JP2853101B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for manufacturing a semiconductor device, and more specifically, to a method for forming a resist pattern, and relates to a method for exposing a resist film. In order to provide a method of forming a resist pattern that can minimize variations in the patterning dimensions of the film, in the step of patterning the resist film formed on the light-transmitting film on the semiconductor substrate, From the relationship between the minimum exposure energy (Eth) required to form an opening by exposing and developing the resist film and the thickness of the light-transmitting film or the thickness of the resist film, Determining a film thickness of at least one of the translucent film and the resist film so that the exposure energy (Eth) is substantially an extreme value; Sequentially forming a light-transmitting film and a resist film having the film thickness determined in the step, and selectively irradiating the resist film with light, and then developing the resist film. Constitute.

[Industrial applications]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for forming a resist pattern.

In recent years, with the miniaturization of pattern dimensions, it has been demanded to pattern a resist film with higher precision.

[Conventional technology]

In the process of manufacturing a semiconductor device, a resist film is patterned when forming a field oxide film, opening a window for impurity diffusion, opening a window for contacting an electrode, forming an electrode or forming a metal wiring layer, and the like. I have.

FIGS. 5A to 5F are cross-sectional views illustrating a conventional method for patterning a resist film when forming a field oxide film.

First, as shown in FIG.
After the SiO ₂ film 2 of 0 ° is formed by the thermal oxidation method, the SiO ₂ film 2 is formed.
A 1100-mm-thick Si ₃ N ₄ film 3 is formed thereon by CVD. At this time, the thickness of the Si ₃ N ₄ film 3 is made sufficient to mask oxygen when a field oxide film is selectively formed on the Si substrate 1 in an oxidizing atmosphere later. Next, Si ₃ N
₄ A positive resist film 4 having a thickness of about 0.8 μm is formed on the film 3.

Next, the resist film 4 is patterned. That is, the mask 5 is set on the resist film 4 and irradiated with light having a wavelength of 436 nm (FIG. 2B). Then, the polymer structure of the resist film 4 changes at the place where the light is irradiated, and the resist film 4 is dissolved in the developing solution. Therefore, the resist film 4 is immersed in a developing solution to remove the resist film 4 in a portion exposed to light. Thus, the opening 6 is formed (FIG. 3C).

Next, the Si ₃ N ₄ film 3 and the SiO ₂ film 2 are removed by etching through the opening 6 (FIG. 4D).

Subsequently, after removing the remaining resist film 4, Si ₃ N ₄
Using the film 3 as a mask, the Si substrate 1 is oxidized in an oxidizing atmosphere to selectively form a field oxide film 7 (FIG. 3E). Finally, the Si ₃ N ₄ film 3 used as the mask is removed with phosphoric acid or the like, and the formation of the field oxide film 7 is completed (FIG. 1F).

[Problems to be solved by the invention]

By the way, when the resist film 4 shown in FIG. 5B is exposed, light passes through the resist film 4, the Si ₃ N ₄ film 3 and the SiO ₂ film 2 and reaches the surface of the Si substrate 1. Here, the light is reflected on the surface of the Si substrate 1 and returns upward. Therefore, the incident light and the reflected light interfere with each other, and the intensity of the light in the resist film 4 becomes lower than that of the base.
It becomes stronger or weaker depending on the thickness of the SiO ₂ film 2 and the Si ₃ N ₄ film 3.

Accordingly, overexposure or underexposure occurs due to the variation in the thickness of the Si ₃ N ₄ film 3, and accordingly, the patterning dimension of the resist film 4 becomes larger than the pattern dimension of the mask. Or become smaller. As a result, the width dimension of the field oxide film 7 to be formed also varies.

When the width is reduced, there is a problem that the isolation between adjacent elements becomes insufficient.

On the other hand, if the width is increased, the isolation region extends to the element formation region. Therefore, it is necessary to increase the element formation region in advance, and there is a problem that the density of the semiconductor device cannot be increased. .

The present invention has been made in view of the problems of the conventional example, and when exposing a resist film, minimizes variations in patterning dimensions of the resist film due to variations in exposure intensity caused by light interference. It is an object of the present invention to provide a method for forming a resist pattern that can be performed.

[Means for solving the problem]

The above object is to provide a resist film formed on a light-transmitting film on a semiconductor substrate in a patterning step, by exposing and developing the resist film to form a minimum exposure energy (Eth) required to form an opening. ) And the thickness of the light-transmitting film or the thickness of the resist film, the light-transmitting film and the resist film are set so that the minimum exposure energy (Eth) becomes substantially an extreme value. Determining a film thickness of at least one of the films, a step of sequentially forming a light-transmitting film and a resist film having the film thickness determined in the step on the semiconductor substrate, and selectively forming the resist film on the semiconductor substrate. The problem is solved by a method of manufacturing a semiconductor device, comprising a step of developing the resist film after irradiating light.

(Operation)

The operation of the method of manufacturing a semiconductor device according to the present invention will be described based on the results of simulations and experiments performed by the inventor of the present application.

FIG. 2 is a diagram showing the result of a simulation of the minimum exposure energy Eth required to form an opening in the resist film, using the resist film thickness and the Si ₃ N ₄ film thickness as variables.

The sample used for the simulation is shown in FIG.
As shown in, using a structure in which SiO ₂ film and the Si ₃ N ₄ film as a transparent film on the Si substrate as a semiconductor substrate, and the resist film are sequentially formed, SiO ₂ film having a film 300 mm thick
The refractive index of the resist film / Si ₃ N ₄ film / SiO ₂ film is 1.64 / 2.00 / 1.45, respectively.

In the simulation, Eth was calculated assuming that the sample was exposed to light having a wavelength of 436 nm. Note that E
th is expressed as an exposure time in seconds with the light power being constant at 400 mW / cm ² .

As a result of the simulation, as shown in FIG. 2, Eth periodically changes with respect to the resist film thickness or the Si ₃ N ₄ film thickness.
It has a local maximum and a local minimum.

FIG. 3 shows measured values of Eth when the resist film thickness is fixed and the Si ₃ N ₄ film thickness is changed. FIG. 4 is a diagram showing the relationship between the exposure energy (indicated by a multiple of Eth) and the line width (μm) of the resist film removal pattern. Here, a mask having a pattern size of 1 μm is used.

In the experiment, a positive resist film having a thickness of about 0.795 μm and a refractive index of about 1.64 was used as the resist film.
After exposure with light of 400 mW / cm ² for a predetermined time, the developer NPR
It was immersed in D 0.153N (trade name) for 60 seconds and developed. Then, this series of operations was performed while changing the exposure time, and the minimum exposure time Eth required for forming an opening in the resist film was measured.

According to experiments, as shown in FIG. 3, Eth varies periodically with respect to the film thickness of the Si ₃ N ₄ film, Si ₃ N ₄ film thickness 800 Å, 1300 Å,
It has an extreme value around 1800Å. Therefore, if the target value of the film thickness is set to one of these values, the variation of Eth can be reduced even if the film thickness varies.

Thereby, the variation in the exposure intensity in the resist film can be suppressed to a small value, so that the variation in the line width of the resist pattern can be suppressed to a small value.

For example, Si ₃ N ₄ film set target value of thickness 1300Å of (Eth 0.
(Equivalent to 165 seconds), even though the thickness of the actually formed Si ₃ N ₄ film varies by ± 10% (1170 to 1430 °), as shown in FIG. The variation is only in the range of 0.174 seconds (corresponding to a variation width of about + 5.4%). This is the set exposure amount for actual exposure 1.
5 × Eth (second) is equivalent to + 5.4% variation. From FIG. 4, the line width of the resist film removal pattern is 1.065 to 1.085.
It varies only in the range of μm. That is, the variation width of the line width of the pattern can be suppressed to 0.02 μm, which is smaller than that of the related art.

In the conventional case, the thickness of the Si ₃ N ₄ film is determined without considering the variation in the exposure intensity.
± 10% of Si ₃ N ₄ film thickness when i ₃ N ₄ film thickness is 1100Å
The variation in the line width dimension of the resist film removal pattern is as large as 0.1 μm.

Further, even when a light-transmitting film is formed on a light-reflective film on a semiconductor substrate, for example, a metal film, the same operation and effect as described above can be obtained.

As described above, according to the method for manufacturing a semiconductor device of the present invention, the thickness of at least one of the resist film and the light-transmitting film under the resist film is set to a film thickness such that Eth is substantially an extreme value. By setting, the variation in the patterning dimension of the resist film due to the variation in the exposure intensity can be kept extremely small.

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIGS. 1A to 1F are cross-sectional views illustrating an embodiment in which the method of manufacturing a semiconductor device according to the present invention is applied to a case where a field oxide film is formed.

First, as shown in FIG. 1A, an SiO ₂ film 9 having a thickness of 300 ° is formed on a Si substrate 8 at a temperature of 900 ° C. by a thermal oxidation method. Subsequently, the thickness of 1300 is applied by the CVD
The Si ₃ N ₄ film 10 is formed. Here, a two-layer SiO ₂ film 9 / Si ₃ N ₄ film 10 as a light-transmitting film is formed.

Next, a resist film 11 having a thickness of 0.795 μm is formed by spin coating.

