JPH0962012A - Resist pattern formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the formation of a resist pattern suitable for plating process by forming a photoresist film on a substrate to be treated, heat-treating, exposing and developing the photoresist film under the heating condition where a solvent in the photoresist film is evaporated. SOLUTION: A resist film 6 consisting of a novolak-based positive photoresist is applied on a GaAs substrate 2 on which a metallic wiring 4 is formed. Next, pre-baking is conducted at a temperature which is considered to evaporate the coating solvent in the resist film 6 and to evaporate little photosensitive agent. In succession, the resist film 6 is exposed by using UV(ultra Violet) light. Thereafter, the resist pattern 6 having an opening 8 on the metallic wiring 4 is formed by immersing the resist film 6 into an organic alkaline solution. Next, post-baking is conducted to remove an alkaline solution remaining in the resist film 6 after the resist pattern 6 is pulled up from the alkaline solution. Thereafter, the resist pattern 6 is immersed in a gold plating liquid to form a gold-plated layer 10 on the metallic wiring 4.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a resist pattern forming method for forming a thick film resist pattern used for a plating process.

[0002]

2. Description of the Related Art Recently, an MMIC (Microwave Monolithic Integrated) using a GaAs substrate for mobile communication has been used.
Circuit) is being used. This M
In the MIC, the increase in the resistance value due to the miniaturization and lengthening of the metal wiring connecting the elements and the metal wiring forming the inductor has a great influence on the performance of the GaAs MMIC. Therefore, it is considered to use a plating process in order to reduce the resistance of these metal wirings (mainly the second layer wirings). In this plating process, a thick film (for example, 6 μm or more) resist pattern having an opening is formed on the metal wiring already formed on the semiconductor substrate, and the semiconductor substrate on which the resist pattern is formed is immersed in a plating solution. A plating layer of, for example, gold having a film thickness of, for example, 2 μm to 3 μm is formed on the metal wiring.

[0003]

When the above-described plating process is used, the unevenness of the plating layer, the roughening of the surface of the plating layer, and the phenomenon that the resistance of the plated metal wiring is increased occur, and the plating process is performed. There was a problem that the original purpose of using it could not be achieved.

The present invention has been made in consideration of the above circumstances, and provides a resist pattern forming method capable of forming a resist pattern suitable for a plating process for reducing the resistance of metal wiring. To aim.

[0005]

A first aspect of a method for forming a resist pattern according to the present invention is a step of forming a photoresist film by applying a photoresist on a substrate to be processed, and a step of forming the photoresist film in the photoresist film. The method is characterized by including a step of performing a heat treatment under a heating condition in which a solvent evaporates, and a step of forming a photoresist pattern by exposing and developing the photoresist film.

A second aspect of the resist pattern forming method according to the present invention is the method of the first aspect, wherein the photoresist is a novolac type positive resist and the heat treatment is performed at 120 to 125 ° C. for 2 hours. It is characterized by performing for more than a minute.

A third aspect of the method of forming a resist pattern according to the present invention is characterized in that, in the forming method of the first or second aspect, the photoresist film thickness is 6 μm or more.

[0008]

According to the present invention, various problems have been investigated regarding the problem that the resistance of the metal wiring is not reduced when the plating process is performed using the resist pattern formed by the conventional resist pattern forming method. Then, it was found that a novolac-based positive resist was used for forming the conventional resist pattern, and the prebaking temperature of this resist pattern was 90 ° C. Therefore, when the pre-baking after coating the resist is performed at 90 ° C., the present inventor has a problem that the coating solvent remains in the resist film, and the resist dissolves in the plating solution together with the residual solvent to deteriorate the plating solution. We thought that it might have occurred, and conducted an experiment to support this.

In this experiment, two kinds of substrates coated with a thick film resist were prepared, and the prebaking of the resist film on one substrate was performed under the first heating condition (for example, novolak) which is considered not to evaporate the resist coating solvent completely. In the case of a system resist, it is presumed that the resist film on the other substrate is prebaked at 90 ° C. for 2 minutes or more), but the solvent for coating the resist is almost completely evaporated, but the photosensitizer in the resist is not so much evaporated. It was performed under the second heating condition (for example, in the case of a novolac-based resist, 120 ° C. for 2 minutes or more). Then, these two types of resist films are exposed and developed, and then each is subjected to post-baking at 80 ° C.
The profile of the resist film when post-baked at ℃ was investigated. From this examination result, the resist film profile when pre-baked under the first heating condition caused a resist flow and was not a 90-degree vertical profile. On the other hand, when the resist film was pre-baked under the second heating condition, the resist flow did not occur in the profile of the resist film.
It was a vertical profile.

Further, the resist film prebaked under the first heating condition and the resist film prebaked under the second heating condition are exposed and developed to a predetermined temperature (for example, 100).
Post bake was performed at (° C.). Then, the substrate on which these resist film patterns were formed was immersed in a plating solution, and the reduction in the film thickness of the resist film after forming the plating layer was measured. According to these measurement results, the resist film when prebaked under the second heating condition showed a smaller decrease in film thickness than the resist film when prebaked under the first heating condition. That is, it was found that pre-baking the resist film under the second heating condition caused less resist elution into the plating solution.

The operation of the present invention will be described based on the above experimental results.

According to the first aspect of the resist pattern forming method of the present invention configured as described above, the heat treatment (prebaking) is performed under the heating condition that the solvent in the photoresist film is evaporated. From this and the above experimental results, resist flow does not occur, the formed resist pattern has a 90-degree vertical profile, and
There is little reduction in the resist film after plating, it is possible to suppress the elution of the resist into the plating solution, and it is possible to obtain a resist pattern suitable for the plating treatment.

According to the second aspect of the resist pattern forming method of the present invention configured as described above, the photoresist is a novolac type positive resist, and the heat treatment is performed at 120 to 125 ° C. for 2 minutes or more. Be seen. From this fact and the above experimental results, the solvent in the photoresist film was almost evaporated, resist flow did not occur, the formed resist pattern had a vertical profile of 90 degrees, and there was little film loss of the resist film after plating. It becomes possible to suppress the elution of the resist into the solution. This makes it possible to obtain a resist pattern suitable for plating.

According to the third aspect of the resist pattern forming method of the present invention configured as described above, since the thickness of the resist film is 6 μm or more, it is possible to obtain a thick resist pattern suitable for plating. You can

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a resist pattern forming method according to the present invention will be described with reference to FIGS. First, the present inventor has variously investigated the problem that the resistance of the metal wiring is not reduced when the plating process is performed using the resist pattern formed by the conventional resist pattern forming method. Then, a novolac-based positive resist is used for forming the conventional resist pattern,
It was found that the prebaking temperature of this resist pattern was 90 ° C. Therefore, the present inventor thinks that the pre-baking after the resist coating is carried out at 90 ° C., the coating solvent remains in the resist film, and the above-mentioned problem is caused by the influence of this residual solvent, and this is supported. Experiments for This experiment will be described below.

In the experiment, a novolac-based positive photoresist was used as the thick film resist. First, the resist 6 is applied to a thickness of 6 μm on the GaAs substrate 2 on which the metal wiring 4 having a thickness of 1 μm is formed, and prebaked at 90 ° C. for 2 hours.
Two types were prepared: one for 1 minute, and one for prebaking for 2 minutes at 120 ° C., which is a temperature at which the coating solvent is almost evaporated and the photosensitizer contained in the resist is not likely to be evaporated. Then, these two types of resist films were exposed and developed, and thereafter, the taper angle θ (see FIG. 4) was measured when post-baked at 80 ° C. and when post-baked at 100 ° C., respectively. The measurement result at this time is shown in FIG.
Shown in In FIG. 3, the measurement results when prebaked at 90 ° C. are shown by white circles, and the measurement results when prebaked at 120 ° C. are shown by white triangles.

As can be seen from FIG. 3, the flow of the resist film, that is, the resist film 6 is deformed as shown by the broken line in FIG. 4 as the pot-baking temperature is increased, and the post-baking temperature is 100 ° C. in particular. Then, it was found that the taper angle became 58 degrees and the flow of the resist film 6 became remarkable.

On the other hand, when prebaking was performed at 120 ° C., no resist flow was observed even if the post-baking process was increased, and the taper angle θ was 90 °, which was 90 °, and the vertical profile (FIG. 4). The profile of the resist film 6 indicated by the solid line is maintained.

Next, the post-baked resist pattern is immersed in a gold plating solution having a liquid temperature of 65 ° C. and a current density of 0.5 A / dm ² for 370 seconds to form a gold plating layer having a thickness of about 2 μm. The measurement result of the decrease in the film thickness of is shown in FIG. As can be seen from FIG. 2, the reduction in the film thickness of the resist pattern prebaked at 90 ° C. is 0.21 μm.
On the other hand, the reduction in the film thickness of the resist pattern prebaked at 120 ° C. was 0.06 μm.

From this, it can be seen that the resist elution into the plating solution is less when prebaked at 120 ° C.

Based on the above experimental results, an embodiment of the resist pattern forming method according to the present invention will be described with reference to FIG.

FIG. 1 is a sectional view of the manufacturing process of this embodiment. First, as shown in FIG. 1A, a resist film 6 made of a novolac-based positive photoresist is applied to a GaAs substrate 2 on which a metal wiring 4 having a thickness of 1 μm is formed, for example, to a thickness of 6 μm. Next, pre-baking is performed for 2 minutes or more at a temperature at which the coating solvent in the resist film 6 is evaporated and the photosensitive agent is not likely to be evaporated (for example, 120 to 125 ° C. for a novolac-based positive photoresist). See FIG. 1B).

Subsequently, the resist film 6 having a wavelength of, for example, 436 is formed.
Exposure amount of 550 using UV (Ultra Violent) light
Exposure is performed at mj / cm ² (see FIG. 1C). afterwards,
2 minutes 3 in an organic alkali solution with an alkali concentration of 2.38%
By immersing for 0 seconds, a resist pattern 6 having an opening 8 is formed on the metal wiring 4 (see FIG. 1D).

Next, after the resist pattern 6 is lifted from the alkaline solution, a post-baking treatment is performed at 100 ° C., for example, to remove the alkaline solution remaining in the resist film 6.

Thereafter, the temperature is 65 ° C. and the current density is 0.5 A / dm.
By immersing 370 seconds in a ^second gold solution to form a gold plating layer 10 having a thickness of about 2μm on the metal wiring 4 (see FIG. 1 (e)).

No resist flow is observed in the resist pattern formed by the forming method of the present embodiment,
A vertical profile of 90 degrees is maintained, and even if plating is performed using this resist pattern, the surface of the plated layer formed is not roughened and the resistance with the metal wiring 4 is reduced. I was able to.

[0027]

As described above, according to the present invention, a resist pattern suitable for the plating process can be formed.

[Brief description of drawings]

FIG. 1 is a sectional view of a manufacturing process of an embodiment of a resist pattern forming method according to the present invention.

FIG. 2 is a graph illustrating an effect of one embodiment.

FIG. 3 is a graph illustrating an effect of one embodiment.

FIG. 4 is an explanatory diagram illustrating a problem of a conventional resist pattern forming method.

[Explanation of symbols]

 2 semiconductor substrate (GaAs substrate) 4 metal wiring 6 resist film 8 opening 10 gold plating layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 21/30 569B

Claims (3)

[Claims] 1. A step of forming a photoresist film by applying a photoresist on a substrate to be processed, a step of heat treatment under a heating condition in which a solvent in the photoresist film is evaporated, and the photoresist. A step of forming a photoresist pattern by exposing and developing the film, and a resist pattern forming method. 2. The photoresist is a novolac-based positive resist, and the heat treatment is 120 to 125 ° C.
The method according to claim 1, wherein the method is performed for 2 minutes or more. 3. The method according to claim 1, wherein the photoresist film has a thickness of 6 μm or more.