JPH07201722A - Resist pattern forming method - Google Patents

Abstract

PURPOSE:To improve the thermal resistance while sustaining the high resolving power of a resist pattern within the resist pattern using a chemical amplification type negative resist material. CONSTITUTION:The resist pattern forming method is composed of the five steps as follows i.e., the first step (a) of forming a resist film 2 on a substrate 1, the second exposure step (b) of irradiating the resist film 2 with light 4 through the intermediary of a photomask 3, the third baking step (c) for making the exposure part 2a unsoluble in a developer in the latter step at 100 deg.C for about one minute, the fourth step (d) of developing by removing not yet exposed part 2b using an alkalic developer and the fifth step (e) of baking the exposure part 2a for accelerating the thermal bridge reaction at 120 deg.C for five minutes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resist pattern forming method required in a manufacturing process of integrated circuits and the like, and more particularly to a resist pattern forming method with improved heat resistance.

[0002]

2. Description of the Related Art At present, when manufacturing a semiconductor integrated circuit device, a mask for manufacturing an integrated circuit, a printed wiring board, a printed board, etc., a base substrate is selectively processed by etching or diffusion. At that time, for the purpose of selectively protecting the portion to be processed of the base substrate, a composition which is sensitive to actinic rays such as ultraviolet rays, X-rays and electron beams, that is, a so-called photosensitive resist film is formed on the base substrate. Next, a resist pattern is formed on the base substrate by using a mask in the case of ultraviolet rays or X-rays or by direct drawing in the case of electron beams.
This resist is classified into a positive type and a negative type. The former is a type in which an exposed portion is dissolved in a developing solution but the unexposed portion is not dissolved, and the latter is an opposite type.

By the way, the high integration of semiconductor integrated circuit devices is advancing at an astonishing rate, and DRAM (Dynamic Rand)
For example, a 64 Mbit DRAM is required to be processed with a minimum pattern size of about 0.35 μm. For this reason, various methods for improving the resolution and the process margin have been developed, and as a promising method there is a phase shift method, and among them, the phase shift method called the Levenson method is known to exert a great effect. . In the case of this phase shift method, a pattern cannot be formed with a positive resist due to the arrangement of the pattern, and thus a negative resist is required.

Conventionally, as a negative resist used in photolithography, a cross-linked resist composed of a cyclized rubber and a bisazide compound is well known. However, since this type of resist uses an organic solvent for development, swelling of the resist pattern occurs during development and high resolution cannot be obtained. In recent years, many researchers have proposed a chemically amplified resist that utilizes an acid generated in a light-irradiated portion for a reaction. Among them, as a negative resist, a type in which a reaction between a base resin and a cross-linking agent is caused by an acid generated in an exposed area is well known. In general, this type of resist undergoes a thermal cross-linking reaction between the base resin and the cross-linking agent during baking after exposure and before development, resulting in a three-dimensionally high molecular weight, so that the obtained resist pattern has very high heat resistance. Is said to have.

A conventional basic resist pattern forming method of this type will be described below with reference to the process flow of FIG. First, a solution of a chemically amplified negative resist material is dropped on the substrate 1 to be processed, the film thickness is adjusted by so-called spin coating, and then 10 on a hot plate to remove the solvent.
A resist film 2 having a film thickness of about 1 to 2 μm is formed by baking at 0 ° C.
Are formed (FIG. 6A). Here, as the resist material, novolac resin, polyvinylphenol (PVP)
It is composed of an alkali-soluble base resin such as a cross-linking agent and a photo-acid generator. And this cross-linking agent,
In addition to melamine compounds, benzyl compounds, N-substituted imide compounds, and other electrophilic compounds that cause an addition reaction with the base resin are adopted.

Next, as shown in FIG. 6B, a stepper irradiates light (i-line) 4 through a photomask 3 in which a desired pattern is drawn. Then, when baking is performed on the hot plate at 100 ° C. for about 1 minute, thermal crosslinking in the exposed portion 2a progresses as shown in FIG. 6C, and an insolubilizing reaction with respect to the alkaline developing solution in the subsequent step occurs. 2b is an unexposed portion.

Next, when the resist film 2 is developed with an alkaline developer such as an aqueous solution of tetramethylammonium hydroxide having a concentration of 2.38%, only the unexposed portion 2b of the resist film 2 is removed and the exposed portion 2a remains to form a desired pattern. Resist film 2
Is obtained (FIG. 6 (d)).

