JPH02208934A - Pattern formation - Google Patents

Abstract

PURPOSE:To form a pattern stably by lift off process by a method wherein two-layer structured resist film is provided while the pattern opening width of the upper surface of the lower layer resist is made larger than that of the lower surface of the upper layer resist. CONSTITUTION:A lower layer resist 2 and an upper layer resist 1 are formed on a gallium arsenide substrate 3. Then, a single-line pattern is exposed to the substrate 3 using electron beams A to develop the upper layer resist 1 in organic alkali developer. Next, the lower layer resist 2 is developed in the mixed solution of MIBK and ECH to make the time opening width wider in upper surface than lower surface. Next, the substrate 3 is recess-etched by wet etching process and then an aluminum 4 is deposited on the upper layer resist 1 by vacuum evaporation. Then, the lower layer resist 2 is resolved in acetone and then the aluminum 4 is lifted off to form a pattern 4 in T-type section. Through these procedures, the T-type pattern 4 can be formed of the resists 1, 2 only by the lift off process.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a pattern forming method of the present invention.

BACKGROUND OF THE INVENTION Conventional cross-sectional forming techniques have been used to form T-shaped patterns, and a foot-off method is shown in FIGS.

In FIGS. 2(a) to 2(f), 3 is a gallium arsenide substrate, 5 is an upper resist layer, 6 is a lower resist layer, 7 is a silicon nitride film, and A is an electron beam.

First, electron beam exposure is performed (FIG. 2(a)). Next, the upper resist 5 is developed (FIG. 2(b)). Next, the lower resist 6 is developed (FIG. 2(C)). Next, the gallium arsenide substrate 3 is wet-etched (FIG. 2(d)).

Next, aluminum is deposited (FIG. 2(e)). Next, the aluminum is lifted off (FIG. 2(f)).

In this case, the opening width of each resist has the following relationship: upper surface of upper resist>lower surface of upper resist>lower resist. or,
When the upper resist 5 and lower resist 6 use the same developer, development is performed simultaneously to obtain the pattern shown in FIG. 2(C). In this case, a resist with higher sensitivity than the lower resist 6 is used as the upper resist 5.

Problems to be Solved by the Invention The opening width of the upper resist layer 5 is such that the upper surface>the lower surface as shown in FIG. 2(C). In the conventional method, it is necessary to make the opening width of the upper resist layer wider than the opening width of the lower resist layer, so a relatively highly sensitive material is used as the upper resist layer 5.As a positive electron beam resist Generally speaking, the contrast after development deteriorates in the resists used in the high-sensitivity resists.For this reason, it is difficult to make the cross-sectional shape of the upper resist 5 equal to the upper opening width (lower opening width). When aluminum 4 is vapor-deposited as shown in FIG. 2(e), the necessary portion of aluminum 4 and the portion to be removed are connected, and as a result, only the unnecessary portion of aluminum cannot be removed during lift-off. Further, there is a problem that unnecessary parts are left as blanks.

A method conventionally used to solve this problem is the method shown in FIG. Silicon nitride film 7 on top of upper resist layer 5
By forming a pattern, the necessary and unnecessary parts of the aluminum 4 are separated. In this method, a silicon nitride film 7 is formed on an upper resist layer 5 by plasma CVD, a resist is further applied thereon, exposed to electron beam and developed, and then silicon nitride film 7 is etched by RIE. After that, a complicated process of developing the upper resist 5 and the lower resist 6 is required.

The conventional technology has the above-mentioned problems.

Means for Solving the Problems In order to solve the above-mentioned problems, in the pattern forming method of the present invention, a resist film having a two-layer structure is formed on a substrate. Top surface of resist> Bottom surface of upper layer resist A pattern with a cross-sectional shape is formed, and lift-off is performed using this resist pattern.

The working overlayer resist separates the parts to be removed and the parts that are needed, such as deposited metal. Furthermore, since the opening width of the lower resist is from the upper surface to the lower surface, the cross-sectional shape of the pattern after lift-off becomes T-shaped.

