JPS63205647A - Formation of resist pattern - Google Patents

Abstract

PURPOSE:To improve stability by using a photosensitive layer contg. a thin film forming material which is soluble in both of a nonpolar org. solvent and aq. alkaline soln. at the time of forming a resist pattern by subjecting a photosensitive layer and resist layer to a developing process. CONSTITUTION:The materials which are soluble in both of the nonpolar org. solvent and aq. alkaline soln., more specifically, rosins such as abietic acid and gum rosin essentially consisting of abietic acid are used as the film forming material contained in the photosensitive layer 33 in a process for forming the resist pattern by selectively exposing the resist layer 32 via the photosensitive layer 32 to enhance the contrast of the incident light on the resist layer 32, then subjecting the photosensitive layer 33 and the resist layer 32 to the developing process. Since the rosins are thereby dissolved in an ordinary positive resist type developing soln., the rosins are eventually processed and removed simultaneously at the time of the development and the stability as the soln. in the nonpolar org. solvent is improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a resist pattern forming method suitable for manufacturing semiconductor integrated circuits, and particularly to a resist pattern forming method for forming ultra-fine patterns with high precision. .

(Prior art) As the density of semiconductor integrated circuits increases, the minimum pattern dimensions of circuits to be integrated are becoming increasingly finer, and with this, fine resist patterns of about 1 μm or submicron or less can be formed with high precision. There is a high demand for technology to do this.

In general, photolithography technology has been widely used as a means of increasing resolution and patterning with high precision, but other lithography technologies have also been developed that use electron beams, X-rays, or ion beams as radiation sources. . However, in consideration of mass production, economy, and workability, photolithography technology using light is advantageous.

A number of proposals have been made as methods for forming resist patterns using such photolithography techniques, but for example, in the literature IEE Electron Device XL/
IEEE Electron Device
Letters), EDL-4, 1983, PI3
--Contrast enhanced photolithography technology disclosed in 16 (Contrast, Enhan
ced Photolithography, Q lower C
EPL technology (abbreviated as EPL technology) is attracting attention because it is capable of forming high-resolution resist patterns by adding simple processes.

The principle of this CEPL technology will be explained below with reference to FIG.

FIGS. 2A to 2E are process diagrams for explaining the principle of CEPL technology, and each figure is schematically shown as a sectional view.

First, as shown in FIG. 2(A), a lower resist layer 2 to be patterned is provided on a silicon substrate 11, and a contrast enhancement layer 2 is formed on this lower resist layer lz.
A thin film-like photosensitive layer 13 (hereinafter also referred to as a CEL layer) called a cement layer is provided.

Initially, the CEL layer has a large absorption at the exposure wavelength, but as it is bleached by light irradiation and the amount of exposure increases,
◇ By the way, when light passes through the photomask 14, the light diffraction and focusing effect cause the mask 1 to move toward the light source.
Since the light reaches the shaded region 4, the light intensity distribution behind the photomask 14 becomes as shown in FIG. 2(B). As a result, the contrast of the projected light image of the photomask becomes lower than the contrast threshold of the lower resist@12, making it impossible to perform resist patterning with a sufficiently satisfactory resolution.

In this CEPL, the optical image of the photomask 14 shown in FIG. 2(B) is transmitted to the lower resist layer 1 through the CEL film 13.
Selective exposure of the resist layer 12 is performed by projecting onto the photoresist layer 2. In this way, as shown in FIG. 2(C), a portion 13m where the CEL film 13 is bleached due to a large dose of light (exposure amount) and a portion 13b where the dose is small and is unbleached. It is formed. Due to the difference in bleaching depending on the intensity distribution of this light,
The transmittance of the CEL film 13 is partially thick (changes), so in an ideal case, the intensity distribution of transmitted light is as shown in Figure 2 (D).
The situation will be as shown below. As a result, the CEL film 13
The contrast of the light that passes through it will be enhanced. By irradiating the resist layer 12 with this contrast-enhanced light, selective exposure of the resist layer 12 is performed, and the subsequent development process produces a beautiful, sharp, for example, positive type image as shown in FIG. 2(E). A resist pattern 12a is thus formed.

(Problems to be solved by the invention) However, in the case of such a conventional CEPL process,
As is clear from FIG. 3, which corresponds to FIG. 1 of the present invention described later, a separate work step was required to remove the CEL layer prior to developing the resist layer after exposure.

To explain this with reference to FIG. 3, a lower resist layer 32 and a CEL film 33 are provided in this order on a substrate 31 (A and B in the same figure).
Next, ultraviolet rays 40 are irradiated through the photomask 34 to form exposed portions 32a, 33m and unexposed portions 32b, 33b in the same manner as described above (FIG. 3C).

Next, as shown in the same figure, the CEL layer 33 (33a, 33b)
After removing the resist layer 32, the resist layer 32 is developed (see E in the figure).

That is, while the development of the resist layer is carried out with an alkaline aqueous solution, the removal of CEL is carried out with an organic solvent, which has the disadvantage that the above-mentioned separate process is added and complicated.

On the other hand, there are reports that the coating solution used is made water-soluble in order to omit the above-mentioned CEL[33 removal step, but in this case it contains a diazonium salt as a photobleaching agent, and the diazonium salt is unstable in an aqueous solution. Another problem was that the coating solution lacked long-term stability.

The object of the present invention is to provide an excellent resist pattern forming method that solves the problems of the complexity of the work process and the instability of the coating solution applied to the CEL layer.

(Means for Solving the Problems) This invention selectively exposes this resist layer to light through a photosensitive layer to increase the contrast of light incident on the resist layer, and then exposes the photosensitive layer and the resist layer. In the contrast-enhanced lithography process in which a resist pattern is formed by a development process, materials soluble in both non-polar organic solvents and alkaline aqueous solutions, specifically abietic acid and abietin, are used as film-forming materials contained in the above-mentioned CEL film. This method of forming a resist pattern is characterized by using a rosin such as gum rosin containing acid as a main component.

(Function) In the present invention, by using a material soluble in a non-polar organic solvent and an alkaline aqueous solution as the above-mentioned CEL film forming material, it dissolves in a normal positive resist developer, so it can be used simultaneously during development. It will be removed by processing, and its stability as a solution in an inorganic organic solvent will be significantly increased.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In the following examples, preferred specific conditions and numerical examples within the scope of the present invention will be explained, but these are merely illustrative, and the present invention is not limited to them unless specifically limited. It's not a thing.

Example 1 In this example, Chinese rosin was used as the film forming material.

First, a resist material (
NPR-820 (manufactured by Nagase Sangyo Co., Ltd.) was applied using a spinner, and then baked on a hot plate at 105° C. for 60 seconds to form a lower resist film 32 with a thickness of 0.9 μm.

Next, a CEL coating solution obtained by dissolving 1.0 g of Chinese rosin and 1.0 g of the photobleach α-(4-diethylaminophenyl)-N-phenylnitrone in 10.0 g of monochlorobenzene was applied to the resist layer 32 using a spinner. Apply to
A CEL film 33 having a thickness of 0.7 μm was formed as a photosensitive layer.

Next, ultraviolet light in the wavelength range of approximately 350 to 450 nm from a mercury lamp is applied to the lower resist layer 32 through the CEL film 33 and through the mask pattern of the photomask 34.
Irradiation was carried out at a dose of 500 mJ/d at 40 mJ/d (Fig. 1(C)). The reason why the wavelength range is set to 350 to 450 nm is that the sensitivity of the resist decreases outside this wavelength range, and the absorption spectrum characteristics and bleaching characteristics of CEL deteriorate. In addition, the exposure device is PerkinElmer product number 500.
An HT 1:1 reflection projection exposure system was used. In the figure, portions of the CEL film 33 and resist film 32 exposed to ultraviolet light 11i1140 are indicated by 33a and 32&, respectively, and unexposed portions are indicated by 33b and 32b, respectively.

Due to this ultraviolet irradiation, the amount of light directly irradiated onto the CEL film 33 from the light transmission area of the photomask 34 is 450.
mJ/ad, so the light transmittance at that part is about 95%.
It will be about. However, since the amount of light decreases in the area where the light is blocked by the mask 34, the transmittance in the part of the CEL film 33 that is shaded from the light from the boundary between the two head areas decreases rapidly, and near the center of the mask's shadow, the light intensity decreases. The transmittance is close to zero,
Therefore, the light intensity at the boundary between the portion 32m of the resist layer 32 that is irradiated with light through the CEL film 33 and the portion 32b of the resist layer 32 that is not irradiated changes sharply, that is, substantially stepwise.

