JPS6180247A - Formation of micropattern - Google Patents

Abstract

PURPOSE:To enhance sensitivity of a resist and resolution of a pattern by forming a resist film on a substrate, exposing it to radiation to form a pattern, and at that time, heat treating the resist film before or after the exposure, and quenching it. CONSTITUTION:A silicon substrate is coated with a radiation-sensitive resist, such as positive type resist contg. a quaternary ammonium salt, to form a resist film, and a resist pattern is formed by exposing it to radiation. At that time, the resist film is heat treated before or after the exposure, at a temp. higher than the glass transition point of a resist polymer and lower than the m.p. of a quaternary ammonium salt. Then, the film is quenched and developed with ketone or alcohol. Since a solvent is removed by a heat treatment to enhance adhesion to the substrate, the resist pattern high in resolution can be formed with high sensitivity.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for processing a high-sensitivity, high-resolution positive resist that is applied in the manufacture of high-density semiconductor integrated U-way circuits, high-frequency semiconductor devices, etc. The present invention relates to a method of forming a fine resist pattern on a substrate.

[Technical background of the invention and its problems]

BACKGROUND ART In semiconductor integrated circuits and high-frequency semiconductor devices, densification is progressing, and thin film microfabrication technology has become an extremely important elemental technology.

This has made it possible to process submicron areas by introducing a dry etching process, but in order to achieve this, the resist pattern must have high dimensional accuracy. This is because the shape processed by dry etching faithfully reflects the profile of the resist pattern.

Various approaches have been proposed to improve the resolution of resist patterns, and some results have been obtained. However, conventional results have shown that measures to increase resolution work to lower sensitivity. Sensitivity is, needless to say, a fundamental property of resist materials that is as important as resolution, so it is undesirable for this to decrease.

For resist design and process development, it is ideal to satisfy both resolution and sensitivity at the same time, but materials and processes are selected with emphasis on either resolution or sensitivity depending on the application. There is. In other words, for research use, high resolution was required, and for production use, high sensitivity was required from the perspective of emphasizing throughput. However, even for production purposes, we are already entering the era of ultra-fine processing, and it is becoming necessary to satisfy both high sensitivity and high resolution.

[Purpose of explanation]

The present invention has been made to solve the above-mentioned problem, and it is possible to form a high-resolution resist pattern that is fully compatible with ultra-fine processing in the sub-micron region without impairing the image quality. The aim is to provide a resist process.

[Summary of the invention]

In the process of forming a thin film of a radiation-sensitive resist on a substrate, irradiating the thin film with radiation in a pattern, and then developing it in a continuous manner to form a resist pattern, the composition of the thin film can be applied to 1 to 20 plates. Forming a thin film using a resist containing a percent-grade ammonium salt on a PA plate, and further heat-treating the resist thin film and subsequent quenching treatment at least once before or after radiation irradiation. It is characterized by using an alcohol-based mixed solvent as a developer, and its purpose is to enable microfabrication in the submicron region by using a resist process that is highly sensitive to radiation and has excellent resolution. It's a place where you can get used to it.

The effect of adding a quaternary ammonium salt to a positive resist is to increase the development rate. When compared under the same conditions,
When additives are present, the development time is shortened, and the greater the amount added, the shorter the development time. However, in this case, there is a drawback that the film loss in the unirradiated area is also large, making it difficult to obtain contrast between the irradiated and unirradiated areas.

This problem can be solved by modifying the developer composition as described below.

The effect of addition is obvious at 1% or more, and is significant at 5% or more. Moreover, if it is 20 or more, the dissolution rate is too high and the contrast cannot be obtained completely. As a result of various studies, tetrabutylammonium perchlorate was selected as a quaternary ammonium salt.

and tetrabutylammonium tetrafluoroborate were particularly excellent.

Heat treatment of a resist thin film is usually carried out by spin-coating a resist solution onto a substrate and then pre-baking the resist solution, and the purpose is to remove the solvent, improve adhesion between the resist substrates, or relax stress in the resist thin film. It is also common for the baked resist film to be left to cool at room temperature after being removed from the baking device. It has been found that in this process, if a rapid cooling process is performed to cool the resist film to room temperature, the sensitivity of a positive resist can be improved. Possible reasons for this include improved polymer solubility due to void formation and stress cracking, or improved main chain cleavage efficiency due to residual molecular strain due to free rotational freezing of the main chain, but it is not possible to clearly determine the cause. Not yet reached. In the course of this investigation, the present inventors have discovered that when a polymer containing fluorine in its structure is used as a resist, the degree of sensitization is particularly large and the sensitivity is improved by more than one order of magnitude. However, when a quaternary ammonium salt is used as an additive, it shows a sensitizing effect regardless of the presence of fluorine in the polymer skeleton, and according to the method of the present invention, any type of positive resist can be sensitized. is possible. It goes without saying that the sensitization is further accelerated when a fluorine-containing polymer is used. Examples of fluorine-containing polymer resists include polytrifluoroisoglobyl α-chloroacrylate, polytrifluoro-t-butyl α-chloroacrylate,
Poly-1-methoxydifluoroethyl-α-chloroacrylate, polytrifluoroethyl methacrylate,
Polyhexafluorobutyl methacrylate, polytrifluoroethyl-α-chloroacrylate, polymethyl-
Examples include α-trifluoromethyl acrylate.

Furthermore, it goes without saying that a copolymer containing these components as a component also has an effect. The fact that these fluorine-containing polymers have particularly high sensitivity can be considered, for example, as follows.

Fluorine compounds have high cohesive energy and high surface tension. However, this should be considerably smaller in the baking state. If the polymer is rapidly cooled in this state, it is possible to freeze the polymer in a state where the molecular cohesive force is small. This means that the free volume fraction of the polymer is large in a thermodynamic sense, and this contributes to improving the solubility of the polymer, which in turn leads to improved sensitivity. In the present invention, the term "freezing" means freezing into a glass state. Baking is carried out above the glass transition point, that is, in a rubbery state, but as is well known, there is a significant difference in the physical properties of the polymer before and after the glass transition point. Essentially, the above explanation can also be explained by the expression that the Brownian motion of a polymer segment in a rubber state is caused to undergo a glass transition by means of rapid cooling, thereby freezing it into a glass state. In the case of a resist containing fluorine, it is inferred that there is a large difference in molecular cohesive force between the rubber state and the glass state due to the specificity of fluorine.

Furthermore, the fact that it is a relatively bulky substituent and therefore provides steric hindrance to the formation of folding loops is also considered to be a complex factor.

It has also been confirmed that similar effects can be obtained even when the rapid cooling treatment is considered separately from the baking. Tip 9: Even when patterning is performed by radiation irradiation after baking and cooling at room temperature as in the past, sensitization is possible by performing heat treatment again to about the baking temperature and then performing rapid cooling treatment at this point. Therefore, it is clear that the sensitization referred to here mainly refers to development sensitization, and is related to the solubility and acceptability of the polymer.

This fact is not contradictory to previous reasoning. Therefore, heat treatment and quenching treatment may be performed at least once before or after radiation irradiation. In addition, since the heat treatment temperature mentioned here takes advantage of the characteristic difference in glass transition, it is naturally necessary to be higher than the glass transition point, but according to the results of the study by the present inventors, it is better to have a larger difference from the glass transition point. It was found that the sensitizing effect was favorable. However, the fourth added
If heat treatment is performed at a temperature higher than the melting point of the ammonium salt, the uniformity of the resist film will be impaired, which is undesirable. Therefore, the heat treatment temperature range is set to be above the glass transition point of the resist polymer and below the melting point of the added quaternary ammonium salt. Furthermore, the decomposition of the polymer itself is also an issue to be considered, and specifically, the optimum temperature can be determined in detail for each individual polymer and its combination with the added quaternary ammonium salt.

Furthermore, the faster the cooling series in the rapid cooling process, the greater the effect.

As is clear from the above explanation, it is possible to obtain a highly sensitive resist process using the above-described method. However, it is clear that the resolution of the resist pattern obtained by this method is lower when compared with the slope of the sensitivity curve, γ, which is an index thereof. As clear image solvents for positive resists, halogenated hydrocarbons, ketones, esters, alcohols, etc. are used. Due to the above-mentioned reasons, the solubility of the rapidly cooled polymer is increased, and it is considered that the dissolution rate ratio of the irradiated/non-irradiated areas is difficult to control. Therefore, by suppressing the dissolution rate by combining a good solvent and a poor solvent for the resist polymer, it is possible to obtain a process in which the dissolution rate ratio of irradiated/non-irradiated areas can be easily controlled. In this case, it can be expected that a profile with high γ will be obtained. According to the study results of the present inventors, methyl ethyl ketone, methyl isobutyl ketone,
A ketone solvent consisting of the cyclohexanone group, that is, a good solvent for positive resist, normal globil alcohol, and isopropyl alcohol.

When development is performed using an alcoholic solvent from the group of normal butyl alcohol and isobutyl alcohol, that is, a mixed solvent with a poor solvent for positive resist, a profile with a high γ value can be obtained.

Therefore, as in the present invention, a positive resist containing 1 to 20 percent of quaternary ammonium salt as an additive is used, and a sensitization process is performed by performing heat treatment and rapid cooling treatment, and a mixed solvent of ketone type and alcohol type. By using the development process, γ can be increased without losing the initial sensitivity.
It is possible to obtain a high resist profile.

This adjustment can be carried out using a developer, and the composition ratio of the good solvent is preferably 70 to 30.

The details are determined by the resist used and the combination of good and poor solvents. The present invention is characterized by using a positive resist containing 1 to 20 percent quaternary ammonium salt in its composition, and applying a spin-coded resist thin film at least once before or after radiation irradiation. It is a combination of performing a heat treatment-quenching treatment and developing the resist latent image using a mixed solvent of a ketone solvent and an alcohol solvent in a limited range and in a limited composition ratio.

〔Effect of the invention〕

According to the method of the present invention, a resist pattern with high sensitivity and high resolution can be obtained in an ultra-fine resist process, and both sensitivity and resolution can be satisfied.

However, the heat treatment-quenching process for the purpose of sensitization has the same effect both before and after the radiation irradiation process, and the process design is highly discernible. In particular, when it is performed before radiation irradiation, the so-called pre-bake is a substitute for heat treatment, so the total processing time is not longer than in the past, but rather the advantage is that the processing time can be shortened because of the subsequent rapid cooling process. Furthermore, it is possible to control sensitivity and resolution by appropriately selecting the heat treatment temperature and quenching rate, and by appropriately selecting the combination and composition ratio of ketone alcohol-based positive resist solvents and poor solvents. .

According to the method of the present invention, the resist solution is uniformly applied onto a substrate to form a thin film, subjected to heat treatment and quenching treatment, and irradiated with radiation such as an electron beam in a pattern to form a resist solution of either a specified ketone type or an alcohol type. By developing with a mixed solvent of a specified composition ratio, it is possible to obtain a highly sensitive and high-resolution resist pattern, and by etching using this as a mask, the substrate can be formed to a thickness of IAn or less, and under preferable conditions, 0.5 μm. The following microfabrication is possible.

[Embodiments of the invention]

A resist solution containing 5% by weight of tetrabutylammonium perchlorate added to polymethyl methacrylate (PMMA) was prepared and coated onto a silicon substrate by a spin coating method to form a 0.6 μm thick resist).
I got M. Immediately after baking this at 200° C. for 60 minutes, the resist film was rapidly cooled by bringing the resist film substrate into contact with a cooling medium. This sample was irradiated with an electron beam in a pattern at an accelerating voltage of 20 KV to create a latent image. The sample was developed with the following five types of developer, with the development temperature set at 28' (1) and the development time set at 5 minutes, and the sensitivity was comparatively evaluated.

