JP2002111420A - Wafer for elastic surface wave device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superior wafer for elastic surface wave device and a manufacturing method for the same, which allows easily and simply applying mirror surface grinding to side portions of the wafer while it is a part of an ingot and high quality wafer processing. SOLUTION: The wafer for an elastic surface wave device has at least a side which is a mirror surface comprising lithium tantalite single crystal with an arithmetic average roughness (Ra) of the side being below 1.5 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device wafer using a lithium tantalate single crystal as a substrate material and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a single crystal of lithium tantalate is used as a substrate of a surface acoustic wave device using a wafer having a polished surface. After a single crystal having a diameter of about 80 to 100 mm is grown on the wafer by the Czochralski method or the like, which is a single crystal growing method, an orientation flat (hereinafter, referred to as an orientation flat) serving as a reference plane when a surface acoustic wave element is manufactured is processed. Then, a circumferential grinding process for adjusting the outer diameter is performed, and sliced into a disk having a thickness of about 500 μm along a required crystal orientation.

After that, the surface of the wafer is GC # 1000-
After being lapped and polished with abrasives of about GC # 2000, the back surface of the wafer is GC # 2 to reduce bulk spurious.
After roughening with abrasive grains of about 40 to GC # 2000, chamfering is performed with a grindstone # 600 to # 1500 using a metal bond or the like. In some cases, a mirror surface is chamfered, and the main surface is mirror-finished by mechanochemical polishing.

[0004] The wafer polished in this manner is coated with a metal film such as Al as an electrode material on the mirror surface, and a comb-shaped electrode having a desired shape is formed on the wafer surface by a fine processing technique using photolithography or the like. Then, the surface acoustic wave element is manufactured by dicing into individual chips.

[0005]

In order to mirror-process the chamfered portion of the wafer, the chamfered portion of the wafer is ground with a grindstone and then mirror-polished by an apparatus having a buff groove shape corresponding to the shape of the wafer chamfered portion. However, there are problems such as a large amount of time required for processing and a decrease in yield due to cracks due to variations in the thickness of the wafer and displacement of the center when the wafer is fixed.

On the other hand, in the case of a wafer whose chamfered portion is not mirror-polished, cracks are apt to be formed from the edge portion due to a heating process in the wafer processing step or the device manufacturing step, and chipping is likely to occur. In particular, in the case of a lithium tantalate single crystal wafer, since the {012} plane has a cleavage plane, chipping tends to occur along the cleavage plane, and the chipping of the edge portion becomes a starting point due to thermal stress or mechanical stress. Thus, there is a problem that cracks occur in the wafer and the yield in the wafer process and the device process is reduced. In particular, this problem is serious for a rotated Y-cut wafer having a rotation angle of 42 ° or less, which is suitable as a piezoelectric substrate of a surface acoustic wave device, because it is affected by a rough surface close to the vertical direction of the wafer surface.

[0007] Further, since the side surface of the wafer is rough, particles enter the side surface portion, thereby deteriorating the quality and decreasing the yield.

Accordingly, the present invention solves the above-mentioned problems and provides an excellent elastic surface capable of easily and simply performing mirror polishing of the side surface of a wafer in an ingot state and realizing high quality wafer processing. It is an object of the present invention to provide a wave element wafer and a method for manufacturing the same.

[0009]

In order to solve the above-mentioned problems, a single crystal wafer for a surface acoustic wave device according to the present invention is characterized in that at least a side surface of a wafer made of a single crystal of lithium tantalate is a mirror surface and an arithmetic operation of the side surface is performed. The average roughness (Ra) is not more than 1.5 nm. In particular, it is assumed that the peripheral portion of one main surface of the wafer is formed on a slope.

[0010] The method of manufacturing a single crystal wafer for a surface acoustic wave device according to the present invention comprises the steps of: mirror-polishing the side surface of a cylindrical ingot made of lithium tantalate single crystal; A step of dicing and cutting into a disc-shaped wafer; and a step of mirror-polishing one main surface of the wafer.

Particularly, the inclined surface shape of the side surface portion of the wafer is 0.01t ≦ R ≦ 1t in the wafer circumferential direction (R) and 0.01 ≦ T ≦ t / 2 in the wafer thickness direction (T) (however, t is the size of the wafer thickness).

[0012] A nonwoven fabric having a hardness (Asker-C) of 100 or less is polished under a processing pressure of 0.02 GPa or more.

[0013] Further, the present invention is characterized in that a wax-pitch-resist-film-like material is used to protect the mirror surface.

According to the above construction, the chamfering can be performed simply and easily with high efficiency, no cracks or chips are generated in the heating step, and particle contamination due to chips from the chamfered portion is eliminated, and the yield is reduced. Can be prevented.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

In order to cut out a piezoelectric substrate suitable for use as a surface acoustic wave device, a Y-cut lithium tantalate single crystal wafer rotated at 36 ° to 46 ° must be obtained. In a furnace, the crucible is heated to a predetermined temperature to melt the raw material, a seed crystal is immersed in the melt, and a crystal is grown at a predetermined rotation speed and a pulling speed at a growth axis of 36 ° to 46 ° and a Y axis. Then, a cylindrical single crystal ingot is obtained.

Next, after cutting or grinding the both end faces of the obtained crystal ingot, as shown in FIGS. 1 and 2, the jig 5 for centering the center of both end faces of the crystal ingot 1 and The crystal ingot 1 is centered by disposing it on the V block 2 or the like using the cylindrical center jig 3 and then fixed to a cylindrical grinding device described later. In the figure,
4 is a taper centering groove.

Here, cylindrical grinding is performed, for example, in # 200 to # 1.
Using a grinding wheel using a metal bond of 000, grinding is performed by adjusting an orientation flat serving as a reference direction of the surface acoustic wave element and an outer diameter. After rough grinding on the side surface of the crystal ingot 1, a mirror-surface cylindrical grinding device shown in FIG.
A mirror surface cylindrical processing is performed using the nonwoven fabric grindstone 11 having a groove shape as shown in (a) to (c). Thereby, the arithmetic mean roughness (Ra) of the side surface of the ingot is set to 1.5 nm or less. That is, after the cylindrical grinding, by pressing the tapered centering groove 4 shown in FIG. 3 from both ends with the mirror-surface cylindrical grinding device cylindrical taper centering jigs 12, the core for the cylindrical grinding in the previous process can be secured. Thereafter, while rotating the ingot 1 and rotating the nonwoven fabric grindstone 11 shown in FIG. 4, the nonwoven fabric grindstone 11 is sent in the left-right direction to perform mirror-surface cylindrical processing. Is made.

Next, the cylindrical crystal ingot 1 is removed, and, for example, a wax, a pitch, a resist, or a film is pasted or applied to protect the mirror surface on the side surface. Next, the wafer is sliced to a thickness of about 500 μm along a predetermined crystal plane, and the wafer is wrapped.

Thereafter, as shown in FIG. 5, processing of an inclined portion on the back surface, for example, using a metal bond to # 1000
In the circumferential direction (R) of the wafer 10, 0.01t ≦ R ≦ 1
t, in the thickness direction (T) of the wafer 10, 0.01 ≦ T ≦ t /
2 (t is the thickness of the wafer 10) of the inclined surface 10a is processed.

In particular, since the rotational Y-cut wafer having a rotational angle of 42 ° or less is affected by a cleavage plane close to the vertical direction of the wafer surface, the circumferential direction (R) has a working pressure of 27 μm or more (a processing pressure of 0.03 GPa or more). ) Is desirable. Also, R
Is 1 t or more, the effective area of the wafer becomes narrow, and 0.01 t
Below, the effect of chamfering cannot be obtained. When a film is used to protect the mirror surface of the side surface of the ingot, the film is removed before the main surface is polished, and when a protective film is used, the film is peeled off after the main surface is polished.

The mirror polishing of the main surface is performed by using a woven cloth type having a hardness (Asker-C) of 100 or less and performing polishing at a processing pressure of 0.02 GPa or more to obtain a peripheral edge of the wafer main surface. The polishing of the inclined surface in the portion is mainly performed in the circumferential direction (R) with dimensions of 0.01t ≦ R ≦ 1t and in the wafer thickness direction (T) with dimensions of 0.01 ≦ T ≦ t / 2 (t is the wafer thickness). It can be manufactured in the same process as the mirror polishing of the surface. This makes it possible to obtain a wafer that is free from chipping due to the slope 10a produced.

Then, after removing the protective film by washing,
In the device manufacturing process, a substrate can be manufactured in which cracking and chipping due to the heat process do not occur and the yield does not decrease at all. In addition, excellent surface acoustic wave characteristics that improve the yield of device characteristics such as particles can be obtained by the mirror surface of the side surface.

As described above, in the surface acoustic wave device wafer of the present invention, one principal surface and side surfaces of the wafer made of lithium tantalate single crystal are mirror surfaces, and the arithmetic mean roughness (Ra) of the side surfaces is 1 unit. 0.5 nm or less. Further, a peripheral portion of one main surface of the wafer is formed on a slope. Further, the manufacturing method of the present invention is a step of mirror-polishing the side surface of a cylindrical ingot made of lithium tantalate single crystal, and a step of dicing in a direction crossing the center axis of the ingot to cut into a disk-shaped wafer, A process of mirror-polishing one main surface of the wafer, so that a large amount of mirror-polishing can be performed at once on the side surface of the wafer in an ingot state, resulting in low cost, high-quality wafer processing without chipping and the like. Becomes possible.

[0025]

EXAMPLE A lithium tantalate single crystal grown on a rot36 ° Y-axis in a high-frequency heating furnace was cut at both ends with a diamond cutter, and both ends were fixed to a cylindrical center grinding jig using a V block or the like. . An ingot was attached to the cylindrical grinding, and the cylindrical grinding and the orientation flat grinding were performed by # 325 using a metal bond.

Next, a non-woven fabric type polishing pad was subjected to mirror surface cylindrical processing and orientation flat mirror surface processing using abrasive grains of colloidal silica. When the arithmetic surface roughness (Ra) of this mirror-finished cylindrical ingot was measured, the arithmetic average roughness (Ra) was 1.5 nm.

Next, the ingot was removed from the apparatus, and for example, a resist was applied to the cylindrical mirror portion and the orientation flat mirror portion to form a protective film.

Next, after setting the orientation within a range of 0.1 ° on the Y-plane rotated by 36 ° by X-ray diffraction and setting it on a multi-wire saw, slicing was performed using free abrasive grains to a thickness of about 500 μm. Was. The cut wafer is GC # 1000
Lapping polishing was performed to a thickness of 365 μm with the abrasive grains of No. 1. Further, the processing of the inclined back surface was performed using a # 1000 grindstone using a metal bond, for example, in a circumferential direction (R) of 36 μm and in a wafer thickness direction (T) of 36 μm.

Next, the main surface is mirror-polished by, for example, a nonwoven fabric type having a hardness (Asker-C) of 100, and one side (one main surface) of the wafer is subjected to mechanochemical polishing at a processing pressure of 0.03 GPa. For example, mechanochemical polishing was performed to 350 μm with colloidal silica and a nonwoven fabric. The relationship between the processing pressure and the flat inclined portion was as shown in Table 1.

[0030]

[Table 1]

The 50 wafer substrates, 50 wafers obtained by grinding with a grindstone up to # 1200 using a metal bond on the side surface, and 50 wafers after cylindrical grinding without chamfering are cleaned, and the aluminum substrate is cleaned. After the film was formed, the wafer substrate was put into IPA (isopropyl alcohol) at room temperature (25 ° C.) to 83 ° C. and taken out. When the wafer side surface was cylindrically ground, the wafer had an arithmetic average roughness (Ra) of 0.6 μm. All wafers were cracked by heat shock.

Further, a metal bond 120 is provided on the side surface of the wafer.
Polishing is performed with a No. 0 whetstone, and the arithmetic average roughness (Ra) is 0.
Ten of the 13 μm wafers were cracked by thermal shock.

Further, the wafer side portion was subjected to mechanochemical polishing, and the wafer substrate having an arithmetic average roughness (Ra) of 1.5 nm was not broken at all by the heat shock. Then, after coating the film made of Al on the mirror surface of the wafer, the desired shape,
For example, when a surface acoustic wave device was manufactured by forming a comb-shaped electrode on the surface of a wafer and then dicing it into chips, the remaining wafer substrate obtained good characteristics without any cracks.

The side surface of the wafer is covered with a metal bond 120.
Polished with No. 0 whetstone, average roughness (Ra) 0.13μm
The device yield of the wafer substrate was 96% due to particles and the like on the side surface. However, the side surface of the wafer was subjected to mechanochemical polishing, and the arithmetic average roughness (R
The wafer substrate with a) of 1.5 nm showed good results with a device characteristic yield of 100%.

[0035]

According to the present invention, it is possible to perform a large amount of mirror polishing on the side surface of a wafer at a time in the state of an ingot, thereby enabling low cost and high quality wafer processing.

The arithmetic mean roughness (R
By setting a) to 1.5 nm or less, cracking and chipping in the thermal process can be reduced, particles and the like can be easily removed, and the device can be manufactured at a high yield in the device process and can be manufactured at a low cost. Can be provided.

[Brief description of the drawings]

FIG. 1 is a side view schematically illustrating a cylindrical center bonding method according to the present invention.

FIG. 2 is a side view of a cylindrical centering jig according to the present invention.

FIG. 3 is a side view of the cylindrical mirror polishing apparatus according to the present invention.

FIG. 4 is a plan view illustrating a groove surface of the cylindrical mirror-surface buffing wheel according to the present invention.

FIG. 5 is a cross-sectional view of a wafer schematically illustrating an embodiment of the present invention.

[Explanation of symbols]

 1: ingot 2: V block 3: cylindrical center jig 4: taper centering groove 5: center centering jig 10: wafer 10a: inclined surface 11: non-woven grindstone 12: cylindrical taper centering jig

Claims (3)

[Claims] 1. A wafer for a surface acoustic wave device, wherein at least a side surface of a wafer made of a single crystal of lithium tantalate is a mirror surface, and an arithmetic average roughness (Ra) of the side surface is 1.5 nm or less. . 2. The single crystal wafer for a surface acoustic wave device according to claim 1, wherein a peripheral portion of one principal surface of the wafer is formed on a slope. 3. A step of mirror-polishing a side surface of a cylindrical ingot made of a lithium tantalate single crystal, a step of dicing in a direction crossing a center axis of the ingot, and cutting into a disk-shaped wafer. 2. The method for producing a surface acoustic wave device wafer according to claim 1, further comprising the step of: mirror polishing one principal surface.