JP2682430B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a fine pattern.

[0002]

2. Description of the Related Art In an exposure method in a semiconductor device manufacturing process, light emitted from a light source is focused by a lens, irradiated onto a mask, and light transmitted through the mask is focused by an objective lens to form an image on a wafer. . Due to this image formation, the photoresist film previously coated on the wafer is exposed and a difference in dissolution rate occurs, so that a pattern is formed in the developing process.

The resolution R obtained by such an exposure optical system is generally represented by R = k ₁ (λ / NA). Here, λ is the exposure wavelength, NA is the numerical aperture of the lens, and k ₁ is a constant determined by the process.

In recent years, with the reduction in device dimensions, improvement of resolution (smaller R) has become an important issue. It is said that the value of k ₁ is limited to 0.6, and NA is also limited. Therefore, in order to improve the resolution R, the exposure wavelength λ has been shortened in recent years. For example, light having a wavelength of 248 nm generated by a KrF excimer laser has come to be used.

The depth of focus DOF of the above-mentioned exposure optical system
Is known to be represented by the following equation.

DOF = k ₂ (λ / NA ² ) where k ₂ is a constant determined by the process. As can be seen from this formula, the depth of focus is inevitably reduced as the wavelength of the exposure light is shortened. Therefore, improving the depth of focus in lithography has become an extremely important issue. Various methods have been proposed so far as methods for expanding the depth of focus.

For example, an IEEE electron device
Letters (EFECTRON DEVICE LETT
ERS) VOL. EDL-8, NO. 4 APRIL1
In 987 P179, as shown in FIG. 2, the focal point 14 (14A to 14C) is exposed through the mask 12 and the objective lens 13 stepwise at different positions on the optical axis with respect to the photoresist layer. There has been proposed a method (FLEX method) of shifting the exposure optical system to substantially increase the depth of focus. In this case, the depth of focus is improved by 2.7 times from 3 μm to 8 μm at the i-line (365 nm) by shifting the focus by 3 μm and exposing.

[0008]

The above-mentioned conventional stepwise exposure method in the lithography process has the following problems in transferring a fine pattern. That is, the exposure apparatus is complicated because the exposure is performed at a plurality of positions, and the exposure time is long because the exposure is performed many times. Further, although the depth of focus increases, the optical images are averaged, so that there is a drawback that the optical contrast at the optimum focus position decreases.

An object of the present invention is to provide a method of manufacturing a semiconductor device which can easily increase the depth of focus during exposure.

[0010]

According to a method of manufacturing a semiconductor device of the present invention, a first process is performed on a film to be processed formed on a semiconductor substrate.
The step of forming a photoresist film, the step of forming a second photoresist film on the first photoresist film, which is evaporated by exposure light to reduce the film thickness, and the first and second photoresists. And a step of simultaneously exposing the film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. 1A to 1C are cross-sectional views of a semiconductor chip for explaining an embodiment of the present invention.

First, as shown in FIG. 1A, a processed film 2 such as an insulating film or a conductor film is formed on a silicon substrate 1, and then a first photoresist film 3 is applied. The first photoresist film 3 is a deep-UV sensitive resist,
For example, positive type chemically amplified resist CAMP from OCG Inc.
6 to form a thickness of about 0.7 μm. Next, a second photoresist film 4 which is evaporated by exposure light is applied on the first photoresist film 3 to a thickness of about 0.5 μm. This second photoresist is, for example, Polymer Engineering and Science (Polymer Eng.
inering and Science) De
c. , No. 18, pp1012-1018, 1983.
PPA (polyphtalal)
3% by weight of an acid generator such as triphenylsulfonium.

Next, as shown in FIG. 1B, an exposure light (DUV) 6 having an intensity corresponding to the mask pattern is formed on the substrate by using a reduction projection exposure machine or the like using an excimer laser light having a wavelength of 248 nm. Irradiate through the objective lens 5.
At this time, the second photoresist film 4 is decomposed by the exposure light 6 and evaporated. At this time, the intensity distribution of the exposure light has a bell shape with a large central portion in the fine mask pattern, so that the exposed portion of the second photoresist film 4 has a thin film thickness and is concave. Second photoresist film 4
1 has a refractive index of 1 or more as in a general photoresist film, the incident light 6 is incident almost vertically by refraction to expose the first photoresist film 3 as shown in FIG. 1B. . As a result, the depth of focus DOF is doubled or more, which is equivalent to that of the conventional FLEX method in which the focus is shifted during exposure.

After that, the two-layer photoresist film simultaneously exposed by the exposure light 6 is baked (PE) after the exposure.
In step B), heat treatment is performed at 115 degrees for 60 seconds. In this heat treatment step, the second photoresist film 4 evaporates, so that the phenomenon of the first photoresist film 3 is performed without any trouble, and the fine pattern 7 is transferred as shown in FIG. 1C. A mask is obtained. Thereafter, the film 2 to be processed is patterned by using the mask made of the first photoresist film 3.

As described above, according to this embodiment, 248 nm
Depth of focus 1μ in conventional exposure method using short wavelength
Since m can be improved to 2 μm or more, exposure can be performed with a sufficient depth of focus even when there is a step of 1 μm in the film to be processed. Further, since the thickness of the second photoresist film is reduced at the time of exposure, the effect of multiple reflection occurring in the photoresist film is reduced, and the variation of the pattern dimension due to the standing wave effect is also reduced. Further, in the present embodiment, unlike the method of mechanically shifting the wafer to increase the depth of focus as shown in the conventional example, the exposure apparatus may be a normal one and the throughput is not deteriorated. .

Although a positive resist was used as the first resist in the above embodiment, the same effect can be obtained by using a negative SNR-248 resist (Chipley Co.).

[0017]

As described above, according to the present invention, in the lithography process of the semiconductor manufacturing process, the second photoresist film which is evaporated by the exposure light is further formed on the first photoresist film applied on the film to be processed. By applying the above method, a concave lens is formed on the second photoresist film during the exposure, so that the depth of focus can be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor chip for explaining one embodiment of the present invention.

FIG. 2 is a diagram for explaining a conventional exposure method.

[Explanation of symbols]

 1 Silicon Substrate 2 Processed Film 3 First Photoresist Film 4 Second Photoresist Film 5 Objective Lens 6 Exposure Light 7 Pattern 11 Exposure Light 12 Mask 13 Objective Lens 14 Focus Position

Claims (3)

(57) [Claims] 1. A step of forming a first photoresist film on a film to be processed formed on a semiconductor substrate, and a second step of evaporating the first photoresist film on the first photoresist film by exposure light to reduce the film thickness. And a step of exposing the first and second photoresist films at the same time, the method of manufacturing a semiconductor device. 2. The method of manufacturing a semiconductor device according to claim 1, wherein an excimer laser is used as an exposure light source. 3. The method for manufacturing a semiconductor device according to claim 1, further comprising a step of heat-treating and removing the second photoresist film after exposure.