JPH03235331A - Forming method for grating pattern - Google Patents

Abstract

PURPOSE:To improve the smoothness, precision and diffraction efficiency of the side wall of a pattern by a method wherein a resist pattern having a slanting cross section is formed by exposing a resist to inclined focused beams and by developing it and the pattern is transferred onto a substrate by using anisotropic dry etching. CONSTITUTION:A resist 11 is applied by coating on a substrate 12 and baked. A focusing column being inclined at a prescribed angle, subsequently, exposure is made by using focused ion beams 13 and development is executed, so as to form a resist pattern 11a. The pattern 11a being used as a mask, then, anisotropic dry etching is executed to transfer the pattern. By this method, the pattern being excellent in the smoothness and precision of the side wall thereof and having a high diffraction efficiency can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming a grating pattern used in a semiconductor device or a diffraction grating manufacturing process, etc., and more specifically relates to a method for forming a grating pattern using a focused ion beam. .

[Prior art and its problems 1 Grating patterns are used as diffraction gratings for light or X-rays, solid-state lasers, etc., and their diffraction efficiency depends on the smoothness of the pattern wall surface of the grating pattern, the repetition period, and the accuracy of the angle.

A conventional grating pattern forming method will be explained with reference to FIG. First, a novolak positive type resist 41 is applied onto the substrate 42 (FIG. 4(a)).

Next, the novolak positive type resist 41 is exposed to ultraviolet light 44 through a mask 43 (FIG. 4(b)).

At this time, the amount of exposure is made insufficient compared to that during normal pattern formation. Thereafter, by performing development in an aqueous potassium hydroxide developer, a wavy resist pattern as shown in FIG. 4(C) is formed.

Thereafter, using this resist pattern as an etching mask, the pattern was transferred to the substrate by anisotropic dry etching such as CF4 reactive ion etching, thereby forming a grating pattern as shown in FIG. 4(d). .

However, in this conventional method, the wave-shaped resist pattern is directly transferred onto the substrate, resulting in a wave-shaped grating pattern, and the problem is that the smoothness and precision of the pattern sidewalls cannot be obtained, and high diffraction efficiency cannot be obtained. It had a point.

An object of the present invention is to provide a grating batten forming method that allows formation of a grating pattern with excellent smoothness and precision of pattern side walls and high diffraction efficiency.

[Means for Solving the Problems] The present invention includes a step of applying a resist on a substrate, exposing and developing the resist with a focused ion beam having an angle other than perpendicular to the substrate and the resist, and forming an inclined cross section. This grating pattern forming method is characterized by comprising a step of forming a resist pattern having a shape, and a step of transferring the pattern onto a substrate by anisotropic tri-etching using the resist pattern as a mask.

[Effect] The principle of the present invention will be explained using FIGS. 2 and 3.

Resist exposure using a focused ion beam is less susceptible to proximity effects due to forward and backward scattering, compared to resist exposure using an electron beam, which is currently commonly used as a means for forming fine patterns. It is possible to form fine patterns that would otherwise be impossible to form, with perpendicular pattern sides. Therefore, Fig. 2 (a
) and (b), by performing exposure with the focused ion beam 23 having an angle other than perpendicular to the substrate 22 and the resist 21, the incidence of the beam as shown in FIG. 2(C) is achieved. It is possible to form a resist pattern having an oblique cross-sectional shape that accurately reflects the angle.

First, as shown in FIG. 3(a), the resist thickness and pattern width are adjusted so that the opening width Wa of the resist pattern is equal to the width Wb of the top and bottom of the resist pattern.
A resist pattern 31 is formed on a substrate 32 by selecting an incident angle. Next, using this resist pattern 31 as a mask, the substrate 3 is etched using dry etching 33 such as reactive ion etching (RIE), which has excellent vertical anisotropy.
3 (b) and (C)
As shown in FIG. 3, as the resist mask retreats due to etching, the substrate surface is exposed when viewed from the vertical direction, and etching of the substrate 32 progresses. Therefore, the etching depth becomes deeper in the order of exposed parts of the substrate 32, and as a result, as shown in FIG.
A V-shaped groove 32a as shown in d) is formed on the substrate 32.

In the above process, the sidewalls of the resist pattern 31 have excellent linearity due to the characteristics of focused ion beam exposure, and the receding of the resist pattern due to dry etching also progresses linearly, resulting in the formation of a The side walls of the V-shaped groove 32a thus formed also have smooth surfaces with excellent linearity.

Furthermore, by appropriately selecting the difference in etching speed between the resist pattern 31 and the substrate 32, the depth of the V-shaped groove to be formed can also be accurately controlled.

Therefore, based on these results, by forming a large number of patterns with the repetition period of the resist pattern set to 1:] and performing pattern transfer, it is possible to form repeating ■-shaped grooves, that is, a grating pattern.

If an exposure method such as light other than a focused ion beam or an 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. Because of the difficulty, it is difficult to apply this method.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention in the order of steps. First, polymethyl methacrylate 11 is spin-coated as a resist on a substrate 12 to a thickness of about 1.0, and heated at 170°C.
, and bake for 30 minutes (Figure 1(a)).

The focusing column was then tilted 14 degrees and the B
The resist is exposed using the e-focused ion beam 13 (FIG. 1(b)). At this time, the beam diameter of the Be focused ion beam was approximately 0.1 mm, the writing line width was 0.25/J, and the repetition period was 0.5 IJJn. Further, the exposure amount of the resist was approximately 1.5xlO13ions/cm2.

Thereafter, the resist pattern 11a as shown in FIG. was formed. At this time, the effective opening line width of the substrate 12 as viewed from the normal direction of the substrate 12 was approximately 0.

Next, using this resist pattern 11a as a mask, CF4 reactive ion etching 1 is performed as anisotropic dry etching.
Pattern transfer was performed using Step 4 (FIG. 1(d)). At this time, the CF4 flow rate is 10 SCCM, and the high frequency power is 250 SCCM.
W, etching time was 20 minutes.

As a result, as shown in FIG. 1(e), the repetition period is 0,
In comparison with the conventional method, it was possible to form a grating pattern on the substrate 12 with excellent smoothness and precision on the side surfaces of the pattern.

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 resist or a coated substrate, or both 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 a grating pattern with a desired period to be formed on the substrate.

Furthermore, in this example, Au was used in the focused ion beam exposure process.
A Be focused ion beam with an acceleration energy of 260 keV obtained from a -3i -1ee alloy ion source was used.
Other hO rate energies may be used, and other Li, Ga,
Single metal ion source such as Au, Au-3i, Pt-3
b, Alloy-1' such as Pb-Ni-B; t'/I,
Alternatively, a focused ion beam using a combination of ion species obtained from a gas ion source such as He, H2, 02, F2, etc. may be used. The exposure dose of focused ion beam exposure is
The exposure amount may be set to 1.5 X 1013 ions, /C1n 2, or may be set to 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, a combination of polymethyl methacrylate and a mixture of methyl isobutyl ketone and isopropyl alcohol = 1:3 was used as a positive resist and a developer, but the combination is not limited to this. combination of other positive resist and developer, or chloromethylated polystyrene and isoamyl acetate: ethyl cellosolve = 15:85
A combination of a negative resist and a developer may be used, such as a mixed solution of.

Although CF4 reactive ion etching was used as the anisotropic dry etching under the conditions of 10 SCCH, 250 W, and 20 minutes, the etching method and conditions are not limited thereto, and other etching methods and conditions that provide anisotropy may be used.

[Effects of the Invention] As explained above, according to the present invention, it is possible to form a grating pattern with excellent pattern smoothness and precision that 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 in the order of steps, FIGS. 2 and 3 are partial cross-sectional views of a substrate for explaining the present invention in detail, and FIG. FIG. 3 is a partial cross-sectional view of a substrate for explaining a conventional grating pattern forming method step by step. 11... Polymethyl methacrylate 11a, 31... Resist pattern 12, 22.
32.42... Substrate 13... Be focused ion beam 14... CF4 reactive ion etching 21... Resist 23... Focused ion beam 32a... Groove 33... Dry etching 41...・Novolac positive resist 43...mask 44...ultraviolet light

Claims (1)

[Claims] (1) A step of applying a resist onto a substrate, and a step of exposing and developing the resist with a focused ion beam having an angle other than perpendicular to the substrate and the resist to form a resist pattern having an inclined cross-sectional shape. A method for forming a grating pattern, comprising the steps of: transferring a pattern onto a substrate by anisotropic dry etching using the resist pattern as a mask.