After the above-mentioned exposure was completed, development was immediately performed for 35 seconds using a metal-free developer (Nagase Sangyo Co., Ltd. 838) without performing a step of peeling off the CEL film 33. The CEL film 33 is instantly dissolved and removed after the start of development, development of the resist layer 32 is started, and the exposed portion 32B is removed and the unexposed portion 32b remains, resulting in a positive type film as shown in FIG. 1(D). A resist pattern was formed.

When the cross-sectional shape of the obtained resist pattern was observed using a scanning electron microscope, it was found that in the large pattern of 1.5 μm living space, the sidewalls of the pattern were formed in a steep state almost perpendicular to the substrate surface. Therefore, a clean and sharp resist pattern with an almost rectangular cross-sectional shape was obtained. Moreover, a line and space of 1 μm was also obtained.

Comparative Example 1 A pattern was formed by exposure, development, and other treatments in exactly the same manner as in Example 1, except that the CEL film was not provided on the resist layer. Note that the exposure amount was 100 mJ/cd.

When the obtained resist pattern was similarly observed with a scanning electron microscope, it was found that the slope of the side wall of the pattern with respect to the substrate surface was gentler than that of the pattern of Example 1, and the cross-sectional shape was almost trapezoidal. However, a clean and sharp resist pattern could not be obtained. In addition, when trying to obtain a line and space of 1 μm, the thickness of the resist layer becomes less than half the thickness of Example 1.
It was found that the function as a resist layer could not be expected.

Example 2 Chinese Rosin 1. 0.5 g of photobleach a-(4-diethylaminophenyl)-N-(3',4'-dichlorotetraphenyl)nitrone and 7.0 g of monochlorobenzene.
6 to obtain CEL#L cloth Sa, and this solution was applied on the resist layer 32 in the same manner as in Example 1 to give a film thickness of 0.7
A CEL film 33 having a thickness of μm was formed as a photosensitive layer.

Next, the mask pattern of the photomask 34 is applied to the lower resist layer 32 through this CEL film 33.
Exposure was carried out using an NSR1505GgA reduction projection type exposure layer apparatus. Immediately after the step of peeling off the CEL film 33, the same development as in Example 1 was performed. When we examined the cross-sectional shape of the obtained resist pattern by observing it with a scanning electron microscope, we found that the cross-sectional shape of the sidewall of the pattern, which is perpendicular to the substrate surface, was almost rectangular and had a line-and-space of 0.6 μm. II A beautiful and sharp resist pattern was obtained.

Comparative Example 2 A pattern was formed on a resist layer made of the same material by the same exposure, development, and other treatments as in Example 2, without providing the CEL film of Example 2 on the resist layer.

Note that the exposure amount was 1001 TIJ/(!Il).

When the obtained resist pattern was similarly observed using a scanning electron microscope, it was found that the sidewalls of the pattern had a gentle slope with respect to the substrate surface, the cross-sectional shape was almost trapezoidal, and the diameter was 0.7 μm.
A pattern of 0.6 μm could not be formed.

(Effects of the Invention) As explained in detail above, according to the present invention, the CEL
By using a rosin or the like that is soluble in an alkaline aqueous solution as a thin film forming material, it is possible to develop the CEL film immediately after exposure without adding a separate removal process, which simplifies the work process. Furthermore, since the coating solution used is a non-polar organic solvent, it becomes extremely stable without causing decomposition of the photobleaching agent, and therefore can sufficiently withstand long-term storage, thereby solving the above-mentioned problems.

[Brief explanation of the drawing]

FIG. 1 is a process explanatory diagram of this resist pattern forming method, FIG. 2 is an explanatory diagram of the principle of CEPL, and FIG. 3 is a process explanatory diagram of a conventional method. 31...Substrate, 32...Resist layer, 33...C
EL film (photosensitive layer), 34... Photomask, 32m
, 33m... exposure section, 32b, 33b, 1. End exposed area. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] Abietic acid, A method for forming a resist pattern, comprising using a photosensitive layer containing a thin film-forming material soluble in both a nonpolar organic solvent such as a rosin such as gum rosin containing abietic acid as a main component and an alkaline aqueous solution.