JP2713061B2 - 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 method for forming a resist pattern, and more particularly, to a method for forming a resist pattern used in a photolithography process in the process of manufacturing semiconductor devices and other thin film elements.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of a semiconductor device (semiconductor integrated circuit), a photolithography technique has been employed to form a resist pattern. The photolithography technique is a step of transferring a mask pattern to a resist.

A photolithography process for forming a general resist pattern will be described with reference to FIG.
First, an SiO ₂ film 32 as a base film is formed on a Si substrate 31, then a resist 33 made of a photosensitive polymer is applied, and then prebaked to remove an organic solvent contained in the resist 33 (FIG. 7 (a)). Next, the mask pattern 34 is transferred onto the resist 33 by exposure (FIG. 7 (b)). Thereafter, the resist 33 is developed, and then post-baked to cure the resist 33 to form SiO _2.
The adhesion to the film 32 is increased. Thus, a resist pattern 33a corresponding to the mask pattern 34 is formed (FIG. 7C).

The cross-sectional shape of the resist pattern 33a formed by the above-described photolithography process has a rectangular shape as shown. The resist pattern 33a
When the SiO ₂ film 32 is etched using the method, a rectangular contact hole 35 is formed (FIG. 7D).

Although the contact hole 35 formed by the above-described process has a rectangular shape, it may be desirable to obtain a cross-sectional shape with a taper angle for application of a device. By making the cross-sectional shape of the contact hole 35 of the SiO ₂ film 32) tapered, disconnection in the upper wiring can be prevented,
This is the case where the embedding characteristics of the metal material are improved to prevent poor conduction. As a method for obtaining a contact hole having such a tapered shape, there are a method of performing dry etching while depositing a polymer on a side wall of a resist pattern, and a method of forming a taper angle in a resist pattern used as a mask material at the time of etching. and so on.

First, a pattern forming method by dry etching using a polymer film will be described with reference to FIG. First, an SiO ₂ film 42 as a base film is formed on a Si substrate 41, and then a resist 43 is applied. Thereafter, pre-baking is performed to remove the organic solvent contained in the resist 43, and a mask pattern (not shown) is transferred onto the resist 43 by exposure, followed by development (FIG. 8A). Further, using the resist 43 as a mask, CCl ₂ F ₂ / C ₂ H
₆ Anisotropic etching is performed by reactive dry etching using a mixed gas system. In this case, at the same time that the SiO ₂ film 42 is etched,
3 is deposited on the sidewall polymer film 45 is formed, it is possible to form a pattern having a taper angle in the SiO ₂ film 42 (Figure 8 (b)). Next, the unnecessary resist 43 is dissolved and removed (FIG. 8C).

[0007] A method of forming a taper angle on a resist pattern used as a mask material at the time of etching is to form a resist pattern having a taper angle by applying heat treatment to the developed resist. By performing this, a contact hole having a taper angle is formed in the SiO ₂ film.

[0008]

In the case of the method of performing dry etching using the polymer film 45, a taper angle is formed in the SiO ₂ film 42 by using a polymer deposited on the side wall of the resist 43. As the number of sheets increases, the etching rate decreases due to the influence of the polymer film 45, and there is a problem that controllability and reproducibility of each pattern are poor. Furthermore, in the case of a method in which a resist pattern used as a mask material at the time of etching has a taper angle, expansion and contraction caused when a heat treatment is performed on the resist occurs uniformly due to a difference in pattern width and pattern density. And a difference occurs in the tapered shape of the resist,
There was a problem that controllability and reproducibility were poor.

The present invention has been made in view of the above problems, and has an excellent controllability and reproducibility of a tapered shape by controlling the film thickness of a resist and then exposing the film to form a gentle skirt. It is an object of the present invention to provide a method for forming a resist pattern having a reduced taper angle.

