JPH0319310A - Formation of resist pattern - Google Patents

Abstract

PURPOSE:To prevent damage of a substrate and deterioration in device characteristics by a method wherein a resist, with which an ultraviolet ray irradiation part will be silylated selectively, is coated on the substrate, it is exposed by a focussing ion beam, and ultraviolet rays are collectively made to irradiate on the resist. CONSTITUTION:First, a silylated resist of about 2.0mum in thickness, for example, is spin-coated on a GaAs substrate 12, and it is baked at 90 deg.C for 30 minutes. Then, a formed gate pattern part of 0.1mum in line width is exposed using a Be focussing ion beam of accelerating energy of 260keV obtained from an Au-Si-Be alloy ion source. Subsequently, ultraviolet rays are collectively projected on the whole surface of resist in order to selectively take in Si to an unexposed part. Then, Si is selectively taken into only a part unirradiated with a converged Be ion beam by exposing the resist into a hexamethyldisilazane(HMDS) atmosphere. Lastly, a dry developing operation is conducted on a pattern using O2RIE.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of forming a resist pattern used in a semiconductor device manufacturing process, etc., and more particularly to a method of forming a pattern using a focused ion beam. .

(Prior art) GaA. In order to improve the operating speed of sMESFETs and the like, shortening the gate length is an effective means. Currently, the practical limit of resolution f for light exposure using steppers, etc. is 0.
The thickness is about 5 pm, and electron beam exposure or focused ion beam exposure has been used to form even finer gate electrodes. Among these, focused ion beam exposure is particularly effective in microfabrication, as compared to electron beam exposure, it is less susceptible to proximity effects due to forward and backward scattering, and is less susceptible to charge accumulation due to its sensitivity being one to two orders of magnitude higher. It has a sexual nature.

Therefore, focused ion beam exposure is currently used to form fine gates with a line width of about 0.1 pm.

FIG. 3 shows a method of forming a pattern for GaAs MESFET gate lift-off according to the prior art. First, a positive resist polymethyl methacrylate 31 is placed on the substrate 32.
was spin-coated to a thickness of about 1.0 pm and baked at 170'C for 30 minutes (Figure 3(a)). Then the beam diameter is 0.1
A polymethyl methacrylate 31 is exposed using a Be focused ion beam 33 focused to about pm (see Fig. 3).
b)). At this time, the acceleration energy of the Be focused ion beam was 260 keV, and the exposure amount was 1.5 x 1013 ions.
It was s/cm2.

Then, by developing for 3 minutes in a mixture of methyl isobutyl ketone and isopropyl alcohol = 1:3, and rinsing for 1 minute in isopropyl alcohol, the line width is 0.
It featured a fine resist pattern of about 1 pm (
Figure 3 (C)). However, although this conventional method can form fine patterns with a line width of about 0.1 pm that cannot be formed using other exposure methods, it is necessary to expose the resist to the substrate surface when exposing the resist using a focused ion beam. Therefore, exposure ions were inevitably implanted into the substrate, damaging the substrate, and the implanted ions became impurities, resulting in deterioration of device characteristics such as a decrease in source-drain current ( For example, Journal of Vacuum Science and Technology B5, p21L 1987, Morimoto et al.).

An object of the present invention is to form a resist pattern that is thicker than the ion penetration length in pattern formation by focused ion beam exposure without damaging the substrate due to ion irradiation during focused ion beam exposure as in the conventional method. The purpose of this invention is to provide a pattern forming method that can be used.

(Means for Solving the Problems) According to the present invention, in forming a resist pattern by focused ion beam exposure, a step of applying a resist on a substrate in which a portion irradiated with ultraviolet light is selectively silylated; a step of exposing a desired region with a focused ion beam; a step of irradiating the exposed resist with ultraviolet light; a step of silylating the portion of the resist not exposed to the ion beam; The resist pattern is obtained by a resist pattern forming method characterized by comprising a step of removing the resist immediately below.

(Function) The molecular structure of the silylated resist undergoes a chemical change in the portion irradiated with ultraviolet light, and then by exposing it to an atmosphere containing Si, Si is selectively incorporated into the molecular structure only in the irradiated portion. Dry etch resistance is improved compared to the unirradiated portion where Si was not incorporated. Therefore, after that, a negative pattern can be formed by dry etching by utilizing the difference in dry etching resistance. When charged particles such as ions and electrons are irradiated instead of ultraviolet light, the energy given to the resist is much larger than that of ultraviolet light, so the resist structure molecules may be irradiated with main chain and side chain cleavage or cross-linking. Reactions that could not occur when irradiated with ultraviolet light occur, and the original function is lost. Therefore, even if the charged particle irradiated area is then irradiated with ultraviolet light and exposed to a Si atmosphere, no Si will be taken in (for example, solid state
Technology Japan Edition, September 1987 issue, p34).

On the other hand, ions have very large masses compared to electrons.

Therefore, when resist exposure is performed using ions, the penetration length into the resist is very short compared to that of electrons, and in the range of acceleration energy of about 50 to 300 keV normally used for focused ion beam exposure, the mass is relatively large. Even if Be ions are used that have a light penetration length and a long penetration length, the penetration length is approximately 0.5
~1.7pm.

Therefore, by making the resist coating film thicker than the penetration length of the focused ion beam used into the resist, ions irradiated during exposure will not reach the substrate surface.

Based on the above, the operation of the present invention will be explained using FIG. 2. First, the silylated resist 21 coated on the substrate 22 is exposed to a focused ion beam 23 (FIG. 2(a)). At this time, the resist coating thickness and ion energy are selected so that the exposure ions do not reach the substrate surface. Further, the exposure amount is selected so that the molecular structure of the resist is destroyed and the silylation reaction does not occur. Next, in order to silylate the unexposed portions, the entire surface of the resist is irradiated with ultraviolet light 24 (FIG. 2(b)). Then, in an atmosphere containing Si such as hexamethyldisilazane (HMDS), Si
The incorporation is silylated (Fig. 2(C)). At this time, the focused ion beam exposed portion loses its original function due to destruction of the molecular structure, and only the unexposed portion is selectively silylated.

Therefore, by dry etching using 02RIE, which has a high selectivity ratio between Si and organic resist film, only the non-silylated focused ion beam exposed portions are selectively etched away, forming a pattern (see Figure 2). (d)). At this time, the resist coating thickness and ion energy are selected in advance so that the exposure ions do not reach the substrate surface, so the substrate is not damaged or impurities are caused by pattern formation, suppressing deterioration of device characteristics. be able to.

(Example) As an example of the present invention, GaAs with a line width of 0.1 pm will be described below.
Formation of a resist pattern for MESFET gate lift will be explained using FIG. 1. First, GaAs substrate 1
A silylated resist 11 is spin-coated on 2 to a thickness of about 2.0 pm, and baked at 90°C for 30 minutes (Fig. 1(a)).
). Next, using a Be focused ion beam with an acceleration energy of 260 keV obtained from an Au-Si-Be alloy ion source, a gate pattern portion with a line width of 0.1 μm to be shaped is exposed. The exposure amount is 1. O X 1013ions
/cm2. Here, with a combination of acceleration energy of 260 keV and Be ions, the ion penetration length into the resist is 1.5 μm #. Since the resist is exposed to light at a depth of about 1.5 llm from the surface, the molecules constituting the resist are destroyed by exposure (FIG. 1(b)). Thereafter, in order to selectively incorporate Si into unexposed areas, the entire surface of the resist is irradiated with ultraviolet light (FIG. 1(C)). At this time, the irradiation amount was 350 mJ/cm2. The appropriate wavelength of the ultraviolet light for illumination was 300 to 500 nm. Next, the resist was exposed to a hexamethyldisilazane (HMDS) atmosphere and B
e. Selectively incorporate Si only into the areas that have not been irradiated with the concentrated ion beam (Fig. 1(d)). At this time, the time is 3 minutes, and Si is taken in to a depth of about 0.3 μm from the surface. The silylation time was 1 to 5 minutes, and the substrate temperature was 1
00-200'C was suitable. And finally 02R
Dry the pattern using IE (Fig. 1(e))
). At this time, 02 flow rate 30SCCM, RF power 1.5kW
, the etching time was 5 minutes. The portions not exposed to the Be focused ion beam have improved 02RIE resistance due to the incorporated Si, and only the portions exposed to the Be focused ion beam are selectively etched away. Therefore, as a result, a resist pattern for gate lift-off with a line width of about 0.1 pm as shown in FIG. 1(e) was formed. At this time, since Be ions during focused ion beam exposure did not reach the substrate surface, no decrease in source-drain current due to damage to the substrate was observed before and after forming the resist pattern for gate lift-off.

