JPH081884B2 - Method of forming resist pattern - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a resist pattern using electron beam exposure.

2. Description of the Related Art As semiconductor device patterns have become finer, electron beam exposure has come to be used for pattern formation.
Further, in order to improve the resolution and reduce the influence of the unevenness of the substrate, consideration is given to making the resist a multilayer structure.
Further, in electron beam exposure using a multi-layered resist film, if the thickness of the lower layer resist is large, the lower layer resist is charged by the incident electrons, and the electron beam is bent to cause misalignment of the drawing pattern. A conductive silicon (Si) thin film is placed in between to prevent the lower layer resist from being charged.

Problems to be Solved by the Invention In such a conventional method, it is necessary to form an electrically conductive Si thin film, which is originally unnecessary, between resists having a multi-layer structure. It is necessary to perform processing such as plasma CVD or vapor deposition, and these steps are
Since it is different from the photoresist process including coating and heat treatment processes, there is a problem that the process becomes complicated.

Means for Solving the Problems The present invention has been made in order to eliminate such problems, and after coating at least an ammonium polystyrenesulfonate film on a substrate, the ammonium polystyrenesulfonate film is applied. This is a method of forming a resist pattern in which heat treatment is performed, and then electron beam exposure treatment and development treatment are performed to form a pattern on the ammonium polystyrene sulfonate film.

Effect According to the resist pattern forming method of the present invention, the charging phenomenon can be prevented without using a Si thin film, and a highly accurate resist pattern free from pattern distortion and positional deviation can be realized.

Example Hereinafter, the method for forming a resist pattern of the present invention will be described in detail with reference to FIGS. 1 to 5.

FIG. 1 is a diagram for explaining a first embodiment of a method for forming a resist pattern of the present invention. In this method, first, a conductive polymer thin film 2 is formed on the surface of a semi-insulating GaAs substrate 1. As a film, an ammonium polystyrene sulfonate film is formed. This thin film was formed by spin-coating an aqueous solution of ammonium polystyrene sulfonate at 4000 rpm and then performing heat treatment at 200 ° C. for 30 minutes in a nitrogen (N ₂ ) atmosphere. Next, electron beam exposure is performed using an electron beam 3 having an accelerating voltage of 25 kV with an exposure amount of 120 μc / cm ² [FIG. 1 (a)]. Pattern 4 is formed by developing the thin film that has been subjected to the predetermined pattern exposure in methyl alcohol for 10 seconds [FIG. 1 (b)].

No distortion or misalignment was found in the pattern formed through the above processing.

When a semi-insulating GaAs substrate was used and PMMA (polymethylmethacrylate) was used as the resist, it was confirmed that the pattern after electron beam exposure and development had large pattern distortion and misalignment. It was

By the way, as shown in FIG. 2, the structure of ammonium polystyrene sulfonate is composed of an anion group of polystyrene sulfonate and a salt of a positively charged ammonium group, and has ion conductivity. Further, the ammonium group is composed of nitrogen and hydrogen and does not contain a metal, so that there is no possibility of contaminating the semiconductor substrate, and it is particularly suitable for forming a resist pattern in a manufacturing process of a semiconductor device. Of course, a group having a positive charge other than the ammonium group can be used.

FIG. 3 is a diagram showing changes in the sheet resistance of the ammonium polystyrenesulfonate film when the heat treatment temperature is changed and the sheet resistance of the Si film formed by sputter deposition. As is clear from this figure, the sheet resistance of the ammonium polystyrene sulfonate film increases as the heat treatment temperature increases. However, at a heat treatment temperature of 200 ° C., a sheet resistance of 6 × 10 ⁷ Ω / □ is obtained, which is slightly higher than the sheet resistance of the Si film formed by sputter deposition. Therefore, a resistance value low enough to discharge the incident electrons at the time of electron beam exposure is obtained, and the incident electrons are not charged.

FIG. 4 is a diagram showing a sensitivity curve when the ammonium polystyrenesulfonate film was developed with methyl alcohol for 10 seconds, and a sensitivity of 100 μC / cm ² and a γ value of 1.5 were obtained. Water can be used instead of methyl alcohol. As the resolution, a line and space of 0.4 μm was obtained.

FIG. 5 is a diagram showing another embodiment in which a silicon substrate is used as a substrate, a three-layer resist having a polystyrene polystyrene sulfonate film as an uppermost layer is formed on the substrate, and the resist is patterned.

In this method, a silicon substrate 5 is prepared, and a novolac-based positive resist film is applied thereon as an organic thin film 6 to a thickness of 2 μm, and heat treatment is performed at 270 ° C. for 30 minutes. Next, a coated silicon oxide film (SOG) 7 is coated to a thickness of 1 μm and heat-treated at 250 ° C. for 30 minutes. Further, a polystyrene sulfonate ammonium film is applied as the conductive polymer film 2 to a thickness of 0.5 μm, and heat treatment is performed at 200 ° C. for 30 minutes [FIG. 5 (a)].

Next, electron beam exposure is performed at an exposure amount of 120 μC / cm ² , and development is performed using methyl alcohol to form pattern 4 [FIG. 5 (b)]. Finally, the coated silicon oxide film 7 is selectively removed by CHF ₃ / O ₂ plasma etching using the conductive polymer film 2 as a mask, and further, the coated silicon oxide film 7 is used as a mask and O ₂ plasma is used. A pattern 8 is formed by etching the organic thin film 6 [FIG. 5 (c)]. In the pattern formed through such a process, a high overlay accuracy of ± 0.1 μm (3σ) was obtained. When a normal electron beam resist was used as the uppermost layer of the three-layer resist, the formed pattern was misaligned due to charging, and only a low overlay accuracy of ± 0.7 μm (3σ) was obtained.

EFFECTS OF THE INVENTION As is apparent from the above description, according to the resist pattern forming method of the present invention, electron beam exposure can be performed without charging the resist film with incident electrons, and therefore the electron beam can be bent. It is possible to form a resist pattern without pattern distortion and pattern displacement.

Further, since it is not necessary to use a conductive film such as a Si film, an effect of simplifying the process is also obtained.

[Brief description of drawings]

1 (a) and 1 (b) are sectional views showing a process of forming a resist pattern by the method for forming a resist pattern of the present invention, and FIG. 2 is a molecular structure diagram showing the structure of ammonium polystyrene sulfonate, and FIG. The figure is a characteristic diagram showing the change in sheet resistance of the ammonium polystyrenesulfonate film when the heat treatment temperature is changed and the sheet resistance of the Si film formed by sputter deposition. FIGS. 5A to 5C are sectional views showing a process of forming a resist pattern according to another embodiment of the resist pattern forming method of the present invention. 1 ... Semi-insulating GaAs substrate, 2 ... Conductive polymer thin film, 3
... electron beam, 4 pattern, 5 silicon substrate, 6 organic thin film, 7 coated silicon oxide film, 8
…pattern.

Claims (1)

[Claims] 1. A coating of at least an ammonium polystyrenesulfonate film on a substrate, a heat treatment of the polystyrenesulfonate ammonium film, an electron beam exposure treatment and a development treatment of the polystyrenesulfonate ammonium film. A method for forming a resist pattern, which comprises forming a pattern.