JPH0878988A - Manufacture of surface acoustic wave device - Google Patents

Abstract

PURPOSE: To linearly cut a pattern edge part and to form an electrode pattern in which the film thickness is uniform by making a process forming a metallic film the process in which a substrate surface is set at the location where metallic particles are vertically entered and a film formation is performed. CONSTITUTION: On a lithium niobate piezoelectric substrate 1, a negative type photoresist 2 is applied and the formation of a pattern is performed by an exposure development. Next, an Al film 3a is formed on the substrate 1 and a pattern 2 by using an ion beam sputter. Next, the resist 2 and the Al film 3a are lifted off with resist exfoliation liquid and an Al electrode 3 is formed. The edge part of this electrode 3 is not notched, this chip is mounted on a package and a surface acoustic wave device is obtained. When the Al film is formed, the ion beam comining from an ion gun 5 hits a target 4, Al metallic particles springs out from the target, the particles adhere to the substrate 1 and the Al film 3 is formed. At this time, a substrate surface is set so that the Al particles may be vertically entered the substrate 1 by inclining the substrate 1 by an angle θ from the surface parallel to the target 4.

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 used in a mobile phone or the like.

[0002]

2. Description of the Related Art In recent years, many surface acoustic wave devices have been used as elements such as filters, delay lines, and oscillators of electronic equipment utilizing radio waves. In particular, surface acoustic wave filter devices that are small and lightweight and have high sharp cutoff performance as filters have become widely used as filters for RF and IF stages of mobile terminal devices in the field of mobile communications. Along with the increase in the frequency band of use, the miniaturization of the metal electrodes forming the surface acoustic wave device is remarkable. Therefore, minute unevenness at the end of the electrode pattern, which has not been a problem in the past, causes an electrode short circuit defect,
A slight variation in electrode width may affect the characteristics. Therefore, more advanced pattern forming technology is required.

A conventional method of manufacturing a surface acoustic wave device will be described with reference to the drawings. The electrode pattern is formed by the following steps shown in FIG. First, the photoresist 2 is applied on the piezoelectric substrate 1 (FIG. 5A). Next, a pattern is formed by exposure and development (FIG. 5 (b)). A metal film 3a of Al or the like is formed on the substrate and the photoresist pattern (FIG. 5C). The metal film is formed by injecting and adhering metal particles to the substrate by ion beam sputtering or the like. A model diagram of the film forming apparatus is shown in FIG. The ion beam generated by the ion gun 5 hits the target 4, metal particles fly out from the target 4 and adhere to the substrate 1 placed on a surface parallel to the target surface to form a metal film 3a. Conventionally, the substrate may be rotated during film formation in order to achieve uniformity. Next, the photoresist and the metal film on the resist are lifted off with a resist stripping solution to form the metal electrode 3 (FIG. 5D). The chip thus produced is mounted in a package to obtain a surface acoustic wave device.

[0004]

However, the above-mentioned FIG.
At the time of forming the metal film shown in (c), the metal film adheres to the side surface of the resist. In addition, there is a portion behind the resist where a predetermined film thickness cannot be formed. FIG. 7 shows how the metal film adheres to the side surface of the resist. As a result, when lift-off is performed with the stripping solution, as shown in FIG. 5D, the metal film on the side surface of the resist is not cut cleanly and the pattern end is notched, or an electrode pattern with a film thickness gradient is formed. Or the line width varies depending on the thickness gradient.
For these reasons, there have been problems such as occurrence of electrode short circuit defects and large variations in surface acoustic wave device characteristics.

The present invention has been made to address such a problem, and in order to stabilize the characteristics of a surface acoustic wave device in which the miniaturization of metal electrodes is progressing, the pattern end is linearly cut. It is an object of the present invention to provide a method of manufacturing a surface acoustic wave device capable of forming an electrode pattern having a uniform film thickness.

[0006]

A first method of manufacturing a surface acoustic wave device according to the present invention comprises a step of forming a photoresist pattern on a piezoelectric substrate and a step of forming a metal film on the substrate and the resist. And a step of forming a pattern of this metal film by lift-off, in the method of manufacturing a surface acoustic wave device, the step of forming a film is a step of forming a film by setting a substrate surface at a position where metal particles are vertically incident. It is characterized by being.

A second method of manufacturing a surface acoustic wave device according to the present invention comprises a step of forming a photoresist pattern on a piezoelectric substrate, a step of forming a metal film on the substrate and the resist, and a step of forming the metal film. In the method of manufacturing a surface acoustic wave device, which comprises a step of forming a pattern by lift-off, the step of forming a film includes forming a substrate surface at a position where an incident direction of metal particles and a surface acoustic wave propagation direction of a piezoelectric substrate are perpendicular to each other. It is a process of setting and forming a film.

In the present invention, the substrate surface is set at a position where the metal particles are vertically incident, or the substrate surface is set at a position where the incident direction of the metal particles and the surface acoustic wave propagation direction of the piezoelectric substrate are perpendicular to each other. Is a device in which metal particles struck from the target jump out in a certain direction, for example,
Using an ion beam sputtering device, a collimation sputtering device, or the like, the angle in the fixed direction is examined by several trial film formation experiments, and the substrate surface is set according to the angle. Specifically, it is performed by fixing the angle of the substrate surface set according to the incident direction of the metal particles.

The photoresist according to the present invention is preferably a negative photoresist. By using a negative photoresist, the resist cross-sectional shape after patterning becomes an inverted trapezoid, the pattern end is cut more linearly, and an electrode pattern with a uniform film thickness can be formed.

[0010]

[Function] When the angle of the substrate is set so that the metal particles are vertically incident on the substrate during the film formation, the metal film does not wrap around the side surface of the photoresist, so that the resist stripping solution easily penetrates at the time of lift-off, and the stripping property is good. . In addition, the metal film pattern after lift-off is also clean without any jagged edges because the film is cut off by the resist during film formation. Further, since there is no portion that is behind the resist and is thinly formed, a predetermined film thickness is formed uniformly and there is little variation in characteristics.

When the angle of the substrate is set at a position where the incident direction of the metal particles and the surface acoustic wave propagation direction of the piezoelectric substrate are perpendicular to each other, in addition to the above-mentioned effect, the surface acoustic wave propagation direction with a narrow interval is obtained. It is possible to further suppress the occurrence of short-circuit defects and variations in characteristics.

[0012]

Embodiments Embodiments will be described below with reference to the drawings. Example 1 FIG. 1 is a diagram showing a manufacturing process of a surface acoustic wave device according to Example 1. First, as shown in FIG. 1A, a negative photoresist 2 is applied on a piezoelectric substrate 1 made of lithium niobate, and a pattern is formed by exposure and development as shown in FIG. Note that lithium tantalate or the like can be used as the piezoelectric substrate 1. Next, as shown in FIG. 1C, an Al film 3 is formed on the substrate 1 and the photoresist pattern 2a by ion beam sputtering.
Form a. Next, the photoresist 2 and the Al film on the resist were lifted off with a resist stripper,
The Al electrode 3 as shown in (d) is formed. Got
The schematic pattern of the Al electrode is shown in FIG. 2A is a plan view and FIG. 2B is a sectional view taken along the line AA '. The Al electrode 3 is formed without jagged edges. The chip thus obtained is mounted on a package to obtain a surface acoustic wave device.

The formation of the Al film will be described with reference to FIG. FIG.
FIG. 3 is a model diagram of a film forming apparatus. In the Al film formation, the ion beam emitted from the ion gun 5 hits the target 4 as shown in FIG. 3, Al metal particles fly out from the target 4, and these particles adhere to the substrate 1 to form an Al film.
At this time, by tilting the substrate 1 by an angle θ from a plane parallel to the target 4, Al particles are vertically incident on the substrate 1.

Therefore, in the method of Example 1, since the Al film does not wrap around the side surface of the photoresist, the resist stripping solution easily penetrates during lift-off and the stripping property is good.
Further, the Al film pattern after lift-off is also clean because the film 3 is cut off by the resist 2 at the time of film formation, and there are no jagged edges. Further, since there is no portion that is behind the resist 2 and is thinly formed, a predetermined film thickness is uniformly formed. Further, the surface acoustic wave device obtained in this example has no short circuit between patterns and has little variation in characteristics.

Example 2 Prior to the formation of the Al film, the piezoelectric substrate 1 was manufactured in the same manner as in Example 1.
A photoresist pattern is formed on top. The Al film is formed in the substrate pattern direction (surface acoustic wave propagation direction)
l This was performed by changing the direction in which the particles are incident on the substrate. The result is shown in FIG. FIG. 4 (a) is a plan view of the pattern, and FIGS. 4 (b), (c), and (d) show the adhered state of the Al film, respectively.

First, an Al film was formed while rotating the substrate. In this case, Al particles fly randomly as shown in FIG.
l Membrane wraps around. Therefore, jagged edges of the electrode pattern occur everywhere, and short-circuit defects and characteristic variations are likely to occur.

