JP2524993B2 - Method of forming resist pattern - Google Patents

Description

TECHNICAL FIELD The present invention relates to a resist pattern forming method suitable for manufacturing a semiconductor integrated circuit, and more particularly to a resist pattern forming method for forming an ultrafine pattern with high accuracy. .

(Prior Art) With the increase in the density of semiconductor integrated circuits, the minimum pattern size of circuits to be integrated is further miniaturized, and accordingly, a fine resist pattern of about 1 μm or less than submicron is formed with high accuracy. High demand for technology.

Conventionally, the conventional ortholithography technology has been widely used as a means for increasing the resolution and patterning with high accuracy, but in addition, the lithographic technology using an electron beam, an X-ray or an ion beam as a radiation source has been developed. ing.
However, the photolithography technique using light is advantageous in consideration of mass productivity, economy, and workability.

Various proposals have been made as a method for forming a resist pattern by such a photolithography technique. For example, literature IEE Electron Device Letters, EDL-4.19 has been proposed.
83. Contrast enhancement disclosed in pages 14-16
Photolithography technology (Contrast.Enhanced Photolit
According to hography (hereinafter abbreviated as CEPL technology), it has been noted that a high-resolution resist pattern can be formed by adding a simple process.

The principle of the CEPL technology will be described below with reference to FIG.

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

First, as shown in FIG. 2A, a lower layer resist layer 12 to be patterned is provided on a silicon wafer (silicon substrate) 11, and a thin film called a contrast enhancement layer (Contrast Enhancement Layer) is formed on the lower layer resist layer 12. A photosensitive layer 13 (hereinafter, also referred to as a CEL film) in the shape of a stripe is provided. This CEL film initially has a large absorption with respect to the exposure wavelength, but is formed of a material in which the absorption becomes smaller and the transmittance becomes higher as the exposure amount is increased due to bleaching by light irradiation.

By the way, when light passes through the photomask 14, the mask 14 is exposed to the light source due to the diffraction and focusing effect of the light.
Since the light reaches the shaded area, 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 layer 12, and the resist patterning cannot be performed with a sufficiently satisfactory resolution.

In this CEPL, the photo mask shown in FIG.
Selective exposure of the resist layer 12 is performed by projecting the optical image of 14 onto the lower resist layer 12 through the CEL film 13. As a result, as shown in FIG. 2 (C), a portion 13a where the CEL film 13 is bleached due to a large light dose amount (exposure amount) and a portion 13b where the dose amount is unbleached are unbleached. It is formed.
Bleaching according to the altitude distribution of this light
ng), the transmittance of the CEL film 13 is largely changed, and in the ideal case, the intensity distribution of the transmitted light is as shown in FIG. 2 (D). This results in
The light transmitted through the CEL film 13 has its contrast enhanced. The resist layer 12 is selectively exposed by irradiating the resist layer 12 with this contrast-enhanced light, and by the subsequent development processing, a clean and sharp image, for example, a positive type as shown in FIG. Thus, the resist pattern 12a is formed.

(Problems to be Solved by the Invention) However, in the case of such a conventional CEPL process, as is apparent from FIG. 3 corresponding to FIG. 1 of the present invention described later, prior to development of the resist layer after exposure, An additional work step was needed to remove the CEL layer.

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), and then ultraviolet rays 40 are radiated through a photomask 34, and the same as above. The exposed portions 32a, 32a and the unexposed portions 32b, 32b are shown (C in the figure).

Next, after removing the CEL layers 33 (33a, 33b) as shown in FIG. 4D, the resist layer 32 is developed (E in FIG. 3).

That is, the development of the resist layer is carried out with an alkaline aqueous solution, whereas the removal of CEL is carried out with an organic solvent, so that there is a drawback that the above-mentioned separate step is added and is complicated.

On the other hand, there is also a report that the coating solution used to omit the step of removing the CEL layer 33 is made water-soluble, but in this case, since the diazonium salt is contained as a photobleaching agent and the diazonium salt is unstable in an aqueous solution, There is another problem that the coating solution lacks long-term stability.

As a method of solving the above-mentioned problems, the present inventors have
Selectively exposing the resist layer through a photosensitive layer that enhances the contrast of light incident on the resist layer, and then removing the photosensitive layer and developing the resist layer to form a resist pattern, It was found that it is effective to use a photosensitive layer containing a thin film-forming material soluble in both non-polar organic solvents such as abietic acid and rosins such as gum rosin containing abietic acid as a main component and an alkaline aqueous solution, and filed a patent application.

Then, the research on the pattern forming method was continuously carried out and the present invention was reached.

(Means for Solving the Problems) The present invention is directed to selectively exposing the resist layer through a photosensitive layer that enhances the contrast of light incident on the resist layer, and then removing the photosensitive layer and removing the resist layer. In the contrast enhancement trisographic process of forming a resist pattern by performing a development treatment, as a film forming material contained in the above-mentioned CEL film, as a material soluble in both a non-polar organic solvent and an alkaline aqueous solution, especially 7,8,13 50% of 14,14-tetrahydroabietic acid or its main component
A method for forming a resist pattern is characterized in that the photosensitive layer is removed and the resist layer is developed using an aqueous alkali solution continuously using the hydrogenated rosins contained above.

(Operation) In the present invention, as the above-mentioned CEL film forming material, in a material soluble in a non-polar organic solvent and an alkaline aqueous solution, particularly 7,
By using 8,13,14-tetrahydroabietic acid, it dissolves in the developing solution of a normal positive resist, so that it is removed at the same time during development, and the rosin is hydrogenated. The stability is increased, and the stability as a solution in a nonpolar organic solvent is further enhanced.

(Examples) Examples of the present invention will be described below with reference to the drawings.

In the following examples, preferred specific conditions and numerical examples within the scope of the present invention will be described, but these are merely examples, and the present invention is limited thereto unless particularly limited and described. Not a thing.

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

First, a resist material (NPR-820, Nagase & Co., Ltd., NPR-820) was applied on a Si substrate (silicon wafer) 31 with a spinner, and then baked on a hot plate at 105 ° C for 60 seconds to obtain a film thickness of 0.9.
A lower resist film 32 having a thickness of μm was formed.

Next, 1.0 g of hydrogenated rosin (Arakawa Chemical Co., Ltd., trade name Hyper, 7,8,13,14-tetrahydroabietic acid content of 50% or more) and photobleaching agent α- (4-diethylaminophenyl) -N-phenylnitrone 1.0 g was dissolved in 10.0 g of nonpolar organic solvent monochlorobenzene to obtain a CEL coating solution, and this solution was coated on the resist layer 32 with a spinner to form a CEL film 33 having a thickness of 0.7 μm as a photosensitive layer. .

Next, through the CEL film 33, the lower resist layer 32 is irradiated with ultraviolet rays 40 having a wavelength of about 350 to 450 nm from a mercury lamp through the mask pattern of the photomask 34 at a dose amount of 500 mJ / cm ^2. It was performed (FIG. 1 (C)). The reason why the wavelength range is set to 350 to 450 nm is that the sensitivity of the resist is lowered and the absorption spectrum characteristic and bleaching characteristic of CEL are deteriorated outside this wavelength range. As the exposure apparatus, a 1: 1 reflection projection type exposure apparatus with a product number of 500HT manufactured by Perkin Elmer was used.
In the figure, portions of the CEL film 33 and the resist film 32 exposed by the ultraviolet ray 40 are indicated by 33a and 32a, respectively, and an unexposed portion is indicated by 33a.
b and 32b respectively.

Due to this ultraviolet irradiation, the amount of light that is directly irradiated from the light transmitting region of the photomask 34 to the CEL film 33 is 450 mJ / cm ² , so the light transmittance in that portion is approximately 95%. However, since the amount of light is reduced in the region where the light is blocked by the mask 34, the CEL film 33 that becomes a shade of light from the boundary between both regions is formed.
The transmittance at the portion of the mask rapidly decreases, and the transmittance becomes close to zero near the center of the shadow of the mask. Therefore, the portion 32a of the resist layer 32 which receives light irradiation through the CEL film 33 does not receive it. The light intensity at the boundary with the portion 32b of the resist layer 32 changes sharply, that is, substantially stepwise.

After completion of the above exposure, a metal-free developer (Nagase Sangyo Co., Ltd. 934) was used immediately without performing the peeling process of the CEL film 33. 3
Development was carried out for 5 seconds. This developer contains water (95-99%) and tetramethylammonium hydroxide (1-5%).
%) Is a mixed alkaline aqueous solution. CEL film 33 above
Is dissolved and removed immediately after the start of development, the development of the resist layer 32 is started, the exposed portion 32a is removed, and the unexposed portion 32b remains to form a positive resist pattern as shown in FIG. 1 (D). Was done.

When the cross-sectional shape of the obtained resist pattern was observed by a scanning electron microscope, in the pattern larger than the line and space of 1.5 μm, the side wall portion of the pattern was formed in a steep state nearly perpendicular to the substrate surface. Therefore, a clean and sharp resist pattern having a substantially rectangular cross section was obtained. 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 except that the CEL film of Example 1 was not provided on the resist layer. The exposure amount was 100 mJ / cm ² .

When the obtained resist pattern was similarly observed with a scanning electron microscope, the inclination of the side wall of the pattern with respect to the substrate surface was more gentle than that of the pattern of Example 1, and the cross-sectional shape was almost trapezoidal. No clear and sharp resist pattern was obtained. Further, it was found that when a line and space of 1 μm was to be obtained, the film thickness of the resist layer was half the film thickness in the case of Example 1 and the function as the resist layer could not be expected.

Example 2 1.0 g of hydrogenated rosin (previously described as Hype) and photobleach α
-(4-Diethylaminophenyl) -N- (3'.4'-
0.5 g of dichlorophenyl) nitrone was dissolved in 7.0 g of nonpolar organic solvent monochlorobenzene to obtain a CEL coating solution, which was coated on the resist layer 32 in the same manner as in Example 1 to form a film having a thickness of 0.7 μm. The CEL film 33 was formed as a photosensitive layer.

Next, with respect to the lower resist layer 32 through the CEL film 33,
The mask pattern of Photo Mask 34 is set to Nikon NSR 1505 G3A.
Exposure was performed with a mold reduction projection type exposure layer. Then, the same development as in Example 1 was performed immediately without performing the peeling process of the CEL film 33 as in Example 1. When the cross-sectional shape of the obtained resist pattern was observed by a scanning electron microscope, the cross-sectional shape of the side wall of the pattern was almost rectangular, and the line and space of 0.6 μm was clean and sharp. A good resist pattern was obtained.

Comparative Example 2 Without forming the CEL film of Example 2 on the resist layer, a resist layer of the same material was subjected to the same exposure, development and other treatments as in Example 2 to form a pattern. The exposure amount is 100m
It was set to J / cm ² .

When the obtained resist pattern was observed with a scanning electron microscope in the same manner, the sidewall of the pattern had a gentle inclination with respect to the substrate surface, and the cross-sectional shape was almost trapezoidal.
Pattern could be formed, but the pattern of 0.6 μm could not be formed.

(Effects of the Invention) As described in detail above, according to the present invention, the CEL
Soluble in alkaline aqueous solution as thin film forming material 7,8,13,14
-By using tetrahydroabietic acid or hydrogenated rosins containing 50% or more of tetrahydroabietic acid, it is possible to perform development immediately after exposure without adding a separate removal step to the CEL film, thus simplifying the work process. In addition, the coating solution used is extremely stable because it does not decompose the photobleaching agent due to the use of a non-polar organic solvent, and rosin is hydrogenated, which increases its stability. It is possible to solve the above-mentioned problems such as sufficiently enduring storage of time.

[Brief description of drawings]

FIG. 1 is a process explanatory diagram of this resist pattern forming method, FIG. 2 is a CEPL principle explanatory diagram, and FIG. 3 is a process explanatory diagram of a conventional method. 31 ... Substrate, 32 ... Resist layer, 33 ... CEL film (photosensitive layer), 34 ... Photomask, 32a, 33a ... Exposure section, 32b,
33b …… End exposure unit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Yoshio Yamashita 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (72) Takateru Asano 1-9-17 Azabudai, Minato-ku, Tokyo Fuji Pharmaceutical Co., Ltd. (72) Inventor Kenji Kobayashi 1-9-17 Azabudai, Minato-ku, Tokyo Fuji Pharmaceutical Co., Ltd. (56) Reference JP 61-143744 (JP, A) JP 61 -121053 (JP, A) JP-A-57-95005 (JP, A) JP-A-60-149050 (JP, A) JP-A 61-84644 (JP, A) JP-A-62-198856 (JP, A) )

Claims (1)

(57) [Claims] 1. A resist pattern in which the resist layer is selectively exposed through a photosensitive layer that enhances the contrast of light incident on the resist layer, and thereafter the photosensitive layer is removed and the resist layer is developed. In forming, 7,8,13,14-tetrahydroabietic acid, or 7,8,13,
Using a photosensitive layer containing hydrogenated rosins containing 50% or more of 14-tetrahydroabietic acid as a main component, the removal of the photosensitive layer after exposure and the development treatment of the resist layer were continuously performed using an alkaline aqueous solution. And a resist pattern forming method.