Embodiment An embodiment of the present invention is shown in FIGS. 1(a) to 1(f). In FIG. 1, 1 is an upper resist layer, 2 is a lower resist layer, 3 is a gallium arsenide substrate, 4 is aluminum, and A is an electron beam. First, on the gallium arsenide substrate 3, a copolymer of phenyl methacrylate and methacrylic acid with a concentration of 0.7
Coated to a thickness of μm, beta-baked at 220°C for 20 minutes,
A lower resist 2 is formed. Next, 0.3μ of PMG 1 (borodimethylglutarimide) was applied on the lower resist 2.
The upper resist layer 1 is formed by applying the resist to a thickness of m and baking at 220° C. for 20 minutes. A 0.2 μm single line pattern is exposed on this substrate using a 25 KeV electron beam A at an exposure dose of 90 μC/c+j (FIG. 1(a)). next,
Upper layer resist 1 (PMGI) is developed for 200 seconds using an organic alkaline developer at a liquid temperature of 23°C. This time aperture width is approximately 0.5 μm. (Figure 1(b)). next,
Lower resist 2 (copolymer of phenyl methacrylate and methacrylic acid) is MIBK (methyl isobutyl ketone)
and ECH (ethylcyclohexane) at a weight ratio of 4:1 (liquid temperature: 23° C.) for 450 seconds. The width of this time opening is approximately 0.3 μm on the bottom surface and approximately 0.7 μm on the top surface.
μm (Fig. 1(C)). Next, the gallium arsenide substrate 3 is recessed to a depth of 0.2 μm by wet etching (FIG. 1(d)). Next, aluminum 4 is deposited to a thickness of 0.35 to 0.4 μm by vacuum evaporation (FIG. 1(e)). Next, the lower resist 2 is dissolved with acetone, and the aluminum 4 is lifted off to obtain an aluminum pattern 4 having a T-shaped cross section (see the first diagram).

Incidentally, as the upper layer resist 1, a novolac-based resist may also be used. In this case, after the novolac resist is developed, the novolac resist is thermally crosslinked by post-baking to make it insoluble in the organic developer of the lower resist 2.

In addition, as shown in this example, upper layer resist 1 (:PMCI
Alternatively, when a novolak resist or a resist developed with an organic solvent is used as the lower resist 2, development of the upper resist and development of the lower resist can be independently controlled. Furthermore, when a copolymer of phenyl methacrylate and methacrylic acid is used for the lower resist, the adhesion between the lower resist 2 and the gallium arsenide substrate 3 is good, and during recess etching,
This prevents the etching solution from entering the interface between the lower resist 2 and the substrate 3 and etching the substrate.

Effects of the Invention The upper layer resist separates the portion of the electrode that is removed from the portion that remains. The cross-sectional shape of the lower resist layer is such that the opening width increases toward the top, and the cross-sectional shape of the electrode becomes T-shaped. With these, a T-shaped pattern can be created using only two layers of resist.
It can be stably formed using the lift-off method.

In the present invention, a resist with relatively low contrast and high sensitivity can be used as the lower resist in order to make the cross-sectional shape of the lower resist wider upward, thereby increasing the throughput of electron beam exposure.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of one embodiment of the pattern forming method of the present invention, FIG. 2 is a process diagram showing a conventional example, and FIG. 3 is a diagram showing another conventional example. 1... Upper layer resist (PMGI), 2...
... lower layer resist (copolymer of phenyl methacrylate and methacrylic acid), 3 ... gallium arsenide substrate,
4... Aluminum, 5... Upper layer resist (high sensitivity), 6... Lower layer resist (low sensitivity), 7... Silicon nitride film, A.・・・・・・25
K e V electron beam. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1.-2 layered cyst (Pmon Gt) (f)

Claims (6)

[Claims] (1) Consisting of a lower layer resist and an upper layer resist on the substrate 2
forming a resist film with a layered structure, then forming a pattern in the two-layered resist film so that the resist pattern opening width is such that the upper surface of the lower resist layer is greater than the lower surface of the upper resist layer;
A pattern forming method characterized by performing lift-off using this resist pattern. (2) In the pattern forming method according to claim 1, the resist pattern is formed by exposing the resist film to synchrotron radiation or an electron beam, and wet-developing both the upper resist layer and the lower resist layer. pattern formation method. (3) A pattern forming method according to claim 1, characterized in that PMMA (polymethyl methacrylate) is used as the lower resist. (4) A pattern forming method according to claim 1, characterized in that a copolymer of phenyl methacrylate and methacrylic acid is used as the lower resist. (5) A pattern forming method according to claim 1, characterized in that PMGI (polydimethylglutarimide) is used as an upper layer resist. (6) A pattern forming method according to claim 1, characterized in that a novolak resist is used as the upper layer resist.