JPH02187011A - Formation of resist pattern - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for forming a resist pattern used in semiconductor device manufacturing processes, etc., and more specifically, the present invention relates to a method for forming a resist pattern used in a semiconductor device manufacturing process. and a method of forming a pattern using the present invention.

(Prior Art) Focused ion beam exposure has superior resolution compared to other exposure methods. Currently, the limiting resolution of light exposure using a stepper or the like is about 0.5 pm. Also, compared to electron beams, it is less susceptible to forward and backward scattering, and is less susceptible to charge accumulation, so it is possible to
Focused ion beam exposure is mainly used for level pattern formation. Figure 3 shows GaAs produced by two conventional methods.
This figure shows a method for forming a resist pattern for T-type gate lift-off used in MESFETs and the like. Positive resist coated on the substrate to a thickness of 1.2 pm (Figure 3(a))
Next, primary exposure is performed using Si ions with an acceleration energy of 260 keV (FIG. 3(b)). Then acceleration energy 2
Secondary exposure is performed using 60 keV Be ions (third
Figure (C)). At this time, the penetration length of 260 keV Si ions into the resist is about 0.6 pm, and the penetration length of 260 keV Be ions is about 1.311 m, so by performing development after exposure, as shown in Figure 3(d), A resist pattern with a T-shaped shape was formed (for example, Journal of Vacuum Science and Technology B
5. p211, 1987. Morimoto et al.). However, the 50 to 300
In the keV range, even if Be ions are used, which is the lightest metal ion source currently in practical use, the penetration length in the resist is 0.5 to 1.711 m. Therefore, this conventional method has the problem that a pattern cannot be formed on a resist that is thicker than the resulting ion penetration length.

An object of the present invention is to provide a resist pattern forming method that can form a pattern on a resist that is thicker than the original penetration length of ions into the resist in resist pattern formation using focused ion beam π light. .

(Means for Solving the Problems) According to the present invention, in resist pattern formation by focused ion beam exposure, a step of applying a positive resist with a film thickness equal to or greater than the ion penetration length on a substrate, and a plurality of steps are performed. It is obtained by a resist pattern forming method characterized by comprising a step of exposing a resist with a focused ion beam and a subsequent step of developing the resist.

(Function) Since only the exposed portions of the positive resist become soluble in the developer, even after the exposure and development step, the unexposed portions can be exposed and developed again. Based on this fact, the present invention will be explained in detail below using FIG. 2. First, a resist coated on a substrate (FIG. 2(a)) is subjected to primary exposure using a focused ion beam (FIG. 2(b)), and then developed (FIG. 2(c)). Next, alignment is made with the previous exposure, and the portions left unexposed due to the short ion penetration length in the previous exposure are subjected to secondary exposure using the same focused ion beam (Figure 2 (d)). Perform development (Figure 2 (e)
). At this time, a pattern can be formed on the resist that is thicker than the original penetration length of the ions because a pattern can be formed in the direction of the depth of the ion penetration from the unexposed and remaining part due to the spray light. can be formed.

(Example) As an example of the present invention, the formation of a T-type gate lift-off resist pattern used in GaAs MESFETs will be described below with reference to FIG. First, GaAs
Polymethyl methacrylate 11 is spin-coated to a thickness of about 2.0 pm as a positive resist on the substrate 32, and 170
Bake at °C for 15 minutes (Figure 1 (a)). Then A
Using a Be focused ion beam with an acceleration energy of 260 keV obtained from a u-8i-Be alloy ion source, TW
Expose the part corresponding to the upper agate wiring. The exposure amount is 1
．． It was set to 5×101 ons/am. Here, with the combination of acceleration energy 260 keV and Be ions, the penetration length of the ions into the resist is about 1.311 m, so the main chain and side chains of the resist are removed by exposure to a depth of about 1.3 pm from the surface. A cutting reaction occurs and a latent image is formed (FIG. 1(b)). Next, development was carried out for 3 minutes in a mixture of methyl isobutyl ketone and isopropyl alcohol = 1:3, followed by rinsing in isopropyl alcohol for 1 minute to selectively remove the exposed areas, as shown in Figure 1 (C A resist pattern as shown in ) is formed. Next, Yuri is applied to the previous exposure, and the same < Au-
Acceleration energy obtained from 8i-Be alloy ion source 2
A 60 keV Be focused ion beam is used to expose a portion corresponding to the lower wiring of the 1-ri gate. The exposure amount is also the same.
It was set to 1.5×101 ons/am. Here, since the film thickness of the resist in the exposed area has been reduced to about 0.7 pm by the previous exposure and development, the resist is fogged up to the substrate surface by exposure (FIG. 1(d)). Therefore, the exposed areas were selectively removed by developing again for 3 minutes in a mixture of methyl isobutyl ketone and isopropyl alcohol = 1 = 3, and rinsing in isopropyl alcohol for 1 minute. A resist pattern having a T-shape as shown in e) is formed. Summary of the penetration of the Be focused ion beam into the resist with an acceleration energy of 260 keV used at this time: Thickness 2.0 mm thicker than 1.311 m
A pattern could be formed on the pm resist.

This example relates to the formation of a resist pattern for T-type gate lift-off in a GaAs MESFET that requires two exposure and development steps; however, the embodiments of the present invention are not limited thereto, and include multiple exposure and development steps of two or more times. It is possible to form resist patterns having other shapes.

In this example, Au-8i-
Acceleration energy 260k obtained from Be alloy ion source
Although a Be focused ion beam of eV was used, other acceleration energies and other single metal ion sources such as Li, Ga, and Au, alloy ion sources such as Au-3i, Pt-8b, and Pb-N1-B, or He, A focused ion beam using a combination of ion species obtained from gas ion sources such as H2, 02, F2, etc. may also be used. The exposure amount for the focused ion beam exposure was 1.5 x 101 ons/am, but this can be any amount of exposure as long as it causes an image forming reaction in the resist used and does not reduce the resist film due to ion bombardment. It can also be expressed as a quantity. In addition, in this example, a combination of polymethyl methacrylate and a mixture of methyl isobutyl ketone and isopropyl alcohol = 1 = 3 was used as the positive resist and developer, but the combination is not limited to this. Other combinations of positive resist and developer may also be used.

(Effects of the Invention) As explained above, according to the present invention, since the resist exposure process is performed using a focused ion beam multiple times, it is difficult to form a resist using a conventional method using a focused ion beam.
It is now possible to form a pattern on a resist that is thicker than the length of the ion's penetration into the resist.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a substrate for explaining one embodiment of the present invention, and FIG. 2 is a partial cross-sectional view of the substrate for explaining the present invention in detail. Further, FIG. 3 is a partial cross-sectional view of a substrate for explaining the prior art. In the figure, 11... polymethyl methacrylate, 1
2...GaAs substrate, 13...Be focused ion beam, 14...latent image, 21...positive resist, 22
...Substrate, 23...Focused ion beam, 24...
Latent image, 31... Polymethyl methacrylate, 32...
・Substrate, 33...Si focused ion beam, 34...
It is a Be focused ion beam.

Claims (1)

[Claims] (1) In forming a resist pattern by focused ion beam exposure, there is a step of coating a positive resist on a substrate with a film thickness equal to or greater than the ion penetration length, a step of exposing the resist multiple times with a focused ion beam, and a step of developing the resist. A resist pattern forming method comprising: