JPH0319217A - Fine pattern formation - Google Patents

Abstract

PURPOSE:To enable a pattern finer than a beam diameter to be formed by a method wherein a focussed ion beams making an angle excluding the right angle are exposed to a resist coated on substrate. CONSTITUTION:When a resist pattern in opening width alpha almost equivalent to the beams diameter making an oblique angle theta of substrate 22 or a focussed column with a resist 21 in thickness of t is formed, the effective opening width alphaof the substrate 22 is represented by a formula I. Accordingly, the effective opening width alpha can be made narrower than the beam diameter l by properly selecting the thickness t and the angle theta. That is, when a pattern is transferred to the substrate 22 in the vertical direction by dryethcing process, etc., having anisotropy, the linear width b region masked under the overhung resist 21 is not etched away but a region in the width alpha only is etched away so that a fine pattern narrower than the beam diameter l may be formed on the substrate 22.

Description

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

(Prior art) When compared to resist exposure using an electron beam, which is currently commonly used as a method for forming fine patterns, resist exposure using a focused ion beam is less likely to be affected by the proximity effect caused by forward and backward scattering. It is difficult to receive, and the sensitivity is 1
Since it is about ~2 high, it is not easily affected by charge-up. In this way, compared to electron beams, focused ion beams are
It has better microfabrication properties, and currently a fine resist pattern with a line width of about 0.1 pm is formed by focused ion beam exposure.

FIG. 3 shows a method of forming a fine pattern on a substrate according to the prior art. A positive resist polymethyl methacrylate 31 (FIG. 3(a)) coated on a substrate 32 is exposed using a Be focused ion beam 33 with a beam diameter of approximately 0.1 pm and an acceleration energy of 260 keV (FIG. 3(a)).
b)). Next, development was performed for 3 minutes in a mixed solution of methyl isobutyl ketone and isobrobyl alcohol = 1 = 3, followed by rinsing for 1 minute with isopropyl alcohol, resulting in a resist with a line width of approximately 0.1 pm, which is approximately equal to the beam diameter. The pattern is formed (Fig. 1 (C)). Therefore, using the resist pattern as a mask, CF4 RIE
A pattern is transferred to the substrate 32 by anisotropic etching using a 300 nm (FIG. 3 (C)), and by removing the resist, a fine pattern with a line width of approximately 0.1 llm, which is approximately equal to the beam diameter, is formed on the substrate. (Figure 3(e)).

However, even when using focused ion beam exposure, the beam diameter is limited to 50 nm to 0.1 pm to obtain the amount of ion current necessary for resist exposure due to aberrations of the ion focusing lens. It is. In addition, the pattern width of the resist exposed by the focused ion beam is basically equal to or greater than the beam diameter, and the pattern width of the pattern transferred onto the substrate using the resist pattern as a mask is also equal to or greater than the beam diameter. That's all.

Therefore, conventional pattern forming methods have the problem that it is difficult to form a pattern on a substrate that is smaller than the beam diameter of the obtained beam (for example, semiconductor ring graphing technology: written by Koichiro Otori, Sangyo Tosho P197). ~).

An object of the present invention is to provide a pattern forming method for forming a finer pattern on a substrate than the beam diameter obtained, which has been difficult in the past in forming fine resist patterns.

(Means for Solving the Problems) According to the present invention, in a method of forming a fine pattern on a substrate by focused ion beam exposure, there are a step of applying a resist on the substrate, and a step of applying a resist to the substrate and the resist. A method for forming a fine pattern is obtained, which comprises a step of exposing the resist with a focused ion beam having an angle.

(effect medicine The principle of the present invention will be explained using FIG. 2.

Typically, a resist-coated substrate, a focusing column for focusing ions, and a focused ion beam obtained therefrom are maintained in a perpendicular relationship. If the substrate coated with resist is now tilted or the focusing column is tilted, the ion beam will be incident at an angle other than perpendicular to the resist coated on the substrate. A partial cross-sectional view of the resist exposed in such a state after development is shown in Figure 2 (a).
) is shown. In FIG. 2(a), when a resist pattern with an aperture width 1 approximately equal to the beam diameter is formed on a resist 21 with a thickness t by tilting the substrate 22 or the focusing column at an angle e, The effective opening width a of the substrate 22 when viewed from the linear direction is expressed by the following equation.

a=1-b=1-t-tane Therefore, by appropriately selecting the thickness t of the resist 21 and the inclination angle 0, the effective aperture width a of the substrate 22 can be set to the aperture width 1 of the resist 21, that is, the focused ion beam. can be made narrower than the beam diameter of Therefore, when the pattern is transferred to the substrate 22 by vertically anisotropic dry etching or the like, the area of line width b masked by the overhanging resist 21 is not etched, and the effective substrate Only the area with the opening width a of 22 is etched away (FIG. 2(b)). Furthermore, by subsequently removing the resist 21, a fine pattern with a line width a narrower than the aperture radius 1 of the resist, that is, the beam diameter of the focused ion beam, is formed on the substrate (FIG. 2(C)).

If an exposure method such as light other than a focused ion beam or electron beam is used as the exposure means, it is difficult to obtain a pattern profile with good parallelism to the incident beam due to the effects of diffraction, forward and backward scattering, etc. Therefore, it is difficult to apply this method.

(Example) Hereinafter, an example of the present invention will be described using FIG. 1. First, polymethyl methacrylate 11 was spin-coated as a resist on the substrate 12 to a thickness of about 1.0 pm, and
Bake for 30 minutes (Figure 1(a)). Next, the focusing column is tilted 7 degrees, and the resist is exposed using a Be focused ion beam with an acceleration energy of 260 keV obtained from an Au-Si-Be alloy ion source (see Fig. 1).
b)).

At this time, the beam diameter of the Be focused ion beam is approximately 0.1 pm.
The drawing line width was 0.15 pm. Further, the exposure amount of the resist was approximately 1.5×10 13 ions/cm 2 . After that, development was performed for 3 minutes in a mixture of methyl isobutyl ketone and isobrobyl alcohol = 1:3, and rinsing was performed for 1 minute with isopropyl alcohol, resulting in a resist pattern as shown in Figure 1(e). Formed. At this time, the effective opening line width of the substrate 12 as viewed from the normal direction was about 30 nm. Then, using this resist 11 as a mask, anisotropic dry etching is performed using CF4.
By performing pattern transfer by RIE (FIG. 1(d)) and removing the resist with methyl ethyl ketone, a fine pattern as shown in FIG. 1(e) was formed on the substrate 12. At this time, it was possible to form a fine pattern on the substrate 12 with a line width of about 30 nm, which was even finer than the beam diameter of the focused ion beam, which was about 0.1 im.

In this embodiment, a method of tilting a focusing column is used as the tilting method, but the method is not limited to this, and a method of tilting a substrate coated with a resist, or both of these methods may be used. Further, the inclination angle, the resist film thickness, and the line width drawn on the resist can be freely set within a range that allows the desired line width to be formed on the substrate. Furthermore, in this example, a Be focused ion beam with an acceleration energy of 260 keV obtained from an Au-Si-Be alloy ion source was used in the focused ion beam exposure process, but other acceleration energy and other Li, G
a, Single metal ion source such as Au, Au-Si, Pt-
Alloy ion source such as Sb, Pb-Ni-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 dose of focused ion beam exposure is 1.5 x 101
Although the exposure amount was set at 3 ions/am2, the exposure amount may be any value as long as it causes an image-forming reaction in the resist used and does not reduce the resist film due to ion bombardment. Further, in this example, polymethyl methacrylate and methyl isobutyl ketone:isopropyl alcohol=1=3 are used as a positive resist and a developer.
A combination of other positive resists and developers, such as a novolac positive resist and an alkaline aqueous developer, or a combination of a novolac positive resist and an alkaline aqueous developer, or a mixture of chloromethylated polystyrene and isoamyl acetate: ethyl cellosolve was used.
A combination of negative resist and developer, such as a 5:85 mixture, may also be used. In addition, CF4 is used as an anisotropic dry etching method.
Although RIE is used, the etching method is not limited to this, and other etching methods that can obtain anisotropy, such as SF5 and CC12F2, may be used.

(Effects of the Invention) As described above, according to the present invention, in forming a fine pattern on a substrate by focused ion beam exposure, there are two steps: applying a resist on the substrate, and Since the resist is exposed with a focused ion beam having an angle, it is possible to form a pattern with a finer beam diameter than that which could not be obtained by conventional methods.

[Brief explanation of drawings]

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. 3 is a partial cross-sectional view of the substrate of FIG. In the figure, 11...polymethyl methacrylate, 12
...Substrate, 13...Be focused ion beam, 21.
...Resist, 22...Substrate, 31...Polymethyl methacrylate, 32. . . . Substrate, 33 . . . Be focused ion beam. Figure 1

Claims (1)

[Claims] (1) A method for forming a fine pattern on a substrate by focused ion beam exposure, which includes a step of applying a resist onto the substrate, and exposing the resist with a focused ion beam having an angle other than perpendicular to the substrate and the resist. A method for forming a fine pattern, comprising the steps of: