JPH06283405A - Exposure method - Google Patents

Abstract

PURPOSE:To effectively perform reduction-alignment with a resolution of several +nm level by using a light beam flux as a light beam flux whose wavelength area ranges from a visible light area to an ultraviolet ray area and a soft X-ray light beam flux as a light beam flux for reproducing hologram, respectively. CONSTITUTION:A hologram recorder is made of an optical system in which a light source 51, a filter 52, a lens 53, a pinhole 54, a mask 55, and a hologram 56 are arranged in order. A KrF (krypton fluoride) excimer laser (wavelength lambda=249nm) is used as the light source 51. For reproducing a hologram board 12, in a case where a PMMA film is used for a screen layer 11b, a soft X-ray (wavelength lambda=3-4nm) whose wavelength is shorter than that of an absorption end (absorption end of carbon C) of the X-ray of PMMA is necessitated as a reference light for the reproduction. Therefore, the soft X-ray of 4nm in wavelength is employed as supply light 15. Thus, by properly using light having different wavelengths for recording and reproducing, fine patterns can be easily formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure technique for mask transfer in substrate etching or the like in a semiconductor process, and more particularly to an exposure method for performing minute mask transfer by a holographic technique.

[0002]

2. Description of the Related Art In a projection exposure method using a reduction optical system using ultraviolet light to X-rays, the reduction ratio is adjusted by a complicated combination of a plurality of lenses and the like, or by operating the optical path. This is generally composed of an optical system including a light source, a condenser lens, a diaphragm, a mask, a projection lens and a projection surface. In this case, resolution, depth of focus, aberration,
Due to the need for a well-balanced design such as ensuring a uniform exposure area, the reduction rate is limited to about 1/5 to 1/20, and the resolution can be only about submicron to 50 nm.

As another exposure method, there is a contact or proximity exposure method using ultraviolet light to X-rays. For this, for example, a Xe-Hg lamp light source, an elliptical mirror in the optical system, and a fly-eye lens for obtaining an optimal NA and uniform illumination are adopted, and the influence of the diffraction phenomenon with a good light collection rate is suppressed as much as possible. There is something aimed at the structure. The features of this exposure method are that the device is simpler than the reduction optical system and alignment is easy. However, in this case as well, due to various problems such as blurring due to geometrical arrangement diffraction and technical difficulty of mask production, a reduction ratio of 1/1 and several μm to 0.1 μm.
Only a resolution of about μm can be realized.

A general holographic projection exposure method that uses light of the same wavelength for recording and reproduction also includes, for example, a holographic exposure method that uses interference of light to fabricate a grating or the like.

Further, there is an example applied as a kind of microscope as a technique for operating the enlargement ratio according to the wavelength ratio of the recording light and the reproducing light by using the holographic technique. However, it is not generally used as a projection exposure method.
In the configuration intended for magnified projection, the wavelength ratio of the recording light and the reproducing light can be made large, so that high resolution can be achieved. Technology for expanding and reproducing holograms recorded with X-rays, etc. with visible light having a wavelength longer than that of X-rays has been realized, but conversely, holograms recorded with visible / ultraviolet light must be reduced and reproduced with X-rays. Cannot get coherence,
Moreover, it has not been realized due to reasons such as difficulty in obtaining good contrast.

[0006]

SUMMARY OF THE INVENTION The present invention provides a high resolution of several tens of nm, which is difficult to achieve by a projection exposure method using a reduction optical system or an exposure method using a conventional holography method. In addition, an exposure method having a reduction rate of 1/100 level is provided.

[0007]

A hologram recording medium on which a desired pattern is recorded by a hologram recording light beam is irradiated with the hologram reproducing light beam, and a reproduced image of the pattern is formed on a surface of a substrate coated with a photoconductor. In the exposure method using the holography technique for projecting and exposing a light beam, a light beam having a wavelength range from a visible light region to an ultraviolet region is used as a hologram recording light beam, and a soft X-ray light beam is used as a hologram reproducing light beam. It is characterized by

[0008]

According to the present invention, in the exposure method using the above holographic technique, the wavelength of the light beam for hologram reproduction is smaller than the wavelength of the light beam for hologram recording.
On the surface of the substrate coated with the photoconductor, the reproduced image is projected and exposed by reducing the size of the object. For this reason,
Reduction exposure can be performed more efficiently than a reduction projection method performed by a simple operation of an optical system such as a combination of lenses or a change in image formation position.

