JPH07154178A - Manufacture of surface acoustic wave device - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for the surface acoustic wave device in which a fine pattern of comb-like electrodes is formed by an easy process with an excellent reproducibility and a high precision. CONSTITUTION:A photo resist 2a is coated on a piezoelectric substrate 1 and the photo resist 2a is exposed by using a photo mask 3 provided with a light wave phase shift region 12 and a light transmission region 11 and development processing is applied to form a resist pattern to expose part of the piezoelectric substrate 1 to be a predetermined pattern. Then electrodes 4a, 4b are coated to the exposed surface of the piezoelectric substrate 1 and a resist pattern is removed from the piezoelectric substrate 1 to a form an electrode pattern on the piezoelectric substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a surface acoustic wave device such as a surface acoustic wave filter or a surface acoustic wave resonator used in mobile communication, optical transmission systems and the like.

[0002]

2. Description of the Related Art Generally, a surface acoustic wave (SAW) device is more advantageous in miniaturization and weight reduction than a device using a dielectric resonator, and has a reception system timing in an analog or digital communication field or an optical transmission system. Widely used in extraction devices and the like. Particularly in recent years, the importance of high frequency surface acoustic wave devices has been increasing due to higher performance of mobile communication and optical transmission systems, and electrode line widths of 0.5 μm or less are required for realizing GHz band surface acoustic wave devices. The development of submicron process for the manufacture of devices with To date, a phase shift exposure method has been proposed as such sub-micron photolithography (for example, MD Levenson et al.
al., IEEE Trans. Electron. Devices, Vol.ED-29,12 (198
2), P.1828).

In the phase shift exposure method, the light transmitted through the ultraviolet light transmitting region of the photomask (region consisting of only the mask substrate) and the phase shift region (region in which the mask substrate is provided with a film for shifting the phase of light) is used. Although this is a method of improving the pattern accuracy by interference, it is necessary to dispose the phase shift region at an appropriate position with respect to the substrate on which the electrode is formed, and the drawback is that the photomask pattern to which the phase shift exposure method can be applied is restricted. There is.

Since the comb-shaped electrode pattern of the surface acoustic wave device has a constant basic periodicity, it is more suitable for the phase shift exposure method than other devices, but it is the mainstream of high resolution and high sensitivity photoresist. When an attempt is made to form a resist pattern for etching an electrode film using a certain positive photoresist, the light-transmitting portions of the photomask adjacent to each other form one continuous opening pattern in the comb-shaped electrode pattern. Can not be placed in.

Therefore, conventionally, two types of photomasks P1 and P2 as shown in FIGS. 3A and 3B are used, and first,
After exposure with a photomask P1 having an ultraviolet blocking region 21, an ultraviolet transmitting region 22, and a phase shift region 23, alignment and exposure is performed with a photomask P2 having an ultraviolet blocking region 24 and an ultraviolet transmitting region 25, and a predetermined exposure is performed. Resist pattern was formed.

[0006]

However, since two types of photomasks are used in the above conventional resist pattern forming method, not only two photomasks are required, but also the alignment of these two photomasks is required. , Equipment for accurately achieving this alignment is required, and the process becomes very complicated, and especially with surface acoustic wave devices with electrode line widths of sub-micron or less, it is completely impossible to cope with good reproducibility. Moreover, there is a problem that a desired device cannot be manufactured with a high yield.

A method of forming an electrode pattern by etching is possible by using only one type of photomask using a negative photoresist, but the resolution and sensitivity of the negative photoresist used is low, so that it can be used as a device. The highly precise fine patterning required is extremely difficult.

[0008]

It is therefore an object of the present invention to solve the above problems and to provide an epoch-making method of manufacturing a surface acoustic wave device capable of forming a fine pattern of an electrode with high reproducibility and high accuracy in a simple process. The purpose is to provide.

[0009]

In order to achieve the above object, a method of manufacturing a surface acoustic wave device according to the present invention comprises applying a photoresist onto a piezoelectric substrate to form a light wave phase shift region and a light transmission region. A photoresist pattern is exposed using a photomask provided with and a development pattern is formed to expose a part of the piezoelectric substrate to a predetermined pattern to form a resist pattern, and then an electrode film is deposited on the exposed surface of the piezoelectric substrate. After that, the electrode pattern is formed on the piezoelectric substrate by removing the resist pattern from the piezoelectric substrate.

[0010]

Embodiments of the present invention will be described in detail with reference to the drawings. First, a dielectric substrate (hereinafter also simply referred to as a substrate) 1 made of a single crystal of lithium tetraborate, lithium niobate, lithium tantalate, etc., having a thickness of 0.5 to 1.0 mm and having both sides polished, is prepared. Sufficiently perform ultrasonic cleaning with pure water, acetone, etc.

Next, as shown in FIG. 1A, a positive photoresist is applied on the substrate 1 by a spin coating method to form a single-layer photoresist 2 having a thickness of about 0.1 to 1.5 μm.
Deposit a. Then, the substrate 1 is placed on the sample table of the exposure machine, and the ultraviolet light blocking region 10, as shown in FIG.
Through the photomask 3 having the ultraviolet light transmitting region 11 and the phase shift region 12, the ultraviolet light L is irradiated and exposed from above the photoresist 2a. Here, photo mask 3
Is formed by depositing a metal layer 3b made of chrome or the like on a plate body (mask substrate) 3a such as a glass plate, patterning the metal layer 3b, and performing a predetermined phase shift (the phase is inverted by 180 °).
A phase shifter 3c made of a silica-based glass (for example, SOG) layer or the like is formed in the region to be formed.

Next, as shown in FIG. 1B, the substrate 1 is placed on the sample table of the exposure machine with the front and back reversed, and the entire surface of the photoresist 2a is passed from the back side of the substrate 1 through the substrate 1. The ultraviolet light L is irradiated. When the substrate 1 is mounted upside down, a ring-shaped one is used as a spacer so that the entire surface of the substrate 1 does not contact the surface of the sample table. In this way, the photoresist 2a is faithfully exposed to the photomask pattern by the irradiation of the ultraviolet light L from the front surface side of the substrate 1, and the entire surface of the substrate 1 is irradiated with the ultraviolet light L from the rear surface side of the substrate 1 side. To a predetermined thickness.

Next, by dipping the substrate 1 in a developing solution, the photoresist 2a on the substrate 1 is patterned, and the photoresist 2a is developed as shown in FIG. A resist 2b is formed. The lift-off resist pattern at this time is shown in FIG.
As shown in (b), a shaded region 13 (a region having a photoresist) and a region 14 formed in an electrode shape.
(Region without photoresist).

Next, as shown in FIG. 1D, Au (gold), Cr (chrome), Al (aluminum), etc., which will be comb-shaped electrodes, are formed on the overhang-shaped photoresist 2b and the substrate 1. The metal films (electrode films) 4a and 4b are simultaneously deposited by vacuum evaporation to a thickness of about 50 to 10000Å. Then, as shown in FIG. 1 (e), the comb-shaped electrode (by a so-called lift-off method) in which the photoresist 2b is dissolved and removed with acetone or the like, and the metal film 4a formed on the photoresist 2b is peeled off is removed. Electrode pattern) 4b is formed. As a result, the electrode line width of 0.5 μm or less can be easily formed, and in the present embodiment, the electrode line width of about 0.2 to 0.5 μm can be formed.

In this embodiment, the description has been given of the case where the ordinary exposure machine is used for exposing the photoresist.
The present invention can also be applied to exposure by a so-called reduction projection exposure machine using lines, g-lines, etc., and a photomask (reticle) used in this reduction projection exposure machine can also be applied.

[0016]

As described above, according to the method of manufacturing an elastic surface device of the present invention, a high-resolution and high-sensitivity positive photoresist can be used, and adjacent light transmitting regions are independent of each other. Since a photomask pattern that is used can be used, the phase shift region can be arranged at an appropriate position on the photomask, so that a comb-shaped electrode having a fine pattern can be formed with high accuracy and reproducibility.

[Brief description of drawings]

1A to 1E are diagrams showing respective steps of an example according to the present invention.

FIG. 2A is a plan view showing a pattern of a photomask of an example according to the present invention, and FIG. 2B is a plan view showing a pattern of a photoresist of an example according to the present invention.

3A and 3B are diagrams showing a pattern of a pair of photomasks used for patterning a conventional photoresist, respectively.

[Explanation of symbols]

1 ・ ・ ・ Substrate 2a ・ ・ ・ Photoresist 2b ・ ・ ・ Photoresist 3 ・ ・ ・ Photomask 3a ・ ・ ・ Plate 3b ・ ・ ・ Metal film 3c ・ ・ ・ Phase shifter 4a ・ ・ ・ Electrode metal film 4b・ ・ ・ Metal film for electrode 10 ・ ・ ・ UV light blocking area 11 ・ ・ ・ UV light transmitting area 12 ・ ・ ・ Phase shift area 13 ・ ・ ・ Photoresist area 14 ・ ・ ・ No photoresist area 21 ・..UV light blocking region 22 ... UV light transmitting region 23 ... Phase shift region 24 ... UV light blocking region 25 ... UV light transmitting region

Claims (1)

[Claims] 1. A part of a piezoelectric substrate in which a photoresist is deposited on a piezoelectric substrate, and the photoresist is exposed and developed using a photomask provided with a light wave phase shift region and a light transmitting region. Forming a resist pattern that exposes a predetermined pattern, then depositing an electrode film on the exposed surface of the piezoelectric substrate, and then removing the resist pattern from the piezoelectric substrate to form the electrode pattern on the piezoelectric substrate. A method of manufacturing a surface acoustic wave device, comprising: