JPH0319697B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing electronic circuit devices, and more particularly to a lift-off leveling method.

(Prior Art) A lift-off planarization method using a conventional canopy structure cutting die is described, for example, in Solid State Tech., August 1981, pages 74-80. In this first conventional technique, a photoresist with a low solubility is layered on a photoresist with a high solubility, and the lower layer is overdeveloped than the upper layer by utilizing the difference in solubility between the upper and lower resist layers. Lift-off of the deposited film was performed by forming an overhang structure. In the second conventional example, for example, after etching the base layer using a photoresist etching method in which a hardly soluble layer is formed as the uppermost layer, a part of the photoresist etching mask is dissolved and over-etched, except for the uppermost layer. Lift-off of the deposited film was performed by forming a hang structure.

(Problems to be Solved by the Invention) However, in the first conventional technique, the film thickness of the upper resist layer decreases during underlayer etching, and the strength of the overhang decreases, so the film thickness of the upper resist layer must be made sufficiently thick. The need arose. Further, in the second prior art, the thickness of the hardly soluble layer decreases during the underlayer etching, and the strength of the overhang decreases, so it is necessary to make the thickness of the hardly soluble layer sufficiently thick. That is, the upper layer resist in the first conventional example and the second
In the conventional example, the required thickness of the hardly soluble layer is
In addition to the thickness necessary for the underlying etching mask, it was necessary to have a thickness that would not lose its strength as an overhang. Therefore, it has been impossible to transfer fine patterns with high precision using conventional techniques.

An object of the present invention is to provide a lift-off planarization method that allows the use of a thinner positive photoresist than conventional methods and is suitable for transferring fine patterns with high precision.

(Means for Solving the Problem) In the lift-off planarization method of the present invention, after applying a first positive photoresist based on a phenol resin on a thin film substrate, the first positive photoresist is aromatized. a first step of exposing to a group-based solvent;
After the first step, a second step of coating a second positive photoresist on the first positive photoresist, and a second step of exposing and developing the second positive photoresist. After patterning the photoresist, the first positive photoresist and the thin film substrate are selectively etched using the second positive photoresist as an etching mask, and then the first positive photoresist is etched. The third step is to expose the
and depositing a thin film after the third step, and then dissolving the first positive photoresist and the second positive photoresist.

(Function) When the first positive type photoresist, which is formed on a thin film substrate and has a phenolic resin as a base, is exposed to an aromatic solvent, the low-molecular compound is dissolved in the areas where the solvent has permeated, and the parts are dissolved. has a slow dissolution rate in the developer. Since the solvent permeates through diffusion from the resist surface, a region where the dissolution rate is slow is formed near the resist surface after the first step. Next, layer the second layer on top of this difficult-to-dissolve area.
When a positive type photoresist is applied, exposed and developed, patterning of the second positive type photoresist is completed. The development of the second positive type photoresist can be terminated when the underlying first positive type photoresist hardly soluble region is exposed. Using the second positive photoresist pattern as an etching mask, the hardly soluble layer and the underlying thin film can be continuously etched. That is, the thickness of the second positive type photoresist is required to be the minimum thickness required as an etching mask in the above-mentioned etching, and can be made thinner than conventional ones.

Next, when this sample is exposed to a developer, a portion of the first positive photoresist exposed by etching is dissolved. At this time, the hardly soluble region formed near the surface of the first positive photoresist is hardly dissolved, and the region close to the substrate is preferentially dissolved. As a result, an overhang is formed in the first positive photoresist layer. When the thin film is then deposited, the thin film will not be deposited under the overhang, and the thin film deposited on the resist sidewalls will be discontinuous at the overhang. As a result, the resist can be easily dissolved in the resist solution. After lift-off, the sample surface is free of the residue and grooves that conventionally occur on resist sidewalls, making it possible to achieve a high-quality flat surface.

(Example) FIGS. 1A to 1F are cross-sectional views of a lift-off planarization process for explaining an example of the present invention. For example, a first positive type photoresist 3 is applied to a thickness of 50 nm using Microposit 1300-31 manufactured by Shipley Co., Ltd. on a sample in which a silicon dioxide film 2 with a thickness of 100 nm is deposited by sputtering on a niobium substrate 1. After that, heat treatment was performed at 70°C for 30 minutes in nitrogen gas.
Next, it was immersed in chlorobenzene for 7 minutes to form a layer 4 hardly soluble in a developer. (Figure 1a) Next, 70℃,
After heat treatment in nitrogen gas for 30 minutes, a second positive type photoresist 5 is applied to a thickness of 1.0 μm using, for example, Shipley Microposit 1300-31, and then heated at 80° C. in nitrogen gas. Heat treatment was performed for 30 minutes. Thereafter, it was selectively irradiated with 40 mJ of ultraviolet light and developed for 30 seconds using a Microposit Developer manufactured by Shipley. (Fig. 1b) After washing with water, heat treatment in nitrogen at 80°C for 30 minutes, and then using a parallel plate reactive ion etching apparatus under the conditions of CF ₄ gas pressure of 5 Pa and discharge voltage density of 0.16 W/cm ² . The positive type photoresist 3 and the silicon dioxide film 2 were successively etched to expose the niobium substrate 1 in the opening of the second positive type photoresist. (FIG. 1c) Thereafter, it was immersed in a Microposit Developer manufactured by Shipley for 15 seconds to dissolve a portion of the first positive type photoresist. In this case, since hardly soluble layer 4 was dissolved, six undercuts could be formed. (Fig. 1d) For example, a niobium film 7 is placed on the sample.
was deposited to a thickness of 100 nm using a sputtering method. (1st
Figure e) The niobium film 7 was not deposited under the undercut 6. Next, for example, when the first positive photoresist 3 was dissolved in acetone, the niobium film 7 remained only in the recessed portions of the silicon dioxide film 2. As a result, it was possible to form a sample surface with good flatness as shown in FIG. 1(f).

(Effects of the Invention) According to the present invention, a flattening lift-off process suitable for highly accurate fine pattern transfer is made possible by using a thinner positive photoresist than before in the lift-off process of filling the recesses of the substrate in a self-aligned manner. .

[Brief explanation of drawings]

FIGS. 1a to 1f are process cross-sectional views showing an embodiment of the present invention. In the figure, 1 is the Nb substrate, 2
is the SiO ₂ film, 3 is the first positive photoresist,
4 is a hardly soluble layer, 5 is a second positive type photoresist, 6 is an undercut, and 7 is a Nb film.

Claims (1)

[Claims] 1 After applying a first positive photoresist based on phenolic resin on a thin film substrate,
a first step of exposing the positive photoresist to an aromatic solvent; and a second step of applying a second positive photoresist on the first positive photoresist after the first step. After the second step, the second positive photoresist is patterned by exposure and development, and then the second positive photoresist is used as an etching mask to form the first positive photoresist and the thin film. a third step of selectively etching the substrate and then exposing the first positive photoresist to a developer; depositing a thin film after the third step; A lift-off planarization method comprising the step of dissolving the second positive type photoresist.