JPH03114310A - Substrate for surface acoustic wave filter and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an excellent filter characteristic by forming a multi-branch layer to faces of a piezoelectric substrate with an interdigital electrode pattern formed thereto except the major face and making the face of the piezoelectric substrate with the multi-branch layer formed thereto not flat. CONSTITUTION:Interdigital electrodes 12, 13 are formed on one face of a piezoelectric substrate 11. Moreover, a multi-branch layer 14 having a rugged part formed by radiating a laser beam to other face of the piezoelectric substrate 11. When the multi-branch layer 14 is provided to the piezoelectric substrate 11, a wafer 26 being the piezoelectric substrate is fixed on a wafer fixing base 25 of a package 24 in water and the wafer 26 is irradiated with the laser beam scanned by a beam scanning unit 23 via a solvent 27. Thus, the reflection of an undesired wave such as a bulk wave or a Raileigh wave in the border between the multi-branch layer 14 and a single branch layer is prevented and an excellent filter characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a substrate for a surface acoustic wave filter and a method for manufacturing the same.

(Prior Art) In recent years, surface acoustic wave filters that utilize surface acoustic waves propagating on the surface of a piezoelectric substrate have been developed.

Examples of such surface acoustic wave filters include the following.

FIG. 8 is a diagram showing a conventional surface acoustic wave filter.

As shown in the figure, this filter has an input/output quadrature transducer 4.5 formed by a comb-shaped electrode 2.3 on the surface of a piezoelectric substrate 1, and an electrical signal applied to the input quadrature transducer 4 is This is converted into a surface acoustic wave propagating on the surface of the piezoelectric substrate 1, and this is converted back into an electric signal by the output transducer 5.

Incidentally, this surface acoustic wave filter emits not only surface acoustic waves from the input quadrature transducer 4 but also bulk waves that propagate through the piezoelectric substrate 1 . Then, this bulk wave is reflected by the flat back surface of the piezoelectric substrate 1, so that it reaches the input/output quadrature transducer 5 again on the front surface and is detected. For this reason, bulk spurious occurs in the characteristics of the surface acoustic wave filter, deteriorating the filter characteristics.

Therefore, in order to prevent this, as shown in FIG. 9, a large number of recesses 6 such as grooves and holes are regularly formed on the back surface 1b of the piezoelectric substrate 1, which is opposite to the surface 1a on which the comb-shaped electrodes 2.3 are formed. Something is being done.

(Problems to be Solved by the Invention) However, in the conventional backside processing of the substrate described above, grooves are formed by randomly roughening the substrate using abrasive grains, or by dicing or honing.

The former is prone to thickness variations due to random roughening, and furthermore, processing distortion is large due to the roughening of the entire surface.
There is a problem with the board being easy to break.

The latter also has some areas that are not roughened, but the depressions are continuous and the grooves are inevitably weak, causing cracks during wafer and device processes.

The present invention is intended to solve the above-mentioned conventional problems,
It is an object of the present invention to provide a substrate for a surface acoustic wave filter, which can effectively remove unnecessary waves such as bulk waves, and improve the flatness of a predetermined surface of the substrate, and a method for manufacturing the same.

[Structure of the Invention (Means for Solving the Problem) The substrate for a surface acoustic wave filter of the present invention has a comb-shaped electrode pattern formed on the main surface of a piezoelectric substrate, and the main surface on which the comb-shaped electrode pattern is formed. A multi-region layer is formed on a surface other than the surface of the substrate, and the surface of the substrate on which the multi-region layer is formed is non-planar.

Further, the method for manufacturing a substrate for a surface acoustic wave filter of the present invention includes forming a comb-shaped electrode pattern on the main surface of a piezoelectric substrate, immersing this substrate in a solvent solution, and A laser beam is irradiated onto the surfaces other than the main surface to make the surfaces other than the main surface non-planar, and the thickness is 20 μm to 300 μm.
It is characterized by forming a multi-region layer of μ0.

(Function) In the present invention, the comb-like f-3 of the surface acoustic wave filter substrate
By applying appropriate laser irradiation to a portion other than the IF pattern forming portion, a multi-region layer can be formed partially and bulk waves in the thickness direction can be suppressed.

Furthermore, by multi-banding the side surfaces and the peripheral portion of the electrode surface on the end surface side of the chip, reflection of Rayleigh waves can also be prevented, and good filter characteristics can be obtained. Furthermore, the wafer itself is not subjected to external processing distortion, improving yield in wafer processing and reducing cracks in device processing.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side sectional view showing a surface acoustic wave filter substrate according to an embodiment of the present invention.

In the figure, 11 indicates a piezoelectric substrate.

On one surface of this piezoelectric substrate 11, a comb-shaped electrode 12.1 is provided.
3 is formed. Further, on the other surface of the piezoelectric substrate 11, a multi-domain layer 14 having an uneven portion formed by laser beam irradiation is provided.

Next, a laser processing apparatus used to form the multi-domain layer 14 on the piezoelectric substrate 11 described above will be explained using FIG. 2.

In the figure, 21 indicates a laser oscillator. Laser light from this laser oscillator 21 is reflected by a reflecting mirror 22 and introduced into a beam scanning unit 23 . Also,
Reference numeral 24 indicates an underwater container, and a wafer 26 serving as a piezoelectric substrate is fixed on a wafer fixing table 25 of this underwater container 24. Moreover, in the underwater container 24, for example, water,
A solvent 27 such as silicone oil is contained.

Then, the laser beam scanned by the beam scanning unit 23 is irradiated onto the wafer 26 via the solvent 27.

Next, an example of the method for manufacturing a surface acoustic wave filter substrate of the present invention will be described.

(Example 1) LiNbOz single crystal 76φXO, 62mm t
A sliced wafer of 1289Y plate was lapped on both sides with GCII2500 abrasive grains to a thickness of 0.52 mm. This wafer is mounted in the underwater processing container of the laser processing apparatus described above, and the cooling device is operated to circulate water.

The laser device is oscillated and stabilized at LOW continuous output (CW).

The Q-switch was then run at 5kHz. Groove-like processing with a pitch of 0.6n+lu was performed at a processing feed rate of 5 mm/s.

The results showed that there was no melt on the surface, and the wafer had no chipping and warpage was as good as 3 μm. Using this wafer, we fabricated a TV rough filter device on the mirror side, and it was able to efficiently remove reflected waves from bulk waves.
A good SAW filter was obtained, with the conventional 0-point trap dropping to -50 dB compared to -45 dB. In addition, there is less processing distortion and less cracking (device process yield is also 10%).
An improvement of more than % was obtained. Furthermore, when the cross section of this chip was polished to a mirror surface and etched with hydrofluoric nitric acid at 120°C for 1 hour, the surface of the chip 31 excluding the comb-shaped electrode forming surface 31a constituting the filter was irradiated with a laser beam, as shown in FIG. The polarization is inverted to form a multi-domain layer a1 with a thickness of 30 μm, and the vicinity of the laser focal point irradiated in a groove shape is polarized in a groove-like manner, forming a multi-domain layer b1 with a width of 600 μm and a thickness of 1.
00 μm.

(Example 2) A sliced wafer of LiNb03 single crystal "76φXO, 62mm t, 128°Y plate was lapped on both sides with GCII 2500 abrasive grains to a thickness of 0.52mm t.
Arrange it to. This wafer is placed in an underwater processing container of a laser processing device, and the cooling device is operated to circulate water. The laser processing device is oscillated and stabilized with continuous LOW output.

The Q-switch was then run at 5k) Iz. Grooves with a pitch of 0.5 mm were processed at a processing feed rate of 3 mff1/s.

The result was that there was no melt on the surface. Further, this wafer had no chipping and warpage was 4 μI, which was good. When this wafer was used to fabricate a TV rough filter device on the mirror side, the reflected waves due to bulk waves were effectively removed, and the zero point trap was reduced to -52 dB compared to -45 dB for the conventional 0-point trap, resulting in good SAW filter characteristics. Ta. In addition, there is less processing distortion and less cracking (device process yield is also 1
An improvement of 0% or more was observed. Furthermore, when the cross section of this chip was mirror-polished and etched with hydrofluoric and nitric acid at 120°C for 1 hour, as shown in FIG. The polarization is inverted by irradiation and the multi-domain layer a2 has a thickness of 40 μm.
At the same time, the polarization was inverted in the vicinity of the focal point of the laser irradiated in a groove shape, and a multi-region layer b2 was formed with a width of 500 μm and a thickness of 150 μm.

(Example 3) An X-plate sliced wafer of LiTa03 single crystal 76φXO, 82 tan t was lapped on both sides with GClt 2500 abrasive grains to a thickness of 0.52 tnIIlt. This wafer is placed in an underwater processing container of a laser processing device, and the cooling device is operated to circulate water. The laser processing equipment is oscillated and stabilized at a continuous output of 20V.

The Q-switch was then operated at 5kHz. Groove-like processing with a pitch of 0.51 was performed at a processing feed rate of 3 aun/s.

The result was that there was no melt on the surface. Moreover, this wafer had no chipping and warpage was 3 μm, which was good. When this wafer was used to fabricate a TV rough filter device on the mirror side, the reflected waves due to bulk waves could be efficiently removed, and the drop was reduced to -52 dB compared to -45 dB for the conventional 0-point trap, resulting in good SAW filter characteristics. Ta. In addition, there is less processing distortion and less cracking (and the device process yield is 1%).
An improvement of 0% or more was observed. Furthermore, when the cross section of this chip was polished to a mirror surface and etched with hydrofluoric nitric acid at 120°C for 1 hour, the surface of the chip 31 except for the comb-shaped electrode forming surface 31g constituting the filter was irradiated with a laser, as shown in FIG. The polarization is inverted to form a multi-domain layer a2 with a thickness of 40 μm, and the polarization of the vicinity of the laser focus irradiated in a groove is inverted in a groove-like manner, forming a multi-domain layer b2 with a width of 500 μm and a thickness of 1.
It was formed to have a thickness of 50 μm.

(Example 4) LiNb03 single crystal 76φX O, 62mm t 1
A sliced wafer of a 28° Y plate is lapped on both sides with GC12500 abrasive grains to a thickness of 0.52 m+nt. This wafer is placed in an underwater processing container of a laser processing device, and the cooling device is operated to circulate water. The laser processing device is oscillated and stabilized at a continuous output (CW) of 30W.

The Q-switch was then run at 5 kllz. Grooves with a pitch of 0.6 mm were processed at a processing feed rate of LO mm/s.

As a result, there was no melt on the surface, and as shown in Figure 5,
The laser beam irradiated onto the chip 51 in a groove shape has a width of 400 μm to 500 μm (W) and a depth of 60 μm to 1
A groove 52 with a thickness of 00 μll1 (D) was formed, and a multi-region layer 53 with a thickness of 40 μff1 to 50 μG+ (C) was formed on the inner wall surface of this groove 52. The surface of this wafer was polished to a thickness of 10 μm to 20 μm using Colloidal 5i02. This wafer had no occurrence of chipping and had a good warpage of 10 μm. Using this wafer, we fabricated a rough filter device for TV on the mirror side, and the reflected waves due to bulk waves could be efficiently removed, resulting in a good SA of 155 dB compared to 145 dB of the conventional 0-point trap.
W filter characteristics were obtained. Furthermore, the device process yield was improved by more than 10% due to less processing distortion and less cracking.

(Example 5) LiTaJ Qi crystal 76φX Q, 4'l +++a
+ A sliced wafer of tOX plate was lapped on both sides with GC$2500 abrasive grain to a thickness of 0.40111m.
Arrange it to. This wafer is placed in an underwater processing container of a laser processing device, and the cooling device is operated to circulate water. The laser processing device is oscillated and stabilized at a continuous output (CW) of 40W.

The Q-switch was then operated at 5 kHz. Groove-like processing with a pitch of 0.61 was performed at a processing feed rate of 8+n+u/s.

As a result, there was no melt on the surface, and as in Fig. 5, chip 5
The width of the laser beam irradiated in a groove shape on 1 is 300μIl~
400μll1(W), depth 60μIII~80μ1(
D) groove 52 is formed, and the inner wall surface of this groove 52 has a thickness of 2
A multi-area layer 53 of 0 μl to 30 μl was formed. The surface of this wafer was coated with Colloidal 5i02 for 10μ
Polishing was performed to a thickness of m to 20 μm. Further, this wafer had no chipping and warpage was 20 μm, which was good.

Using this wafer, we fabricated a TV rough filter device on the mirror side, and it was able to efficiently remove reflected waves from bulk waves.
It was possible to obtain good SAW filter characteristics.

Furthermore, the device process yield was improved by 8% or more with less processing distortion and less cracking.

(Comparative Example 1) LiNb03 single crystal 76φXO, 62mm t
A sliced wafer of 1288Y plate was lapped on both sides with abrasive grains of GC$2500 to a thickness of 0.52 mm. This wafer is set in a laser processing device, and the laser processing device is caused to oscillate and stabilized at a continuous LOW output.

Next, the Q-switch was turned on for 5 kllz. Grooves with a pitch of 0.5 mm were processed at a processing feed rate of LO mm/s.

As a result, molten matter adhered to the surface, cracks occurred in various places, and the processing yield was less than 10%. Using this wafer,
When I fabricated a TV rough filter device on the mirror side, I was able to remove some of the reflected waves due to bulk waves, and I was able to obtain a SAW filter characteristic that dropped to -52 dB compared to -45 dB for the conventional 0-point trap, but it also caused processing distortion. It was easy to break and the device process yield decreased to 20%. Further, when the cross section of this chip was polished to a mirror surface and etched with hydrofluoric nitric acid at 120° C., the laser irradiation area was multi-regioned in the form of a groove with a depth of 350 μm. In some cases, the multiregional layer reached the surface layer.

(Comparative Example 2) LiTaO3 single crystal 76φX O, 62mm t
The thickness of the sliced wafer was adjusted to 0.52 mtnt by lapping both sides with GC #2500 abrasive grains. This wafer is set in a laser processing device, and the laser processing device is caused to oscillate and stabilized at a continuous output of 15W.

Next, the Q-switch was operated at 5 ktlz.

Processing feed speed is 10m+n/s and pitch is 0.5nu
++ groove-like processing was performed.

As a result, molten matter adhered to the surface, cracks occurred in various places, and the processing yield was less than 10%. Using this wafer,
By fabricating a TV filter device on the mirror side, we were able to remove some of the reflected waves due to bulk waves, and we were able to obtain SAW filter characteristics that dropped to -52 dB compared to -45 dB for the conventional zero-point trap, but it also caused processing distortion. It was easy to break and the device process yield decreased to 10%. Further, when the cross section of this chip was polished to a mirror surface and etched with hydrofluoric nitric acid at 120° C., the laser irradiation area was multi-regioned in the form of a groove with a depth of 350 μm. In some cases, the multiregional layer reached the surface layer.

Note that the formation shape of the multi-region layer described above is not limited to the above-mentioned embodiment, and as shown in FIG.
A strip-shaped multi-region layer 62 having a width of 200 p m to 6 (10 μre (W) and a thickness of 100 μl to 300 μm (T)) may be formed on the chip 1, and as shown in FIG. A multi-region layer 72 with a thickness of 20 μI11 to 50 μm is formed on the entire surface except the surface 71a to be formed, and the vicinity of the laser focal point irradiated in a groove shape has a width of 100 μI1.
1 to 800μ1 (W), depth 80μm to 100μm
It may also have a shape in which the groove 73 shown in (D) is formed.

[Effects of the Invention] As explained above, the surface acoustic wave filter substrate of the present invention and the manufacturing method thereof include immersing the surface acoustic wave filter substrate in a solvent solution, and removing the comb-shaped electrode pattern forming portion of the substrate. Since a multi-domain layer is formed by irradiating laser light on the areas to be removed, the random polarity of the multi-domain layer prevents the reflection of unnecessary waves such as bulk waves and Rayleigh waves at the boundary between the multi-domain layer and the single-domain layer. can be prevented and good filter characteristics can be obtained. Further, the wafer itself is not subjected to external processing distortion, and yields in wafer processing and device processing can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a surface acoustic wave filter substrate according to an embodiment of the present invention, FIG. 2 is a diagram for explaining a laser processing apparatus applied to the manufacturing method of this embodiment, and FIG. The figure is a diagram for explaining a substrate obtained by the method for manufacturing a surface acoustic wave filter substrate according to an embodiment of the present invention, and FIGS. 4 and 5 respectively show surface acoustic wave filters according to other embodiments of the present invention. FIGS. 6 and 7 are diagrams for explaining the substrate obtained by the filter substrate manufacturing method, and are for explaining the shape of the multi-region layer in the surface acoustic wave filter substrate of other embodiments of the present invention. , FIG. 8, and FIG. 9 are views showing conventional surface acoustic wave filter substrates, respectively. 11... Piezoelectric substrate, 12.13... Comb-shaped electrode, 14
...Multi-domain layer, 21...Laser oscillator, 23...
Beam scanning unit, 24... Underwater container, 26...
Wafer, 27...solvent.

Claims (2)

[Claims] (1) A comb-shaped electrode pattern is formed on the main surface of the piezoelectric substrate,
A surface acoustic wave characterized in that a multi-domain layer is formed on a surface other than the main surface on which the comb-shaped electrode pattern is formed, and the surface of the substrate on which the multi-domain layer is formed is non-planar. Substrate for filter. (2) A comb-shaped electrode pattern is formed on the main surface of a piezoelectric substrate, this substrate is immersed in a solvent solution, and a laser beam is irradiated to the surface of the substrate other than the main surface on which the comb-shaped electrode pattern is formed. The surface other than the main surface is non-planar, and the thickness is 20 μm to 3
A method for manufacturing a surface acoustic wave filter substrate, the method comprising forming a multi-band layer of 00 μm.