JPH01220829A - Pattern forming method - Google Patents

Abstract

PURPOSE:To improve dimension controllability in the depth direction by spreading resist having different sensitivity in multilayer, and making exposure quantity arbitrarily change. CONSTITUTION:A positive type resist poly(methylisopropenylketon) 12 as a lower layer, and a positive type resist methacrylic acid-acrylonitrile copolymer 11 as an upper layer are spread on a substrate 13. By using electron beam 14, the positive type resist methacryslic acid-acrylonitrile copolymer 11 of upper layer is exposed with the exposure quantity between the following; one is the exposure quantity wherein the residual film percentage of the metacrylic acid-acrylonitrile copolymer becomes 0%, and the other is the exposure quantity wherein the residual film percentage of the poly(methylisopropenylketon) begins to decrease from 100%. Next, by using the electron beam 14, the methacrylic acid-acrylonitrile copolymer 11 of upper layer and the poly(methylisopropenylketone) 12 of lower layer is exposed with the exposure quantity larger than or equal to the value wherein the residual film percentage of the poly(methylisopropenylketon) becomes 0%. After that, developing is performed in a mixed liquid of methylisobutylketon : isopropylealcohol=1:3. Thereby the shape in the depth direction can be controlled accurately and with excellent treproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pattern forming method in a semiconductor manufacturing process.

(Conventional technology and its problems) A resist pattern with a shape that changes arbitrarily in the depth direction is used as a lift-off pattern when forming a T-shaped gate, which is effective for achieving both high-speed performance and low noise in GaAs MESFETs, etc. It can be used for. Conventionally, when forming a resist pattern having an arbitrary shape in the depth direction, assuming that the sensitivity characteristics of the resist used are as shown in Figure 6, the exposure time is such that the residual film rate after development of the resist starts to decrease from 100%. The amount α1 and the exposure amount a at which the residual film rate is 0%. A method is known in which exposure (Fig. 5 (b)) and development (Fig. 5 (d)) are carried out using an exposure amount α that yields a desired residual film rate of X% (for example, in microelectronic engineering). 1.P295, 1983). However, in general, resists have a steep rise in sensitivity characteristics in order to improve their resolution, that is, α and α in FIG. It is required that the area between the two layers be extremely narrow, and almost all resists currently in practical use have characteristics that satisfy this requirement. Therefore, α1 in Figure 6
and α. In the region between, the residual film rate changes significantly due to very small changes in the exposure dose and development conditions, and it is difficult to control the resist depth dimension accurately and with good reproducibility using conventional methods. Met. SUMMARY OF THE INVENTION An object of the present invention is to provide a pattern forming method that allows dimension control in the depth direction of a resist to be performed more accurately and reproducibly than ever before.

(Means for Solving the Problem) According to the present invention, in a method for forming a resist pattern having an arbitrary shape in the depth direction, resists having different sensitivities are applied in multiple layers and the exposure amount is arbitrarily changed. A method for forming a pattern can be provided.

(Operation) Next, the principle of the present invention will be explained using FIGS. 3 and 4. Assume that there are resists A and B that exhibit significantly different sensitivities as shown in FIG. 4 under certain exposure methods and development conditions. These two types of resists are shown in Figure 3 (a).
), and the exposure amount for resist A is set to the exposure amount α at which the remaining film rate of resist A is 0% in FIG.

Above and 1. If the exposure amount I3 at which the residual film rate of Regis B starts to decrease from 100% is the following exposure amount α,
In FIG. 3(b), only the upper resist A is exposed, and the lower resist B is not exposed due to insufficient exposure. Also,
The exposure amount for resist B is shown in FIG.
The exposure amount p is 13 o or more at which the residual film rate of
In other words, since this is the exposure amount at which the remaining film rate is 0% even in resist A, both the upper resist A and the lower resist B are exposed as shown in FIG. 3(C).

Therefore, by performing a development process after that, as shown in Fig. 3 (d).
) A resist pattern having an arbitrary shape in the depth direction can be formed. At this time, Figure 3 (b
), the exposure amount α for exposing the upper resist A is the fourth
α in the figure. As long as the above range is 131 or less, and the exposure amount β for exposing the upper resist A and the lower resist B in FIG. 3(C) only needs to be 13o or more in FIG. There is no need to control the exposure amount and development conditions, and the dimensions in the depth direction can be accurately controlled by the coating thickness of each layer, so the shape of the pattern in the meridian direction can be controlled accurately and with good reproducibility. It can be carried out.

