JP2003017983A - Wafer for elastic wave and elastic wave device employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer for elastic waves that manufactures elastic wave devices with excellent yield by preventing the wafer from being cracked to the utmost in processes until exciting electrodes are formed even in the case of an LT(Lithium Tantalate) wafer of 0.3 mm or less in thickness and providing a stable exposure condition and to provide the elastic wave device employing the wafer. SOLUTION: This invention provides the wafer for elastic wave devices to form the exciting electrode for stimulating an elastic wave on one major side of the wafer comprising lithium tantalate single crystal and the wafer is characterized in that the arithmetic mean roughness (Ra) of the other major side of the wafer is less than 0.6 micron and a bent of the other major side is 10 μm-40 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an elastic wave device wafer which can be suitably used for an elastic wave device such as filtering an electric signal or generating a reference signal, and an elastic wave device using the same.

[0002]

BACKGROUND OF THE INVENTION Conventionally, a surface acoustic wave filter as a typical acoustic wave device is provided with at least one excitation electrode composed of a pair of comb-shaped electrodes intersecting each other on the surface of a piezoelectric substrate, and the shape of the excitation electrode. Since a desired filter characteristic or resonance characteristic can be obtained by changing the value of, it is widely applied to electronic devices. In addition, the demand for surface acoustic wave devices has greatly increased due to the expansion of the market of communication devices and information devices typified by mobile phones in recent years. Particularly, as a piezoelectric substrate for a surface acoustic wave device, a lithium tantalate single crystal (hereinafter referred to as LT) wafer having excellent electromechanical coupling coefficient and temperature characteristics is widely used.

In the production of this type of surface acoustic wave device,
The process of forming electrodes on the wafer will be described. First, on the mirror surface of the LT wafer with one surface mirror-finished,
Aluminum serving as an excitation electrode is formed by vapor deposition, and a photoresist is spin coated thereon.

Next, a reduction projection exposure machine (commonly called a stepper)
Is used to expose the photoresist, and the developer is developed to pattern the photoresist. Further, the electrode is patterned by RIE (reactive ion etching), and the photoresist on the electrode is peeled off to form an aluminum electrode on the wafer.

Incidentally, with the expansion of the market of electronic equipment, electronic parts constituting the electronic equipment are also required to be downsized, low in height and low in cost, and an acoustic wave device represented by a surface acoustic wave device is required. Similarly, there is a demand for downsizing, height reduction, and cost reduction. For this reason, it is necessary to thin the wafer used for the device, and it is becoming indispensable to improve the yield of the device and improve the productivity.

In the process of forming the electrodes described above, cracks often occur on the wafer. Cracks are liable to occur during the work of adsorbing and fixing the wafer to the manufacturing apparatus during spin coating, exposure, and development using a developer, and in particular, the extremely thin LT with a thickness of 0.3 μm or less.
The present inventors have found that cracks are extremely likely to occur in a wafer.

As described above, all the LT wafers having cracks must be discarded from the viewpoint of the reliability of the surface acoustic wave device. Therefore, the LT wafer cracks greatly reduce the yield of the surface acoustic wave device, which is a problem. is there.

Even when the wafer is not cracked, when the wafer is adsorbed at the time of exposure and the flatness on the mirror surface side for producing the element is poor (the warpage is large), the exposure is performed using a stepper. Usually, it is divided into 5 to 10 mm square sites and sequentially exposed to expose the entire surface, but it is necessary to correct the focal length and angle for each shot, which takes a very long time. If the exposure is performed without correcting the focal length and the angle for each shot, the exposure condition is not stable, a short circuit failure occurs, the yield of the device is reduced, and the manufacturing cost of the acoustic wave device is increased.

Therefore, according to the present invention, even in an LT wafer having a thickness of 0.3 mm or less, cracking of the wafer is prevented as much as possible in the process up to the formation of the excitation electrode, and stable exposure conditions are provided, so that the yield elasticity is improved. An object of the present invention is to provide an elastic wave device wafer for producing a wave device and an elastic wave device using the same.

[0010]

In order to achieve the above object, the elastic wave device wafer of the present invention has an excitation electrode for generating an elastic wave formed on one main surface of a wafer made of a lithium tantalate single crystal. A wafer for an acoustic wave device, wherein the arithmetic mean roughness (Ra) of the other main surface of the wafer is less than 0.6 μm, and the warp amount of the other main surface is 10 μm to 40 μm (10 μm or more and 40 μm or more. Less than)).

In particular, the wafer has a thickness of 0.3 mm.
In addition to the following, one main surface of the wafer is concave and the other main surface is convex. The flatness (TTV) of the wafer is less than 5 μm.

In the elastic wave device of the present invention, an excitation electrode for generating an elastic wave is formed on the wafer or on one main surface of a substrate obtained by cutting the wafer into a predetermined shape.

Here, the warp amount is, for example, a technical standard QIAJ-B-0 established by the Japan Crystal Device Industry Association.
07 (established February 10, 2000) is the Sori measured by the method, showing the undulation of the wafer in an unclamped state, and using the plane in contact with the back surface of the wafer as the reference plane, The maximum value.
Further, the flatness TTV is the same as the technical standard QIAJ-B.
-007 (established February 10, 2000)
TV (Total Thickness Variation), which is the difference between the maximum height and the minimum height when the wafer is clamped and the back surface of the wafer is the reference plane.

The present inventors have found that the thickness L is 0.3 mm or less.
The cracking of the T-wafer occurs when the one main surface side of the wafer is adsorbed to the manufacturing apparatus in the process of manufacturing the surface acoustic wave device, and the shape of the wafer and the arithmetic average roughness of the rough surface side where the excitation electrode is not formed. By finding that there is a relationship with (Ra), it has been found that the above-mentioned configuration eliminates any cracks in the wafer.

Specifically, the mirror surface (R
a is less than 1 nm) is concave and the rough surface (non-mirror surface) side where the excitation electrode is not formed is convex, and the warp on the rough surface side is 1
By setting the thickness to 0 μm to 40 μm, the occurrence of cracks is drastically reduced or eliminated.

In particular, when the wafer thickness is 0.3 mm or less, cracks are likely to occur, but Ra of the rough surface is 0.6 μm.
By setting it to be less than, the occurrence of cracks can be minimized. Furthermore, thickness unevenness (flatness (TTV)) is 5μ
When a wafer having a size of less than m is adsorbed on the wafer, the flatness on the mirror surface side for producing the device becomes less than 5 μm, and it is not necessary to correct the focal length and angle for each shot by the stepper.

By using a wafer having a flatness of less than 5 μm, the exposure time is shortened, and the exposure accuracy is improved without correcting the focal length and angle for each shot, so that a short-circuit defect does not occur and the surface acoustic wave device. Significantly improves the yield of.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Below, the thickness is from 0.25 mm to
The 0.3 mm single crystal wafer according to the present invention and its manufacturing process will be described in detail.

A single crystal wafer made of a lithium tantalate single crystal is usually subjected to cylindrical grinding by poling a crystal ingot grown by the Czochralski method and having a wafer thickness of 0.4 mm to 0.5 mm in a predetermined orientation. To cut. In order to obtain a crystal orientation having excellent characteristics as a surface acoustic wave filter, the 33 ° -45 ° rotated Y-cut surface is cut so as to be the main surface.

Then, the thickness is 0.3 m by lapping.
By setting m to 0.35 mm, unevenness of the wafer surface due to cutting is removed, and unevenness of the wafer thickness (flatness (TT
V)) is eliminated. The thickness unevenness at this time is set to be less than 5 μm because the mirror surface (Ra having a thickness of 1 nm or less) forming the excitation electrode in the subsequent step has a concave shape and the rough surface (non-mirror surface) side has a convex shape.

After that, one surface is mirror-polished using colloidal silica, cerium or the like, and the wafer thickness is 0.26 m.
m to 0.31 mm. A wafer whose one surface is mirror-finished has a large warp due to the Twyman effect. This wafer is etched by immersing it in acid. By controlling the etching time and the temperature of the acid that is the etching solution, the mirror surface 1a side of the wafer 1 is concave and the rough surface 1b side is convex, as shown in FIG. The warp amount is set to 10 μm to 40 μm.

Since the mirror surface is concave and the rough surface is convex by etching, and the warp of the rough surface is 10 μm to 40 μm, the mirror surface is mirror-polished again because the mirror surface is corroded by acid. Is 0.25 mm to 0.3 mm.
Since the strain on the re-polished wafer is removed by etching, an excellent wafer having no warp or shape change before and after re-polishing can be obtained.

Then, as shown in FIG.
Alternatively, one or more excitation electrodes formed of, for example, a pair of comb-teeth electrodes that generate elastic waves are formed on one main surface of the substrate 11 obtained by cutting the wafer 1 into a predetermined shape along the cutting lines L1 and L2. It is possible to obtain an acoustic wave device such as a surface acoustic wave filter or a vibrator.

Thus, in the wafer for acoustic wave device of the present invention, the arithmetic mean roughness (Ra) of the main surface of the wafer on which the excitation electrodes are not formed is less than 0.6 μm, and the amount of warpage is 10 μm to 40 μm. As a result, even if the thickness of the wafer is 0.3 mm or less, cracking of the wafer does not occur in the manufacturing process of the excitation electrode.

An elastic wave device having improved productivity and reliability is formed by forming an exciting electrode for generating an elastic wave on one of the main surfaces of such a wafer and a substrate obtained by cutting the wafer into a predetermined shape. Can be obtained.

[0026]

Example (Example 1) A diameter of φ10 mm crystal ingot grown by the Czochralski method was poled to obtain a diameter of φ10.
Cylindrical grinding was performed to 0 mm, and the wafer was cut in the Y direction of 38 ° rotation so that the thickness of the wafer was 0.5 mm. GC # 80
Lapping is performed at 0 to 1000, and the thickness is 0.4 mm.
After that, one surface was mirror-polished with colloidal silica to a thickness of 0.31 mm.

These wafers were treated with nitric acid at 40 ° C .: hydrofluoric acid =
After soaking in a 1: 3 mixture for 10 to 30 minutes, the mirror side is mirror-polished with colloidal silica again, and the diameter is φ100 mm.
A wafer having a thickness of 0.3 mm was produced.

The process for producing electrodes on the produced wafer was put into the process, and the wafer was tested for cracks.

[0029]

[Table 1]

Table 1 shows the relationship between the amount of warp of the rough surface and the relationship between Ra and the crack of the wafer in a wafer having a thickness of 0.3 mm and a concave surface on the mirror surface side and a convex surface on the rough surface side. Here, the amount of warpage was obtained by measuring the interference fringes on the rough surface side with an optical interference type flatness measuring device.

When the mirror surface side is concave and the rough surface is convex, the occurrence of cracks has a great relationship with the amount of warp on the rough surface side. As is clear from Table 1, the amount of warp on the rough surface side is 10 μm to 40 μm.
It was found that when Ra on the rough surface side was less than 0.6 μm, no cracks occurred.

Regarding wafers having a convex surface on the mirror surface side and a concave surface on the rough surface side, most of the wafers were cracked during the process introduction regardless of the amount of warp on the rough surface side and Ra on the rough surface side.

Further, the diameter is 125 to 1 by the same method.
As a result of making a 50 mm wafer and examining the wafer shape, the amount of warpage, Ra on the rough surface side and cracks, the same results as in this example were obtained. (Example 2) The same test as in Example 1 was performed on a wafer having a wafer thickness of 0.25 mm.

In the same manner as in Example 1, a diameter φ110 mm crystal ingot grown by the Czochralski method was poled, cylindrically ground to a diameter φ100 mm, and cut in the Y direction of 38 ° rotation. At this time, cutting was performed so that the thickness of the wafer was 0.4 mm. After lapping with GC # 800-1000 to a thickness of 0.3 mm, one side was mirror-polished with colloidal silica to a thickness of 0.26 mm.

These wafers were treated with nitric acid at 40 ° C .: hydrofluoric acid =
After dipping in a solution of 1: 3 for 10 to 30 minutes, the mirror surface side was mirror-polished again with colloidal silica to prepare a wafer having a diameter of 100 mm and a thickness of 0.25 mm.

[0036]

[Table 2]

Table 2 shows the results of testing the wafer for cracks by introducing it into the process for manufacturing the excitation electrode on the manufactured wafer. The occurrence of cracks in a wafer having a thickness of 0.25 mm has a great relationship when the mirror surface side is concave and the rough surface side is convex, as in the case of the 0.3 mm wafer, and the warp amount on the rough surface side is 1
It was found that no cracks occur at 0 μm to 40 μm and when Ra is less than 0.5 μm.

As to the wafer having a convex surface on the mirror surface side and a concave surface on the rough surface side, similar to the 0.3 mm wafer, most of the wafers are irrespective of the amount of warp on the rough surface side and Ra on the rough surface side in the process introduction. A crack occurred.

Example 3 First, a φ100 mm wafer having a TTV of 1 μm to 7 μm was prepared. Here, the TTV was measured by an optical interference type flatness measuring device with the rough surface side clamped.

Next, the entire surface of the wafer was exposed in a 20 mm square shot area using a stepper without correcting the focal length and angle for each shot.

Then, an excitation electrode was prepared so as to be a surface acoustic wave element having a center frequency of 1.9 GHz, and the relationship between short circuit failure and TTV was investigated. The results are shown in Table 3.

[0042]

[Table 3]

As is clear from Table 3, TTV is 5 μm.
It was found that the occurrence of short circuit defects greatly changed at the boundary. That is, when TTV was less than 5 μm, there were no short-circuit defects.

[0044]

The elastic wave device wafer of the present invention is a wafer for an elastic wave device for forming an excitation electrode for generating an elastic wave on one main surface of a wafer made of a lithium tantalate single crystal. On the other hand, the arithmetic mean roughness (R
a) is less than 0.6 μm, and the warp amount of the main surface is 10 μm to
It was 40 μm. As a result, it is possible to provide an excellent acoustic wave device which not only improves the productivity and reliability of the produced acoustic wave device but also has a low profile and a small size.

The flatness (TTV) of the wafer is 5 μm.
If it is less than, the exposure time at the time of manufacturing the acoustic wave device is shortened, and the exposure accuracy is improved without correcting the focal length and the angle for each shot, so that the short circuit failure does not occur and the yield of the acoustic wave device is significantly increased. Can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a wafer according to the present invention.

FIG. 2 is a plan view schematically showing a wafer according to the present invention.

Claims (4)

[Claims] 1. A wafer for an acoustic wave device for forming an exciting electrode for generating an acoustic wave on one main surface of a wafer made of a lithium tantalate single crystal, the arithmetic mean roughness of the other main surface of the wafer. (Ra) is less than 0.6 μm, and the warp amount of the other main surface is 10 μm to 40 μm. 2. The acoustic wave device wafer according to claim 1, wherein the thickness of the wafer is 0.3 mm or less. 3. The flatness (TTV) of the wafer is 5 μm.
The wafer for acoustic wave device according to claim 1, wherein the wafer is less than 1. 4. An elastic wave device, wherein an excitation electrode for generating an elastic wave is formed on one main surface of the wafer or a substrate obtained by cutting the wafer into a predetermined shape.