JP3091886B2 - Method of forming resist pattern - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using photolithography.

[0002]

2. Description of the Related Art A conventional photolithography process will be described below. As shown in FIG. 2A, for example, a positive photoresist 4 is applied on a desired base substrate 1, and a desired pattern on a mask is exposed by a reduction exposure apparatus or the like. Next, by performing development, a resist pattern as shown in FIG. 2B can be obtained. A semiconductor device is manufactured by performing an implantation process, an etching process, or the like using this photoresist pattern as a mask.

[0003]

In order to resolve a finer line width, it is necessary to use an exposure machine having a higher NA and a larger amount of incident light, and the line width at the pitch of the exposure wavelength level is resolved. I couldn't do that.

[0004]

In order to solve the above problems, according to the present invention, after forming a lower resist on a base substrate, an upper resist having a predetermined thickness is formed, and the upper photoresist is formed into a predetermined pattern. After exposure and development, the lower resist is exposed and developed.

[0005]

According to the above-described manufacturing method, the phase of light at the time of incidence on the lower resist changes between a portion where the upper resist is present and a portion where the upper resist is not present during exposure of the lower resist.
Since light is not injected below the upper layer pattern edge portion due to light interference at the upper layer resist pattern edge portion, under the upper layer pattern edge portion periphery during development,
The lower resist remains, and the resist is otherwise removed. Thereafter, if the underlying substrate is etched in accordance with the lower resist pattern, a finer pattern is formed than when the etching is performed with the upper resist.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG.
Kind of UV-sensitive resin, ie, photoresist,
Coat layer. At this time, the upper layer photoresist and the lower layer photoresist use different solvents,
In addition, the upper photoresist is a positive photoresist.

At the time of exposing the lower resist, a phase difference occurs between the light that has passed through the upper photoresist and the light that has passed through the exposure atmosphere (for example, the atmosphere) due to the difference in refractive index. This phase difference is represented by k'λ-kλ. (Where k is the wave number in the atmosphere and k 'is the wave number in the upper photoresist film.) Since this phase difference is π, k′λ−kλ = k (αλ−λ) = ( R: Any integer α: Refractive index of upper resist to exposure atmosphere λ: Constant k = (R + 0.5) / (α−1) to satisfy wavelength for exposing lower resist Once set, the desired thickness T of the upper photoresist can be expressed as: T = kλ = {(R + 0.5) / (α−1)} λ.

The upper photoresist is preferably thinner for reasons of transparency, resolution at the time of exposure of the upper layer, and depth of focus at the time of exposure of the lower layer. In general, since the refractive index α of the photoresist is 1 <α, when R = 0,
The thickness of the upper photoresist can be minimized. If the film thickness at that time is To, then To = λ / {2 (α−1)}.

A film thickness satisfying the above equation, for example, To
Is coated with an upper layer photoresist, and a desired pattern is exposed on the upper layer photoresist and developed. At this time, since the upper layer photoresist and the lower layer photoresist have different solvents, the lower layer resist is insoluble in the developing solution of the upper layer resist, and the shape after development is as shown in FIG.
The shape is as shown in FIG.

Next, the entire surface is exposed at a wavelength λ. Then
Ultraviolet light having a wavelength of λ is injected into the entire surface of the upper resist, but the lower resist has a phase shift of π between a position where the resist is present in the upper layer and a position where the resist is not present. No light is injected below due to light interference. Here, when developed with a developer for the upper layer resist, the entire upper layer photoresist can be removed because the entire surface contains ultraviolet light.

Next, when the resist is developed with a developing solution for the lower photoresist, if the lower resist is, for example, a positive photoresist, the resist remains under and around the edge of the upper resist to which the light wave was not injected, and the other resist remains. At the place where the light wave is injected, the resist is not dissolved by the development. Therefore, a fine pattern as shown in FIG. 1C can be formed.

When the lower resist is a negative photoresist, a pattern of the resist is formed in a portion where the light wave is sufficiently injected, and the light wave is not sufficiently injected below an edge portion of the upper resist, so that the resist is not formed. Disappears. Therefore, a fine pattern as shown in FIG.

[0013]

According to the present invention, as described above, since the lower photoresist is exposed by shifting the phase by using the upper photoresist, an extremely fine photoresist pattern of about the wavelength of light is formed. It is possible. Since the upper resist is flattened by the lower resist and is thinly coated, at the time of exposure, it is possible to expose even with an exposure apparatus where it is difficult to obtain a depth of focus,
At the time of full-surface exposure, it is not necessary to use light passing through a lens with a high NA as long as it is a parallel short-wavelength light, so that a very fine photoresist pattern can be formed even at a step portion as a whole. is there. In addition, by using a resist having a high transmittance for short-wavelength ultraviolet rays, even in a wavelength band where it is difficult to create a high NA lens, as long as parallel rays can be created,
Since the contrast of the light intensity is generated by the interference of the light waves, there is an effect that it is possible to perform the patterning of the line width or the space smaller than the wavelength.

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views in a process order showing a method of forming a resist pattern.

FIGS. 2A and 2B are cross-sectional views in the order of steps showing a conventional method for forming a resist pattern.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Undersubstrate 2 Lower photoresist 3 Upper photoresist 4 Positive photoresist

Claims (1)

(57) [Claims] A step of applying a negative type or positive type first photoresist to a lower layer on a semiconductor substrate; and a step of coating a positive type second resist having a solvent different from that of the lower layer and having transparency to the upper layer. a step of applying a predetermined film thickness, the upper layer of the second
A step of exposing and developing a predetermined shape to resist, a step of exposing the entire surface parallel rays of short wavelength, consists of a step of developing the lower layer of the first <br/> resist, a second of said upper layer The film thickness of the resist is such that when the first resist of the lower layer is exposed, the phase of light upon incidence on the lower layer resist is a half wavelength between a portion where the second resist is present and a portion where the second resist is not present. A resist and pattern forming method using photolithography, wherein the thickness is shifted by an odd number.