult to be compatible with conventional etching [3], and empty pJi4, which is not attached to the etched surface of the substrate 1, is created near the boundary of the N resist film 2.

Such a void 4 is not etched and remains as a non-etched region 5 as shown in FIG.

Furthermore, in order to confirm this phenomenon, the following experiment was conducted. In FIG. 2 1a), in order to fabricate a diffraction grating, an N resist film 2 is formed on a substrate 1 by three-beam interference exposure or the like so that the period of concavities and convexities is about 2500A.

Even if such a substrate 1 is immersed in the etching solution 3, the etching solution 3 does not reach the surface of the substrate 1 that is exposed from the N resist film 2 serving as a mask and is to be etched, as shown in FIG. I can do 4.

Therefore, as shown in FIG. 2(c), there is a non-etched area 5 in the substrate 1 that is not etched at all, and even if the etching process is performed, the unetched area 5 shown in FIG.
Figure (c) The shape is the same as after etching shown in K.
The desired diffraction grating is not formed.

As described above, when conventionally etching is performed using a non-hydrophilic photoresist, simply dipping it in an etching solution causes so-called blurring in the vicinity of the mask boundary of the N resist film 2, resulting in the formation of a precisely shaped etched film. There were problems in that a pattern could not be obtained or periodic irregularities were not formed at all.

The present invention has been made to solve the above-mentioned problems, and is characterized in that at least the entire surface of the non-hydrophilic 7-otoresist has an affinity for the non-hydrophilic 7-otoresist during etching. The method includes a step of realizing a state in which the solvent is attached.

In the following explanation, OMR made of cyclized rubber is used as a non-hydrophilic negative photoresist, and InP is used as a semiconductor substrate.
and hydrobromic acid (HBr) as an etching solution.

This will be explained using a mixed solution of nitric acid (HNO8) and water (H2O) (hereinafter referred to as "nitric acid etching solution") as an example.

(Example 1) FIG. 3 is an example according to the present invention, and shows an etching process. Figure 3(a) is exactly the same as Figure 2(al), and shows the state before etching the substrate 1 using OMR as the N resist and OMR2' as a mask in manufacturing the diffraction grating. Next, as a preparatory work for etching, which is a feature of the present application, 0M
Spin-coating a solvent having affinity (hereinafter referred to as "affinity solvent") to the surface of R2' and the surface of the substrate 1 exposed from this 0MR2' and to be etched (hereinafter referred to as "upper entire surface"). Or substrate 1 in FIG. 3(a)
In addition, methyl alcohol 6 is used as the affinity solvent in the figure, but an organic solvent such as acetone or a surfactant that lowers the surface tension of water can also be used. But that's fine. 3rd
In Figure (c), methyl alcohol 6 is applied to the entire upper surface of the substrate 1, and then the substrate 1 is immersed in an etching mixture 7 which is a mixture of a conventional nitric acid etching solution 3 and an affinity solvent. If you do this, the adhesion of methyl alcohol 6 will result in zero
The wettability of MR2' is improved and the etching mixture 7
Since the etchant itself has affinity, it can sufficiently reach the surface of the substrate 1 to be etched. Therefore, the substrate 1 can be mounted using the OMR 2' as a mask (
It is etched like dl.

Although the etching liquid mixture 7 is used in FIG. 3C, the etching liquid 3 may be used instead.

As described above, the present invention improves the compatibility between the etching solution 3 and the non-hydrophilic photoresist by attaching an affinity solvent to at least the entire surface of the non-hydrophilic photoresist film in advance, thereby improving etching. This is what I did.

(Example 2) Fig. 4 shows another embodiment according to the present invention, and Fig. 4(a)
3(a), there is an uneven 0MR on the substrate 1.
2' is formed. The substrate 1 is placed in a container 8 containing methyl alcohol 6, which is a type of affinity solvent.
and soak as shown in the same figure (b). Next, as shown in FIG. 2C, approximately the same amount of the enching liquid 3 as the methyl alcohol 6 is poured into the container 8 containing the methyl alcohol 6, and the mixture is stirred with a stirring rod 9 or the like. Then,
The methylfluor 6 and the etching liquid 3 are mixed to form an etching mixture 7, and this etching mixture 7 reaches the entire surface of the substrate 1 to be etched, resulting in good etching as shown in the figure (dl).

Further, in step (b), the substrate is immersed in a conventional etching solution 3, and then in step (c), methyl alcohol 6
may be mixed.

The major difference from Example 1 is that the surface K of 0MR2'
) The process of attaching chill alcohol 6 is omitted, and the same effect is achieved in the process of preparing the etching mixture.

As described above, the present invention provides at least non-hydrophilic 0MR2
By adhering an affinity solvent such as methyl alcohol 6 to the surface of the substrate, or by mixing an affinity solvent into the etching solution, it is possible to perform etching in a good manner and with good reproducibility.

In the above explanation, we talked about a mixture of hydrobromic acid, nitric acid, and water as an etching solution, but it is a hydrochloric acid-based etching solution.

Applicable to all aqueous solutions such as sulfuric acid. It goes without saying that the substrate to be etched is not only a semiconductor substrate such as InP or GaAs, but also a dielectric substrate such as glass or LiNbO3.

Further, although OMR has been described as a non-hydrophilic 7 photoresist, it can be applied to all other non-hydrophilic photoresists.

(Effects of the Invention) As described above, the present invention improves the compatibility between an etching solution and a non-hydrophilic photoresist, thereby etching a substrate using a non-hydrophilic photoresist as a mask with good reproducibility. Therefore, it is possible to improve the performance of various devices using pattern formation and diffraction gratings that take advantage of the characteristics of non-hydrophilic photoresists, and the effect is extremely large.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views for explaining a conventional etching method, FIG. 3 is a schematic cross-sectional view for explaining an embodiment according to the present invention, and FIG. 4 is a schematic cross-sectional diagram for explaining another embodiment according to the present invention. FIG. 1... Substrate, 2... Negative photoresist film,
2'...OMR, 3...Etching liquid, 4...Void, 5...Non-etching area, 6...Methyl alcohol, 7...Etching mixture liquid, 8...Container, 9・・・
- Stirring stick.

Claims (4)

[Claims] (1) In an etching method in which a non-hydrophilic photoresist mask is formed on the surface to be etched of the object to be etched, and then etching is performed with an etching solution, a solvent having an affinity with the photoresist is used when performing the etching. An etching method characterized by including a step of realizing a state in which the photoresist is adhered to the photoresist. (2) The etching method according to claim 1, wherein the photoresist is immersed in the etching solution after the solvent having the affinity is attached to the surface to be etched. (3) The etching method according to claim 1, wherein an additive is added in advance to the etching solution so that the etching solution has the above-mentioned affinity. (4) The etching method according to claim 1, wherein an additive is added to the etching solution during the etching process so that the etching solution has the above-mentioned affinity.