KR102508006B1 - Substrate for surface acoustic wave device and manufacturing method thereof - Google Patents

Abstract

A substrate for a surface acoustic wave element made of a piezoelectric material and having a chamfer on an outer circumferential surface, wherein both the arithmetic mean roughness Ra1 of the roughness curve in the thickness direction and the arithmetic average roughness Ra2 of the roughness curve in the circumferential direction of the outer circumferential surface are 1 μm or less, Moreover, Ra1/Ra2 is 1.2 or more.

Description

Substrate for surface acoustic wave device and manufacturing method thereof

The present disclosure relates to a substrate for a surface acoustic wave element used in a surface acoustic wave element such as a surface acoustic wave filter, and a manufacturing method thereof.

A surface acoustic wave element converts an electrical signal into a surface acoustic wave and performs signal processing. As the substrate for the surface acoustic wave element, a single crystal substrate made of lithium tantalate (LT) or lithium niobate (LN) having piezoelectric properties is used.

The substrate for the surface acoustic wave device is processed by processing the outer shape of a single crystal ingot into a desired shape, cutting into a plurality of substrates each having an outer circumferential surface and an element formation surface, lapping the substrate to a desired thickness, and chamfering the outer circumferential surface of the substrate. and polishing the element formation surface of the substrate. Surface acoustic wave elements are fabricated by forming electrodes made of aluminum or the like on the element formation surface of the obtained substrate to form a plurality of elements, and then dividing and cutting each element.

Piezoelectric material substrates such as LT and LN are more prone to cracking and chipping than semiconductor substrates such as silicon. In particular, cracks and brittleness are likely to occur starting from the outer periphery including the outer circumferential surface. Therefore, attempts have been made to reduce cracks and chipping starting from the outer circumferential surface in the substrate processing step and the device forming process by reducing the surface roughness of the outer circumferential surface (for example, Patent Documents 1 and 2). Patent Literature 3 describes that cracking and chipping are reduced by chamfering the outer peripheral surface using a grindstone containing two types of abrasive grains having different grain sizes. Patent Literature 4 describes that cracking and chipping are reduced by chamfering the outer circumferential surface of a substrate using two types of grindstones having different particle diameters of abrasive grains.

[0003] Nowadays, substrates for surface acoustic wave devices that are less prone to cracking and wrinkling than those of the prior art are required in accordance with the demand for larger diameter and thinner substrates.

Patent Publication No. Hei 11-306404 Japanese Unexamined Patent Publication No. 2002-167298 Patent Publication No. Hei 9-181021 Patent Publication No. Hei 11-284469

A substrate for a surface acoustic wave element of the present disclosure is made of a piezoelectric material, has a chamfer on an outer circumferential surface, and both the arithmetic mean roughness Ra1 of the roughness curve in the thickness direction and the arithmetic mean roughness Ra2 of the roughness curve in the circumferential direction of the outer circumferential surface are 1 µm or less. , and Ra1/Ra2 is 1.2 or more.

A method of manufacturing a substrate for a surface acoustic wave device of the present disclosure includes a step of preparing a substrate made of a piezoelectric material and having an outer circumferential surface extending in a thickness direction and a circumferential direction, while rotating the substrate in a circumferential direction, at least the thickness of the outer circumferential surface of the substrate A step of chamfering by bringing a rotating grindstone into contact with both ends of the direction, and a step of etching the chamfered outer circumferential surface are included.

Fig. 1(a) is a top view showing an example of a substrate for a surface acoustic wave device according to the present disclosure, and Fig. 1(b) is a side view thereof.

<Substrate for Surface Acoustic Wave Device>

Hereinafter, a substrate for a surface acoustic wave device according to the present disclosure will be described.

1(a) and 1(b) show schematic diagrams of a substrate 1 for a surface acoustic wave device (hereinafter, simply referred to as a substrate 1) according to an embodiment of the present disclosure. Fig. 1(a) is a top view, and Fig. 1(b) is a side view. The substrate 1 has an upper surface and a side surface with the upper end in contact with the upper surface.

As the substrate 1, a material having piezoelectricity such as a single crystal of lithium tantalate (LT) or a single crystal of lithium niobate (LN) is used. The 36°Y to 46°Y-LT single crystal is suitably used for pseudo surface acoustic wave elements among surface acoustic wave elements. In this embodiment, a substrate 1 for a pseudo surface acoustic wave element made of a 42 DEG Y-LT single crystal is described as the substrate 1.

The substrate 1 includes a first main surface 1a (upper surface) as an element formation surface through which surface acoustic waves propagate, a second main surface 1b as a main surface (lower surface) opposite to the first main surface 1a, and a first main surface It is provided with the outer peripheral surface 1c (side surface) which connects (1a) and the 2nd main surface 1b. The outer peripheral surface 1c has a chamfer.

Both the arithmetic average roughness Ra1 of the roughness curve in the thickness direction D1 and the arithmetic mean roughness Ra2 of the roughness curve in the circumferential direction D2 of the outer peripheral surface 1c are 1 µm or less, and Ra1/Ra2 is greater than 1.2. That is, the overall surface roughness of the outer peripheral surface 1c is relatively small, and the surface roughness in the thickness direction D1 is relatively large with respect to the circumferential direction D2.

As indicated by arrows in Fig. 1(b), the thickness direction D1 is a direction perpendicular to the first main surface 1a and the second main surface 1b. The circumferential direction D2 is a direction parallel to the first main surface 1a and the second main surface 1b, and is a direction perpendicular to the thickness direction D1.

As described above, the substrate 1 of the present embodiment has a relatively small arithmetic average roughness Ra of the outer peripheral surface 1c (1 μm or less). Therefore, the starting point of cracks and sagging is reduced, and cracks and sagging of the substrate 1 are less likely to occur. In addition, by making the arithmetic average roughness Ra1 of the roughness curve of the outer peripheral surface 1c in the thickness direction D1 larger than the arithmetic average roughness Ra2 of the roughness curve in the circumferential direction D2, the crack starting from the outer peripheral surface 1c is It is advantageous in making it difficult to extend in the directions of the first main surface 1a and the second main surface 1b. Therefore, with the above structure, it is possible to reduce cracks and sagging of the substrate 1 in the substrate processing step and the device forming step, and to improve the yield of the substrate processing step and the device forming step.

Since the arithmetic average roughness Ra1 is larger than Ra2, the outer peripheral surface 1c is easily maintained when the substrate 1 is held horizontally, and the substrate 1 is difficult to fall. Therefore, in the process of rotating the substrate 1 in the circumferential direction, for example, in the resist application process prior to the electrode formation process, cracking due to impact during rotation is less likely to occur, and mixing of the resist to the back surface is less likely to occur. That is, it is effective also for reliability and productivity improvement.

The chamfer of the outer peripheral surface 1c may be any of C chamfer and R chamfer. In the case of R-chamfering (circular arc-shaped chamfering), cracking and fraying can be particularly reduced. As for the chamfer, as shown in Fig. 1 (a), it is preferable that the entire outer circumferential surface 1c is R-chamfered (full R-chamfered), but at least a part of the outer circumferential surface 1c may be R-chamfered.

It is better if Ra1/Ra2 is 1.4 or more. In this case, it is advantageous in enhancing the effect of suppressing the extension of the crack starting from the outer peripheral surface 1c in the direction of the peripheral surface.

The relationship between the average length Rsm1 of the elements of the roughness curve in the thickness direction of the outer peripheral surface 1c and the average length Rsm2 of the elements of the roughness curve in the circumferential direction may be Rsm1/Rsm2 greater than or equal to 1.1. Similar to the arithmetic mean roughness (Ra), the larger the average length Rsm of the element in the thickness direction (D1) is advantageous in preventing the extension of cracks in the directions of the principal surfaces (the first principal surface 1a and the second principal surface 1b). do.

Both Rsm1/Ra1 and Rsm2/Ra2 may be 14 or less.

In this embodiment, the arithmetic average roughness (Ra) and the average length (Rsm) of elements are based on JIS B 0601:2001. The arithmetic average roughness (Ra) and the average length (Rsm) of elements can be measured using, for example, a laser microscope device VK-9510 manufactured by KEYENCE CORPORATION. The measurement conditions are, for example, set the measurement mode to color super depth, the measurement magnification to 400 times, the measurement pitch to be 0.02 μm, the cutoff filter λs to be 2.5 μm, the cutoff filter λc to be 0.08 mm, and the measurement length to be about 30 μm. The roughness curve of 1c) is measured at three or more locations in the thickness direction (D1) and the circumferential direction (D2), respectively, and the average value is taken as the measured value.

<Method for Manufacturing Substrate for Surface Acoustic Wave Device>

As a method for manufacturing a substrate for a pseudo surface acoustic wave device according to the present disclosure, a method for manufacturing a substrate for a pseudo surface acoustic wave device made of a single crystal of 42 DEG Y lithium tantalate (LT) will be described. First, an ingot made of an LT single crystal (hereinafter, simply referred to as LT) is grown by the Czochralski (CZ) method. It is particularly preferable that the pulling orientation of the ingot growth is the same as the crystal orientation of the main surfaces (first main surface 1a and second main surface 1b) of the substrate 1 to be finally used. The pulling orientation of the ingot growth may be a crystal orientation close to that of the main surfaces (first main surface 1a and second main surface 1b) of the substrate 1 such as 38 DEG Y.

The ingot is end-ground, if necessary, so that both end faces have a predetermined crystal orientation, and the outer shape is processed to conform to the shape of the substrate 1 (for example, a disk shape with an orientation flat). In addition, a single polarization treatment is performed in which a voltage of 500 V or more is applied in a state of being heated to a Curie temperature of LT or higher (about 610° C.) to match the polarization direction of each polarization domain in the same direction.

Next, the ingot is sliced using a multi-wire saw or the like to form a substrate 1 having a first main surface 1a, a second main surface 1b, and an outer peripheral surface 1c of a predetermined crystal orientation and having a predetermined thickness. process

Subsequently, processing strain and the like generated in the substrate 1 by slicing are reduced. To this end, the processed layer is removed by an etching treatment using hydrofluoric acid, nitric acid or a mixed acid thereof as an etchant.

Since the LT crystal has pyroelectricity, the substrate 1 may be damaged by sparks caused by electrification in the manufacturing process of the substrate 1 and the surface acoustic wave device. For this reason, it is sufficient to perform a conductivity adjusting process for adjusting the conductivity of the substrate 1 to prevent electrification. The conductivity adjustment treatment may be performed by a known reducing atmosphere treatment or the like.

Next, a chamfer is formed on the outer peripheral surface 1c. The formation of the chamfer is made by using a core chamfer, etc., while rotating the substrate 1 in the outer circumferential direction with respect to a rotating diamond grindstone having a processing surface shape corresponding to the shape of the chamfer with a grain size of #1000 to #2500. It is good to form it. Here, the arithmetic average roughness (Ra) of the outer peripheral surface 1c may be processed to 0.5 µm or less. Two types of grindstones with different grain sizes are prepared, the outer circumferential surface 1c is chamfered with a grindstone with a large abrasive diameter (small number of grain sizes), and then the outer circumferential surface is chamfered with a grindstone with a small grain diameter (large number of grain sizes). (1c) may be polished.

Next, in order to reduce the warpage generated in the substrate 1 in the steps up to this point and to roughen the second main surface 1b, the substrate 1 is lapped. In the lapping process, diamond abrasive grains having a particle size of #1000 to #2500 are used, and the second main surface 1b is roughened so that the arithmetic mean roughness (Ra) is 0.1 to 0.5 μm. A double-sided lapping device may be used for the lapping process, or the first main surface 1a and the second main surface 1b may be machined single-side.

On the outer peripheral surface 1c after chamfering and on the first and second main surfaces 1a and 1b after lapping, defects such as microcracks and residual stresses that cause cracks and warping of the substrate 1 are introduced. Processed layer There is a possibility that it exists on this surface. Therefore, an etching treatment may be performed using hydrofluoric acid, nitric acid, or a mixed acid thereof as an etchant to remove a processed layer containing defects or residual stress.

Etching conditions are, for example, 50 minutes to 120 minutes at 75 ° C. In addition, it may be etched for 60 to 90 minutes to increase the removal effect of the processed layer and productivity. By this etching process, the arithmetic average roughness Ra of the outer peripheral surface 1c becomes larger than before etching. Both the arithmetic mean roughness Ra1 of the roughness curve in the thickness direction and the arithmetic mean roughness Ra2 of the roughness curve in the circumferential direction of the outer peripheral surface 1c of the substrate 1 after the etching treatment are 1 μm or less. Moreover, Ra1/Ra2 becomes 1.2 or more. Further, the relationship between the average length Rsm1 of the elements of the roughness curve in the thickness direction and the average length Rsm2 of the elements of the roughness curve in the circumferential direction is such that Rsm1/Rsm2 is 1.1 or more.

In addition, since the substrate 1 made of a piezoelectric material has pyroelectricity (property of generating electric charge due to temperature change), it is easily charged and the charged state is easily changed. Since non-uniformity in the electrified state can cause non-uniformity in the etching rate, the substrate 1 may be subjected to static elimination treatment by an electrostatic eliminator (ionizer) prior to the etching treatment.

Subsequently, the first main surface 1a is subjected to CMP polishing by chemical mechanical polishing (CMP). The arithmetic average roughness Ra of the first main surface 1a after CMP polishing is 1 nm or less. You may rough-polish the 1st main surface 1a before CMP polishing.

(Example)

Hereinafter, embodiments of the present disclosure will be described.

A cylindrical lithium tantalate single crystal ingot having a diameter of 108 mm was grown using a CZ method single crystal growth furnace. This was cylindrically ground to a diameter of 100 mm with a cylindrical grinding machine, and the ingot subjected to the single polarization treatment was sliced using a multi-wire saw to obtain 200 substrates 1 having a crystal orientation of 42° Y and a thickness of 400 μm. The substrate 1 was subjected to a reducing atmosphere treatment after etching the layer of processing strain generated on the substrate 1 using a mixed acid having a mixing ratio of hydrofluoric acid and nitric acid of 1:1 by volume.

Subsequently, a chamfer of full R as shown in Fig. 1 (a) was formed on the outer peripheral surface 1c using a metal wheel with a diamond abrasive grain having a grain size of #1000 by a core chamfering machine (roughing). Further, the outer peripheral surface 1c was polished by using a metal wheel equipped with diamond abrasive grains having a particle size of #2000 to 2500. The processing amount of the outer diameter size was set to 0.3 to 0.5 mm for roughing and 0.1 mm or less for polishing. In condition 2, the time of finishing polishing was shortened with respect to condition 1, and it was implemented.

Subsequently, the first main surface 1a and the second main surface 1b were formed to a thickness of about 250 μm by using a diamond abrasive grain having a particle size of #1000 by a double-sided lapping device, and subsequently using a diamond abrasive grain having a particle size of #2000. lapping was done.

Subsequently, the substrate 1 was etched at about 80° C. for 50 minutes to 120 minutes using a mixed acid having a mixing ratio of hydrofluoric acid and nitric acid of 1:1 by volume. In conditions 1, 3, and 4, the etching time was lengthened in the order of condition 4 > condition 1 > condition 3.

As a comparative example, in Condition 5, polishing was performed with a diamond grindstone equivalent to #2000 in the chamfering step, and then mirror polishing was performed by brush polishing so that the arithmetic average roughness Ra was 1 μm or less. In this comparative example, the mixed acid etching after the chamfering step was not performed.

Further, the first main surfaces 1a of the substrates 1 of Examples and Comparative Examples were subjected to CMP polishing. CMP polishing was performed using a slurry containing colloidal silica having a particle size of 30 to 120 nm as an abrasive and a polishing cloth. The obtained first main surface 1a was in a mirror-finished state with a surface roughness Ra of 0.1 to 0.2 nm.

Thus, the arithmetic mean roughness (Ra) of the outer peripheral surface 1c of the substrate 1 and the average length (Rsm) of the elements were measured in the thickness direction and the circumferential direction respectively using a laser microscope device VK-9510 manufactured by KEYENCE CORPORATION. The location was measured, and the average value was made into the measured value. Table 1 shows the measurement results.

Substrates 1 were fabricated by changing the processing conditions of the outer peripheral surface 1c under each condition, and 100 substrates 1 under each condition were put into the element formation process, and the defective rate due to cracks and fraying was counted. Examples in which the defect rate is 0% are indicated as ○, examples in which the defect rate is greater than 0% and 5% or less are indicated as △, and examples in which the defect rate exceeds 5% are indicated as ×, and are shown in Table 1. As shown in Table 1, it was found that the defect rate was improved in the examples compared to the comparative examples.

As mentioned above, although embodiment of this indication was described, this indication is not limited to the above-mentioned embodiment, You may perform various improvement and improvement in the range which does not deviate from description of a claim.

1: substrate for surface acoustic waves (substrate) 1a: first main surface
1b: second peripheral surface 1c: outer peripheral surface

Claims (15)

A substrate for a surface acoustic wave device made of lithium tantalate and having a chamfer on an outer circumferential surface, comprising:
The arithmetic mean roughness Ra1 of the roughness curve in the thickness direction and the arithmetic mean roughness Ra2 of the roughness curve in the circumferential direction of the outer peripheral surface are both 1 µm or less, and Ra1/Ra2 is 1.2 or more. According to claim 1,
A substrate for a surface acoustic wave device having Ra1/Ra2 of 1.4 or more. According to claim 1 or 2,
The surface acoustic wave element substrate according to claim 1 , wherein a relationship between the average length Rsm1 of the elements of the roughness curve in the thickness direction of the outer peripheral surface and the average length Rsm2 of the elements of the roughness curve in the circumferential direction is Rsm1/Rsm2 of 1.1 or more. According to claim 3,
A substrate for a surface acoustic wave device in which both Rsm1/Ra1 and Rsm2/Ra2 are 14 or less. According to claim 1 or 2,
A substrate for a surface acoustic wave device in which the lithium tantalate is formed of a single crystal of 36°Y to 46°Y lithium tantalate. preparing a substrate made of lithium tantalate and having an outer circumferential surface extending in a thickness direction and a circumferential direction;
a step of contacting at least both ends in the thickness direction of an outer circumferential surface of the substrate with a rotating grinding stone to chamfer it while rotating the substrate in the circumferential direction;
A method of manufacturing a substrate for a surface acoustic wave element according to claim 1, comprising the step of etching the chamfered outer circumferential surface. According to claim 6,
The method of manufacturing a substrate for a surface acoustic wave device according to claim 1, wherein the rotating grindstone is a rotating grindstone having an abrasive grain size of #1000 to #2500. According to claim 6 or 7,
The manufacturing method of claim 1, further comprising a step of etching the outer circumferential surface by using hydrofluoric acid, nitric acid, or a mixed acid of hydrofluoric acid and nitric acid as an etchant after the chamfering step. According to claim 6 or 7,
A method for manufacturing a substrate for a surface acoustic wave device, wherein the substrate is made of a 36°Y to 46°Y lithium tantalate single crystal. According to claim 6 or 7,
A method of manufacturing a substrate for a surface acoustic wave device, wherein a static charge removal treatment is performed on the substrate before the etching treatment. According to claim 3,
A substrate for a surface acoustic wave device in which the lithium tantalate is formed of a single crystal of 36°Y to 46°Y lithium tantalate. According to claim 4,
A substrate for a surface acoustic wave device in which the lithium tantalate is formed of a single crystal of 36°Y to 46°Y lithium tantalate. According to claim 8,
A method for manufacturing a substrate for a surface acoustic wave device in which the lithium tantalate is made of a single crystal of 36°Y to 46°Y lithium tantalate. According to claim 8,
A method of manufacturing a substrate for a surface acoustic wave device, wherein a static charge removal treatment is performed on the substrate before the etching treatment. According to claim 9,
A method of manufacturing a substrate for a surface acoustic wave device, wherein a static charge removal treatment is performed on the substrate before the etching treatment.

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