JPS59191330A - Holographic exposure apparatus - Google Patents

Abstract

PURPOSE:To deteriorate the rate of coherence and avoid the speckle noise and realize the photoresist printing without defect by introducing an excimer laser which emits ultraviolet rays as a light source for reproduction of a hologram. CONSTITUTION:A hologram 13 formed from an original pattern is illuminated by a coherent light and a reproduced image is printed on a photoresist film 17. At that time, an excimer laser, such as XeF, XeCl, KrF, KrCl and ArF, which emits ultraviolet rays, is introduced as a light source 10 of the coherent light. With this constitution, even if a part of the hologram is missing, the defect in the reproduced image can be neglected. Therefore, the pattern printing without defect can be realized even if there is the adhesion of a foreign substance or the damage on the hologram.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a holographic exposure apparatus that reproduces an original pattern from a hologram mask in photolithography and prints it onto a V cyst film.

[Background technology]

Generally, in the photo-visualization process of semiconductor devices, a photomask with a predetermined pattern is used to bake a photoresist film to form a resist coating, and a semiconductor substrate is processed based on this resist coating. Therefore, if foreign matter such as dust adheres to the photomask or there are scratches, this will be baked onto the resist film.
This will result in pattern defects on the semiconductor substrate.

Incidentally, in recent years, exposure apparatuses have been proposed that perform pattern printing using holography to prevent defects from occurring during printing. That is, this device illuminates a hologram (mask) with coherent light, and exposes the photoresist with a conjugate image (real image) created by interference of the diffracted light.

Here, in holography, a reconstructed image of the entire hologram can be obtained even from a part of the hologram, so even if a part of the hologram is missing or a part of the hologram has a defect, this defect will not be burned in and it will be completely removed. This makes it possible to expose defects. However, in conventional devices, the intensity of the laser light source is low and it is inconvenient to handle.Furthermore, the speckles associated with the coherent toy generate a lot of noise, and this speckle noise is reflected in the pattern. It is occurring. Therefore, if a figure line width changes due to speckle noise or a new defect occurs, a negative result occurs, making it difficult to put this type of device into practical use.

[Purpose of the invention]

The object of the present invention is that once a defect-free hologram is formed, a defect-free reproduced image can be formed on the photoresist even if foreign matter adheres or scratches occur afterward, and defects caused by speckle noise can also occur. The purpose of the present invention is to provide a holographic exposure device that is completely free of defects.

Another object of the present invention is to provide a holographic exposure device that has a satisfactory exposure intensity and is easy to handle.

The above and other objects and novel features of the present invention will become clear from the description of this specification and the accompanying drawings. The explanation is as follows:

In other words, by using an excimer laser that emits ultraviolet light as the light source used to reproduce the hologram, the degree of coherence is degraded and speckle noise is prevented, thereby making it possible to print photoresist without defects. be.

〔Example〕

The first section shows a hologram whose original shape is made of points and its principle. As shown in the figure, a part of the wall 1 has a figure (pattern).
When a small hole 2 is formed as a small hole 2 and parallel coherent light 3 is applied from behind, transmitted light 4 and diffracted light 5 are generated in front. Then, on the surface of the hologram 6 placed in front, this diffracted light 5 interferes with a parallel reference light 7 that is separated from the same light source and hits the hologram 6, forming a Fresnel ring 8. A hologram is a photosensitive material printed with this brightness and darkness. This inner region is a concentric circle of repeated brightness and darkness, and has the same effect as a lens. If the hologram 6 is illuminated in the opposite direction from the other side in Fig. 1 with parallel coherent light of the same wavelength as that used to produce the hologram 6, then
A point-like focal point is formed on the small hole 2 as the original figure.

Furthermore, since the size of this Fresnel ring determines the resolution limit of the reconstructed image, this relationship is equal to the relationship between the aperture diameter and resolution limit of a normal optical lens. Since the figure WJ bond on the hologram corresponding to the small hole (= point, diameter a) of the original figure (-reproduced image) is wide, even if there is a defect caused by a foreign object of several micrometers, this will not appear on the reproduced image. Deterioration in resolution caused by this is not a problem, and no corresponding defects occur. The diameter of the Fresnel ring corresponding to the original figure depends on the degree of coherence of the illumination light used when producing the hologram 6. Laser light is generally used for this coheren H, and the narrower the spectral width, the larger the diameter of the Fresnel ring. Generally, the wavelength is 4・a
Light with a spectral width narrower than /D is required for illumination. For example, if a is 3μB, D is 20μB, and the wavelength of illumination light is 350OA, then 3500X3/2000
0X4=2, IA, and a spectral width of 2.1λ or less is required. This is about the same as the spectral width of the green luminance of a mercury lamp by one or two people. Also, the resolution of holography improves as D increases. Therefore, due to these relationships, it is necessary to use highly coherent monochromatic light with a narrow spectral width in order to fabricate a hologram with a fine pattern. However, in addition to the spectral width, coherence has a temporal length (temporal coherence), and mercury lamps have poor temporal coherence, so light with a path difference does not interfere. Therefore, in the fabrication of holograms, there is a lack of coherence due to this path difference. Furthermore, in the reproduction of two-dimensional figures, the path difference is very short, so a re-main image can be formed, but the resolution is poor.

(11) Production of holograms A hologram is created using an original figure mask and a hologram imaging device to create one off-axis Fresnel transformation hologram. Here, it is necessary to use light with the wavelength used for reproduction as the illumination light. At this time, the original shape mask must be defect-free, and defects in the light-blocking and transparent parts must be completely repaired.Furthermore, holograms can be simulated by computer without producing the original shape mask. Therefore, the original figure data is converted to binarized hologram data using a computer, and from this it is possible to directly produce a hologram.Since the data of a hologram is redundant compared to the original figure, the number of rectangles to be drawn is This increases significantly.For this reason, electron beam lithography is suitable for manufacturing.

Note that with a raster scanning type electron beam lithography apparatus, a mask can be drawn in a fixed time of about 45 minutes, regardless of the number of rectangles to be drawn.

For the hologram, a figure is formed by photo-etching a cladding plate in which chromium is deposited to a thickness of 70 to 120 nm on a glass plate. Therefore, there is no intermediate tone and the result is a binarized hologram. A photoresist is applied to the clad plate to a thickness of about 0.5 μm and dried. Here, the photoresist uses a high-resolution positive type made of Novolapk resin (), Knoll tree MF resin, and a dissolution inhibitor added.On the surface of this photoresist, a 9-light device shown in The entire holographic pattern of the original pattern mask is exposed to light using a chromium etchant.Then, it is developed with an alkaline developer, washed with water, and dried to reveal a d-type resist.After heat-treating this resist, the resist is coated with a chrome etchant. By dissolving the unused chromium film and finally dissolving the unnecessary resist with a stripping solution, a chrome pattern is obtained and the Shirokram mask is completed.In addition, even if the black and white of the hologram is reversed, the brightness and darkness of the reproduced image will be reversed. The exact same original shape can be reproduced without

(2) Reproduction of hologram Figure 2 shows a conceptual diagram of the exposure apparatus. In the figure, 1
0 is a laser light source, and 11 and 12 are lenses serving as beam expanders. These optical systems create parallel light beams and irradiate the hologram 13 with them. 14 is transmitted light. At this time, the same laser beam as used for manufacturing the hologram 13 is used. As a result, hologram 1
Diffraction waves are generated from the periphery of the light-shielding film 3, and a virtual image 15 and a conjugate image 16 can be reproduced by their interference. Here, the hologram works like a 7-Renel lens and is imaged at an off-axis position.

Next, a wafer 18 coated with a 7-photoresist 17 is placed on the surface on which the aforementioned conjugate image is to be formed, and the original pattern is exposed to the resist. At this time, an original shutter 19 may be arranged in front of the Ueno shutter 18 and opened during resist exposure. Furthermore, a matching pattern is provided around the wafer 180 for alignment with a pattern already existing on the wafer. Then, a position alignment mark corresponding to the original figure of the hologram is provided so that the position of this reconstructed image and the position of the alignment mark on the hologram match. For this reason.

The wafer 18 is placed on a stage 20 that can rotate and move in the X and Y directions, and the stage 20 can change the distance and tilt in the hologram direction in order to focus the reconstructed image. .

The resolution limit R of the reproduced figure is determined by the diameter of one point (picture element) of the original figure expanded over 7 Renel zones, and if the distance from the hologram 13 to the reproduced image (wafer) 18 is b, then R=2bλ/ It is represented by D. For example, D is 60
If fil and λ are 0135 μrrL%b is 300 am, the resolution limit R is 3.5 μm. To reduce the resolution limit, shorten the distance and increase the diameter of the Fresnel ring to which one point corresponds.

Here, as the light source 10, it is necessary to use an ultraviolet laser and a visible light laser with a wavelength of 500 nm or less. XeF excimer laser (353 nm), nitrogen laser (337 nm).

He-Cd laser (442 nm), argon laser (4
88 nm) etc. can be applied. Among these, the excimer laser emits strong ultraviolet rays, so it is optimal for exposing photoresist in terms of wavelength. However, since this laser has poor coherency, an r-unstable resonator must be used to improve it.

Excimer lasers with improved coherent toy emit terrible ultraviolet rays, and because the degree of coherence is poor, spec noise can be ignored.
It is the perfect light source for holographic exposure. In other words, although a device using a stable oscillator cannot normally be used to produce a hologram, it can still form a reproduced image, although the resolution limit deteriorates during reproduction. This poor coherence is effective in reducing speckle noise occurring in reproduced images. In this case, even if the hologram is reproduced with a well-coherent laser beam such as an argon-neon laser and the resist film is exposed with the hologram, the resist pattern will have a ridged spectrum pattern and the resolution will be significantly degraded. However, if an excimer laser is used as the light source, even if an unstable resonator is used, argon
Speckle noise can be ignored since it is less coherent than neon lasers. In addition, hologram masks for lithography printing increase the resolution of reproduced images,
The size of the hologram corresponding to one point on the original figure (the diameter of a Fresnel ring) is about several tens of meters. The reconstructed image from such a wide area hologram has speckle noise,
It is essentially reduced because it is averaged over a wide area.

[Effect] +11 Holographic exposure IK using a hologram as a mask: Since Yorihan IZ-n printing is performed, the figure with an area of several square centimeters or more of the hologram is one part of the reproduced image.
Since the recording corresponds to the points and has a high degree of redundancy, even if a part of the hologram is missing, the defects in the reconstructed image can be ignored.
Defect-free pattern printing can be performed even when foreign matter adheres to the hologram or there are scratches.

(2) A hologram mask can also be directly formed by computer simulation, and in this case, even if a defect occurs during the manufacturing process, it will not be a defect in the reconstructed image.

(3) Since an excimer laser is used as a light source, it is possible to oscillate monochromatic light that is strong in the ultraviolet 2 and deep ultraviolet rays, and even if diffracted light is used, exposure can be completed in a few minutes.

(4) By using an excimer laser, speckle noise can be ignored by adjusting the degree of coherence, and exposure can be performed without line width variations due to speckle. (6) Since an excimer laser is used, handling is extremely easy.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor.

For example, in addition to the above-mentioned excimer laser, XeCA (3
08 nm), KrF (249 nm), KrC-e (2
22 nm) and ArF (193 nm) may be used.

[Application field]

The above explanation has mainly been about the case where the invention made by the present inventor is applied to the photolithography technology of semiconductor devices, which is the background field of application.
The invention is not limited to this, and can be applied to all things that utilize photographic technology.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the principle of holography, and FIG. 2 is a conceptual diagram of a holographic exposure apparatus. 10... Ray f light source (excimer laser), 11.12.
・Lens, 13... Hologram, 16... Conjugate image, 17
...Photoresist, 18...Wayno, 20...Stage.

Claims (1)

[Scope of Claims] 1. A hologram formed from an original figure is illuminated with coherent light, and the reproduced image is printed on a photoresist film, and the coherent light source is an excimer that oscillates ultraviolet rays. A holographic exposure device characterized by using a laser. 2. Excimer laser is XeF, XeCJ%KrF. The holographic exposure apparatus according to claim 1, wherein the holographic exposure apparatus is an excimer laser such as KrC1:, ArF, or the like. 3. A circuit pattern of a semiconductor device is used as the original figure for manufacturing the hologram, and a semiconductor wafer constituting the circuit can be placed at the conjugate image position. The holographic exposure apparatus described in 2.