JP2555675B2 - Pattern formation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a microfabrication method in manufacturing a semiconductor element or the like, and relates to pattern formation in photolithography.

[Conventional technology]

As the degree of integration of semiconductor elements is improved, the miniaturization of patterns is also progressing. Optical lithography using light as a light source is still used there. At present, the reduction projection exposure method is the mainstream because of its high resolution and excellent alignment accuracy. The problems in forming a fine pattern by the one-layer resist method by photolithography are the pattern size change (bulk effect) due to the local variation of the resist film thickness due to the substrate step, and the resist local due to the scattered light from the substrate step side wall. Of pattern size due to static overexposure (notching effect, and reduction projection exposure uses a contact optical system, so monochromatic light is used as a light source. Therefore, the problem caused by using this monochromatic light is Interference occurs between the incident light, the light reflected from the resist surface, and the light reflected from the resist / substrate interface, and fluctuations in the effective light amount absorbed in the resist due to slight fluctuations in the resist film thickness. It occurs in the cycle of λ / 2n (λ: exposure wavelength, n: refractive index of resist), and the resist pattern size varies (intra-film multiple reflection effect), resist thickness A periodical light intensity distribution occurs in the depth direction, and a corrugated shape corresponding to it occurs on the resist pattern cross section after development (standing wave effect). These are all causes of variation in resist pattern size and poor resolution. Become.

As a method for solving these problems of the conventional one-layer resist method, a multilayer resist method, an ARC method, an ARCOR method, and the like have been proposed. However, the multi-layer resist method has a problem that the number of steps is large and the throughput is low because three resist layers are formed and then a pattern is transferred to form a resist pattern serving as a mask. The ARC method has a problem that since the antireflection film formed under the resist is wet-etched by development, the amount of side etching is large, which causes a large decrease in dimensional accuracy. The ARCO method is a method of coating a single-layer or multi-layer interference type antireflection film on a resist film to suppress multiple reflection in the resist film, but there is a problem that the number of steps and materials used considerably increase. The multilayer resist is described in JP-A-51-10775. Further, as the ARC method, Japanese Patent Laid-Open No. 59-934
No. 48 and the ARCOR method are described in JP-A No. 62-62520.

[Problems to be Solved by the Invention]

Among these problems of the conventional one-layer resist method, a conventional post-exposure pre-development bake method has been used as a method of suppressing the standing wave effect described above, smoothing the resist pattern cross-sectional shape, and eliminating residual defects after development. (This method is IEEE T
ransactions on Electron Devices, Vol.ED-22, No.7, Ju
ly 1975, pp. 464-466. ). In this direction, it is an excellent method that allows continuous processing with only one additional step. SPIE Prceedins Vol.469 Advances
As described in P65 to 711 of In Resist Technology (1984), it has conventionally had the following drawbacks. That is, the amount of exposure (Eo) required to obtain a resist pattern dimension that is the same as the mask dimension increases, and the film thickness of the unexposed portion is reduced depending on the type of resist. Further, except for smoothing the standing wave effect, that is, the corrugation of the resist pattern cross-sectional shape, it is almost impossible to solve the problems of the conventional one-layer resist method.

The present invention has been made to solve the problems of the conventional resist method as described above, and compensates for the defects of the conventional baking method before exposure and after development, and has a performance higher than that of the conventional method.
That is, a method of not only suppressing the standing wave effect but also reducing the bulk effect, indirectly suppressing the multiple reflection effect in the film, and further improving the resolution and the depth of focus without decreasing the sensitivity and increasing the film loss. Aim to get.

[Means for solving the problem]

A step of applying a positive photoresist composed of a quinonediazide-based photosensitizer and an alkali-soluble novolac resin on a substrate and heat-treating, a step of immersing the surface of the heat-treated positive photoresist film in an alkaline solution and then drying, The positive photoresist film, which was dipped in an alkaline solution and then dried, was selectively exposed to ultraviolet light (wavelength range 180 nm to 450 n
m), the step of selectively heating the positive photoresist film that has been irradiated with ultraviolet light, and the heat treatment of the positive photoresist film with ultraviolet light (wavelength range 180 nm to 450 n
m) is entirely exposed, and a step of developing the positively exposed photoresist to form a resist pattern is provided.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First
In FIG. 1A, 1 is a silicon crystal substrate, and a positive photoresist MCPR2000H (trade name of Mitsubishi Kasei Co., Ltd.) is spin-coated on the silicon crystal substrate to form a resist layer 2 having a thickness of 1.16 μm. This sample is then placed on the hot plate 3
Prebaking was performed for 60 seconds at a temperature of ℃ to 110 ℃ [Fig. 1 (2)]. Then, the surface of this sample was covered with 1% to 5% TMAH.
It was dipped in an alkaline aqueous solution 4 of (tetramethylammonium hydroxide) for 10 to 50 seconds, then rinsed with pure water, and spin-dried [Fig. 1 (3)].

Next, as shown in FIG. 1 (4), the photoresist was selectively exposed using a reduction projection exposure apparatus (stepper) equipped with a lens of NA = 0.42 using light of a wavelength of 436 nm. After that, as shown in Fig. 1 (5), 90 ℃ ~ 15
It was baked at a temperature of 0 ° C. for 60 seconds. Next, Fig. 1 (6)
As shown in Fig. 3, the entire surface was exposed with an energy of 1 to 30 mJ / cm ² by using an ultrahigh pressure mercury lamp having a bright line spectrum at wavelengths of 436 nm and 365 nn. Next, as shown in Fig. 1 (7), TMAH2.
It was developed with a 38% aqueous solution to form a resist pattern 2'on a silicon substrate. With this method, the exposure dose (Eo) that makes the resist pattern dimension the same as the mask pattern dimension is the same as or less than that of the conventional one-layer resist method in which resist coating prebaking, exposure, and development are performed in this order, and the sensitivity is reduced. Was not seen. The conventional one-layer resist method is 0.
Although the pattern of 6 μm width / spacing was resolved, the 0.5 μm width / spacing pattern had a weak aerial image contrast of the mask pattern, so that the light intensity of the spacing pattern (that is, the exposed portion) was weak and the resist remained after development. However, in the present invention, the dissolution rate at the time of development of the exposed portion due to the entire surface exposure before development, the effect of alkali in the patterning exposure and resist, and the uniform distribution of the concentration of the photosensitizer by the heat treatment after the patterning exposure. , And the spacing pattern of 0.5 μm width / spacing pattern was resolved. On the other hand, in the unexposed area, the alkali surface treatment renders the surface layer extremely insoluble, and the patterning near the resist surface where the concentration of the photosensitizer is high forms the insoluble layer by heat treatment after exposure. The thickness of the remaining pattern (width pattern) is not reduced even with a 0.5 μm width / spacing pattern, and the corrugated shape of the resist pattern cross section due to the standing wave effect is also smooth, resulting in a vertical resist pattern cross section shape. Was obtained up to a 0.5 μm width / spacing pattern. In addition, the resolution capability of the space pattern, which is difficult to resolve, is 0.7μ in the conventional resist process.
On the other hand, in the present embodiment, 0.5 μm was resolved in a substantially vertical sectional shape similar to a large pattern size, and a large improvement in resolution was obtained.

In addition, the depth of focus was improved by about 50% or more compared to the conventional resist process. Further, by changing the resist film thickness around 1.16 μm, the resist pattern dimension change amount (A) due to the bulk effect and the dimension change amount (B) due to the in-film multiple reflection effect shown in FIG. It was drastically reduced and a remarkable improvement was obtained.

In the above Examples, when the bake after the exposure and before the development was omitted, there was almost no improvement in the pattern profile and the depth of focus among the above performance items.

Also, if the whole surface exposure is omitted, the resolution is reduced to 0.6.
Only the μm width / spacing pattern was resolved.

Further, in the above-mentioned embodiments, the case where the patterning exposure wavelength is 436 nm for the g-line is described, but the i-line (3
65 nm), Xe-Cl excimer laser light (308 nm), KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), and the multi-wavelength light source, the present invention is also effective. The same applies to the wavelength of overall exposure.

Further, in the present embodiment, an aqueous solution of an organic alkali was used as the alkaline solution, and an aqueous solution of TMAH (tetramethylammonium hydroxide), which is one of the developers for positive photoresist, was used.
The method of the present invention was effective with an aqueous solution of an inorganic alkali such as KOH, and also with other alkaline organic solutions. Further, even when the entire surface was exposed to ultraviolet rays immediately after the selective irradiation of ultraviolet rays (patterning exposure), and then the film was subjected to heat treatment and development, almost the same performance as the above was obtained. In addition, even if the heat treatment is performed once or more in vacuum according to the material composition of the positive photoresist, which uses the heat treatment up to three times in the process from resist coating to development, the above-mentioned present invention can be used. Controlling the cross-sectional shape of the resist pattern after development has become easier while maintaining excellent performance.

On the other hand, when forming a fine resist pattern on a base substrate with a high reflectance (for example, A1 thin film), a pattern is formed using a positive photoresist to which a light absorber is added in order to suppress the influence of reflection from the substrate. Although formed, the method of the present invention is effective in such cases.

Further, even when the method of the present invention is applied to the pattern formation of the upper layer resist by the three-layer resist method, the pattern size variation due to the in-film multiple reflection due to the slight reflection from the interface between the upper layer resist and the intermediate layer is suppressed, and the resist It is also effective in terms of improving the pattern cross-sectional shape and further increasing the depth of focus. Even if the method of the present invention is introduced into the pattern formation of the upper layer resist of the PCM two-layer resist method or the Si-based two-layer resist method using the Si-containing type novolak-naphthoquinonediazide positive photoresist as the upper layer resist, it is effective. .

An antireflection film (ARC) method for forming a resist pattern by forming an absorption type antireflection film having high absorbance between the base substrate and the positive type photoresist or an interference type antireflection film whose refractive index and film thickness are controlled. In addition, the method of the present invention is also effective in a pattern forming method in which a positive type photosensor resist is coated with an interference type single-layer or multi-layer antireflection film whose refractive index and film thickness are controlled to form a pattern. Is.

〔The invention's effect〕

As described above, according to the pattern forming method of the present invention, the surface of the photoresist film is dipped in an alkaline solution,
After that, it is provided with a step of drying, a step of heating the positive photoresist film selectively irradiated with ultraviolet rays, and a step of exposing the heat treated positive photoresist film to ultraviolet rays over the entire surface. The standing wave effect can be suppressed without lowering the film thickness and the film loss, (2) the resolution and the depth of focus can be improved, and (3) the cross-sectional shape of the resist pattern can be easily controlled. There is an effect that a resist pattern similar to that of a multi-layer resist can be formed without using an extremely simple and expensive device and material.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of the present invention. Second
The figure is a diagram for explaining the problems of the conventional method. In the drawings, the same reference numerals indicate the same or corresponding parts. 1 ... Si substrate, 2 ... positive photoresist, 3 ... hot plate, 4 ... alkali solution, 5 ... ultraviolet,
2 '... resist pattern after development

Claims (1)

(57) [Claims] 1. A pattern forming method including the following steps. (1) A step of applying a positive photoresist composed of a quinonediazide-based photosensitizer and an alkali-soluble novolak resin onto a substrate and subjecting it to heat treatment. (2) A step of immersing the surface of the heat-treated positive photoresist film in an alkaline solution and then drying it. (3) UV light (wavelength range 180 nm) is selectively applied to the above-mentioned positive type photoresist film which is dipped in an alkaline solution and then dried.
~ 450 nm) irradiation step. (4) A step of heating the positive photoresist film selectively irradiated with ultraviolet rays. (5) A step of entirely exposing the heat-treated positive photoresist film to ultraviolet rays (wavelength range 180 nm to 450 nm). (6) A step of forming a resist pattern by developing the above-mentioned positive photoresist which has been entirely exposed.