JPH02173781A - Image forming method and pattern transfer method - Google Patents

Abstract

PURPOSE:To accomplish high accuracy pattern transfer by forming an image on a substrate where pattern formation is performed through an off-axis type hologram by Fresnel diffraction which is obtained by forming light from a light source in the manner of a computer synthetic hologram. CONSTITUTION:By using the off-axis type computer synthetic hologram 3 formed by calculation based on the Fresnel diffracted wave of a desired image, the light 5 from the light source is transmitted through the hologram 3 and conducted to the substrate 4. On the other hand, the light is directly conducted to the substrate 4 and diffracted on the hologram 3 so as to form the diffractive wave into the image. Namely, by using the off-axis type computer synthetic hologram 3 formed based on the Fresnel diffractive wave, a distance from the hologram 3 to an image forming position is made small and an optical system(Fourier transforming lens) consisting of many lenses is not needed. Therefore, project exposure can be performed even in a short wavelength area where a material having sufficient characteristic as glass material for a lens can not be obtained. Thus, the high accuracy fine pattern is formed.

Description

Detailed Description of the Invention (Object of the Invention) (Industrial Application Field) The present invention relates to an image forming method and a pattern transfer method,
In particular, the present invention relates to a method for transferring a desired pattern with high precision.

(Prior art) In the field of manufacturing semiconductor devices such as VLSIs, light is irradiated onto a substrate through a mask and lens system formed with a desired light-shielding pattern, and a fine pattern is transferred by reduction projection exposure. This technique is widely used.

Such pattern transfer technology can reduce the effects of mask defects, dust adhesion, etc., and in recent years, it has become possible to obtain fine patterns with remarkable light penetration.

By the way, the dissolving power of projection exposure II is determined by the numerical aperture (NA>) of the imaging element such as the lens system used and the wavelength (λ) of the light used.

That is, the minimum resolvable 11fi(L) is Locλ
/NA (1).

Normally, the wavelength of the light source of a widely used projection exposure apparatus is the 9-line (λ=436r+1>) or i-line (λ
=365r+n).

Therefore, in order to further improve the resolution, it is necessary to use a light source that emits light with a shorter wavelength. However, since mercury lamps have low output in the short wavelength region, various other light sources have been proposed, including excimer lasers that can obtain high output in the short wavelength region such as the ultraviolet region.

On the other hand, when using ultraviolet rays in the short wavelength region, there are restrictions on the glass material for the lens, for example, 200~25On+1
The only materials that can transmit light in the nearby wavelength range are quartz and a small number of fluoride crystals, and quartz is currently the only material that can be used particularly for large-diameter lenses.

In the even shorter wavelength region of 200n11 or less, there is no suitable lens material and pattern transfer by projection exposure is impossible. Lighting is being done.

However, in the case of high-quality optical, defects and dust on the mask may be transferred directly to the substrate, and furthermore, the mask will be damaged more quickly due to close contact, so strict quality control of the mask is required. be.

Incidentally, during pattern transfer, the mask must be uniformly illuminated, regardless of whether projection exposure or contact exposure is used. This is important in order to maintain the image quality of the transferred pattern with high accuracy over the entire transferred area.

Therefore, when attempting to transfer a pattern over a fairly large area necessary for manufacturing VLSI, in many cases, a precisely designed illumination optical system using a plurality of lenses called Koehler illumination is required. For this reason, a sufficient illumination effect can only be obtained in a wavelength range in which lens glass materials can be secured.

In addition, in recent years, research has been progressing on so-called holography technology, which uses the coherence of waves to record signal waves emitted from an object on a hologram, and then regenerates the signal waves by applying another light wave to this hologram. Also in the field of semiconductor manufacturing technology, its use in forming fine patterns is attracting attention.

Under these circumstances, what is generally used as a computer-synthesized hologram is a so-called Fourier transform hologram, in which a signal obtained by Fourier transform of a desired image is imaged on a photosensitive material, and the Fourier transform image is recorded. To reproduce this Fourier transform type hologram, it is necessary to use a Fourier transform lens. Therefore, here as well, since the image quality is determined by the accuracy of the Fourier transform lens, there is a problem in that a good reproduced image cannot be obtained in a wavelength range where a good quality lens cannot be obtained.

(Problems to be Solved by the Invention) As described above, when pattern transfer is performed when forming a fine-sized pattern, regardless of whether projection exposure or contact exposure is used, computer-generated holography
Even with the latest technology that uses a high-quality lens, the quality of the image obtained is greatly affected by the length of the lens, and there is a problem that it is not possible to obtain a good reconstructed image in a wavelength range that cannot be accommodated by a high-quality lens. Ta.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an image forming method and a pattern transfer method that can perform highly accurate pattern transfer in any wavelength range.

(Structure of the Invention) (Means for Solving the Problems) Therefore, in the present invention, an off-axis computer-synthesized hologram calculated and formed based on Fresnel diffraction waves of a desired image is used, and light from a light source is transmitted through this hologram. On the one hand, the light is guided directly onto the substrate, and these lights are diffracted on the hologram, and the diffracted waves are imaged.

Further, in the present invention, pattern transfer is performed as described above.

(Function) According to the method of the present invention, since an off-axis computer-synthesized hologram formed based on Fresnel diffraction waves is used, the distance from the hologram to the imaging position can be shortened, and the conventional computer-synthesized An optical system consisting of a large number of lenses (Fourier transform lens), which was necessary when using a hologram, is no longer necessary.

Therefore, projection exposure is possible even in a short wavelength region where it is impossible to obtain a material with sufficient properties as a glass material for lenses, and it is possible to form fine patterns with high precision.

Furthermore, if we consider one point in the projected image reproduced from the hologram, that point is the reproduction edge due to light gathered from the entire hologram.

Therefore, even if part of the hologram is missing,
Playback patterns are largely unaffected. Therefore, restrictions on defects and attached dust on the mask are loose, and even if the illumination is not completely uniform, the influence of this on the pattern-transferred image can be ignored.

Further, by using an off-axis type, it is possible to prevent deterioration in image quality due to effects such as the illumination light of the hologram overlapping a desired image.

Furthermore, by performing a step-and-repeat operation, highly accurate images can be obtained repeatedly.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory diagram showing a pattern transfer method according to an embodiment of the present invention.

Light 5 from an excimer laser light source is imaged onto a substrate 4 on which a pattern is to be formed via a Fresnel diffraction off-axis hologram 3 formed by a computer-generated hologram technique.

Here, the angle of incidence of the light 5 from the excimer laser light source on the off-axis computer-synthesized hologram 3 is 16.1
degree. Also, the distance between the hologram 3 and the substrate is 4.2
3u, the wavelength of light 5 from the excimer laser light source is 157n
II. The half-value bandwidth is assumed to be 0°005 n11.

Next, a method for forming the Fresnel diffraction off-axis computer-synthesized hologram 3 will be described.

First, as shown in FIG. 2, the Fresnel diffraction of a desired image is measured.

When an object with an aperture having an aperture function U○ (Xo, Vo) is placed in Fig. 2, from this the distance @2
A diffracted wave U (x, y) generated by Fresnel diffraction as shown in the following equation is generated at a distance of .

Here, λ: wavelength: wave number Based on this, as shown in FIG. 3, the hologram surface is divided into cells 1 of δνXδ, and the center coordinates of one cell are set as (mδν, nδν).

Here, δν is 0.27 μm.

Then, the object light at this point is expressed as U (x, V) = Annex p (iφnn)
■.

Now, in the cell 1, a frontage 2 having a width Cδν and a height alnδν is provided. At this time, alnδν is alnδνo
The proportionality constant is determined in the sieve machine so that cAnn ■, and blnδν is φIn
Divide by 2π, normalize the remainder by δν, and get Cδ
ν was set to 0.15 μm.

1. Connect 4400x4400 cells 1 like this.
Calculation was performed to create a hologram with an area of 19nnxl and 191n, and calculation data was created.

Based on this data, a resist coated on a chromium-coated lithium fluoride (LiF) substrate is exposed to light using an electron beam lithography system with a positioning accuracy of 0.01 μm, and then developed. Then, using this resist pattern as a mask, chromium was further etched to create a hologram.

As a result, it was possible to form a good image on the substrate that was faithful to the intended resist pattern with a width of 0.3 μm.

Further, by placing the substrate 4 on a step-and-repeat stage, it is possible to repeat and transfer a good pattern.

〔Effect of the invention〕

As explained above, according to the method of the present invention, a Fresnel-type off-axis computer-synthesized hologram formed by needle ringing based on the Fresnel diffraction waves of a desired image is used, and light from a light source is transmitted through this hologram. On the other hand,
Since the light is guided directly onto the substrate, the light is diffracted on the substrate, and the diffracted waves are formed into an image, the focusing distance is shortened and an optical system consisting of many lenses is not required. Projection exposure becomes possible even in the short wavelength region where it is impossible to obtain materials with sufficient properties for glass materials.

In addition, there are loose restrictions on defects and adhesion on the mask and uniformity of illumination, and an image with good image quality can be formed on the substrate.

Furthermore, by performing a step-and-repeat operation, it is possible to repeat images with high precision.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a pattern transfer method according to an embodiment of the present invention, FIG. 2 is a diagram showing a coordinate system for calculating Fresnel diffraction waves, and FIG. 3 is a diagram showing cells on a hologram surface. 1... Cell, 2... Opening, 3... Substrate, 4...
Substrate, 5... Illumination light, 6... First-order diffracted light, 7...
0th order light. Figure 1 Figure 2

Claims (2)

[Claims] (1) Form an image on the substrate using an off-axis computer-synthesized hologram calculated and formed based on Fresnel diffraction waves of a desired image, and guide light from a light source onto the hologram while transmitting the hologram. An image forming method characterized in that the light is guided onto a substrate, the light is diffracted on the hologram, and the diffracted waves are imaged. (2) A pattern transfer method, characterized in that the operation of forming a desired pattern by the image forming method according to claim (1) is repeated by a step-and-repeat operation to repeatedly transfer the pattern onto the substrate.