JPS63135007A - Method for forming electrode pattern - Google Patents

Abstract

PURPOSE:To prevent damage to a photomask and a substrate by forming a metallic film to both faces of the substrate prior to the photolithography process so as to decrease static electricity caused due to the temperature rise/decrease attended with a pre-bake or post-bake. CONSTITUTION:Prior to the pre-bake process, a metallic film 2 and an electrode layer 3 are formed to both faces of a substrate 1. Since the partial existence of electric charges generated in the substrate 1 generated in substrate 1 in the heat of the pre-bake process is canceled by a metallic plate 2 and an electrode film 3, the generation of static electricity is suppressed, no photomask 5 is attracted to the substrate 1 in the succeeding exposure process and the damage to the photomask 5 and the substrate 1 is prevented. Since the production of static electricity is suppressed in the succeeding post-bake process, dust floating in air is not stuck to the substrate 1 during the manufacture process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for forming an electrode pattern suitable for forming, for example, interdigital electrodes and reflectors of surface acoustic wave devices.

"Prior Art and its Problems" In recent years, photolithography has been widely used for patterning electrode films formed on substrate surfaces in the manufacture of various electronic components.

The general process of photolithography will be explained using the method of forming an electrode pattern of a surface acoustic wave device as an example.
As shown in Figure 3, first the piezoelectric substrate is polished and cleaned.
l), forming an electrode film on this substrate surface (S2); Then, the resist film is laid down (S3) and prebaked (S4).
), exposing with a photomask (S5), developing and rinsing if necessary (S6), post-baking (S7), etching (S8), and finally removing the resist (S9). A predetermined electrode pattern is then formed on the substrate surface.

In this process, the substrate coated with resist in the resist coating process (S3) is usually placed in an oven for 70 minutes to volatilize the solvent in the resist film and strengthen the adhesive strength in the next pre-baking process (S4). It is heated to about 90°C. When the development step (S6) is completed, the resist, which has been swollen and softened by development and rinsing, is heated in an oven or the like again in the post-bake step (S7) to improve its adhesive strength and chemical resistance. Ru.

However, if the substrate material is a pyroelectric single crystal such as lithium niobate or lithium tantalate, static electricity is generated on the substrate surface during the process of changing the temperature of the substrate (the above-mentioned pre-hake and post-hake). It's gone. Due to this static electricity, for example, during the exposure step (S5) after the pre-bake step (S4), the substrate surface is attracted to the mask, causing the substrate to peel off, damaging the substrate, or damaging the mask. There was a problem with this. Furthermore, due to this static electricity, there is a problem in that fine particles floating in the air tend to adhere to the substrate. As a result, static electricity generated on the substrate resulted in a significant drop in yield.

[Object of the Invention] An object of the present invention is to provide a method for manufacturing an electrode pattern that solves various problems caused by static electricity generated in the process of heating a substrate.

“Structure of the Invention J” The method for forming an electrode pattern according to the present invention is a method of forming an electrode pattern on a substrate made of a pyroelectric single crystal by photolithography, and the method includes forming an electrode pattern on both sides of the substrate before a 2-ortho process. It is characterized by forming a film.

In this way, by forming a metal film on both sides of the substrate before the photolithography process, uneven distribution of charges generated within the substrate due to temperature rises and falls during the photolithography process can be prevented by forming metal films on both sides of the substrate. can be neutralized or eliminated, reducing static electricity phenomena. For this reason, the substrate is not attracted to the mask placed over the substrate during exposure, and fine particles floating in the air are less likely to adhere to the substrate. Therefore, the generation of defective products due to static electricity generated on the substrate is eliminated, and the yield can be significantly improved.

The method for forming an electrode pattern of the present invention is particularly effective for substrates made of pyroelectric single crystals such as lithium dioffate and lithium tantalate. Examples of devices using a substrate made of a pyroelectric single crystal as described above include surface acoustic wave devices.

"Embodiment of the Invention" FIG. 1 shows an embodiment of the method for forming an electrode pattern according to the present invention. (a) in FIG. 1 is a cross-sectional view of the substrate shown according to the steps, and (b) in FIG. 1 is a flowchart thereof.

First, the square and round lithium niobate substrates 1 are polished and cleaned (Sl), and Cr,
A first metal film 2 is formed using high melting point gold 1 of the 1st grade (
S2), Next, an AI electrode film 3 is formed on the entire surface of the electrode pattern formation surface (S3), and a resist 4 is spin-coded to a predetermined thickness on this electrode film 3 (S4). In order to volatilize the solvent in the film of step 4 and strengthen the adhesive force, heat it in an oven at about 70° C. to 90° C. for a certain period of time (S5), and cover the electrode pattern forming surface with a photomask 5 having a predetermined mask pattern. Ultraviolet L! 2
Exposure is performed by irradiating for about seconds (S6). Next, it is immersed in a developer for 60 seconds to perform development (S7), and a developed resist 4 is formed on the electrode film 3 formed on the substrate 1. Roughly, the development process of this resist 4 (swelling by blowing,
In order to improve the adhesive strength and chemical resistance of the softened resist 4, it was heated in an oven for a certain period of time at about 140 to 150 degrees Celsius (S8), and then immersed in a phosphoric acid-based etching solution to dissolve the exposed parts. Form an electrode pattern (S9)
. Finally, after thoroughly washing the etching solution under running water and drying, the resist 4 was removed using a specified stripping solution (5IO) to create a surface acoustic wave element with a predetermined electrode pattern (Sl+ ). Note that after this, the first gold R film 2 formed on the back surface of the substrate 1 may be removed by etching. In the above, the photolithography process in the present invention includes a resist coating process (S4), a pre-bake process (S5
), an exposure process (S6), a development process (S7), and a post-bake process (S8), and a pre-bake process (S
5) and the post-bake step (S8), the substrate 1 is heated.

In this example, the metal film 2 and the electrode film 3 are formed on both sides of the substrate 1 before the pre-bake step (S5) 8 is performed, so that the metal film 2 and the electrode film 3 are formed on both sides of the substrate 1 before the pre-bake step (S5). Since the uneven distribution of charges is eliminated by the gold a film 2 and the electrode film 3, the generation of static electricity is suppressed, and the photomask 5 is prevented from being attracted to the substrate 1 in the subsequent exposure step (S6). 5
Damage to the substrate 1 and damage to the substrate 1 were prevented. Furthermore, since the generation of static electricity is suppressed in the subsequent post-hake step (S8), it is also possible to prevent dust floating in the air from adhering to the substrate 1 during the manufacturing process. Therefore, it has become possible to significantly improve the yield of products.

FIG. 2 shows another embodiment of the method for forming an electrode pattern according to the present invention. (a) in FIG. 2 is a cross-sectional view of the substrate according to the process, and (b) in FIG. 1 is a flowchart thereof.

In this example, the present invention is applied to an electrode pattern forming method using a lift-off method, and the steps 81 to S8 described in Example] are almost the same. First, the substrate 1 is polished and cleaned (Sl), and a first metal film 2 made of a high melting point metal such as Cr or Ti is formed on the back surface of the electrode pattern forming surface of the substrate 1 by a method that does not increase the temperature of the substrate 1. Form a film (S2), then Cr,
A second metal film 6 made of a high melting point metal such as Ti is formed on the entire surface (S3), and a resist 4 is spin-neat to a predetermined thickness on this electrode film 6 (S4). After that, in step S5), a photomask 5 having a predetermined mask pattern is placed on it, and ultraviolet rays are irradiated for about 2 seconds to perform exposure (
S6) Next, the resist 4 is immersed in a developer for 60 seconds to perform development (S7), and a resist 4 is formed on the second metal film 6.

Roughly, if necessary, this resist 4 is sent to the post (S8).

After completion of Bosthake (S8), a third metal film 7 such as AI or Au is to be entirely formed on the electrode pattern formation surface (S9).
, the resist 4vi is removed and the third metal film 7 is patterned by a lift-off method (510). Thereafter, only the second metal film 6 made of Cr, Ti, etc. is selectively etched by immersing it in an etching solution or the like. As a result, an electrode pattern consisting of the second metal film 6 and the third metal film 7 is formed in which only the portion covered with the third metal film 7 remains (SI + ). In this embodiment, since the first metal film 2 formed on the back surface of the substrate 1 is made of the same material as the second metal film 6, the metal films 2 and 6, which are removed together during the above etching, are removed. The metal film 2 is made of different materials.
may remain. In this way, a bullet injection surface wave device with a predetermined electrode pattern was produced.

In this example as well, before starting the photolithography process,
A second metal film 6 and a first metal film 1 are formed on the front and back surfaces of the substrate 1.
was not formed, it was possible to prevent the generation of static electricity in the pre-hake step (S5) and the post-hake step (S8), and it was possible to obtain the same effects as in the above-mentioned embodiments.

"Effects of the Invention" As explained above, according to the present invention, metal films are formed on the front and back surfaces of the substrate before the photolithography process. can reduce static electricity. This prevents the substrate from being attracted to the photomask (ζ) due to static electricity, preventing damage to the photomask and damage to the substrate.Furthermore, dust floating in the air is prevented from adhering to the substrate due to static electricity. By doing so, it is possible to significantly improve yield.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing one embodiment of the method for forming an electrode pattern according to the present invention, Fig. 2 is a process diagram showing another embodiment of the method for forming an electrode pattern according to the present invention, and Fig. FIG. 3 is a process diagram showing an example of a pattern forming method.

Claims (1)

[Claims] An electrode pattern manufacturing method in which an electrode pattern is formed by photolithography on a substrate made of a pyroelectric single crystal, characterized in that a metal film is formed on both sides of the substrate before the photolithography step. How to form.