JPH0830890B2 - Method of forming resist pattern having thickness distribution - Google Patents

Description

The present invention relates to a method for forming a resist pattern, and more particularly to a method for forming a resist pattern having a thickness distribution such as a blazed diffraction grating.

[Prior Art] Conventionally, as a method of forming a resist pattern having a thickness distribution, for example, Hirohara Nishihara et al.
The electron beam drawing method is known as described on pages 220 to 224 (published by Ohmsha in February 1985).

This method irradiates the electron beam resist with a finely focused electron beam, three-dimensionally cross-links the electron beam resist in the irradiated portion, and forms a resist pattern by the remaining portion which is not dissolved in a developing solution of an organic solvent. This is due to the line lithography. The thickness of the resist pattern is
It can be changed depending on the beam irradiation amount to the electron beam resist. For example, the resist pattern can be made thicker by increasing the beam irradiation amount and can be thinned by decreasing the beam irradiation amount.

By the way, since the spot diameter of the electron beam can be narrowed down to about 0.05 μm, for example, when forming a fine pattern of about 1 μm width, the 1 μm width is divided into 20 and the beam irradiation is performed for each divided line width. A resist pattern having a thickness distribution can be obtained by changing the amount.

[Problems to be Solved by the Invention] The above-described method of forming a resist pattern having a thickness distribution by the conventional electron beam drawing method requires a complicated program for controlling the electron beam and long irradiation time. Since it takes time and the electron beam drawing apparatus used for carrying out this method is expensive, there are major problems in mass productivity.

It is an object of the present invention to provide a method for forming a resist pattern, which is capable of forming a resist pattern having a thickness distribution with high efficiency and at a low cost by solving the above-mentioned problems of the prior art. Is.

[Means for Solving the Problems] In order to solve the above problems, the structure of the method for forming a resist pattern having a thickness distribution according to the present invention has a structure in which one surface of a photomask substrate that transmits ultraviolet rays is UV absorber is embedded in the groove having a depth distribution, the surface is flattened, and the UV mask is formed on at least one surface of the photomask, and the UV absorber embedded surface side of the photomask is formed. The photoresist of the patterned substrate is opposed to the photoresist, the photoresist is exposed to ultraviolet rays from the photoresist side, and then the photoresist is developed.

 More details are as follows.

Using a photomask (details will be described later), a resist pattern having a thickness distribution is formed with high efficiency by photolithography with ultraviolet rays.

That is, a groove having a depth distribution is formed on the upper surface of a quartz substrate or a transparent glass substrate by machining, and a substance that absorbs ultraviolet rays, that is, an ultraviolet absorber is embedded in the groove, and then the absorber on the upper surface is removed. The photoresist obtained by flattening by polishing is used as a photomask, and the photoresist formed on the pattern forming substrate is exposed to ultraviolet rays through the photomask. By developing this photoresist, the resist exposed portion disappears, the resist unexposed portion remains, and a resist pattern having a thickness distribution is formed.

If an ultraviolet ray antireflection film is formed on the absorber-embedded surface, the opposite lower surface, or both surfaces of the photomask, a resist pattern having a more accurate thickness distribution can be formed.

[Operation] A pattern forming substrate is formed on one surface of the photomask substrate by forming a groove having a depth distribution of a desired shape and size and burying an ultraviolet absorber in the groove. When the photoresist is exposed to light, the groove is transferred to the photoresist, and a resist pattern having a desired thickness distribution is produced with high efficiency.

[Examples] Hereinafter, the present invention will be described by examples with reference to the drawings.

FIG. 1 is a manufacturing process diagram showing an example of a manufacturing process of a photomask used for carrying out a method of forming a resist pattern having a thickness distribution according to an embodiment of the present invention, and FIG. 2 shows this manufacturing process. It is a resist pattern formation process figure which shows an example of the process of forming the resist pattern which has thickness distribution using.

The outline of the method of forming the resist pattern will be described with reference to FIGS. 1 and 2. This is because ultraviolet rays are introduced into the groove 2 having a depth distribution formed on one surface of the photomask substrate 1 that transmits ultraviolet rays. Absorbent 3 is embedded, the surface is flattened, and the absorbent-embedded surface side 5a of a photomask 5 having ultraviolet protection films 4 formed on both sides, and a positive photoresist 7 related to photoresist are formed. Board 6
The positive photoresist 7 is opposed to the positive photoresist 7 and the positive photoresist 7 is exposed to ultraviolet rays 11 from the photomask 5 side, and then the positive photoresist 7 is developed. As a result, the resist exposed portion 8 of the positive photoresist 7 disappears and the resist unexposed portion 9 remains, which becomes the resist pattern 10 having a thickness distribution.

 This will be described in detail below.

 First, the photomask 5 will be described.

As the material of the photomask substrate 1, all substances that transmit ultraviolet rays can be used. For example, quartz, synthetic quartz, Si
O ₂ type glass, LiNbO _{3 and the} like are preferable, and among these, synthetic quartz and SiO ₂ type glass, which have good workability and light transmittance, are particularly suitable.

The method of forming the groove 4 having the depth distribution on one surface of the photomask substrate 1 is preferably formed by using a known numerical control type cutting device equipped with a diamond bite. Alternatively, it is formed by pressing a diamond bite with a sharp tip on the surface of the photomask substrate 1, plastically deforming the substrate 1 into a desired shape to form irregularities, and then lapping and removing the convex portions. You may. Furthermore, after performing ultra-precision plastic working using a ruling engine and lapping, fine pattern grooves having a line width of submicron can be formed.

The ultraviolet absorber 3 to be embedded in the groove 2 is preferably selected from materials having a refractive index substantially the same as that of the photomask substrate 1 so that ultraviolet rays are not reflected at the interface with the photomask substrate 1. Specifically, various polymer materials, SiO ₂
Glass, chalcogenide compounds, metal oxides, nitrides, etc. are preferable. Of these, a polymer material is particularly effective, and it is preferable to use a liquid prepared by mixing a polymer material with an ultraviolet absorber and dissolving this in an organic solvent.

As a method of burying the ultraviolet absorber 3 in the groove 2, in the case of the ultraviolet absorber 3 made of a polymer material, a film is applied by a spin coating method and heated to remove the organic solvent, followed by polishing. Then, the extra film may be scraped off.
SiO ₂ glass, chalcogenide compounds, metal oxides,
In the case of the nitride ultraviolet absorber 3, it can be formed by forming a film by a vacuum vapor deposition method, a sputtering method, a CVD method or the like, and then polishing it to scrape off the excess film and flatten it.

The ultraviolet antireflection film 4 is effective in improving the utilization efficiency of ultraviolet rays, reducing the light reflected from the positive photoresist 7 and the pattern forming substrate 6, and further improving the sensitivity and resolution. , Chromium oxide, or a multilayer film of TiO ₂ and SiO ₂ is used. The ultraviolet reaction preventing film 4 also has a function as a protective film for the ultraviolet absorbent 3, and can prevent the ultraviolet absorbent 3 from being scratched or dusted.

Using the photomask 5 configured as described above, the absorbent-embedded surface side 5a and the positive photoresist 7 are brought into close contact with each other, and ultraviolet rays 11 are applied to the positive photoresist 7 through the photomask 5. The resist exposed portion 8 of the mold photoresist 7 is dissolved in the developing solution and disappears, and the resist unexposed portion 9 remains to obtain a resist pattern 10 having a desired thickness distribution.

Next, the principle of forming a resist pattern having a thickness distribution will be described with reference to the drawings.

3 to 5 are for explaining the principle of forming a resist pattern having a thickness distribution by the method according to FIG. 1, and FIG. FIG. 4 is a schematic diagram showing the exposure state of the positive photoresist, FIG. 4 is an exposure dose-residual film rate characteristic diagram showing the relationship between the exposure dose of the positive photoresist and the resist residual film rate, FIG.
The figure is an absorbent thickness-residual film rate characteristic diagram showing the relationship between the thickness of the ultraviolet absorbent and the resist residual film rate.

In FIG. 3, if the incident light intensity incident on the photomask 5 is I _O , the thickness of the ultraviolet absorber 3 is x, the extinction coefficient is α, and the transmitted light intensity transmitted through the ultraviolet absorber 3 is I _x , The transmittance T is represented by the following equation (1).

On the other hand, the relationship between the exposure amount of the positive type photoresist 7 (however, the common logarithmic display) and the resist residual film rate is as shown in FIG. 4, but the linear region is used. Assuming that the inclination angle of this straight line region is θ, this inclination angle θ is expressed by the following equation (2).

θ = tan ⁻¹ γ (2) where γ is a parameter γ value indicating the resolution of the positive photoresist 7.

Further, the exposure amount when the resist residual film ratio becomes 0 is E _O ,
If the exposure amount when the resist residual film ratio becomes 1 is E ₁ ,
The resist residual film rate at the exposure amount E is expressed by the following equation (3).

By the way, when the light amount E ₀ of light is transmitted through the thickness x portion of the ultraviolet absorbent 3, the exposure amount is TE ₀ if the light transmittance T is used. Substituting this TE ₀ into the equation (3),
The resist residual film rate is expressed by the following equation (4).

That is, the relationship between the thickness x of the ultraviolet absorber 3 and the resist residual film rate has a direct relationship as shown in FIG. 5, and the parameter γ value of the positive photoresist 7 and the extinction coefficient α of the ultraviolet absorber 3 are shown. It is possible to form a resist pattern having substantially the same shape as that formed in the groove 4 and having a thickness distribution by using a resist pattern whose value is appropriately controlled.

 A specific example will be described with reference to FIGS.

FIGS. 6 and 7 show specific examples of the method for forming a resist pattern having a thickness distribution. FIG. 6 shows the exposure dose-residual film rate characteristic diagram, and FIG. 7 shows the absorber thickness. -It is a residual film rate characteristic diagram.

A triangular groove 2 as shown in FIG. 1 was formed by cutting with a diamond bite on a synthetic quartz substrate of a photomask substrate 1 having a thickness of 1.5 mm and a size of 10 cm. The depth of the groove 2 was 1.2 μm, the angle of the triangle was 45 °, the pitch between the grooves was 1.2 μm, the length of the groove was 1 cm, and the number was 100. After removing burrs generated during cutting by polishing, a UV absorber 3 of a polymeric material having an extinction coefficient α of 1 × 10 ⁻⁴ (cm ⁻¹ ) was applied by spin coating. Then, the excess ultraviolet absorber was removed by polishing and the upper surface was flattened as shown in FIG. 1, and then an ultraviolet antireflection film 4 of chromium oxide was formed by sputtering to manufacture a photomask 5.

The SiO ₂ glass substrate (BK7) related to the pattern forming substrate 6
A positive photoresist 7 was applied to the glass (1 μm). The relationship between the exposure amount of the positive photoresist 7 and the resist residual film rate is as shown in FIG. 6, and the exposure amount is 50 mj / c.
When m ² (i-line), the resist residual film rate is 0, and the exposure amount is 15.8 mj
When / cm ² (i-line), the residual resist film is 1, and the parameter γ value is 2.

The photoresist 5 was brought into close contact with the positive photoresist 7 on the BK7 glass, and the positive photoresist 7 was exposed. The exposure amount at this time was 50 mj / cm ² . The exposure time is
20 seconds. After this exposure, it was developed with an organic solvent to form a resist pattern. When the relationship between the thickness of the ultraviolet absorber 3 formed on the photomask 5 and the resist residual film rate was examined, the relationship shown in FIG. 7 was obtained. That is, the obtained resist pattern transferred the shape of the groove 2 in which the ultraviolet absorber 3 was embedded, which was formed in the photomask 5, and had a sawtooth-shaped thickness distribution with a maximum thickness of 1 μm and a pitch of 1.2 μm. It was confirmed that the pattern was formed.

BK with resist pattern having such thickness distribution
The -7 glass plate can be used, for example, as a diffraction grating. In particular, since the resist pattern is triangular, it is a so-called blazed diffraction grating and can be used as a diffraction grating having a higher efficiency than a generally rectangular diffraction grating.

 According to the embodiment described above, the following effects can be obtained.

If the desired groove 2 is formed in the photomask substrate 1, and the photomask 5 in which the ultraviolet absorber 3 is put therein is used, the groove 2 is formed.
Is transferred to the positive photoresist 7, the resist pattern 10 having a thickness distribution can be efficiently produced.

The resist pattern 10 having such a thickness distribution,
For example, if it is formed on optical glass, various lenses such as a Fresnel lens and a diffraction grating with good performance can be obtained. Further, by using the resist pattern 10 as a mask, the film or the substrate under the resist pattern is shaved by dry etching or the like, whereby an optical element different in material from the resist material can be formed.

[Effects of the Invention] As described in detail above, according to the present invention, a resist pattern having a thickness distribution, which has been formed over a long period of time by using an expensive electron beam drawing apparatus, can be efficiently manufactured. It is possible to provide a method of forming a resist pattern that can be formed at low cost.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram showing an example of a manufacturing process of a photomask used for carrying out a method of forming a resist pattern having a thickness distribution according to an embodiment of the present invention.
The figure shows a resist pattern forming process diagram showing an example of a process for forming a resist pattern having a thickness distribution using this photomask. FIGS. 3 to 5 show the thickness distribution by the method according to FIG. FIG. 3 is a schematic view showing an exposure state of a positive photoresist by ultraviolet rays passing through an ultraviolet absorber, and FIG. 4 is a diagram showing the positive photoresist. Dose-residual film ratio characteristic diagram showing the relationship between the exposure amount and the resist residual film ratio, and FIG. 5 shows the relationship between the ultraviolet absorber thickness and the resist residual film ratio. 6 and 7 show characteristic examples of a method of forming a resist pattern having a thickness distribution. FIG. 6 is a characteristic diagram of the exposure amount-residual film ratio, and FIG. 7 is an absorption chart. It is an agent thickness-residual film rate characteristic view. 1 ... Photomask substrate, 2 ... Film, 3 ... UV absorber, 4
... UV reflection preventing film, 5 ... Photomask, 5a ... Absorbent-embedded surface side, 6 ... Pattern forming substrate, 7 ... Positive photoresist, 10 ... Resist pattern having thickness distribution, 11 ... UV rays.

Front page continued (72) Inventor Kazuto Kawamoto 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Production Technology Research Laboratory, Hitachi, Ltd. Production Engineering Laboratory, Hitachi, Ltd. (56) Reference JP-A-63-271265 (JP, A)

Claims (1)

[Claims] 1. An ultraviolet absorber is embedded in a groove having a depth distribution formed on one surface of a photomask substrate that transmits ultraviolet light, the surface is flattened, and further, at least one surface of the photomask is provided. The UV absorber embedded surface side of the photomask on which the UV antireflection film is formed and the photoresist of the pattern forming substrate on which the photoresist is formed are opposed to each other, and the photoresist is exposed to UV rays from the photomask side, and then the photoresist is developed. A method for forming a resist pattern having a thickness distribution, characterized in that