Developer ■ Methyl isobutyl ketone, ■ 8:20 mixed solvent of methyl isobutyl ketone and isopropyl alcohol, ■ 70:30 mixed solvent of methyl isobutyl ketone and isopropyl alcohol, ■ 60:40 mixed solvent of methyl isobutyl ketone and isopropyl alcohol ,■ Methylisobutyl and isopropyl alcohol 50:
50 mixed solvent.

Rinsing was performed for 30 seconds using isopropyl alcohol. FIG. 1 shows sensitivity curves in each case. FIG. 2 is a sensitivity curve obtained by baking with polymethyl methacrylate containing no additives, cooling at room temperature, and developing with the developer described in (2) above as a comparative example.

In the figure, the developing solutions used are: ■ Methyl isobutyl ketone, ■ 80:20 mixed solvent of methyl isobutyl ketone and isopropyl alcohol, ■ 70:30 mixed bath medium, ■ 60:40 mixed solvent, ■ 50:30 mixed solvent. 50 mixed solvent.

As a result, when the content of isopropyl alcohol, which is a poor solvent for polymethyl methacrylate, is increased in the developer, the residual film rate becomes 0 when irradiated with an electron beam, which means that the sensitivity decreases, but this is expressed by the slope of the curve. On the contrary, it can be seen that the γ value increases.

Now, the sensitivity curve in the normal process shown as a comparative example in Figure 2, that is, a sample in which a resist consisting of a single component of polymethyl methacrylate was spin-coated, baked and allowed to cool, was irradiated with an electron beam, and a good solvent for the resist was used. Compared to the case where development is carried out using a certain methyl isobutyl ketone, the sensitivity is the same when developer solution (1) is used among the resist processes according to the method of the present invention, and γ shows a higher value.

γ is useful as an index of resolution, and a high value indicates that excellent resolution can be expected. When various patterns were evaluated, it was found that a pattern of 0.5μ could be resolved.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a sensitivity curve when a resist process according to the present invention is used, and FIG. 2 is a diagram of a sensitivity curve when a conventional resist process is used as a comparative example. Agent: Patent attorney Kensuke Chika (and 1 other person)

Claims (6)

[Claims] (1) In the process of forming a radiation-sensitive resist film on a substrate, irradiating it with radiation in a pattern, and then developing it to form a resist pattern, heat treatment of the resist film and subsequent rapid cooling treatment are performed using radiation. A method for forming a fine pattern, characterized by applying the irradiation at least once either before or after irradiation, and developing using a mixed solvent of a ketone type and an alcohol type. (2) The radiation-sensitive resist contains 1 quaternary ammonium salt.
The method for forming a fine pattern according to claim 1, wherein the positive resist contains 20 to 20% by weight. (3) Claims 1 and 2, wherein the quaternary ammonium salt is tetrabutylammonium perchlorate.
The method for forming a fine pattern according to any one of paragraphs. (4) The method for forming a fine pattern according to any one of claims 1 and 2, wherein the quaternary ammonium salt is tetrabutylammonium tetrafluoroborate. (5) The heat treatment temperature is in a range higher than the glass transition temperature of the resist polymer and lower than the melting point of the quaternary ammonium salt, and measures are taken to ensure that the subsequent quenching treatment is performed as quickly as possible. A method for forming a fine pattern according to claim 1. (6) At least one ketone solvent selected from methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, and at least one alcohol solvent selected from normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, and isobutyl alcohol. one whose composition ratio is 70 with respect to ketone solvents.
2. The method for forming a fine pattern according to claim 1, wherein a mixed solvent prepared to have a concentration of 30% to 30% is used as a developer.