JPS5990927A - Photorithography - Google Patents

Abstract

PURPOSE:To enhance resolution and film remaining coefficient by conducting exposure and development under the condition that the surface is shielded from the ambient including the oxygen after forming a photo resist film using the photo resist having reduced sensitivity to oxygen and then covering it with a protection film consisting of the resin having small oxygen transmitting coefficient. CONSTITUTION:As a resin for forming a protection film, a poly-vinyl alcohol system resin, for example, can be considered. The polyvinyl alcohol aqueous solution of 5% is applied on the photo resist film 21. A protection film 22 is formed by removing water in the applied film through heat processing. When the surface is exposed to the ultraviolet rays 5 through the photo mask 4, the photo resist film 21 sensed through the protection film 22. The cross-shaded area of the photo resist 21 is brideged and becomes unsoluble part, while the shaded area is not sensed and dissolves to the developer. The protection film 22 is removed by the exclusive remover and the photo resist film 21 is developed by the n-heptane and then rinsed by the butyl acetate. The surface is dried up and the photo resist image 23 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a photolithography method (also called a photoetching method or a photoetching method), and more particularly to a photolithography method using an oxygen-desensitized photoresist.

[Technical background of the invention]

e) The 17 ng 2 Neu method is an indispensable manufacturing technology in the manufacture of semiconductor devices, etc., in which a precise photoresist image is formed on the object to be etched, such as an insulator, semiconductor, or metal, and this is used as a mask. This is a method of etching the object to be etched. In order to form a precise photoresist image, it is necessary to use a photoresist that is highly sensitive to exposure ultraviolet rays and has high resolution, but cyclized comb photoresists are highly sensitive and easy to handle, so they are suitable for semiconductor manufacturing. It is a negative type photoresist that is often used in processes. However, as described below, there is a problem with resolution in forming photoresist images using cyclized rubber-based negative photoresists, and there is a strong need to solve this problem as semiconductor devices become more highly integrated. .

[Problems with background technology]

Next, problems in forming a conventional photoresist image using a cyclized comb photoresist will be specifically explained with reference to the process diagram of FIG.

In Fig. 1(a) of 7th page, 1 has silicon urethane X, 2
is a silicon oxide film formed by treating a silicon wafer 1 in an oxidizing atmosphere, and the silicon oxide film 2 is the object to be etched in this case. e) To form a conventional photoresist image using the IJ nongraphy method, first, as shown in FIG.
A cyclized rubber-based negative photoresist film 6 having a uniform thickness is coated using a spin coater or the like and dried. Cyclized rubber-based negative type photoresists use cyclized polyisoprene or cyclized polybutadiene as a base resin, and 2,6-C (4'-7 Bisazide compounds such as cyclohexanone)-4-methylcyclohexanone and 2,6-di(4'-azidobenzal-cyclohexanone) are added.Next, as shown in FIG. When the photoresist film 6 is exposed to ultraviolet light 5 through the photoresist film 6, the bisazide compound releases N2 gas and becomes an active bisazide radical in the exposed portions of the photoresist film (cross-hatched lines), crosslinking the base resin and converting it into the developer. The portion of the photoresist film that is not exposed to light (hatched lines) remains soluble in the developer.The type of mask aligner has a contact that exposes the photoresist film 6 and the photomask 4 in close contact with each other. There are two methods, as shown in the figure, a proximity method in which both are slightly heated and exposed, and a projection method in which an image is formed on the photoresist film 6 using a reflective or refractive optical system for exposure.Of course, Among these methods, the contact method has the highest resolution.
As shown in d), the exposed wafer 1 is developed with a developer using a spray developing device or the like to dissolve the non-photosensitive resist film portion, rinsed with a rinse solution, and finally dried with dry air. A resist image 6 was obtained.

However, in the conventional method for forming a photoresist image using a cyclized rubber photoresist, as shown in FIG.
), if oxygen is present in the exposure atmosphere, the bisamide radicals decomposed by exposure will combine with oxygen to form an inert compound before crosslinking the base resin, and therefore no crosslinking reaction will occur even after exposure. The remaining resist film is eluted during development, resulting in a problem that the film thickness becomes thin (remaining film rate is low). This problem is generally called oxygen desensitization.

As mentioned above, the cyclized rubber photoresist is one of the oxygen-desensitized photoresists. Therefore, when a photoresist image is formed using the cyclized rubber photoresist by the above conventional method, the resolution is poor and the degree of crosslinking reaction is low due to exposure energy. Conditions are difficult to manage because they are not proportionate to each other. Therefore, although cyclized rubber-based resists are often conveniently used in contact-type aligners with high resolution, they are currently hardly used in projection-type aligners with low resolution.

[Purpose of the invention]

An object of the present invention is to provide a photoresist image forming method that increases resolution and increases the residual film rate in a photolithography method using an oxygen-desensitized photoresist. Another object of the present invention is to provide a photolithography method in which a precise photoresist image can be formed by applying an oxygen-desensitized photoresist to a projection type aligner.

[Summary of the invention]

In the present invention, a photoresist film is formed on an object to be etched using an oxygen-desensitized photoresist as in the conventional method, and then a protective film made of a resin having a small oxygen permeability coefficient is coated on the photoresist film to form a photoresist film. In a state where the oxygen-containing atmosphere is cut off, exposure is performed using a projection type aligner during mask alignment, and the bisazidoradical generated by exposure is effectively contributed to the crosslinking reaction of the base resin, and the corresponding hind limbs are This is a photolithography method characterized by removing a protective film and then developing the photolithographic film.

It doesn't form a protective film! For example, polyvinyl alcohol-based resins are praised as 7 fats. Polyvinyl alcohol (P'VA) is obtained by saponification of polyvinyl acetate, and various types of polyvinyl alcohol resins with a degree of saponification of 78% or more and a degree of polymerization of 300 or more are commercially available. These polyvinyl alcohol resins have superior oxygen permeability compared to other resins, and PVA with a saponification degree of 98% or more is particularly excellent. In the present invention, the protective film is formed of a resin having a low oxygen permeability similar to that of polyvinyl alcohol resin, but polyvinyl alcohol resin is particularly preferred because it does not leak water.

It has been known that polyvinyl alcohol can be used as an anti-adhesion agent for positive type resists, which tend to stick more easily than negative type resists, but it is completely unknown that polyvinyl alcohol can be used to prevent oxygen desensitization of cyclized rubber resists. Furthermore, its use for preventing oxygen desensitization in projection type exposure that does not require adhesion prevention is a completely new method.

[Embodiments of the invention]

Next, an embodiment of the present invention will be specifically described with reference to the process diagram of FIG. 2.

In FIG. 2(a), silicon wafers 11d, 110
By burning oxygen and hydrogen at a temperature of 0.degree. C. and exposing the silicon oxide film 2 to the atmosphere for about 70 minutes, a silicon oxide film 2 having a thickness of about 50,001 mm is formed, which becomes the object to be etched in this embodiment. Next, as shown in FIG. 2(b), 0MR83SR (cyclized rubber-based negative type photoresist trade name manufactured by Tokyo Ohka Co., Ltd.) was prepared to a viscosity of 30 cp and coated with a spin coater to a thickness of 1.1 μm. Apply. The rotation speed of the spin coater at this time was 2500 rpm. After that, heat treatment was performed on a hot plate at 85°C for 10 minutes to remove the organic solvent in the coating film, and the photoresist film 21
form. Next, as shown in FIG.
) to 1000% polyvinyl alcohol aqueous solution.
Apply to a thickness of λ.

Thereafter, heat treatment is performed on a hot plate at 85° C. for 10 minutes to remove moisture in the coating film and form a polyvinyl alcohol protective film 22. Next, as shown in FIG. 2(d), when UV exposure 5 is performed through the photomask 4 using a mask aligner, the UV light passes through the polyvinyl alcohol protective film 22 and the photoresist film 21 is exposed. Bisazide radicals are generated in the photoresist film 21 when exposed to light and decomposed, but because of the presence of the protective film 22, the base resin in the photoresist is effectively removed without reacting with oxygen in the atmosphere and becoming inactive. Can be crosslinked. The cross-hatched portions of the photoresist film 21 are cross-linked and insolubilized portions, and the diagonal-lined portions are unexposed and soluble in the developer. Next, as shown in FIG. 2<e>, the polyvinyl alcohol protective film 22 is removed using a special remover. Next, as shown in FIG. The film 21 is developed with n-heptane for 60 seconds, rinsed with butyl acetate for 60 seconds, and finally dried with dry air to obtain a photoresist image 26.

F3 Figure U, polyvinyl alcohol (
This figure shows the relationship between the residual film rate (photoresist film thickness after development/photoresist film thickness before development) of the cyclized rubber photoresist film 21 when the film thickness of the protective film 22 (PVA) is changed. As you can see from the figure, the PvA film thickness is 1000^
Even with such a thin film thickness, a high residual film rate of 0.95% can be obtained.
Since a constant residual film rate can be obtained for any film thickness of 100 A or more, manufacturing conditions can be easily managed.

FIG. 4 shows the relationship between the amount of exposure energy and the remaining film rate when the above example and the comparative example were exposed with a glossection aligner (MPA 500 FA) with different amounts of exposure energy. The first thing that can be seen from the figure is that there is a difference of 12 inches in the film remaining ratio between the example (curve a) and the comparative example (curve b). This 12% difference is due to the improvement in oxygen desensitization of the comparative example in the example, and the film thickness deviation of the conventional example can be resolved.

Second, the practical range of exposure energy in the example is the range indicated by arrow 8 or above, which is improved over the practical range (above the arrow) in the conventional example.

Further, in the above example, the resolution was improved compared to the above comparative example. That is, the Example and Comparative Example were used with a glojection aligner (MPA500FA) of 0.5 and 1.0.
, i, 5 , 2.0 , 2.5 , 3.0 , 3.
Tests were conducted using punched patterns of 5, 4.0, and 4.5 μm to determine the pattern width that would not cause any bridging. Improvement was seen.

Incidentally, the pattern width that does not cause bridging in a conventional contact type aligner is 3.0 μm.

In this way, even in the projection method, the present invention can provide a practical resolution.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, even in oxygen-desensitized photoresists such as cyclized gono-type negative type photoresists, the crosslinking agent is not inactivated by oxygen, resulting in a residual film. It has a high rate and high sensitivity.

Moreover, because of its excellent resolution, it has become possible to obtain a sufficiently clear pattern image for practical use even in projection exposure, in which negative type photoresists have rarely been used in the past. Of course, this is effective not only for projection exposure, but also for contact exposure and proximity exposure.

[Brief explanation of drawings]

FIG. 1 is a process diagram of a conventional photolithography method, FIG. 2 is a process diagram of an embodiment of the present invention, and FIGS. 6 and 4 are graphs explaining the present invention in detail. 1... Silicon Ueno, 2... Body to be etched, 3.2
1... Photoresist film, 4... Photomask, 5...
・Exposure ultraviolet light, 6.26...Photoresist image, 22・
·Protective film. Figure 1 Figure 2 fl Figure 3

Claims (1)

[Claims] 1. In a photolithography method using an oxygen-desensitized photoresist, a photoresist film of the above-mentioned photoresist is formed on the object to be etched. 2. Then, on the photoresist film, a polyvinyl alcohol resin or a similar resin with a small oxygen permeability coefficient is formed. A photolithographic method comprising applying a protective film, then exposing, removing the protective film, and developing the photoresist film.