JPH10189426A - Formation of resist pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuation of line width by depositing an inorganic antireflection film thicker than the size of grains in an underlying layer on the underlying layer, polishing the antireflection film until an optimal thickness is attained and then forming a resist pattern on the antireflection film thereby reducing dependency on the underlying layer. SOLUTION: Step coverage is improved by depositing SiON 14, as an antireflection film, by CVD on W 12 deposited on a substrate 10 at a large grain size. Surface of the SiON 14 is not planarized but morphology corresponding to the irregularities of W grains 12 in the underlying layer is preserved. The SiON 14 is then polished flatly by CMP, or the like, and a photoresist is deposited on the SiON 14 and a resist pattern 16 is formed. According to the arrangement, the amplitude of standing wave in the photoresist can be substantially nullified and fluctuation in the line width of pattern can be suppressed at the time of exposure resulting in the formation of a resist pattern having dimensions just defined by a mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a resist pattern, and more particularly, to a method for forming a resist pattern having a pattern with a small dependency on the base and a uniform fine line width on a base layer with a large grain. It is about the method.

[0002]

2. Description of the Related Art When forming a fine pattern of a wiring structure using an optical lithography technique, a line width fluctuates, and it is difficult to uniformly form a pattern having a predetermined line width on a substrate.
This has become a major problem in the manufacture of semiconductor devices.
Moreover, in recent years, with the reduction in design rules, the line width variation rate of a pattern with respect to a predetermined line width has increased. Factors that may cause the line width to vary include the step of the underlying layer on the substrate and the density of the pattern. By the way, along with the miniaturization of design rules, the exposure wavelength of optical lithography
The wavelength has been shortened from g-line (436 nm) → i-line (365 nm) → KrF excimer laser light (248 nm). Therefore, as shown in FIG. 6, multiple interference occurs in the photoresist film, and the line width of the pattern fluctuates. Multiple interference is a phenomenon in which, at the time of exposure, light incident on a photoresist film and light reflected from a substrate interfere with each other to generate a standing wave.
As an effect of the multiple interference, that is, an effect of the generation of the standing wave, the line width varies with the variation of the thickness of the photoresist film. The effect increases as the exposure wavelength becomes shorter. This is because the shorter the exposure wavelength, the shorter the cycle of multiple interference and the higher the substrate reflectance. On the other hand, the thickness of the photoresist film fluctuates according to the level difference of the base layer of the substrate. Therefore, when forming a resist pattern, the line width of the pattern is more varied in the case of photolithography in which exposure is performed at a shorter wavelength. For example, as shown in FIG. 7, the change in the line width when the resist film thickness changes is larger for the KrF excimer laser light than for the g-line for a predetermined mask dimension.

As one of the measures for suppressing the line width variation of a pattern, there is a method of applying an anti-reflection technique as shown in FIGS. 8 (a) and 8 (b). This is on the photoresist film,
Or, by forming a light-absorbing organic film or inorganic film between the photoresist film and the substrate, and utilizing the absorption of light in the film and cancellation by the phase difference, when the thickness of the photoresist film changes. This is a method in which the amount of light absorbed in the photoresist film is kept constant and fluctuations in line width are suppressed. As another anti-reflection technique, for example, a transparent organic film of n (refractive index) = 1.3 is formed on a photoresist film, and the organic film absorbs light and cancels out the light by a phase difference. There is also a method in which the amount of light absorbed in the resist film is kept constant to suppress fluctuations in line width. When a highly reflective substrate having a step is used, as shown in FIG. 9A, it is better to form an absorptive anti-reflection film under a photoresist film when there is no anti-reflection film (FIG. 9A). Compared with (b), the amount of light traveling in various directions is smaller, which is advantageous from the viewpoint of line width change and halation.