Here, E is obtained from the relationship between Figs.
The resist film 11 and S are so set that th takes an extreme value (= 0.165 seconds).
The thickness of the i ₃ N ₄ film 10 is set.

Subsequently, as shown in FIG. 1 (b), the wavelength 43 is applied to the resist film 11 through a mask 12 having a pattern line width of 1 μm.
Light of 6 nm and power of 400 mW is irradiated for 1.5 × Eth seconds. At this time, the light passes through the Si ₃ N ₄ film 10 / SiO ₂ film 9 and reaches the surface of the Si substrate 8, where it is reflected and returned upward to interfere with the incident light.
Therefore, the light intensity in the resist film 11 varies within the same wafer due to the variation in the thickness of the Si ₃ N ₄ film 10. For example, assuming that the variation in the thickness of the Si ₃ N ₄ film 10 is ± 10% with respect to the setting of 1300 °, that is, in the range of 1170 to 1430 °, as shown in FIG. 5.4%
Thus, the exposure energy 1.5 × Eth also varies by the same width.

Next, as shown in FIG.
The opening 13 is formed by immersion in (trade name) for 60 seconds. At this time, since the variation of the exposure energy 1.5 × Eth is about 5.4%, as shown in FIG. 4, the pattern line width of the resist film varies in the range of 1.065 to 1.085 μm. Is as small as about 0.02 μm.

Next, as shown in FIG. 1D, the resist film 11 is used as a mask to continuously dry-etch the Si ₃ N ₄ film 10 and the SiO ₂ film 9 by a reactive ion etching method to form an opening. I do.

Next, as shown in FIG. 4E, the Si ₃ N ₄ film 10 is used as a mask to selectively oxidize the substrate in an oxidizing atmosphere at a temperature of 1000 ° C. to form a field oxide film 14 having a thickness of 6000 mm. (F). At this time, since the opening of the Si ₃ N ₄ film 10 is formed substantially according to the dimensions of the mask pattern, the width of the field oxide film 14 also has dimensions substantially as designed.

 Thereafter, the semiconductor device is completed through a predetermined process.

As described above, according to the method of manufacturing a semiconductor device of the present invention, the width of the field oxide film 14 can be formed substantially as designed, so that unlike the conventional case, isolation between adjacent elements is required and sufficient. And the density of the semiconductor device can be increased.

In the embodiment of the present invention, a light-transmitting film is formed on a light-reflective semiconductor substrate, but a light-transmitting film is formed on a light-reflecting relatively flat metal film. In this case, the present invention can be applied.

Although the present invention has been applied to the case where the opening is formed by patterning the resist film, the present invention is also applicable to the case where the resist film is left after being patterned.

〔The invention's effect〕

As described above, in the method of manufacturing a semiconductor device of the present invention, when patterning a resist film, by adjusting the thickness of at least one of the resist film and the light-transmitting film underlying the resist film, Variations in exposure intensity are minimized with respect to variations in film thickness when the light-transmitting film is formed.

As a result, variations in the pattern line width of the patterned resist film can be minimized. For example, when this method is applied to the formation of a field insulating film, the width of the field insulating film is almost designed. It can be formed according to dimensions.

Therefore, unlike the conventional case, the separation between the adjacent elements is also required and sufficient, and the density of the semiconductor device can be increased.

[Brief description of the drawings]

1 (a) to 1 (f) are cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 2 is a graph showing the minimum exposure energy Eth and Si ₃ N ₄ film thickness / resist film thickness. FIG. 3 is a diagram showing the relationship between the minimum exposure energy Eth and the Si ₃ N ₄ film thickness, FIG. 4 is a diagram showing the relationship between the patterning line width and the exposure energy, and FIG. 7A to 7F are cross-sectional views illustrating a method for manufacturing a conventional semiconductor device. [Reference Numerals] l, 8 ...... Si substrate, 2, 9 ...... SiO ₂ film, 3, 10 ...... Si ₃ N ₄ film, 4,11 ...... resist film, 5,12 ...... mask, 6, 13 ... Opening, 7,14 ... Field insulating film.

Claims (2)

(57) [Claims] In a step of patterning a resist film formed on a light-transmitting film on a semiconductor substrate, a minimum exposure energy required for forming an opening by exposing and developing the resist film. From the relationship between Eth) and the film thickness of the light-transmitting film or the film thickness of the resist film, the light-transmitting film and the resist are so set that the minimum exposure energy (Eth) becomes an extreme value. A step of determining a film thickness of at least one of the films; a step of sequentially forming a light-transmitting film and a resist film having the film thickness determined in the step on the semiconductor substrate; And irradiating the resist film with light, and then developing the resist film. 2. The method according to claim 1, wherein a light-reflective film is formed between the semiconductor substrate and the light-transmitting film.