JPH035654B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pattern forming method, particularly to a pattern forming method using a radiation-sensitive resin.

Conventional Structures and Their Problems High integration and high density of integrated circuits have been increasing due to advances in conventional lithography technology. The minimum line width has also become around 1 μm, and in order to achieve this processed line width, there are three methods: ultraviolet exposure using a reduction projection method with a high aperture lens, electron beam exposure method that draws directly on the substrate, One example is the proximity exposure method using lines. However, with either method, it is difficult to simultaneously obtain good line width control, high resolution, and good step coverage without sacrificing throughput. In particular, unevenness inevitably occurs on an actual integrated circuit, and after coating a radiation-sensitive resin (hereinafter referred to as resist), differences in resist film thickness occur at the uneven parts.
Good line width control becomes impossible.

This will be explained using FIG. 1. Figure 1 shows a single-layer resist film applied to the stepped portion using the conventional method.
This figure shows a state in which patterning is performed across the stepped portion. FIG. 1a is a cross-sectional view of a state in which a step 2 such as a wiring is formed on a substrate 1 such as a semiconductor substrate, and a resist 3 is applied thereon. In this case, when the thickness of the resist 3 on the flat substrate 1 without the step 2 is applied to the thickness t _R1 , the thickness of the resist 3 on the step 2 is determined by the viscosity of the resist itself and the time of coating. The film thickness t _R2 is determined by the rotation speed. At this time, it is physically impossible to set t _R1 = t _R2 , that is, to eliminate the difference in the thickness of the resist film at the uneven portions. FIG. 1b shows a plan view when a pattern is formed with a film thickness of t _R1 ≠ t _R2 in this manner.

This means that if the resist pattern 3 is formed perpendicularly to the step pattern 2, and the pattern width is determined to be l ₁ at the position of the film thickness t _R1 of the resist pattern 3, then the film thickness t _R2 will be Since there is a positional relationship of t _R1 >t _R2 , the pattern width is l ₂ and l ₁ > l ₂ , resulting in a dimensional conversion difference at the stepped portion. In other words, if the pattern becomes very fine, good line width control cannot be obtained, and the edge portion 2 of the stepped object 2
In case a, the film thickness is substantially thicker than the film thickness t _R1 of the flat part, so the resolution is lowered. Generally, the resolution improves as the resist film thickness becomes thinner. This is caused by interference and interference when the wavelength of the radiation itself creates a minute gap.
This is because the incident energy is attenuated due to the diffraction phenomenon. In other words, in order to reduce the resist film thickness difference on the stepped object, even if the resist is simply coated thickly to reduce the apparent resist film thickness difference, the resolution deteriorates, which is not preferable in terms of pattern formation.

A three-layer resist method has been proposed to improve the resolution on steps and the value of the dimensional conversion difference of the conventional single-layer resist. This method will be explained using FIG. 2. Step 2 on board 1
is formed, an organic film such as a photoresist 4 is thickly coated (FIG. 2a), and an inorganic film layer 5 such as a plasma silicon oxide film is further formed on the organic film 4, and then a resist 6 is thinly coated on the uppermost layer (see FIG. 2A). Figure 2 b).
Next, the resist layer 6 is patterned to obtain a resist pattern 6a (FIG. 2c). An inorganic film layer pattern 5a is obtained using the dry etching technique through the resist pattern 6a (FIG. 2d).

Finally, the organic film pattern 4 is formed using oxygen-based gas plasma through the resist pattern 6a and the inorganic film layer 5a.
This is a method of forming a.

In pattern formation using this three-layer structure resist, the uppermost resist 6 can be made thinner, resulting in better resolution.Moreover, since the lowermost organic film layer 4 is coated thickly, the resist pattern 6a can be formed without being affected by the step 2 on the substrate 1. Because of this, there is little difference in dimensional conversion. However, it is difficult to detect the end point of the dry etching technique and the etching conditions cover multiple layers, and the process takes a long time, which is not favorable from the viewpoint of mass production and economy.

Purpose of the Invention Therefore, it is possible to prevent the difference in pattern dimension conversion and the accompanying decrease in resolution, which are obstacles when patterning a conventional single-layer resist on an actual integrated circuit with unevenness, and to develop a three-layer resist. An object of the present invention is to provide a pattern forming method that overcomes the disadvantages in terms of economy and mass production of the pattern forming method according to the present invention.

Composition of the Invention The present invention is designed to reduce the difference in pattern dimension conversion at step portions while applying a thick resist film, and to prevent a decrease in resolution by applying the resist in two layers. In addition, first and second treatments are applied to the surface of the first resist film to sensitize the entire surface of the initially applied resist film to radiation and to separate the second resist from dissolving and mixing with the first resist film. The present invention attempts to provide a pattern forming method in which a second resist film is applied, and finally a pattern is formed simultaneously using the first and second resist films.

The present inventors have discovered through numerous experiments that an altered layer is formed on the surface of the resist film that has undergone the radiation reaction described above, which is separable from the second resist and does not lose its developability. As for the above-mentioned altered layer formation, the present inventors have proposed Japanese Patent Application No. 57-41273 (Japanese Patent Application Laid-Open No. 58-15735).
proposed irradiation with halogen compound plasma such as CF ₄ . It has been found that it is difficult to uniformly apply a resist onto the altered layer formed by this plasma. Therefore, the present inventors have discovered that by further irradiating inert gas plasma such as oxygen after halogen compound plasma irradiation, the first and second resists can be separated and the developability of the first resist is not lost. I found out that there is no such thing. Furthermore, it was found that the second resist could be coated uniformly. This is because after forming an altered layer with fluorine on the resist, irradiation with an inert gas, especially oxygen plasma, is performed as a second treatment, which modifies the surface of the altered layer, that is, returns it to its original resist composition. Conceivable.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIG. As an example, a positive resist, particularly a positive UV resist (hereinafter referred to as "positive UV resist") will be explained as an example. Positive on substrate 1 such as semiconductor substrate
A thick layer of UV resist 7 is applied to make the surface flat, and soft baking is performed (Figure 3a). then positive
The entire UV resist 7 was irradiated with UV light 8 and exposed.
UV resist 7a (Figure 3b). Further, the entire surface of the exposed positive UV resist 7a is irradiated with a halogen compound plasma, such as a fluorine gas plasma 9, to form a positive UV resist altered layer 7b (FIG. 3c).

Next, a second surface treatment is performed on the surface of the positive UV resist deterioration layer 7b using oxygen-containing gas or inert gas plasma 10.
c (Fig. 3 d). Next, the first layer positive
A second positive UV resist 11 of the same type as the UV resist 7 is used as a return layer 7c of the first positive UV resist.
Spread on top and bake. At this time, since the altered layer 7b is formed, the first and second positive
Because the second positive UV resist 11 in the UV resists 7 and 11 does not dissolve during coating, it is possible to form separate layers, and the second altered layer 7c is formed on the first altered layer 7b. 2nd positive UV
The coating characteristics of the resist 11 are good (FIG. 3e).

Next, using a patterned mask 12, the first and second positive UV resists are selectively irradiated with ultraviolet light except for the chromium part 12a, which is a light-shielding part (FIG. 3f). and a second positive UV resist portion 11a other than the UV irradiation, and a first positive UV resist portion 11a;
The UV resists 7a, 7b, and 7c are removed by development (Fig. 3g). Through this series of steps, it is possible to form a fine pattern while applying a thick resist and to reduce the difference in dimension conversion at the stepped portion.

This will be explained in detail. FIG. 4 shows the irradiation characteristics a of a single layer resist (positive type) and the irradiation characteristics b of the resist formed by the pattern forming method according to the present invention. Figure 4a shows the irradiation characteristics of only the first layer of positive UV resist explained in the first embodiment, and the exposure energy E _T that can be completely developed by increasing the thickness of _t1 shown in Figure 3a. becomes larger. Next, FIG. 4b shows two patterns formed by the pattern forming method according to the present invention.
Due to the irradiation characteristics of a layered positive UV resist, even if the thicknesses of the first and second layers (t ₁ +t ₂ ) (see Figure 3) are increased, there is almost no change in the exposure energy required for complete development. In other words, since the first layer of positive UV resist is exposed to light, selectivity is high, proving that there is no decrease in sensitivity. This means that since the exposure energy does not depend on variations in resist thickness, the pattern width variation rate is small despite variations in resist thickness at the step portion. The results of the embodiment of the present invention [see Figure 3] and the irradiation characteristics shown in Figure 4,
According to the conventional method, the pattern 3 patterned on the step pattern 2 is as shown by the dotted line in FIG. 5, but when the pattern forming method according to the present invention is used, the dimensional change is reduced as shown by the solid line in FIG.

In any of the embodiments, the film thickness conditions of the first and second resists should be determined based on the level difference in the unevenness of the underlying substrate. Regarding the type of resist, it is clear that the present invention can be applied to any of X-rays, electron beams, ion beams, ultraviolet rays, and deep ultraviolet rays. In addition, in the description of the first embodiment, the steps in FIG. 3 b and c,
It goes without saying that the present invention is possible even if step d is reversed. That is, step b may be performed after steps c and d.

Furthermore, examples of the first and second altered layers of the present invention will be described. First resist e.g.
Apply 1.0 μm of AZ1470 (manufactured by Shipprey) and heat the first altered layer with CF ₄ plasma at 2.5 torr, 20 W,
A second altered layer was formed by applying oxygen plasma for 1 minute at 150W and 0.5torr for 5 seconds.
As a result of measuring the total film thickness after applying 1.0 μm of resist AZ1470 (manufactured by Shippray), it was found that the first and second resists could be almost separated at 1.9 μm, and the uniformity of the film thickness was within 5%. It was good and warm.

Effects of the Invention As described above, according to the present invention, by coating the resist thickly, it is possible to reduce the unevenness of the stepped portion, and also to reduce the pattern width variation rate at the stepped portion, improving resolution and sensitivity. There is no decrease in
Furthermore, since the resist film is thick, dry etching resistance is improved. In other words, the present invention exhibits important value in the production of semiconductor integrated circuits for future miniaturization.

[Brief explanation of drawings]

Fig. 1a is a cross-sectional view of patterning on a stepped portion using the conventional single-layer resist method, Fig. 1b is a plan view of Fig. 1a, Fig. 2 a to e are process diagrams of the conventional three-layer resist method, and Fig. 3 Figures a to g are process diagrams of a pattern forming method according to an embodiment of the present invention, Figures 4a and b are irradiation characteristic diagrams according to the conventional example and the present invention, and Figure 5 is a plan view of a pattern according to an embodiment of the present invention. It is. DESCRIPTION OF SYMBOLS 1... Substrate, 7... Photoresist, 7a... Photosensitive resist, 7b... Altered layer, 7c... Recovery layer, 8... Fluorine gas plasma, 9... Inert gas plasma.

Claims (1)

[Scope of Claims] 1. A step of applying a first radiation-sensitive resin on a substrate, irradiating with radiation to cause the first radiation-sensitive resin film to react with radiation, and removing the first radiation that has undergone the radiation reaction. The sensitive resin is surface-treated with a first fluorine-based gas plasma to form an altered layer, and a second oxygen, nitrogen or A step of performing surface treatment with argon gas plasma, and applying a second radiation-sensitive resin on the first radiation-sensitive resin that has been subjected to the first and second surface treatments; A pattern characterized by comprising the steps of: irradiating with radiation; and selectively and simultaneously removing the first and second radiation-sensitive resin films by development treatment to form a radiation-sensitive resin pattern. Formation method. 2. The pattern forming method according to claim 1, wherein the first and second radiation-sensitive resins have the same radiation reaction mechanism.