At present, as a material for wiring, usually, A
1, Al / Si alloy, Al / Cu alloy, or W is used. As shown in FIG. 10 (b), W has poor surface morphology and the bottom dimension of the photoresist film is not stable as compared with the Al-based alloy shown in FIG. 10 (a).
Also, when a chemically amplified photoresist is used, the adhesion between the W layer and the photoresist film is required because the adhesion between the W layer and the photoresist film is poor because of poor adhesion to W. Therefore, as a film for improving the adhesion, for example, a SiON film that can be formed by a normal CVD apparatus is used.
An inorganic film such as that described above is used. Further, the SiON film can be controlled so as to have an optimum complex refractive index as shown in FIG. 11 by adjusting the film forming conditions, and thus can be used as an antireflection film for various substrate base layers. In FIG. 11, the horizontal axis represents the real part of the complex refractive index,
The imaginary part of the complex refractive index is taken on the vertical axis, and circles indicate the optimum complex refractive indexes for the Al alloy and W at the exposure wavelength of 248 nm.

[0005]

Therefore, when W is used as a wiring layer, as described above, a film such as a SiON film is used as an antireflection film or as an antireflection film and an adhesion film for a W film. This is very effective. However, such a CVD film such as SiO 2 is formed on the W film having a large grain.
When the N film is formed as an anti-reflection film, the SiON film is
As shown in FIG. 12A, since the step coverage is good, the morphology on W is saved without improving the morphology of W. Therefore, Si
When a photoresist film is formed on the ON film and patterned, as shown in FIG. 12B, the photoresist and the like remain in the recesses between the W grains of the substrate even after development, as shown in FIG. Often. For this reason, an extra removal step or the like is additionally required to remove the remaining photoresist, and if the photoresist remains as it is, the subsequent steps will be hindered.

Therefore, an object of the present invention is to provide a semiconductor device having a low underlayer dependency even on an underlayer having a large grain such as a W film.
Further, it is an object of the present invention to provide a method for forming a resist pattern having a small line width variation.

[0007]

In order to prevent the photoresist from remaining, the inventor of the present invention forms a thick SiON film by a CVD method or the like, and then forms an SIO film by a method such as CMP.
Polishing and flattening the iON film and leaving SiO 2 at that time
It was considered that by controlling the thickness of the N film, the conditions as an antireflection film when forming a resist pattern could be optimized. The inventor of the present invention conceived that a good resist pattern free from the influence of halation or the like due to the morphology of W could be obtained, and confirmed this through experiments to complete the present invention.

In order to achieve the above object, based on the above findings, a method of forming a resist pattern according to the present invention provides a method of forming a resist on a substrate underlayer having a large grain size such as tungsten (W) on its surface. When forming a pattern, a film-forming step of forming an inorganic anti-reflective film having a thickness larger than the grain size of the underlying layer on the under-layer, and an anti-reflective film from an anti-reflective effect to an optimum film thickness. And a step of subsequently forming a resist pattern on the anti-reflection film.

The optimum film thickness from the viewpoint of the antireflection effect refers to the thickness of the antireflection film that shows the optimum antireflection conditions when the remaining polished antireflection film is exposed by photolithography. Is such that the amplitude of the standing wave in the photoresist film becomes close to zero when the photoresist film is exposed. The optimum thickness of the anti-reflection film depends on the exposure wavelength of photolithography and the complex refractive index of the anti-reflection film, and is determined in advance by experiments or the like. An anti-reflection film having an optimum thickness can be formed by forming a thick anti-reflection film and then polishing. Preferably, the thickness of the antireflection film formed on the underlayer is the sum of a thickness equal to the size of the grains of the underlayer, a predetermined thickness, and a polishing margin. In the case of tungsten (W), it may be about 100 nm. The anti-reflection film is made of SiON,
Si _x N _y, polysilicon and alpha-Si (amorphous
(Silicon), or similar. In the polishing step, polishing may be performed by CMP, or etching back by dry etching or wet etching may be performed.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings by way of examples. Embodiment 1 This embodiment is an embodiment of a method for forming a resist pattern according to the present invention, in which a SiON film is used as an anti-reflection film and a K film having a wavelength of 248 nm is used when exposing a photoresist film.
This is an example using rF excimer laser light. FIG.
(A) to (d) are schematic diagrams of a substrate cross section for each step of the present embodiment. As shown in FIG. 1A, the average particle size is 10 nm.
As shown in FIG. 1B, a film having a thickness of about 100 n was formed on the W film 12 formed on the substrate 10 with a large grain size.
m, the real part n of the complex refractive index is 2.1, and the imaginary part k is 0.56.
Was formed as an anti-reflection film. At that time, a P-CVD device as a film forming device and S as a reaction gas were used.
Using iH ₄ , N ₂ O, and He, the gas ratio of the reaction gas was determined in advance by experiments or the like so that a SiON film having a predetermined complex refractive index could be formed. Since the average particle diameter of the W film is about 10 nm, a 100 nm SiO
By forming the film 14, the W film 12 could be completely covered with the SiON film. The complex refractive index n of the W film 12 was n = 3.37, and k was k = 2.87.

Since the SiON film 14 is formed by the CVD method, the step coverage is good, and as a result, the surface of the SiON film 14 is not leveled, and the grain of the W film 12 of the underlayer is formed. The morphology according to the unevenness is preserved. Therefore, as shown in FIG.
The SiON film 14 was polished to an average film thickness of 33 nm using a flattening method such as P (chemical mechanical polish). Subsequently, a photoresist film is formed on the SiON film 14,
Next, as shown in FIG. 1D, a resist pattern 16 was formed by photolithography using KrF excimer laser light.

As shown in FIG. 2, when a photoresist film is formed on a SiON film, the substrate is exposed to light using KrF excimer laser light (248 nm).
The amplitude of the standing wave in the photoresist film could be suppressed to almost zero. Therefore, a change in the line width of the pattern at the time of exposure can be suppressed, so that a resist pattern having the same dimensions as the mask can be formed. In addition, the surface of the SiON film is flattened by polishing to have a good morphology, and when the photoresist film is developed, the photoresist remains in the recesses between the grains as shown in FIG. Also, a resist pattern having a good shape without dependence on the underlayer was obtained. 2 and FIG. 4 to be described later, the solid line is a graph in the case of Example 1 or 2 having a SiON film as an anti-reflection film, and the absorptance in the photoresist film, that is, the line width variability, The thickness increases with an increase in the thickness of the film, indicating that the line width does not vary and is uniform. On the other hand, the dotted line indicates the SiON
FIG. 4 is a graph in the case of having no film, showing that the absorptance in the photoresist film increases while fluctuating as the thickness of the photoresist film increases, and that the line width varies.

Further, in order to confirm the margin of the thickness of the SiON film, the real part n of the complex refractive index of the SiON film is fixed at 2.1, and the imaginary part k and the thickness d of the SiON film are changed. The effect of reducing the standing wave of KrF excimer laser light in the photoresist film was measured, and the results are shown in FIG. In FIG. 3 and FIG. 5 to be described later, the imaginary part k of the complex refractive index of the SiON film is plotted on the horizontal axis, the thickness of the SiON film is plotted on the vertical axis, and the amplitude of the standing wave becomes smaller as the contour lines move toward the center. . As can be seen from FIG. 3, the optimum conditions for the SiON film in which the amplitude of the standing wave in the photoresist film is equal to 0 are n = 2.1, k = 0.56, and the film thickness d set in Example 1. = 33 nm. In addition, n = 2.1 and k = 0.3
2. When the film thickness d was 92 nm, the standing wave was almost zero, and it was found that there was an optimum value. Therefore, Example 1
As a modification example, a 150 nm thick SiON film is formed (n = 2.
After setting (1, k = 0.32), the standing wave can be reduced to 0 by polishing to a thickness of 92 nm using polishing such as CMP. As shown in FIG. 3, in order to keep the standing wave of the KrF excimer laser beam within 3%, n is 2.1 ± 0.2, k is 0.48 to 0.67, and the thickness of the SiON is 30 to 35 nm, or n is 2.1 and k is 0.2
It is necessary that the thickness of the SiON be 5 to 0.40 and the thickness of the SiON be 86 to 95 nm. The film forming conditions by the CVD method and the CM are set so that the complex refractive index and the film thickness of the SiON fall within these ranges.
By setting polishing conditions by P, it is flat and
Optimal anti-reflection conditions can be obtained, and a good resist pattern with no remaining photoresist can be obtained.

Embodiment 2 This embodiment is another embodiment of the method for forming a resist pattern according to the present invention, in which a SiON film is used as an anti-reflection film and a wavelength of 193 nm is used when exposing a photoresist film.
It is an example of using the A _r F excimer laser beam. In the same manner as in Example 1, an average particle size of 10 as shown in FIG.
As shown in FIG. 1B, a film having a large grain diameter of about nm is formed on the W film 12 formed on the substrate 10 as shown in FIG.
In nm, the real part n of the complex refractive index is 1.85 and the imaginary part k is 0.
57 SiON films 14 were formed. At that time, a P-CVD device as a film forming device, SiH ₄ , N ₂ O as a reaction gas,
Using He and He, the gas ratio of the reaction gas was determined in advance by experiments or the like so that a SiON film having a predetermined complex refractive index could be formed. The average particle size of the W film 12 is 10 n.
m, the W film 12 can be completely covered with the SiON film by forming the SiON film 14 with a thickness of 100 nm. Note that the complex refractive index n of the W film 12 is
n = 0.93 and k = 1.02.

Next, as shown in FIG.
The SiON film 14 has an average film thickness of 17
polished to nm. Subsequently, a photoresist film on the SiON film 14, and then, using the A _r F excimer laser light, as shown in FIG. 1 (d), to form a resist pattern 16 by photolithography.

[0016] Thus, in the substrate by forming a photoresist film on a SiON film, as shown in FIG. 4, when the light exposure using the A _r F excimer laser light (193 nm), a constant in the photoresist film The amplitude of the standing wave could be suppressed to almost zero. Therefore, a change in the line width of the pattern at the time of exposure can be suppressed, so that a resist pattern having the dimensions of the mask can be formed. Also, the surface of the SiON film is
The surface is flattened by polishing to obtain a good morphology. When the photoresist film is developed, the photoresist does not remain in the recesses between the grains as shown in FIG. It was possible to obtain a resist pattern having a good shape without any property.

Furthermore, in order to confirm the margin of the film thickness of SiON, fixing the n of the complex refractive index of the SiON film to 1.85, A _r in the photoresist film when changing the k and the thickness d The effect of reducing the standing wave of the F excimer laser light was measured, and the results are shown in FIG. As can be seen from FIG. 5, the optimum condition of the SiON film that can make the standing wave almost zero is the condition adopted in Example 2, that is, n = 1.85, k = 0.57, and the film thickness d.
= 17 nm. In addition to this condition, n = 1.
Even at around 85, k = 0.30, and film thickness d = 70 nm, the standing wave was almost zero, and it was found that there was an optimum value. Therefore, as a modification of the second embodiment, n = 1.85 and k =
After depositing a 150 nm thick SiON of 0.30, the CMP
By making the film thickness of 70 nm using a polishing method such as
The standing wave can be set to zero. As shown in FIG. 5, in order to suppress the standing waves A _r F excimer laser beam within 3%, n is 1.85 ± 0.2, k is 0.43～
0.80, SiON film thickness of 14-22 nm, or n
Is 1.85 ± 0.2, k is 0.25-0.37, SiO
It is necessary that the film thickness of N be 65 to 73 nm. S
In order for the complex refractive index and the film thickness of iON to be within this range,
By setting the film forming conditions by the CVD method and the polishing conditions by the CMP, flat and optimal anti-reflection conditions can be obtained, and a good resist pattern with no remaining photoresist can be obtained.

Embodiment 3 This embodiment is still another embodiment of the method for forming a resist pattern according to the present invention, and uses a polysilicon film as an antireflection film. In this embodiment, as in the first and second embodiments, n = 1.
14. A polysilicon film having a complex refractive index of k = 2.29 and a thickness larger than the grain size of the W film of the underlayer is formed as an antireflection film. By changing the film forming conditions such as the film forming temperature and the film forming apparatus, the degree of denseness and the crystallization ratio of the film can be changed, and the complex refractive index can be controlled. Next, CMP was performed in the same manner as in Examples 1 and 2 so that optimal antireflection conditions were obtained.
The polysilicon film is polished by using the method described above. This makes it possible to obtain a good resist pattern in which no resist remains in the grains of the polysilicon film.

[0019] Example 4 This example is a further embodiment of the method for forming a resist pattern according to the present invention, Si _x N as an antireflection film
_This is an example using a _y film. Si _x N _y film also, Examples 1 to 3
Similarly, by setting the film formation conditions of the Si _x N _y film appropriately, it is possible to adjust the complex refractive index of Si _x N _y film. Therefore, Si _x N _y having optimal complex refractive index
A film was formed as an anti-reflection film on the W film,
Polished to a predetermined thickness as well as to form a resist pattern on Si _x N _y film. Thus, in the same manner as in Example 1-3, a resist remaining free into the grains of the Si _x N _y film, it is possible to obtain a good resist pattern.

[0020] Examples 1-4, but is for excimer lithography using KrF excimer laser beam and A _r F excimer laser beam, of course, apply the present invention is also applicable to lithography using g-line, i-line can do.

[0021]

According to the structure of the present invention, when a resist pattern is formed on a substrate underlayer made of a large grain such as tungsten (W), the inorganic reflection layer having a thickness larger than the grain size of the grains of the underlayer. By forming an anti-reflection film and then polishing the anti-reflection film to a predetermined optimum film thickness, (1)
High-precision line width control is possible within the wafer plane,
(2) An optimal resist pattern can be formed as an etching pattern having a good shape, a large depth of focus, and a large exposure margin. In addition, since there is no dependence on the morphology of the underlayer, no resist remains on the substrate surface.

[Brief description of the drawings]

FIGS. 1A to 1D are schematic views of a cross section of a substrate in each step of Embodiments 1 and 2 of a method for forming a resist pattern according to the present invention.

FIG. 2 is a graph showing the relationship between the thickness of a photoresist film and the light absorptance in the photoresist film.
It is a graph which shows the reduction effect of a 48-nm standing wave.

FIG. 3 is a graph showing the effect of reducing a standing wave having a wavelength of 248 nm when the imaginary part of the complex refractive index and the thickness of the SiON film are changed.

FIG. 4 is a graph showing the relationship between the thickness of a photoresist film and the light absorptance in the photoresist film.
It is a graph which shows the reduction effect of a 93 nm standing wave.

FIG. 5 is a graph showing the effect of reducing a standing wave having a wavelength of 193 nm when the imaginary part of the complex refractive index and the thickness of the SiON film are changed.

FIG. 6 is a conceptual diagram illustrating multiple interference in a photoresist film.

FIG. 7 is a graph illustrating a relationship between a line width variation and an exposure wavelength.

FIGS. 8A and 8B are conceptual diagrams for explaining an anti-reflection technique, respectively.

FIGS. 9A and 9B are conceptual diagrams for explaining the effect of the antireflection film.

FIGS. 10 (a) and (b) respectively show Al
It is a conceptual diagram for explaining the morphology of an alloy film and a W film.

FIG. 11 is a graph illustrating an optimum condition of a complex refractive index.

FIGS. 12A and 12B are conceptual diagrams for explaining the remaining photoresist, respectively.

[Explanation of symbols]

10 ... substrate, 12 ... W film, 14 ... SiON film, 1
6. Resist pattern.

Claims (4)

[Claims] When forming a resist pattern on a substrate underlayer having a large grain size such as tungsten (W) on its surface, an inorganic antireflection film having a thickness larger than the grain size of the underlayer grain is provided. A film forming step of forming a film on the underlayer, a polishing step of polishing the anti-reflection film to an optimum thickness from the viewpoint of anti-reflection effect, and a step of forming a resist pattern on the anti-reflection film A method for forming a resist pattern. 2. A reflection preventing film, SiON, Si _x N _y, method of forming a resist pattern according to claim 1, characterized in that it consists of one of polysilicon and alpha-Si. 3. The method according to claim 1, wherein in the polishing step, polishing is performed by CMP. 4. The method according to claim 1, wherein in the polishing step, the thickness of the antireflection film is reduced by etch-back.