(Example) Hereinafter, as an example of the present invention, formation of a T-type gate lift-off pattern will be described with reference to FIGS. 1 and 2.

FIG. 1 is a partial sectional view of a substrate for explaining the present invention in detail. Furthermore, FIG. 2 shows the sensitivity characteristics of the positive resist used in this example, methyl methacrylate-acrylonitrile copolymer and poly(methyl isopropenyl ketone), to an electron beam at an accelerating voltage of 20 kV. First, on the substrate 13, a positive resist poly(methyl isopropenyl ketone) 12 is spin-coated as a lower layer to a thickness of 0.3 pm, and a positive resist methyl methacrylate-acrylonitrile copolymer 11 is spin-coated as an upper layer to a thickness of 1.011 pm. Figure (a)). Next, using an electron beam 14 with an accelerating voltage of 20 kV, the upper body type resist methyl methacrylate-acrylonitrile copolymer 11 is removed so that the remaining film rate of the methyl methacrylate-acrylonitrile copolymer is 0% in FIG. Exposure it4. OX 10-60/
Exposure amount: 1.5 x 1O, at which the residual film rate of poly(methyl isopropenyl ketone) starts to decrease from 100% from cm2
Exposure with an exposure dose between -6 C/cm2. Here 8,
Exposure was performed at an exposure amount of OX 10-'C/cm2 (
Figure 1(b)). Next, the upper layer of methacrylate, methyl chloride-acrylonitrile copolymer 1 was removed using the same electron beam 14.
1 and the lower layer poly(methyl isopropenyl ketone) 12, in Figure 2, poly(methyl isopropenyl ketone)
Exposure is performed at an exposure amount of n light amount of 6×10 −'C/cm 2 or more so that the remaining film rate is 0%. Here 1.0X10-'C/
Exposure was performed at an exposure amount of am2 (FIG. 1(C)). Thereafter, development was carried out for 5 minutes in a mixture of methyl isobutyl ketone and isopropyl alcohol (1:3) to form a T-shaped resist pattern whose shape was controlled in the depth direction (FIG. 1(d)).

In this case, the thickness of each step formed in a step-like manner in the depth direction of the resist is 1.0 pm in the upper layer and 0.3 pm in the lower layer, which is exactly the same as the thickness of each resist applied initially. , the controllability of dimensions and its reproducibility were significantly improved compared to the conventional method.

In this embodiment, two types of positive resists with different sensitivities were used, but the combination is not limited to such a combination, and a combination of negative resists or a combination of a positive resist and a negative resist may also be used. Furthermore, the method is not limited to two-store coating using two types of resists, and multilayer coating using three or more layers of two types of resists, or multilayer coating using three or more types of resists may be used. In addition, although electron beam exposure was used as the exposure method in this example, ultraviolet light exposure, X-ray exposure,
An exposure method such as ion beam exposure may also be used.

(Effects of the Invention) As explained above, according to the present invention, in the method of forming a resist pattern having an arbitrary shape in the depth direction, resists with different sensitivities are applied in multiple layers and the exposure amount is arbitrarily changed. Dimensional controllability and reproducibility in the depth direction have been significantly improved compared to conventional methods.

[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 diagram showing sensitivity characteristics of a resist for explaining an embodiment of the present invention, and FIG. 3 is a diagram showing the sensitivity characteristics of a resist according to an embodiment of the present invention. FIG. 4 is an example of the sensitivity characteristics of a resist for explaining the present invention in detail; FIG. 5 is a partial cross-sectional view of the substrate for explaining the prior art; FIG. 6 is an example of sensitivity characteristics of a resist for explaining the prior art. 11... Methyl methacrylate-acrylonitrile copolymer, 12... Poly(methyl isopropenyl ketone)
, 13.33.52...Substrate, 14...Electron beam, 31...Positive resist A132...Positive resist B, 51...Positive resist.

Claims (1)

[Claims] (1) A method for forming a resist pattern having an arbitrary shape in the depth direction includes a process of applying multiple layers of resist with different sensitivities onto a workpiece, and a process of patterning the resist by developing it with different exposure doses. A pattern forming method including: