JPH04235404A - Manufacture method for surface acoustic wave element - Google Patents

Abstract

PURPOSE:To manufacture the surface acoustic wave element having the frequency characteristics with high accuracy with high through put without performing the frequency adjusting process after forming the electrode and without increasing the number of processes. CONSTITUTION:This method is composed of the process that metal thin film is formed on the substrate having piezoelectricity or pyroelectricity, the process that the resist pattern for interdigital electrode is formed on this substrate, the process that the dry etching is performed for the metal thin film exposed by defining this resist pattern as a mask and the process that the resist film remained after the dry etching is peeled off. When the interdigital electrode pattern is formed by the dry etching, the dry etching is controlled by allowing a probe 10 for measuring frequency characteristics to contact with at least one part 9 of the formed interdigital electrode pattern and monitoring the frequency characteristics of the surface acoustic wave element that is being manufactured by the said probe.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a surface acoustic wave device, and more particularly to a method for high-precision machining of an electrode pattern in the manufacturing process of a high frequency device such as a surface acoustic wave device having an electrode pattern on its surface.

0002

[Prior Art] Surface acoustic wave elements are made of quartz, LiNbO3
, IDT (interdigital transducer) on the surface of a piezoelectric or pyroelectric substrate such as LiTaO3.
By providing a comb-shaped electrode called a comb-shaped electrode, surface acoustic waves can be excited and received.
It is applied to resonators, electro-optical elements, etc. (Japanese Patent Publication No. 2-22565, Japanese Patent Publication No. 2-24050, etc.).

The manufacturing process of such a surface acoustic wave device is as follows:
Since the structure has only one layer of electrode patterns, the photolithography process is only required once, but high processing accuracy is required because the accuracy of the electrode pattern directly affects the accuracy of the electrical characteristics of the high-frequency element. . Moreover, in the conventional manufacturing process, the IDT electrode pattern of a thin metal film is formed by etching or lift-off method.
If electrical characteristic accuracy higher than the accuracy of the photolithography process is required, it is necessary to perform a frequency characteristic adjustment process after forming the IDT electrode pattern.

[0004] To explain such a method using the manufacturing of a filter element as an example, when the substrate is crystal and the electrode is a vapor-deposited aluminum film, the line width of the IDT electrode finger is If the film is too thin or too thin, the center frequency will shift to higher
There is a method of adjusting the center frequency to a lower side by dry etching the crystal of the substrate using the IDT electrode pattern as a mask. Similarly, if the IDT electrode is composed of a vapor-deposited aluminum film, Al2O3 is used on the electrode aluminum pattern. A method of adjusting the center frequency to a higher side by growing an oxide film layer of
10909) etc.

[0005]

[Problems to be Solved by the Invention] However, in the conventional manufacturing methods described above, in order to manufacture a surface acoustic wave device with highly accurate frequency characteristics, it is necessary to use either the etching method or the lift-off method for forming electrodes. However, it was necessary to perform a frequency adjustment process after forming the IDT electrode.

By the way, dimensions such as the pitch and line width of the IDT electrode fingers of a surface acoustic wave device are closely related to the frequency range in which it operates, and in recent years there has been a demand for this due to the development of mobile communication systems, satellite broadcasting systems, etc. Rapidly increasing number of 100 MH
The designed line width of electrode fingers in devices having an operating frequency of 3 Hz to several GHz ranges from several microns to submicrons. This is a problem in that pattern resolution by aligner exposure using a deep ultraviolet lamp as a light source has reached its limit, and it has become extremely difficult to control electrode dimensions, that is, frequency characteristics control, by controlling resist pattern dimensions in the photolithography process. was occurring.

It is also known that the frequency characteristics are affected by the film thickness of the IDT electrode metal. For example, in the case of vapor-deposited aluminum electrodes, in the aluminum vapor deposition process,
Although it is required that the aluminum film thickness be uniform between lots and within batches, in reality, the film thickness varies by at least several percent. Therefore, in terms of frequency characteristics, the thicker the film, the lower the frequency, and the thinner the film, the higher the frequency.
There were also problems such as a deviation of about z.

For these reasons, in the manufacture of high-precision surface acoustic wave devices, a frequency adjustment step in single-wafer processing (processing of each sheet) after IDT electrode formation is essential. Therefore, in the conventional manufacturing method, the number of steps is increased, which causes problems in terms of throughput and the like.

The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned problems of the prior art and to achieve high precision without performing a frequency adjustment process after electrode formation. It is an object of the present invention to provide a method for manufacturing a surface acoustic wave device having a frequency characteristic with high throughput without increasing the number of steps.

0010

[Means for Solving the Problems] A method for manufacturing a surface acoustic wave device according to the present invention combines a dry etching device with an electrical property measuring device for actually operating an electrode layer during etching, and the measured values are Etching is stopped when the target characteristics are shown, and ID
Etching the T electrode pattern, providing a wiring pattern that can monitor the electrical characteristics of any chip on the substrate during chip mounting of the element on the substrate to be processed, and connecting to the wiring pattern. In order to enable the above-mentioned processing on any substrate to be processed, the pad for contacting the end point detection probe is provided at a common position, and it is also placed on the outer periphery of the substrate so as not to impair etching uniformity. This method is characterized by the following.

That is, the method for manufacturing a surface acoustic wave device of the present invention includes at least the steps of forming a metal thin film on a piezoelectric or pyroelectric substrate, and forming a resist pattern of comb-shaped electrodes on this substrate. In the method for manufacturing a surface acoustic wave device, the comb-shaped electrode pattern is dry-etched. When forming the comb-shaped electrode pattern, a probe for measuring frequency characteristics is brought into contact with at least a portion of the comb-shaped electrode pattern to be formed, and the dry etching is controlled while monitoring the frequency characteristics of the surface acoustic wave element being manufactured with the probe. This method is characterized by the following.

In this case, it is desirable to carry out the dry etching using a dry etching apparatus having an end point detection function that terminates the etching when the frequency characteristics of the surface acoustic wave element being manufactured reach a target value. Further, it is desirable to provide a probe contact pad section for monitoring frequency characteristics on the substrate, and to arrange wiring patterns so as to electrically connect this pad section to any surface acoustic wave element chip on the substrate. Furthermore, several sets of probe contact pad patterns for frequency characteristic monitoring may be provided on the substrate, and the probe contact pads for frequency characteristic monitoring are placed on the outer periphery of the substrate to be processed, and the dry etching equipment It is desirable to provide it at a predetermined constant position corresponding to the position of the probe for measuring frequency characteristics.

[0013]

[Function] Compared to conventional methods, the method of the present invention performs the etching process and the frequency adjustment process in one step, which simplifies the process, improves throughput, improves yield, and improves the accuracy of frequency characteristics. Excellent in this respect.

Furthermore, according to the method of the present invention, the versatility of the dry etching apparatus for the substrate to be processed is expanded, and the probe can be brought into contact with the substrate while maintaining uniformity of the plasma that contributes to the etching of the upper part of the substrate to be processed in the etching chamber. It also becomes possible to monitor any chip on the substrate to be processed.

[0015]

Embodiments Hereinafter, embodiments of the method for manufacturing a surface acoustic wave device of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram for explaining the manufacturing process of a surface acoustic wave device according to the present invention, and shows a case where a negative type resist is used in the photolithography process. In the figure, 1 is a substrate made of piezoelectric or pyroelectric material such as crystal, LiNbO3, LiTaO3, etc., 2 is an electrode metal thin film such as aluminum, 3 is a resist layer, 4 is a photomask,
5 is an ultraviolet ray, 6 is a resist pattern, 7 is a reactive ion, 8 is a comb-shaped electrode, 9 is a pad for connecting a probe, and 10 is a needle-like probe.

First, as shown in FIG. 1(a), an electrode metal thin film 2 is formed on an optically polished substrate 1 by a method such as vapor deposition. The thickness of the metal thin film 2 is approximately one tenth of the width of the electrode finger. Then, as shown in figure (b),
A negative resist is uniformly applied onto the metal thin film 2 by a conventional method such as spin coating, and then heated and dried to form a resist layer 3 having a thickness of approximately 0.1 to 2.0 μm. As shown in Figure (c), a photomask 4 is placed on top of the resist layer 3, and ultraviolet rays 5 are irradiated to expose the resist layer 3.
After developing and rinsing the exposed resist layer 3 with a predetermined developer, a resist pattern 6 as shown in FIG. 3(d) is formed. Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as resist scraps and whiskers remaining on the edges of the resist pattern 6, and then
The substrate is placed on an electrode of a plasma etching apparatus, and the metal thin film 2 exposed through the opening of the resist pattern 6 is dry-etched using reactive ions 7, as shown in FIG. 4(e). At this time, a probe 10 of a frequency characteristic measuring device installed in the vacuum chamber of the etching device is inserted through the resist pattern 6 into a position corresponding to the pad portion 9 and connected to the frequency characteristic of the surface acoustic wave element during etching. is measured. When it is determined that the characteristics of the element have reached a predetermined value, the etching is stopped and the resist pattern 6 is removed by ashing or the like.
A substrate on which electrodes are formed as shown in f) is completed. Next, the substrate is cut into chips and mounted, thereby completing the surface acoustic wave device.

Now, FIG. 2 is a schematic diagram showing the configuration of an example of a dry etching apparatus used to carry out the manufacturing method of the present invention. This apparatus uses a parallel plate type plasma etching apparatus which is often used for dry etching of aluminum films. A parallel plate counter electrode 12 is provided in the vacuum chamber 11, and a substrate to be processed (wafer) 13 is placed on one of the electrodes using an orientation flat (rotational positioning surface) to rotate and shift the substrate to the center of the electrode. Fix it accurately so that there is no damage. A reactive gas such as CCl4 is introduced into the chamber 11 from the inlet 14, and by adjusting the amount of exhaust from the exhaust port 15, the inside of the chamber 11 is maintained at a predetermined pressure. The probe 10 for monitoring the operation of the element during the etching process is connected to the substrate 13.
After being introduced, it is brought into contact with a pad portion 9 (FIG. 1) provided at a predetermined location on the substrate 13 in the chamber. RF power is supplied from the RF power generator 16 to the counter electrode, and a measurement device 17 that operates an arbitrary chip on the substrate 13 through the probe 10 and measures the frequency characteristics determines the frequency characteristics, which are the most important in surface acoustic wave elements. The end point is determined to be the point in time when the etching amount that makes the optimum value is obtained, and a power stop signal is sent to the RF power generator 7, and based on this, the etching operation is stopped.

FIG. 3 shows a chip 21 on a substrate 13 to be processed having a diameter of 3 inches, a pad portion 22 for probe contact, and
It is a diagram showing an example of the imposition of the wiring pattern 23 on the chip to be measured, and the position, shape, and number of the pad portion 22 are paired with the probe 10, and the arrangement of the chip imposition may vary depending on the different chip sizes. Even if the mask changes, the pad portion 22 portion is provided at the same position from when designing the mask so that it is common regardless of the wafer. In the case of FIG. 3, only two pad patterns are provided, but more than two pad patterns may be provided, for example, several sets. Further, the pad portion is preferably provided around the substrate, and preferably at a predetermined constant position corresponding to the position of the probe of the dry etching device.

Next, the quartz substrate with the aluminum vapor deposited film on which the resist pattern was formed using the photomask arranged as described above was placed in the dry etching apparatus shown in FIG. 2, and the aluminum film was etched. Explain the situation. On the substrate 13 to be processed shown in FIG. 3, by the photolithography process shown in FIG.
An IDT electrode shape resist pattern is formed (FIG. 1(d)). By using this pattern as a mask for the aluminum film during etching, an aluminum film IDT electrode is formed. At this time, the resist pattern is formed so that its circumference is approximately 5 to 20% thicker than the design dimension of the IDT electrode to be formed. This is because the etching margin and the size reduction due to dry etching were taken into consideration. Figure 4
shows the relationship between etching time and device operating frequency.
In this figure, from t0 to t after the start of dry etching
Up to point 1, the Al pattern is in a short-circuit state due to incomplete etching and does not function as a device, but
As the etching progresses, the electrode patterns become independent at time t1, escape from the short-circuit state, and begin to operate. However, if the IDT electrode finger size is thick, the operating frequency becomes low, so at t1 the operating frequency is f1
It is. Here, if the etching is further progressed, an undercut state will occur, the electrode finger size will gradually become thinner, and the frequency measured by the measuring device 17 via the probe 10 will also increase accordingly. When the frequency reaches the target f0, a power stop signal is sent to the RF power generator 7, and based on this, the etching operation is stopped.

Although the method for manufacturing a surface acoustic wave device according to the present invention has been described above with reference to embodiments, the present invention is not limited to these embodiments and can be modified in various ways. For example, the dry etching apparatus is not limited to the reactive ion etching apparatus shown in FIG. 2, and various known apparatuses can be used.

[0022]

[Effects of the Invention] As explained above, according to the method for manufacturing a surface acoustic wave device of the present invention, the etching process and the frequency adjustment process can be performed in one step compared to the conventional method, which simplifies the process and increases throughput. It is superior in terms of improved performance, improved yield, and higher accuracy of frequency characteristics.

Furthermore, according to the method of the present invention, the versatility of the dry etching apparatus to the substrate to be processed is expanded, and the probe can be brought into contact with the substrate while maintaining uniformity of the plasma that contributes to the etching of the upper part of the substrate to be processed in the etching chamber. It also becomes possible to monitor any chip on the substrate to be processed.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the manufacturing process of a surface acoustic wave device based on the present invention.

FIG. 2 is a schematic diagram showing the configuration of an example of a dry etching apparatus used to carry out the manufacturing method of the present invention.

FIG. 3 is a diagram showing an example of a chip on a substrate to be processed, a pad portion for contacting a probe, and an example of imposition of a wiring pattern on a chip to be measured.

FIG. 4 is a diagram showing the relationship between etching time and element operating frequency when dry etching is performed according to the present invention.

[Explanation of symbols]

1...Substrate 2...Electrode metal thin film 3...Resist layer 4...Photomask 5...Ultraviolet light 6...Resist pattern 7...Reactive ion 8...Comb-shaped electrode 9...Probe connection pad part 10...Probe 11...Vacuum chamber 12...Counter electrode 13...Substrate to be processed (wafer) 14...Reaction gas inlet 15...Exhaust port 16...RF power generator 17...Frequency characteristic measurement device

Claims (5)

[Claims] Claim 1: At least a step of forming a metal thin film on a substrate having piezoelectricity or pyroelectricity, a step of forming a resist pattern of a comb-shaped electrode on this substrate, and a step of exposing the resist pattern using the resist pattern as a mask. In a method for manufacturing a surface acoustic wave device that includes a step of dry etching a metal thin film and a step of peeling off a resist film remaining after dry etching, when forming a comb-shaped electrode pattern by dry etching, the comb-shaped electrode pattern formed 1. A method of manufacturing a surface acoustic wave device, comprising: contacting at least a portion of the surface acoustic wave device with a probe for measuring frequency characteristics, and controlling dry etching while monitoring the frequency characteristics of the surface acoustic wave device being manufactured with the probe. 2. The dry etching according to claim 1, wherein the dry etching is carried out using a dry etching apparatus equipped with an end point detection function that terminates the etching when the frequency characteristics of the surface acoustic wave element being manufactured reach a target value. A method for manufacturing a surface acoustic wave device. 3. A probe contact pad portion for monitoring frequency characteristics is provided on the substrate, and a wiring pattern is arranged to electrically connect this pad portion to an arbitrary surface acoustic wave element chip on the substrate. The method for manufacturing a surface acoustic wave device according to claim 1 or 2, characterized in that: 4. The method of manufacturing a surface acoustic wave device according to claim 3, wherein several sets of probe contact pad patterns for monitoring frequency characteristics are provided on the substrate. 5. A pad portion for contacting a probe for monitoring frequency characteristics is provided at a predetermined constant position on the outer periphery of the substrate to be processed, corresponding to the position of the probe for measuring the frequency characteristics of the dry etching apparatus. Claim 1
4. The method for manufacturing a surface acoustic wave device according to any one of 4.