[0008]

By the way, in order to manufacture a semiconductor integrated circuit device or the like, after the resist pattern is formed by the above-mentioned method, the substrate 1 to be processed is subjected to etching or ion implantation. For this purpose, it is necessary to remove the solvent and water remaining in the resist film 2, and normally the substrate 1 to be processed is baked for that purpose. Further, the temperature of the resist may rise during the processing depending on the etching conditions and the ion implantation conditions. For these reasons, the resist is required to have high heat resistance. Note that the heat resistance of the resist here is the heat resistance of the resist after the exposure and the phenomenon after the so-called photoacid generation phenomenon in the chemical amplification type, and is the resist material at the stage of being formed on the substrate 1 before the exposure. It is to be distinguished from the heat resistance in.

In the above resist pattern forming method, as described with reference to FIG. 6C, the base resin and the cross-linking agent undergo a thermal cross-linking reaction due to baking after the exposure and before the development, so that the molecular weight is three-dimensionally increased. Results in high heat resistance. Therefore, in the conventional resist pattern forming method, in order to further improve the heat resistance of the resist film, it is considered that the above-mentioned baking temperature is raised to further accelerate the thermal crosslinking reaction. However, if the baking temperature is too high, the thermal diffusion of the acid generated in the exposed portion 2a becomes large and the resolution is lowered, so that the original problem of high resolution for coping with the reduction of the minimum pattern size cannot be achieved. Therefore, the baking temperature before the development after the exposure has to be set from the condition that the resolution by the development in the subsequent step is the best, and as a result, the conventional resist pattern forming method can further improve the heat resistance. There was a problem that I could not get it.

The present invention has been made to solve the above problems, and an object of the present invention is to realize a resist pattern forming method capable of improving heat resistance without impairing high resolution.

[0011]

According to a first aspect of the present invention, a resist pattern forming method further comprises a heating step after the developing step, and the heating is performed so as to obtain the best resolution after exposure and before developing. 1 from the set bake temperature
It is performed at a temperature of 0 to 30 ° C. higher.

In the resist pattern forming method according to the second aspect of the present invention, a step of heating to a temperature higher by 10 to 30 ° C. than the baking temperature at a predetermined rising rate is added after the baking step and before the developing step. .

[0013]

In the present invention, the additional heating is carried out after the development to accelerate the thermal crosslinking of the resist without lowering the resolution and improve the heat resistance.

Further, by additionally heating at a predetermined rising rate before development, the thermal diffusion rate of the acid is suppressed to prevent the influence on the resolution and promote the thermal crosslinking to improve the heat resistance.

[0015]

【Example】

Example 1. Hereinafter, a resist pattern forming method according to Embodiment 1 of the present invention will be described with reference to the process flow of FIG. Steps (a) to (d) in FIG. 1, that is, a step (a) of applying a resist solution to form a resist film 2 on the substrate 1 to be processed, a light 4 is irradiated through a photomask 3. Step (b) of exposing, step (c) of baking after exposure to promote insolubilization reaction to the developing solution by thermal crosslinking in the exposed portion 2a, and removing the unexposed portion 2b of the resist film 2 with an alkaline developing solution. The step (d) of performing development by the same method is the same as the conventional one.

Specifically, a chemically amplified negative resist 2 containing a novolac resin and hexamethoxymethylmelamine is spin-coated on a silicon wafer substrate 1 and
Prebaking was performed on a hot plate at 00 ° C. for 1 minute. At this time, the rotation number of the wafer during coating was adjusted so that the resist film thickness was 1.2 μm. Subsequently, exposure was performed using an i-line stepper, and post exposure bake (PEB) was performed on a hot plate at 100 ° C. for 90 seconds. Then, tetramethylammonium hydroxide (TMA
Development was performed for 60 seconds using a 2.38% aqueous solution of H). When the cross-sectional shape of the sample after development was observed with an electron microscope (SEM), a pattern shape as shown in FIG. 2A was obtained. The pattern is a line and space pattern of 5 μm.

Further, in Example 1, after the developing process,
As shown in FIG. 1E, a baking step for further promoting the thermal crosslinking reaction of the exposed portion 2a of the resist film 2 is added. That is, specifically, the sample after development is treated with the above PEB.
Baking was performed for 5 minutes on a hot plate at 120 ° C., which is 20 ° C. higher than 100 ° C., and the cross-sectional shape was similarly observed by SEM. As a result, a pattern shape as shown in FIG. The shape is almost the same as in the case of FIG.

A heat resistance test was carried out to compare the resist pattern formed through the above steps with that formed by the conventional method. The test conditions were 160 ° C. for 5 minutes in consideration of the LSI manufacturing process. FIG. 3 is an SEM observation of the cross-sectional shape of the pattern after this test. FIG. 3 (a) shows the case according to Example 1, that is, 120 ° C. after development 5
FIG. 2B shows the case where the baking is performed for a minute, and the conventional case, that is, the case where the baking is not performed after the development is shown. In the former, a slight deformation (heat sagging) can be seen,
Almost the resist pattern shape immediately after development was maintained, whereas in the latter conventional case, remarkable deformation (thermal sag) was observed, and it was confirmed that the heat resistance of the present invention was improved.

The heating temperature conditions shown in FIG. 1 (e) are as follows. As a result of experiments under various conditions, the optimum temperature set from the viewpoint of maximizing the resolution before development is +
Under heating conditions of less than 10 ° C., almost no effect of improving heat resistance is observed, and when it exceeds + 30 ° C., the effect of thermal deterioration due to overheating cannot be ignored. After all, the above optimum temperature is 1
It has been found suitable to use a temperature of 0 to 30 ° C. higher. Further, the above-mentioned optimum temperature of the bake performed after the exposure and before the development changes depending on the type of resist material and the light source used, and a specific example thereof is shown in the form of a table in FIG. It should be noted that the conditions of pre-baking performed before exposure are also shown in FIG.

Example 2. Next, a resist pattern forming method according to the second embodiment of the present invention will be described with reference to the process flow of FIG. The steps from FIG. 5A to FIG. 5C are exactly the same as those in the first embodiment. However, in the second embodiment, after heating at 100 ° C. for about 1 minute in FIG. 3C, a heating step of increasing the temperature stepwise as shown in FIG. . That is, in the development (e) in the subsequent step, a baking condition of about 100 ° C. for about 1 minute is sufficient to make the exposed portion 2a insoluble in the alkaline developing solution. , 105
C., 110.degree. C., 115.degree. C., 120.degree. In this way, by increasing the temperature stepwise at a constant rate, the thermal diffusion rate of the acid in the resist is suppressed, and the thermal crosslinking reaction can be further advanced without adversely affecting the resolution.

The resist film 2 is formed by the final development step (e).
When a heat resistance test was performed on the sample from which the unexposed portion 2b of Example 1 was removed under the same conditions as described above, almost no thermal sag was observed, and improvement in heat resistance was confirmed, as in Example 1. In the above, the temperature is raised stepwise, but it may be raised continuously. In short, by setting the raising rate to 5 ° C./1 minute or less, almost the same effect can be obtained. Can be expected. The range of elevated temperature is the same as in the first embodiment.

Example 3. Note that a method may be used in which the above-described first and second embodiments are used together. The materials such as the resist and the conditions such as the baking temperature are not limited to those described in each of the above-mentioned embodiments.

[0023]

As described above, according to the first aspect of the present invention, since the predetermined heating step is added after the developing step, the thermal crosslinking reaction of the resist is promoted without lowering the resolution, and the heat resistance is improved.

Further, as described above, the invention according to claim 2 adds a predetermined heating step of raising the temperature at a predetermined rising rate before development, so that the thermal diffusion rate of the acid is suppressed and the resolution is affected. The thermal crosslinking reaction is promoted without affecting the heat resistance and the heat resistance is improved.

[Brief description of drawings]

FIG. 1 is a process flow chart showing a resist pattern forming method according to a first embodiment of the present invention.

FIG. 2 is a photograph-substitute view showing the cross-sectional shape of a resist pattern formed on a substrate after development.

FIG. 3 is a photograph substitute showing a cross-sectional shape of a resist pattern that has been subjected to a heat resistance verification test.

FIG. 4 is a table showing PEB optimum temperatures for each type of resist material and light source.

FIG. 5 is a process flow chart showing a resist pattern forming method according to a second embodiment of the present invention.

FIG. 6 is a process flow chart showing a conventional resist pattern forming method.

[Explanation of symbols]

 1 substrate to be processed 2 resist film 2a exposed portion 2b unexposed portion 3 photomask 4 light

Claims (2)

[Claims] 1. A step of forming a resist film by applying a chemically amplified negative resist material comprising an alkali-soluble base resin, a cross-linking agent and a photo-acid generator to a substrate to be processed,
The step of exposing the resist film by irradiating light through a photomask having a predetermined pattern, the step of baking after the exposure at a temperature set in order to optimize the resolution by development in the subsequent step, and the step of forming the resist film A method for forming a resist pattern, which comprises a step of performing development for removing an unexposed portion, wherein a step of heating at a temperature higher by 10 to 30 ° C. than the baking temperature is added after the developing step. 2. A step of applying a chemically amplified negative resist material comprising an alkali-soluble base resin, a cross-linking agent and a photo-acid generator to a substrate to be processed to form a resist film,
The step of exposing the resist film by irradiating light through a photomask having a predetermined pattern, the step of baking after the exposure at a temperature set in order to optimize the resolution by development in the subsequent step, and the step of forming the resist film In a method of forming a resist pattern including a step of performing development for removing an unexposed portion, a step of heating to a temperature 10 to 30 ° C. higher than the bake temperature at a predetermined rising speed is added after the bake step and before the development step. A method of forming a resist pattern, comprising: