JP2003078182A - Mono-crystal substrate for surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent mono-crystal substrate for a surface acoustic wave element which can be easily useful for quality management or the like, whose marking contents can be visually easily confirmed by an operator in any process, and whose substrate deterioration can be prevented from being induced. SOLUTION: This mono-crystal substrate for a surface acoustic wave element is constituted so that an exciting electrode for generating a surface acoustic wave can be formed on one main surface of a substrate constituted of tantalic acid lithium mono-crystal. A marking for identification is applied to one main surface of the substrate by scratch, and as for the scratch surface of the marking for identification, arithmetic mean roughness (Ra) is set so as to be not more than 0.3 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal substrate used for a surface acoustic wave device such as a surface acoustic wave filter.

[0002]

2. Description of the Related Art Conventionally, as a method of forming an identification mark on a single crystal substrate such as a wafer, a method of attaching a transfer film material to a predetermined position (see Japanese Patent Laid-Open No. 10-107098), laser processing Method using
7-022301), a method using ink (see JP-A-10-242223, etc.) and the like are known.

Also known is a laser marking method using the principle of laser hologram recording on a piezoelectric lithium niobate or lithium tantalate single crystal substrate.

However, the engraving method using, for example, laser processing cannot be applied to a lithium tantalate single crystal for a surface acoustic wave element, which is particularly prone to deterioration due to heat, because it is processing by heat melting. That is, the static electricity caused by the pyroelectricity of the lithium tantalate single crystal is generated, and the generation of minute cracks, the generation of crystal grain boundaries, and other crystal defects in the substrate made of this increase the quality of the substrate. to degrade. In addition, since the substrate has piezoelectric properties, internal stress may be generated due to static electricity generated by local heating, resulting in destruction of the substrate.

Further, the marking method for the transfer film, ink, etc., is designed to remove the marking for identification after a predetermined manufacturing process after marking, so that the marking easily disappears.
The identification mark cannot be left on the final product and used for quality control.

Further, the engraving method using the laser hologram is very inconvenient because the engraved information cannot be read out without a special laser optical system for exclusive use.

According to the present invention, it can be easily utilized for quality control and the like, and in any process, the operator can easily visually confirm the contents of the marking for identification, and the deterioration of the substrate is not induced. An object is to provide an excellent single crystal substrate for a surface acoustic wave device.

[0008]

In order to solve the above problems, the single crystal substrate for a surface acoustic wave device of the present invention generates a surface acoustic wave on one main surface of a substrate made of a lithium tantalate single crystal. A substrate for forming an excitation electrode, wherein one surface of the substrate is provided with an identification mark by scratch, and the scratch surface of the identification mark has an arithmetic mean roughness (Ra) of 0.3 μm. It is characterized by the following.

Further, the marking for identification is characterized in that it is formed by grinding or blasting by applying ultrasonic waves.

Specifically, in order to form a marking for identification by rubbing, ultrasonic wave applying grinding using a rubbing head having a marking pattern at the tip is applied or a mask having an opening in the marking pattern is used. Perform blast polishing.

At least the scratch surface of the marking for identification, more preferably the scratch surface of the marking for identification and the other main surface of the substrate, have an arithmetic mean roughness (Ra) of a moderately rough surface. 3 μm or less, especially 0.1 to 0.3 μm
Within the range of m, it is easy to visually identify, and particles are not generated due to peeling of minute pieces of the substrate from the scratch surface. Further, if the other main surface of the substrate is a moderately rough surface as described above, even if the surface acoustic wave element is formed by forming the excitation electrode on the substrate, the characteristic deterioration is not induced by the back surface reflection by the bulk wave.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below.

In the present invention, for example, a lithium tantalate single crystal is used as a substrate material of a surface acoustic wave filter element for mobile communication, and one main surface of this substrate (or wafer) is a mirror surface (arithmetic mean roughness (Ra)). 1 nm or less) to form a surface on which an excitation electrode for generating a surface acoustic wave is formed. Further, one main surface of the substrate is provided with an identification mark by scratching, and the scratch surface of the identification mark and the other main surface of the substrate have an arithmetic average roughness (Ra) of 0.
The surface roughness was 3 μm or less, and more preferably 0.1 to 0.3 μm.

It is assumed that the marking for identification is formed by grinding by applying ultrasonic waves or blasting.

Thus, the quality of the board is not deteriorated by generating static electricity due to pyroelectricity on the board, and furthermore, the character string is used so that the quality control by serial number or various symbols can be easily performed visually. By using a system that combines processing heads of each character shape, the substrate to be imprinted can be automatically and quickly engraved by automatic transfer.

Here, when the identification mark is formed by scratches and the surface roughness of the scratch surface and the other main surface is larger than the above range, fine particles are generated from the formed rough surface, which causes a problem in the device process. Generate. In addition, when applying the photoresist for forming the excitation electrode on the mirror surface (one main surface) of the substrate, if the surface roughness of the marking portion is too large, the resist film thickness becomes uneven in the vicinity, and A problem occurs in the peripheral area.

Therefore, when the test was conducted by changing the surface roughness of the marking for identification, when the arithmetic mean roughness (Ra) was 0.3 μm or less, the above-mentioned problems did not occur. It was

On the other hand, if the roughness of the scratch surface is not appropriate, it becomes difficult to visually identify it. That is, the contrast of the engraved portion becomes thin, which causes a problem in visibility. Therefore, this problem was solved by setting the arithmetic average roughness (Ra) to 0.1 μm or more.

[0019]

EXAMPLE A method for forming an identification mark on a single crystal wafer will be described below as a more specific example of the present invention. <Example 1> From a cylindrical lithium tantalate single crystal having a diameter of about 100 mm and a length of 100 mm, a thickness of about 0.5 m
The wafer of m was cut out using a multi-wire saw.

Then, the following steps were sequentially performed to polish one surface of the wafer to a mirror surface (arithmetic mean roughness (Ra) of 1 nm or less) for forming an excitation electrode. (1) The surface shape was made flat by adjusting the thickness by lapping. (2) The chamfering of the edge portion was performed by an automatic chamfering machine. (3) Single-sided mirror polishing was performed with a single-sided mirror polishing machine.

Next, in order to perform quality control by marking the wafers in each lot, the wafers are put in a wafer case containing 25 wafers, divided into lots, and the ultrasonic marking system S is an automatic marking device as shown in FIG. Supplied to.

The ultrasonic marking system S applies ultrasonic waves to the wafer 2 mounted on the wafer transfer belt 1 to perform grinding processing. In the figure, 3 is a marking head roller and 4 is a marking head roller. A housing 3 holds 5, an ultrasonic wave applying unit, and a vertical moving unit 6. FIG. 2 shows a head in which a marking head roller 3 having a marking character 7 formed on a housing 4 is housed.

Using the above device, the marking head roller 3
Is pressed against the marking portion on the mirror surface 2a side of the wafer 2 to apply an ultrasonic wave, whereby the mirror surface 2a of the wafer 2 is scratched. The ultrasonic wave application intensity was adjusted so that the surface roughness at this time was 0.3 μm or less in terms of arithmetic average roughness (Ra). As a result, in the device process, there were no problems such as cracking and chipping due to this marking.

According to the present processing method, the marking head roller having a letter-shaped tip is sequentially replaced, whereby the automation can be performed in combination with the automatic wafer transfer system.
Note that, due to the nature of this system, the type of character is limited to the type of pattern of the processing head having the tip of the character shape in advance. <Example 2> In the same manner as in Example 1, a diameter of 100 mm,
A wafer having a thickness of 0.5 mm was cut out from a cylindrical lithium tantalate single crystal having a length of 100 mm with a multi-wire saw.

Then, in the same manner as in Example 1, a single-sided mirror-polished wafer was processed.

Then, this wafer was put in a wafer case containing 25 sheets for marking each lot and quality control, and each lot was supplied to an automatic marking device.

As the marking device at this time, a blast polishing system using a mask opened in the marking pattern shape was used. The surface roughness at this time is 0.3 in terms of arithmetic average roughness (Ra).
When the blast spraying strength was adjusted so as to be not more than μm, there were no problems such as cracking and chipping due to the main marking in the device process.

In this processing method, by using a system capable of instantaneously forming a pattern opened in a character shape, it can be fully automated in combination with an automatic wafer transfer system.
Further, as a system capable of instantly forming an open pattern in a character shape at this time, when the types of characters are limited, a system for preparing patterns for all types of characters and sequentially exchanging them Full automation is possible by using.

Further, for example, by applying a system in which a plastic film is instantly cut into a character shape pattern by heat or laser, any character or pattern can be dealt with, and pattern formation and blast polishing can be performed instantaneously according to the flow of the wafer. It can be fully automated.

[0030]

As described above, according to the single crystal substrate for the surface acoustic wave device of the present invention, the one surface of the substrate made of the lithium tantalate single crystal, which is difficult to laser-mark, has an appropriate rough marking for identification by scratch. In addition, the marking for identification is formed by grinding or blasting by applying ultrasonic waves.

As a result, in any manufacturing process, the operator can easily visually check the contents of the marking for identification, which is useful for quality control and the like.

Further, it is possible to provide an excellent single crystal substrate for a surface acoustic wave element which does not induce deterioration of the substrate and which can easily and clearly produce the marking for identification quickly.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram schematically illustrating an ultrasonic marking system.

FIG. 2 is a perspective view illustrating an application head used in an ultrasonic marking system.

[Explanation of symbols]

1: Wafer transfer belt 2: Wafer 3: Engraved head roller 4: Case 5: Ultrasonic wave application section 6: Vertical movement part 7: Stamp character S: Ultrasonic marking system

Claims (2)

[Claims] 1. A single crystal substrate for a surface acoustic wave device, comprising a single crystal of lithium tantalate and having an excitation electrode for generating a surface acoustic wave on one principal surface, wherein the one principal surface of the substrate is identified by scratching. A single crystal substrate for a surface acoustic wave device, wherein a scratch mark of the identification mark is formed, and a scratch surface of the identification mark has an arithmetic average roughness (Ra) of 0.3 μm or less. 2. The single crystal substrate for a surface acoustic wave device according to claim 1, wherein the identification mark is formed by grinding or blasting by applying ultrasonic waves.