[0009]

EXAMPLES Reducing a hologram recorded with visible / ultraviolet light by X-rays and reproducing it has not been realized because of the fact that coherence cannot be obtained and it is difficult to obtain good contrast. Therefore, in the present invention, soft X-rays that can obtain a certain degree of coherence and obtain a contrast are used.

Further, in hologram recording, the substrate material is a material that can transmit this light (soft X-rays), and the recording medium is an optical distribution of its light intensity distribution by irradiation with visible ultraviolet light. The conditions are that it can be replaced by a film thickness distribution (a hologram material) and that it has a sufficient light absorption region in the wavelength region of soft X-rays. FIG. 2 is a diagram showing a soft X-ray absorption spectrum of the lithographic material. As shown in the figure, organic resist materials such as polyimide (C ₂₂ H ₁₀ O ₅ N ₂ ) and PMMA (polymethylmethacrylate; C ₅ H ₈ O ₂ ) have sufficient light absorption in the soft X-ray wavelength region. Has an area. Therefore, in this embodiment, PMMA having an extremely effective absorption characteristic is used as a hologram recording medium (screen layer) at 2.5 to 5 nm. [Production of Hologram Substrate for Recording Hologram] First,
A method for producing a hologram that can be reproduced with soft X-rays will be described.

3A to 3C are cross-sectional views showing the steps of manufacturing a hologram substrate for recording the hologram used in this embodiment. This step is similar to the semiconductor process technology in the mask production for general X-ray lithography,
The hologram substrate is manufactured by the steps described below.

In the first step (FIG. 3A), one surface 31a of the mask substrate 31 is polished with high precision. In this embodiment, the mask substrate 31 is a silicon substrate (Si substrate).
Was used. The polishing accuracy at this time is preferably a flat surface with an accuracy of 1/10 to 1/20 or more of the wavelength of the light used for producing the hologram. Also, the other surface 31b
Is not required to be as accurate as the surface 31a.

In the second step (FIG. 3B), the protective film 32 is formed on the surface 31a of the mask substrate 31 which is highly accurately polished by a method such as sputtering or CVD. The protective film 32 functions to protect the mask substrate 31 from physical or chemical changes. As the protective film 32, a material that has optical uniformity and mechanical strength and is transparent to soft X-rays is desirable. In the present embodiment, silicon nitride (Si ₃ N ₄ ) is used.
Although the film is used, for example, a silicon oxide (SiO ₂ ) or beryllium (Be) film may be used. However, when a beryllium film is used, the strength is preferable because it can be about 1 μm, but it is not realistic because it is highly toxic. When a silicon nitride film is used as the protective film 32, the film thickness is controlled to about 0.1 μm.

In the third step (FIG. 3C), the mask 33 for etching the mask substrate is used as the protective film 3 for the mask substrate 31.
It is formed on the surface 31b opposite to the surface 32a on which 2 is formed. In this embodiment, the mask 33 for etching the mask substrate is used.
As the material, a boron nitride film (BN) formed by CVD, sputtering, or the like was used. At this time, the film thickness of the mask substrate etching mask 33 was 0.5 μm.

In the fourth step (FIG. 3D), the protective film 3
2 and the resist 3 on the mask 33 for etching the mask substrate
4 is applied to a thickness of about 1 μm, and a window 34 of a desired size is applied.
form w.

In the fifth step (FIG. 3E), the mask 33 for etching the mask substrate is treated with 5 cc of perchloric acid + second nitric acid.
A window 33w for etching the mask substrate 31 is formed by etching with an etching solution containing 1 g of cerium ammonium + 100 cc of water.

In the sixth step (FIG. 3 (F)), the mask substrate 31 is etched by using hydrazine hydrate or the like as an etching solution, and a window 31 for light beam for hologram reproduction.
form w. At this time, the size e of the window 31w is 1 to 2
The fourth to sixth steps are controlled so as to be about mm.

Finally, the resist 34 is removed to complete a blank hologram substrate on which no image is recorded. [Fabrication of Mask] Next, fabrication of a mask for recording a desired image on the hologram substrate in the blank state will be described.

FIGS. 4 (1) and 4 (2) are views showing the mask used in this embodiment. 4 (1) is a view of the mask as seen from above, and FIG. 4 (2) is (II)-of FIG. 4 (1).
It is a sectional view in (II '). On the mask substrate 41,
A quartz plate is used, and a flat surface with an accuracy of 1/10 to 1/20 or more of the wavelength of light used when producing a hologram is desirable. Further, the light absorption film 42 is provided on one surface of the mask substrate 41.
(Or a light reflecting film) is formed in a desired shape, and in this embodiment, several rectangular groove patterns 42n having a width a = 1 μm and a length b = 5 μm are arranged at intervals of about c = 2 μm. ing. Further, the light absorbing film 42 has a mask substrate 41.
A pinhole 42p for reference light is provided therethrough. The diameter of the pinhole 42p is about 0.5 μm. Also,
The distance d between the pinhole 42p and the groove pattern 42n closest to the pinhole 42p is about 5 μm. The reference light with which the hologram substrate is irradiated through the pinhole 42p interferes with the light wave having the mask pattern information on the hologram substrate to form a hologram.

As the material of the light absorption film 42, a material that does not transmit light used for mask making, for example, chromium (Cr) is used. This mask manufacturing process is carried out in the same manner as a normal photolithographic mask manufacturing method. Chromium is vapor-deposited on the surface of the mask substrate 41, a resist is subsequently applied, and the desired shape described above is obtained by etching by electron beam exposure or the like. To form. [Hologram Recording] Next, hologram recording in this embodiment will be described.

First, a resist is applied on a blank hologram substrate. A positive resist such as PMMA (polymethylmethacrylate) is used as the resist. In this embodiment, PMMA is applied to a thickness of about 1 μm,
Prebaking is performed at about 170 ° C. for about 20 minutes. As the resist, a positive type resist such as PMMA used in this embodiment is used. Further, in order to more accurately reflect the intensity distribution of the hologram and obtain a resist film thickness distribution width sufficient for transfer as a resist film thickness distribution, it is preferable to use a resist having a high γ value.

Subsequently, a hologram is recorded by the hologram recording device shown in FIG. The hologram recording device applied in the present embodiment includes a light source 51, a filter 52, and a lens 5.
3, an optical system in which a pinhole 54, a mask 55, and a hologram substrate 56 are sequentially arranged. Here, the light source 51
A KrF (krypton fluoride) excimer laser (wavelength λ = 249 nm) is used as Alternatively, the light source 5
As No. 1, a high pressure mercury lamp or the like may be used to obtain a quasi-monochromatic color with a filter. An etalon is used as the filter 52. The diameter of the pinhole 54 is about 1 to 10 μm. The distances k1 and k2 between the pinhole 54, the lens 53, and the mask 55 are each about 10 cm. The hologram substrate 56 is coated with a resist 56r (PMMA), and is arranged with its surface facing the mask side. The distance k3 between the mask 55 and the hologram substrate 56 is
It was about 1 mm.

The laser emitted from the light source 51 is quasi-monochromatic by the filter 52, focused on the center of the pinhole 54 by the lens 53, and then transmitted through the mask 55 to be applied to the hologram substrate 56. FIG. 6 shows a resist sensitivity curve represented by a laser irradiation amount (DOSE amount) to the hologram substrate 56 and a resist remaining ratio. At this time, when the hologram is recorded, in order to fully utilize the change in the hologram intensity, the intensity distribution of the hologram and the sensitivity curve of the resist should be matched as shown in A of FIG.
It is necessary to adjust the amount or the film thickness of the resist. That is, the hologram residual strength is set to 1 at the maximum hologram strength, and the resist residual rate is set to 0 only at the maximum hologram strength, so that the etching can be efficiently performed within the hologram intensity distribution range.

The hologram substrate on which the hologram has been recorded is developed with a 1: 3 solution of MIBK (methyl isobutyl ketone) and IPA (isopropyl alcohol) for about 60 seconds, and then rinsed with IPA. [Reproduction of Hologram] The exposure method of this embodiment is shown in FIG.
As shown in FIG. 3, a hologram reproducing system including a photosensitive substrate 11 (a substrate coated with a photosensitive body) and a hologram substrate 12, a light source system 13 for supplying coherent light for hologram reproduction, and a convergent light beam bundle thereof are provided on the hologram substrate 12. It is performed by the apparatus formed from the condensing optical system 14 that irradiates the light.
An enlarged view of the hologram reproducing system of FIG. 1 (1) is shown in FIG. 1 (2).

The photoconductor substrate 11 is composed of a substrate 11a and a screen layer 11b on which a reproduced image of a recorded image of the hologram substrate 12 is projected, and the screen layer 11b is made of, for example, PMMA or polyimide. It is formed with various resist qualities.

