JPH05152200A - Method for forming resist pattern - Google Patents

Abstract

PURPOSE:To form an opening with a given width accurately in a resist layer on a silicon nitride film. CONSTITUTION:An ultraviolet ray with a wavelength of 180 to 220nm is cast to a surface of a silicon nitride film 2 to reform the film surface. After a resist 3 having a carboxyl group as a side chain is applied and the silicon nitride film 2 is baked, an electron-beam drawing process is carried out to form an opening 4 with a given width in the resist 3. In this case, since an ultraviolet ray is cast, no residue 3b remains in the resist.

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 a resist pattern, and more particularly to a method for forming an opening having a predetermined size in a resist coated on a silicon nitride film.

[0002]

2. Description of the Related Art In recent years, various resists having a carboxyl group as a side chain have been developed as resists sensitive to electron beams, and are used for fine processing in a semiconductor process. For example, as shown in FIG. 1, in order to process the silicon nitride film 2 deposited on the GaAs substrate 1, a resist having a carboxyl group of this kind in its side chain may be used as a mask. In the example of the phenyl methacrylate copolymer resist 3, first, the resist 3 is applied to the silicon nitride film 2 with a spin coater to a thickness of 1500Å. Subsequently, after baking at a temperature of 230 ° C. (150 ° C. or higher is required) for 2 hours, a pattern having a line width of 1500Å is drawn by electron beam exposure. Next, methyl isobutyl ketone-ethylcyclohexanol (80:
The resist 3 is developed by using the mixed solution of 20).
The opening 4 is formed in the. Here, the thickness of 2 at the bottom of the opening 4
Since the residue 3b of the resist 3 of 50 to 300Å is generated,
The resist residue 3b is removed by oxygen plasma. After that, the silicon nitride film 2 is etched and patterned with an aqueous solution of hydrogen fluoride or the like using the resist 3 as a mask.

[0003]

By the way, when etching the resist residue 3b by oxygen plasma, it is difficult to give anisotropy to the etching, and at the same time when the resist residue 3b is etched, the side wall 3a of the opening 4 is substantially equivalent. The amount is etched. In the above-mentioned example, since the etching of oxygen plasma is performed at 250 to 300Å, the lateral width (line width) A of the opening 4 is large (500 mm).
There is a problem that it will increase up to about 600Å). Further, since the etching of the resist by oxygen plasma cannot be performed with good reproducibility at a level of several hundred liters (the etching amount should be small), the accuracy of the line width A is lowered.

Reactive ion etching
A possible method is to reduce the amount of etching of the side wall 3a of the opening 4 by anisotropically etching the resist by (RIE), but it is not preferable when there is a shallow channel layer directly under the opening 4. .. This is because the channel layer is damaged and a separate heat treatment must be performed to recover the damage.

SUMMARY OF THE INVENTION An object of the present invention is to provide a resist pattern forming method capable of accurately forming a resist opening having a predetermined size on a silicon nitride film.

[0006]

In order to achieve the above-mentioned object, the present invention applies a resist having a carboxyl group as a side chain on the surface of a silicon nitride film, performs baking, and then performs electron beam drawing. The resist pattern forming method of forming an opening having a predetermined size in the resist is characterized in that the surface of the silicon nitride film is irradiated with ultraviolet rays having a wavelength of 180 nm to 220 nm before applying the resist.

The present invention was created by the following experiments and consideration by the present inventor. The present inventor coated the resist on the surface of the silicon nitride film, baked it at a predetermined temperature, and then dipped the resist in acetone, which is a good solvent.
Originally, the resist should be completely dissolved, but actually, a resist residue having a thickness of about 220 Å was formed on the surface of the silicon nitride film. This is because the imino groups and amino groups on the surface of the silicon nitride film are strongly bonded to the carboxyl groups in the resist by a dehydration reaction and the resist at the interface is in a state of not being dissolved. Therefore, generation of a resist residue can be suppressed by irradiating the surface of the silicon nitride film with ultraviolet rays to modify the surface before applying the resist. Therefore, the etching of the resist residue by oxygen plasma is not necessary or necessary, and the resist opening portion having a predetermined size can be accurately formed.

[0008]

EXAMPLES The method for forming a resist pattern according to the present invention will be described in detail below with reference to examples. A methacrylic acid-phenyl methacrylate copolymer resist is used as a resist having a carboxyl group as a side chain.

First, similarly to the case shown in FIG. 1, a silicon nitride film 2 is deposited on the surface of a GaAs substrate 1 (for simplification, the same reference numerals are used for description). After that, the surface of the silicon nitride film 2 was irradiated with ultraviolet rays having a wavelength of 180 to 220 nm at a room temperature and a light intensity of 0.66 mW / cm ^-2 for 1.5 hours. When the infrared absorption spectrum of the silicon nitride film 2 was measured before and after this ultraviolet irradiation treatment, 1100 to 120 due to NH (bend) observed before ultraviolet irradiation was observed.
The absorption at 0 cm ^-1 was significantly reduced after UV irradiation.
That is, it was found that the imino groups and amino groups on the surface of the silicon nitride film 2 were reduced by the ultraviolet irradiation. Then, the resist (more specifically, 25.4 mol% of methacrylic acid component, 74.6 mol% of phenyl methacrylate component, and 5 wt% methyl cellosolve acetate solution) is applied on the silicon nitride film 2 by using a spin coater. To 1500Å
Applied to the thickness of. Subsequently, baking was performed at a temperature of 230 ° C. (requiring 150 ° C. or higher) for 1 hour, and a 3 nC / cm line pattern was drawn by an electron beam exposure apparatus. next,
Methyl isobutyl ketone-ethyl cyclohexanol
Development was performed using a mixed solution of (80:20) to form openings 4 in the resist 3. Here, the resist residue 3b was etched by 80 Å by oxygen plasma.
After that, when the silicon nitride film 2 was etched with an aqueous solution of hydrogen fluoride using the resist 3 as a mask, pattern processing could be performed with high precision as drawn by an electron beam. As a result, it was indirectly confirmed that the resist residue 3b was formed by the imino group and amino group on the surface of the silicon nitride film 2 being bonded to the carboxyl group in the resist 3. After that, a metal aluminum layer having a thickness of 2000 Å is formed on the GaAs substrate 1 using the resist 3 as a mask.
Just vapor deposited. As a result, 0.15 μm on GaAs substrate
An aluminum electrode having a line width was formed.

On the other hand, in the case where the steps of coating the resist 3 on the untreated silicon nitride film 2 are performed without performing the above-mentioned ultraviolet irradiation treatment, the etching amount of the resist residue 3b by oxygen plasma is 200 Å or less. At this time, there remained a portion where the silicon nitride film 2 was not etched or partially etched. This is because the resist residue 3b could not be completely removed. When the etching amount of the resist residue 3b by oxygen plasma was set to 200 Å, the line width of the aluminum electrode finally increased to 0.2 μm.

The inventors of the present invention have found that the silicon nitride film 2
After applying resist 3 on the surface and baking, resist residue 3b when immersed in acetone (good solvent) before electron beam drawing
As shown in Table 1, it was observed that the amount of H. That is, the thickness of the resist residue 3b is 220Å when the ultraviolet irradiation is not performed, whereas the thickness of the resist residue 3b is 190Å when the ultraviolet irradiation time is 10, 30, and 90 minutes at room temperature. , 145
It turned out to be Å, 80Å. As a result, the effect of the present invention could be confirmed quantitatively.

[Table 1]

[0012]

As is apparent from the above, according to the method of forming a resist pattern of the present invention, a resist having a carboxyl group as a side chain is applied to the surface of a silicon nitride film, baked, and then electron beam drawing is performed. Then, when forming an opening of a predetermined size in the resist, a wavelength of 180 nm to 2 nm is applied to the surface of the silicon nitride film before applying the resist.
Since the ultraviolet rays of 20 nm are irradiated, a resist opening having a predetermined size can be accurately formed on the silicon nitride film.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which an opening is formed in a resist applied on the surface of a silicon nitride film.

[Explanation of symbols]

 1 GaAs Substrate 2 Silicon Nitride Film 3 Resist Having Carboxyl Group in Side Chain 3a Resist Sidewall 3b Resist Residue 4 Opening

Claims (1)

[Claims] 1. A resist pattern is formed by applying a resist having a carboxyl group as a side chain on the surface of a silicon nitride film, baking the resist, and then electron beam drawing to form an opening of a predetermined size in the resist. A method for forming a resist pattern, which comprises irradiating the surface of the silicon nitride film with ultraviolet rays having a wavelength of 180 nm to 220 nm before applying the resist.