Although this embodiment relates to the formation of a resist pattern for fine gate lift-off in a GaAs MESFET, the embodiment of the present invention is not limited thereto, and can be implemented to form a resist pattern using other focused ion beam exposures.

In this example, Au-Si-
Acceleration energy 260k obtained from Be alloy ion source
Although a Be focused ion beam of eV was used, other acceleration energy and other Li, Ga,
Simple metal ion sources such as Au, Au-Si, Pt-Sb,
Alloy ion source such as Pb-Ni-B or He, 8
A focused ion beam of ion species obtained from a gas ion source such as 2, 02, or F2 may also be used. The exposure dose of focused ion beam exposure is 1. O X 1013ions/crn
2, but the exposure amount may be any value as long as it causes destruction of the molecular structure such that no silylation reaction occurs in the silylated resist used. In this example, a silylated resist (PLASMASK resist, trade name, manufactured by Nippon Gosei Rubber Co., Ltd.) was used as the resist, but other silylated resists may be used. Furthermore, the silylation conditions are not limited to these, and any conditions may be used as long as they can selectively incorporate Si into the ultraviolet irradiated portion. Furthermore, the 02RIE conditions are not limited to those of this example as long as they can selectively etch away the non-silylated portions.

(Effects of the Invention) As described above, according to the present invention, in forming a resist pattern by focused ion beam exposure, there are a step of applying a resist on a substrate in which a portion irradiated with ultraviolet light is selectively silylated; A method for forming a resist pattern, which comprises the steps of: exposing the exposed resist with a focused ion beam; and irradiating the exposed resist with ultraviolet light at once; Since there is no need for irradiation, damage to the substrate can be prevented, and deterioration of device characteristics can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a substrate for explaining an embodiment of the present invention, FIG. 2 is a partial cross-sectional view of a substrate for explaining the operation of the present invention, and FIG. 3 is a partial cross-sectional view for explaining the prior art. FIG. In the figure, l1...silylated resist, 12...G
aAs substrate, 13...Be focused ion beam, 14.
...ultraviolet light, 15...hexamethyldisilazane (HM
DS), 21... Silylated resist, 22... Substrate, 23... Focused ion beam, 24... Ultraviolet light, 2
5...hexamethyldisilazane (HMDS), 31.
...Borimethyl methacrylate, 32...GaAs substrate, 33...Be focused ion beam, 34...Damage.

Claims (1)

[Claims] (1) In forming a resist pattern by focused ion beam exposure, there is a step of applying a resist on a substrate in which the portions irradiated with ultraviolet light are selectively silylated; a step of exposing with an ion beam; a step of irradiating an area of the resist including an unexposed portion adjacent to an ion beam exposed portion with ultraviolet light; a step of silylating the unexposed portion of the resist with an ion beam; 1. A method for forming a resist pattern, comprising the steps of removing an exposed portion and a resist directly under the exposed portion.