[0010]

In order to achieve the above object, a method of forming a resist pattern according to the present invention comprises the steps of: forming a resist on a base film such that antinodes of standing waves are generated on the resist surface in a subsequent exposure step; It is characterized in that coating is performed while controlling the film thickness, whole surface exposure, mask exposure, PEB (Post Exposure Bake) processing, and development are performed.

[0011]

According to the above-described method, in a photolithography step in manufacturing a semiconductor device, when a resist-coated wafer is subjected to exposure and development to form a resist pattern, a resist pattern is formed on the underlying film by a subsequent step. In the exposure step, the resist film thickness is controlled so that antinodes of the standing wave are generated on the resist surface, the resist film is applied, and a combination of the overall exposure, the mask exposure and the PEB treatment is performed, and then development is performed. Inhibitors (development inhibitors) in the resist are decomposed by exposure of the resist, so if the intensity of the entire exposure is adjusted, only the surface of the resist is strongly exposed, the inhibitor concentration is reduced, and the developing condition is reduced. Become. Further, as the depth becomes deeper, the intensity of the exposed light becomes weaker, the inhibitor density becomes higher, and the development becomes impossible. That is,
It shows a concentration distribution in which the inhibitor concentration after the entire surface exposure increases as the depth from the resist surface increases. When mask exposure is performed from this state, in the mask exposure, light is irradiated to the resist only from the opening, and the light intensity distribution in the opening is in a state in which the state that can be dissolved by development is greatly expanded nearer to the surface. In the above-described method for forming a resist pattern, when the exposure wavelength is a single wavelength, the wavelength of λ /
When the light intensity changes at a period of 4n (λ; wavelength, n; refractive index), a wavy pattern may appear on the side wall of the resist. Therefore, by performing PEB treatment after the whole surface exposure or the mask exposure to reduce the influence of the standing wave, the inhibitor concentration distribution in the resist after the whole surface exposure and the mask exposure becomes smooth, and the line width is controlled. It will be easier.

When a standing wave is generated in a resist during exposure, the standing wave on the reflecting surface usually becomes a node,
In the following, antinodes and nodes alternate at equal intervals, and the period of the standing wave L
Is L = λ / 2n [Å] (the exposure wavelength is λ [Å] and the refractive index of the resist is n). Then, when a node of the standing wave comes on the resist surface, the resist surface becomes difficult to be dissolved, and a bowl-shaped resist pattern 22a having a sectional shape of the resist pattern as shown in FIG. 5 is formed. When this shape is transferred to the contact hole, the upper layer wiring is likely to have a disconnection or poor conduction. When the antinode of the standing wave comes to the resist surface, the resist surface is easily dissolved, and a resist pattern 12a having a gentle tapered angle as shown in FIG. 6 is formed.

Therefore, according to the above method, the resist film thickness is controlled and applied so that antinodes of standing waves are generated on the resist surface in the exposure step, so that a gentle tail as shown in FIG. 6 is always drawn. Pattern 12 having a tapered angle
a will be formed stably.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for forming a resist pattern according to the present invention will be described below with reference to the drawings.

FIGS. 1A to 1D are cross-sectional views showing steps for explaining a method of forming a resist pattern according to an embodiment. First, PF is placed on a Si (silicon) substrate 11.
Resist 12 such as X15 (manufactured by Sumitomo Chemical Co., Ltd.)
In the vicinity of the antinode of the standing wave generated in the resist.
Spin-coat with a film thickness located on the two surfaces. Table 1 below shows the relationship between the resist film thickness at which a standing wave occurs and the state of the standing wave on the surface of the resist 12. By utilizing this, the film thickness of the resist 12 is controlled so that the vicinity of the antinode of the standing wave is located on the surface of the resist 12. For example, the refractive index of the resist is 1.64 and the exposure wavelength is 4360 ° (g-line).
Then, the period of the standing wave is about 1330 °. Since the standing wave becomes a node on the substrate surface, the film thickness is about (1330k-66).
5) Å and k are natural numbers; if (see Table 1), resist 12
The standing wave on the surface becomes an antinode.

[0016]

[Table 1]

Table 2 below shows examples of the optimum film thickness of the resist so that the vicinity of the antinode of the standing wave comes to the surface of the resist at various refractive indexes and various exposure wavelengths of the resist.
As is clear from this table, various optimum film thicknesses can be selected by a combination of the refractive index of the resist and the exposure wavelength.

[0018]

[Table 2]

Thereafter, a pre-bake is performed to form a resist 12
The organic solvent contained therein is removed (FIG. 1A). Next, the entire surface of the resist 12 is exposed to g-line (4360 °) in an amount of 100 mJ / cm ^{2 by} a stepper (FIG. 1B).
FIG. 2 shows an initial film thickness 1270 of PFX15 used in this embodiment.
0 °, a pre-bake temperature of 100 ° C., and a γ value characteristic at a PEB temperature of 125 ° C. Based on FIG. / cm ² was selected for exposure. For exposure, g-line (4360 °) was used.
H-line (4050 °), i-line (3650 °), Kr
Exposure sources having a single wavelength such as F (2490 °) and ArF (1930 °) can be used. By using various light sources as shown in Table 2, even if the refractive index of the resist used changes. Various thicknesses can be selected.

Subsequently, mask exposure is performed by a stepper using the mask pattern 13 (FIG. 1C). The exposure amount at this time is an amount capable of obtaining dimensions as in the mask, and is 45 mJ / cm ² on the Si substrate. Thereafter, PEB treatment is performed at 125 ° C. for 1 hour.
It is applied for 20 seconds to eliminate the stripe pattern on the side of the pattern due to the standing wave. Next, development is performed using a positive resist developing solution such as NMD-3 (manufactured by Tokyo Ohka Kogyo Co., Ltd.), and then post-baking is performed at 120 ° C. for 120 seconds to harden the resist 12. Thus, a resist pattern 12a having a sectional shape having a tapered angle with a gentle skirt was obtained (FIG. 1D).

In this embodiment, as described above, the resist 1
After performing the entire surface exposure from above without using a mask, mask exposure is performed using the mask. By adjusting the exposure amount at the time of the entire surface exposure, the resist 12 is strongly exposed only at the surface portion,
As it gets deeper, it becomes lightly exposed. In the mask exposure, the openings are strongly exposed, but are also exposed in the depth direction of the resist, and the intensity becomes weaker according to the depth. In other words, the inhibitor concentration after the whole surface exposure shows a concentration distribution in which the concentration increases as the depth from the resist surface increases. As the inhibitor concentration increases, the dissolution by development becomes impossible. The resist 12 is exposed to light having a tapered intensity distribution by a combination of the overall exposure and the mask exposure. In addition, by controlling the film thickness of the resist 12 and performing the PEB treatment after the entire surface exposure and the mask exposure, the distribution of the inhibitor concentration in the resist can be smoothed, and after the development, the sidewalls can be smoothed.
Moreover, it is possible to form the resist pattern 12a having a gentle skirt and a taper angle.

FIG. 3 is a sectional view showing a resist pattern 12a formed under the following conditions. P as resist
Using FX-15 (manufactured by Sumitomo Chemical Co., Ltd.), the thickness of the resist 12 is 12700 °, and the pre-bake temperature is 100 ° C.
For 120 seconds. For the entire surface exposure without a mask, a stepper NSR1505G7E (manufactured by Nikon Corporation)
Exposure of g-line at 120 mJ / cm ² for 240 ms using
For mask exposure, an exposure amount of 50 mJ / cm ² was exposed for 100 ms, and thereafter, PEB treatment was performed at 125 ° C. for 120 seconds. Further, the development processing was performed at 22 ° C. for 65 seconds, and the post-baking was performed for 12 seconds.
Resist pattern 12a when applied at 0 ° C. for 120 seconds
2 shows a cross-sectional shape of the hologram.

FIG. 4 shows a comparative example in which the resist 12 is spin-coated on the surface of the resist 12 so as not to be located near the antinode of the standing wave.
-15 (manufactured by Sumitomo Chemical Co., Ltd.) and resist 12
Has a thickness of 13300 ° and a pre-bake temperature of 100 ° C.
Performed for 20 seconds. Also the overall exposure unmasked g-line exposure 115mJ / cm ^2, and 230ms exposure using a stepper NSR1505G7E (manufactured by Nikon Corporation), the mask exposed 90ms exposure with an exposure amount 45 mJ / cm ^2, the Rear PE
The B treatment was performed at 125 ° C. for 120 seconds. Further, the development processing is performed at 22 ° C. for 65 seconds, and the post-baking is performed at 120 ° C. for 120 seconds.
3 shows a cross-sectional shape of the resist pattern 22a when applied for seconds.

As is apparent from the results, according to the method of forming the resist pattern 12a according to the embodiment, the anti-reflection resist 12a is formed on the base film such that antinodes of standing waves are generated on the surface of the resist 12 in a later exposure step. The resist pattern 1 having excellent taper shape controllability and reproducibility and having a smooth skirted taper angle is obtained by controlling the film thickness, applying a whole surface exposure, a mask exposure, a PEB process, and developing.
2a can be formed.

In the above embodiment, the case where Si is used as the base film has been described as an example. However, SiO ₂ , SiN
_The present invention can be similarly applied when _{x and the} like are present in the base film. That is, even when a resist is applied on an oxide film, it can be dealt with by fixing the oxide film thickness and controlling the resist film thickness in consideration of the oxide film thickness and the refractive index of the oxide film. In the above embodiment, the PEB process is performed after the mask exposure. However, the same effect can be obtained by performing the PEB process after the entire surface exposure and performing the mask exposure. Since the PEB process is performed on the resist, the transmittance of light in the resist also changes, and light in mask exposure becomes easy to enter. Therefore, the mask exposure amount can be estimated to be small, and the standing wave of light during mask exposure can be reduced. Can also mitigate the effects.

[0026]

As described in detail above, in the method of forming a resist pattern according to the present invention, the resist film thickness is set so that antinodes of standing waves are formed on the resist surface in a subsequent exposure step. Control, apply the whole surface exposure, mask exposure, and PEB (Post Exposure Bake) processing, and develop it. By controlling the action of the standing wave, the generation of the bowl-shaped pattern can be suppressed. In addition, it is possible to form a resist pattern having excellent controllability and reproducibility of the taper shape of each pattern and having a tapered angle with a gentle slope.

[Brief description of the drawings]

FIGS. 1A to 1D are schematic cross-sectional views showing an embodiment of a method for forming a resist pattern according to the present invention in the order of steps.

FIG. 2 is a diagram illustrating a γ value characteristic of a PFX15 in an example.

FIG. 3 is a cross-sectional view showing a resist pattern in an example.

FIG. 4 is a cross-sectional view showing a resist pattern in a comparative example.

FIG. 5 is a schematic sectional view of a bowl-shaped resist pattern.

FIG. 6 is a schematic cross-sectional view of a resist pattern having a tapered angle with a gentle skirt.

FIGS. 7A to 7D are schematic cross-sectional views sequentially showing steps in forming a contact hole having a conventional tapered angle.

FIGS. 8A to 8C are schematic cross-sectional views sequentially showing respective steps in forming a contact hole having a tapered angle in another conventional example.

[Explanation of symbols]

 11 Si substrate 12 Resist 12a Resist pattern 13 Mask pattern

Claims (1)

(57) [Claims] 1. An undercoat film is coated by controlling the resist film thickness so that antinodes of standing waves are formed on the resist surface in a subsequent exposure step, and the entire surface is exposed, a mask is exposed, and PEB (Post Expos
ure bake) treatment, and developing.