The light source system 13 cuts the light in the short wavelength region of the supply light 15 which is the reference light for reproducing the recorded image, and further cuts the light in the long wavelength region such as visible light. Filter 13b, a condenser mirror 13c such as a grazing incidence Walter mirror, and a pinhole 13d. As the X-ray supply light 15 supplied to the light source system 13, an X-ray laser is preferable, and SR (synchrotron radiation) undulator light is used in this embodiment.

The condensing optical system 14 uses a Schwarzschild type condensing mirror using a multilayer film. The pinhole 13d is made of an X-ray absorbing material such as gold (Au), tantalum (Ta), or tungsten (W), and has a diameter of 1 μm.
A pinhole of m or less is open. In the present embodiment, the distance r from the pinhole 13d of the light source system 13 to the condensing optical system
Was 2 m or less. The distance p between the hologram substrate 12 and the photoconductor substrate 11 was 1 mm.

To reproduce the recorded image on the hologram substrate 12,
When a PMMA film is used for the screen layer 11b, the X-ray absorption edge (carbon C) of PMMA is used as a reference light for reproduction.
Soft X-rays (wavelength λ = 3 to 4n) shorter than the absorption edge of
m) is necessary, and in the present embodiment, soft X-ray having a wavelength λ = 4 nm is used as the supply light 15. Therefore, the light source system 1
3 supply light 15 (SR undulator light)
Is quasi-monochromatic by the reflecting mirror 13a and the filter 13b, is condensed from the condensing mirror 13c to the pinhole 13d, becomes spatially coherent light, and enters the next condensing optical system 14. Then, in the condensing optical system 14, the hologram reproducing light forms a convergent light beam and is applied to the hologram substrate 12. This time, the hologram substrate 12 is used as a mask to obtain a reduced projection image on the photoconductor substrate 11. Exposure for.

At this time, the reduction ratio of the obtained reduced projection image is
It is obtained by the following formula.

Reduction ratio = (λ _R · X ₁ ') / (λ _O · X ₀ ) where λ _O is the wavelength of the light (KrF excimer laser) used for hologram recording, and λ _R is the reproduction of the hologram. This is the wavelength of light for use, that is, soft X-rays. Further, X ₀ and X ₁ ′ are the distance from the mask to the hologram substrate during hologram recording, and the distance from the hologram substrate 12 to the photoconductor substrate 11 (reproduced image) during hologram reproduction.
In this embodiment, λ _R = 40 nm, λ _O = 2490 nm, X ₁ ′ = X ₀ = 1 mm, and the reduction ratio is 0.016. Therefore, the 1
.mu.m becomes 16 nm when the hologram is reproduced, and the photosensitive substrate 11 is subjected to reduction exposure.

As described above, by using visible light to ultraviolet light for recording a hologram and using soft X-rays having a wavelength smaller than the light used at the time of recording for reproduction, projection exposure with an extremely small reduction rate is possible.

[0032]

According to the present invention, a complicated and expensive reduction optical system is utilized by utilizing the property of expanding / reducing a reproduced image obtained by using lights having different wavelengths for recording and reproducing a hologram. The reduction exposure method is possible without need, and by using visible to ultraviolet light during recording and soft X-ray during reproduction,
Projection exposure with a large reduction rate can be performed, and a fine pattern can be easily formed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an exposure method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a soft X-ray absorption spectrum of a hologram recording material used in one example of the present invention.

3A to 3C are cross-sectional views showing a process of manufacturing a hologram substrate used in one embodiment of the present invention.

FIG. 4 is a schematic diagram showing a structure of a mask used for recording a hologram according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of an apparatus used for recording a hologram according to an embodiment of the present invention.

FIG. 6 is a diagram showing a sensitivity curve of a resist with respect to irradiation light at the time of recording on a hologram substrate according to an example of the present invention.

[Explanation of symbols]

 11 Photoconductor Substrate 12, 56 Hologram Substrate 13 Light Source System 14 Focusing Optical System 41 Mask Substrate 42 Light Absorbing Film 51 Light Source 52 Filter 53 Lens 54 Pinhole 55 Mask

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03H 1/00 8106-2K

Claims (1)

[Claims] 1. A hologram recording medium on which a desired pattern is recorded by a hologram recording light beam is irradiated with the hologram reproducing light beam, and a reproduced image of the pattern is projected and exposed on the surface of a substrate coated with a photosensitive member. In the exposure method using the holography technique, a light beam having a wavelength range from visible light to an ultraviolet region is used as the light beam for hologram recording, and a soft X-ray light beam is used as the light beam for hologram reproduction. Exposure method.