Secondly, the Al film was formed by fixing the substrate so that the incident direction of the metal particles was the same as the propagation direction of the surface acoustic wave. In this case, as shown in FIG. 4C, the Al film wraps around only the side surface of the resist in a certain direction. However, the space is small in this direction, and a short circuit defect is likely to occur. Then, jagged edges occur in the longitudinal direction of the pattern, and variations in line width greatly affect the characteristics.

Thirdly, the direction in which the incident direction of the metal particles is perpendicular to the propagation direction of the surface acoustic wave, that is, the state in which the substrate is rotated 90 degrees from that in the second case, is fixed and the Al is fixed.
A film was formed. In this case, as shown in FIG. 4D, the Al film wraps around only the side surface of the resist in a certain direction. In this direction, the edge of the pattern is small, and the area in which jaggedness occurs is small. Further, the influence of the line width variation on the characteristic is small because it is not in the propagation direction of the surface acoustic wave (AA 'cross section).

Therefore, in this embodiment, the Al film is formed by the third method. Next, in the same manner as in Example 1, the photoresist 2 and the Al film on the resist are lifted off with a resist stripping solution to form an Al electrode 3. The chip thus obtained is mounted on a package to obtain a surface acoustic wave device.

The method of Example 2 was performed on the side surface of the photoresist.
Since the Al film does not wrap around, the resist stripper easily penetrates during lift-off and the strippability is good. Further, the Al film pattern after lift-off is also clean because the film 3 is cut off by the resist 2 at the time of film formation, and there is no jagged edge. Further, since there is no portion that is behind the resist 2 and is thinly formed, a predetermined film thickness is uniformly formed. Further, the surface acoustic wave device obtained in this example has no short circuit between patterns and has little variation in characteristics. In Examples 1 and 2, if a negative photoresist is used, the resist cross-sectional shape after patterning becomes an inverted trapezoid, and the effect of the present invention becomes greater.

The film forming method is not limited to the ion beam sputtering, and the same effect can be obtained as long as directional metal particles are incident on the substrate.

[0022]

According to the first method of manufacturing a surface acoustic wave device of the present invention, since the substrate surface is set at a position where the metal particles are vertically incident, the metal film does not wrap around the side surface of the photoresist and lift-off is performed. In this case, the resist stripping solution is improved.
Further, the metal film pattern after lift-off is also formed neatly without jagged edges. Furthermore, since there is no portion that is behind the resist and is thinly formed, a predetermined thickness is uniformly formed, and variations in characteristics are reduced. As a result, it is possible to obtain a surface acoustic wave device that has few short-circuit defects and stable characteristics.

In the first method of manufacturing a surface acoustic wave device according to the present invention, the substrate surface is set at a position where the incident direction of the metal particles and the surface acoustic wave propagation direction of the piezoelectric substrate are perpendicular to each other. Therefore, in addition to the effects described above, it is possible to further suppress the occurrence of short-circuit defects and the variation in characteristics in the surface acoustic wave propagation direction with a narrow interval.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a surface acoustic wave device according to a first embodiment.

FIG. 2 is a diagram showing a schematic pattern of an Al electrode.

FIG. 3 is a model diagram showing a film forming apparatus.

FIG. 4 is a diagram showing the results of film formation performed by changing the pattern direction of the substrate and the incident direction of Al particles.

FIG. 5 is a diagram showing a manufacturing process of a conventional surface acoustic wave device.

FIG. 6 is a model diagram showing a conventional film forming apparatus.

FIG. 7 is a diagram showing how a metal film adheres to the side surface of a resist.

[Explanation of symbols]

1 ... Piezoelectric substrate, 2 ... Photoresist, 3 ...
… Metal electrodes, 4… Target, 5 ……… Ion gun.

Claims (2)

[Claims] 1. An elastic surface comprising a step of forming a photoresist pattern on a piezoelectric substrate, a step of forming a metal film on the substrate and the resist, and a step of patterning the metal film by lift-off. In the method of manufacturing a surface acoustic wave device, the step of forming a film is a step of forming a film by setting a substrate surface at a position where metal particles are vertically incident. 2. An elastic surface having a step of forming a photoresist pattern on a piezoelectric substrate, a step of forming a metal film on the substrate and the resist, and a step of patterning the metal film by lift-off. In the method for manufacturing a wave device, the step of forming a film is a step of forming a film by setting the substrate surface at a position where the incident direction of the metal particles and the surface acoustic wave propagation direction of the piezoelectric substrate are perpendicular to each other. A method for manufacturing a surface acoustic wave device, comprising: