JP3663845B2 - Crystal surface processing method and crystal piece manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to surface processing of quartz, and for example, in the manufacture of crystal devices such as tuning fork crystal resonators, longitudinal vibration crystal resonators, crystal sensors, crystal filters, and the like. The present invention relates to a crystal surface processing technique suitable for manufacturing a crystal piece.
[0002]
[Prior art]
Conventionally, crystals (artificial crystals) are used in the field of various electronic devices including communication devices such as mobile phones and pagers, information devices such as computers and word processors, various electronic control devices, and consumer devices such as electronic watches and video cameras. Used in various devices such as vibrators, oscillators, filters, and sensors. Among them, tuning fork crystal resonators are widely adopted as clock sources for these electronic devices. In general, the tuning fork crystal unit is manufactured by first cutting a rough crystal into a block shape, cutting it into a wafer having a predetermined thickness, and finally mirror-finishing the surface to a desired thickness. The wafer processing step to be processed, the etching step of forming a wafer into a tuning fork shape by etching using photolithography technology, and forming an electrode and a wiring pattern thereon are obtained in this way. The crystal vibrating piece is mounted on a plug made of, for example, a hermetic terminal, and the frequency is adjusted and then sealed in a vacuum case.
[0003]
In the wafer processing step, as shown in the flowchart of FIG. 9, in order to remove the cut processing layer generated at that time and to obtain a predetermined plate thickness on both surfaces of the crystal wafer cut out from the block, Lapping is performed while gradually reducing the particle size of the particles. As a result, the surface of the wafer becomes a so-called lapped surface having a relatively frosted glass shape. Next, the wafer is etched with an aqueous solution of ammonium fluoride (NH 4 F) to remove and clean the work-affected layer on the lapping surface, and at the same time, the wafer is adjusted to a desired thickness. As a result, a so-called satin-like surface (hereinafter referred to as a satin-like surface) is obtained in which the surface of the wafer has very fine irregularities but has relatively little diffused reflection of light.
[0004]
In this case, in order to remove the work-affected layer, for example, when processing with abrasive grains of about GC # 2000, about 10 μm or more is required for each side of the wafer. However, when the etching amount by the NH4F aqueous solution is increased in this way, a large number of projections 3 called hillocks having a triangular pyramid shape corresponding to the crystal plane direction of the crystal as shown in FIG. The number grows with increasing etching time. For this reason, the wafer surface cannot be maintained on a uniform textured surface, and a surface roughness with a quality sufficient to form a corrosion-resistant film on the wafer surface in a later process and etch it into a tuning fork shape cannot be obtained. .
[0005]
Therefore, conventionally, polishing is then performed using an abrasive mixed with finer abrasive grains such as silica and cerium oxide and an etching solution to remove hillocks, and the wafer surface is processed into a high-quality mirror surface. After cleaning the wafer, it is lightly etched with a mixed aqueous solution of hydrofluoric acid and ammonium fluoride (hereinafter referred to as buffered hydrofluoric acid) (the etching amount is about 0.5 to 1 μm per side) to remove processing distortion caused by polishing. Finally, the wafer is finished to the desired high quality mirror surface, flatness and thickness. Thereafter, the wafer is rinsed and finished and inspected for dirt, scratches, cracks, and the like. Thereby, sufficient adhesion is obtained between the wafer surface and the corrosion-resistant film formed thereon in the subsequent etching process step into the tuning fork shape.
[0006]
[Problems to be solved by the invention]
However, the above-described conventional method for manufacturing a tuning-fork type crystal vibrating piece using the surface processing technology for quartz crystal requires a very long time for polishing the wafer in the wafer processing step, and the thickness of the wafer is reduced by etching with an NH4F aqueous solution. Is already thinned, it is easy to cause damages such as cracks and chips on the wafer during polishing, and the processing work is delicate and cumbersome, requiring a lot of labor, reducing the yield and increasing the manufacturing cost. There was a problem to do.
[0007]
Therefore, the present invention has been made in view of the above-mentioned conventional problems, and the object of the present invention is to use the crystal material in terms of its application and use conditions when the surface of the crystal material is processed smoothly. A quartz surface processing method that can easily obtain good surface roughness and flatness that is substantially free of hillocks and micro-protrusions, without any polishing process, is provided on demand. There is to do.
[0008]
Furthermore, an object of the present invention is to eliminate the conventional polishing process in the wafer processing step in the manufacturing method of the crystal piece for forming the crystal wafer into a desired shape by etching, thereby reducing the time required for the wafer processing. Good surface roughness, which can shorten, simplify work, reduce labor, improve yield and reduce manufacturing cost, and is substantially free of hillocks and micro-projections that are compatible with conventional polishing processes. Another object of the present invention is to provide a simple and inexpensive method capable of processing a crystal piece in flatness and thickness. In particular, an object of the present invention is to provide a method suitable for manufacturing a tuning fork type quartz crystal vibrating piece.
[0009]
[Means for Solving the Problems]
The quartz surface processing method of the present invention is for achieving the above-described object, and includes a process of lapping the surface of the quartz material and a process of etching the lapped surface of the quartz material with hydrofluoric acid. It is characterized by.
[0010]
It is well known that hydrofluoric acid can dissolve quartz crystal under normal temperature and pressure as an etchant, similar to NH4F aqueous solution. The NH4F aqueous solution and NH4F-based etching solution generate hillocks on the etched surface, which grows greatly depending on the etching time, whereas hydrofluoric acid has a substantially constant state regardless of the amount of etching. It is maintained. For this reason, according to the present invention, the lapping surface of the quartz material by lapping can be made into a satin surface with very fine irregularities and relatively little light irregular reflection by hydrofluoric acid etching, and depending on the etching amount. Therefore, it is possible to always maintain a good pear-ground state with almost constant quality without hillocks. Therefore, the processed layer due to lapping is removed only by etching of the quartz material, and a surface state having high quality smoothness in accordance with requirements such as the use and use conditions of the quartz material can be obtained.
[0011]
In this etching process of quartz material surface with hydrofluoric acid, if hydrofluoric acid with surfactant added is used as the etchant, the surface tension is lowered and more uniform etching treatment is performed, resulting in a more uniform surface state as a whole. Is advantageous.
[0012]
Furthermore, the quartz surface processing method of the present invention further includes a step of finishing etching the quartz crystal material with buffered hydrofluoric acid after the etching with hydrofluoric acid. In general, etching with hydrofluoric acid tends to cause nipple-like microprotrusions on the etched surface of the quartz material, which may impair the smoothness of the textured surface. Therefore, by performing finish etching that is light enough to prevent hillocks from being generated by buffered hydrofluoric acid, it is possible to remove the fine protrusions and obtain a so-called matte surface that is smoother and higher quality than the satin surface.
[0013]
Further, according to the present invention, a process of lapping a quartz wafer having a predetermined dimension, a process of etching the lapped crystal wafer to a desired thickness with hydrofluoric acid, and etching the crystal wafer etched with hydrofluoric acid are desired. And a step of forming the crystal piece into a shape.
[0014]
For the lapped quartz wafer, only the etching process of hydrofluoric acid is used to remove the work-affected layer due to lapping from the lapping surface, adjust to the desired thickness, and smoothness required in the subsequent etching molding process to the desired shape High quality pear ground satisfying the characteristics can be obtained. Also in this case, it is advantageous to use a hydrofluoric acid to which a surfactant is added as an etchant in the etching process of the quartz wafer with hydrofluoric acid, because a more uniform surface state can be obtained by a more uniform etching process.
[0015]
Further, when a nipple-like microprojection is generated on the wafer surface by the hydrofluoric acid etching as described above, when the quartz wafer is etched in a later molding process, the microprojection portion is a corrosion-resistant film or a resist protective film. There is a risk that etch pits may occur due to insufficient coverage. According to the present invention, it is advantageous to perform the etching while the quartz crystal wafer is swung in hydrofluoric acid because the generation of the fine protrusions can be suppressed.
[0016]
Furthermore, the method for producing a crystal piece according to the present invention further includes a step of etching the crystal wafer etched with hydrofluoric acid with buffered hydrofluoric acid before forming the crystal wafer into the desired shape. By performing a light finish etching with buffered hydrofluoric acid that does not cause hillocks, the fine protrusions generated on the surface of the quartz wafer are removed and the wafer surface is processed to be flatter, so that the matte surface is smoother than the matte surface. You can get a plane.
[0017]
Preferably, the quartz wafer etched with hydrofluoric acid is cleaned before the final etching with buffered hydrofluoric acid. As a result, foreign matters and dirt deposited or adhered to the surface of the quartz wafer after etching with hydrofluoric acid can be removed in advance, so that even more advanced finish etching can be performed effectively. In particular, by performing ultrasonic cleaning using pure water, it is possible to remove fine precipitates, foreign matter, and dirt that cannot be easily removed by etching with buffered hydrofluoric acid from the surface of the quartz wafer.
[0018]
According to the present invention, a crystal resonator, a crystal sensor, a crystal filter, and the like are formed by forming electrodes and a wiring pattern on the surface of the crystal wafer formed into a desired shape in this way using a photolithography technique. Crystal element pieces constituting the crystal device can be obtained. In particular, a crystal vibrating piece for a tuning fork type crystal resonator can be obtained by forming a crystal wafer into a tuning fork shape.
[0019]
When etching a quartz wafer into a tuning fork shape or other desired shape, according to the present invention, a Cr film formed on the smooth quartz wafer surface obtained by the above-described process, and an Au film laminated thereon It is convenient to form a corrosion-resistant film having a two-layer structure. Further, according to the present invention, when a thick photoresist film is formed on the corrosion-resistant film, hillocks and microprojections are sufficiently covered and protected by the photoresist film, and the generation of the etch pits occurs. This is convenient.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail using preferred embodiments with reference to the accompanying drawings.
FIG. 1 shows a preferred embodiment of a manufacturing process of a tuning-fork type crystal vibrating piece according to the present invention. First, in the same manner as the conventional process described above with reference to FIG. 9, the artificial quartz ore is cut into blocks of a predetermined size and shape, and the outer shape is adjusted by chamfering, polishing, etc., and then using, for example, a multi-blade saw. Cut into a wafer with a predetermined plate thickness. The thickness of the quartz wafer at this time is determined in consideration of the polishing allowance for the subsequent lapping process and the etching amount in the etching process. Next, the surface of the quartz wafer is lapped using a double-side polisher, and the processing layer at the time of wafer cutting is removed while gradually shifting from coarse abrasive grains to fine abrasive grains (for example, about GC # 2000), and Processing to a predetermined wafer thickness and surface condition. The ground glass-like relatively rough surface state obtained at this time is called a lapping surface as described above.
[0021]
According to the present embodiment, the quartz wafer that has been subjected to the lapping is cleaned and then roughly etched using hydrofluoric acid. At this time, if a small amount of surfactant is added to hydrofluoric acid to lower the surface tension of the etching solution and the temperature is adjusted to about 45 ° C., the lapping surface of the wafer can be etched uniformly. . By this rough etching, the work-affected layer is removed from the surface of the quartz wafer, and the wafer is further adjusted to a desired thickness. The etching amount is set so that the work-affected layer generated during the lapping process can be removed. When processed with, for example, GC # 2000 abrasive grains, about 10 μm or more per side is required.
[0022]
Next, in this embodiment, after the wafer surface is cleaned, etching is performed with buffered hydrofluoric acid in the same manner as in the prior art, and finishing is performed. In particular, in the manufacture of a quartz crystal vibrating piece, ultrasonic cleaning using pure water is preferable because of its properties. In another embodiment, ethanol, isopropyl alcohol, or the like can be used instead of pure water. Since buffered hydrofluoric acid is an NH 4 F-based etching solution, the etching amount is advantageously several μm per side, for example, about 5 μm so as not to cause hillocks.
[0023]
It is well known to those skilled in the art that hydrofluoric acid is an etching agent that can dissolve crystal under normal temperature and pressure, similar to the NH4F aqueous solution described above. The surface state of the wafer obtained by the rough etching is the above-mentioned textured surface with very fine irregularities, but it is smooth and good with less specular reflection than the conventional textured surface of etching with NH4F aqueous solution. Surface. This is because in the case of etching with an NH4F aqueous solution, as described above, hillocks increase with the etching time, and the etched surface becomes rough. On the other hand, in the case of hydrofluoric acid, the state of the etched surface is substantially constant regardless of the amount of etching. For this reason, in the rough etching process, even if the etching amount varies from wafer to wafer, there is an advantage that a surface state with a substantially constant quality can be obtained at all times and that the obtained pear ground state can be maintained.
[0024]
However, in the case of etching with hydrofluoric acid, a papillary microprotrusion 2 as shown in FIGS. 2A and 2B may occur on the etching surface 1 of the quartz wafer. The minute protrusions 2 are formed so as to protrude from the apex of the crystal structure of the quartz crystal that appears in a triangular pyramid shape on the etched surface. For this reason, when a corrosion-resistant film is formed on the wafer surface for etching into a tuning fork shape in a later process, the corrosion-resistant film becomes thin or does not form at the portion of the minute protrusion, and this portion is eroded by the etching solution. As a result, etch pits may occur on the wafer surface. The inventor of the present application has confirmed that the generation of the fine protrusions can be suppressed by performing the rough etching while oscillating the crystal wafer in hydrofluoric acid.
[0025]
Further, according to the present invention, fine etching generated on the surface of the quartz wafer can be removed and the wafer surface can be processed more smoothly by performing finish etching with buffered hydrofluoric acid after rough etching with hydrofluoric acid. . The surface state of the wafer thus obtained is not as high as the mirror-like surface by the conventional polishing process, but is required for the subsequent etching process to a tuning fork shape in which unevenness is further reduced from the matte surface and less diffused light is reflected. It is a so-called matte surface that sufficiently satisfies the smoothness.
[0026]
In particular, in this embodiment, the quartz wafer surface is cleaned before the finish etching with buffered hydrofluoric acid, thereby preventing the occurrence of minute projections due to minute foreign matters and dirt existing on the wafer surface during the finish etching. This inventor confirmed this. This is thought to be because foreign matter and dirt deposited or adhered to the wafer surface after the rough etching with hydrofluoric acid were removed, even minute ones that could not be easily removed with buffered hydrofluoric acid, and more reliably with higher quality. A matte surface with sufficient smoothness can be obtained.
[0027]
FIG. 3 shows the surface state after the final etching with an etching amount of 1.0 μm is actually performed on the quartz wafer of FIG. 2 with buffered hydrofluoric acid. At this point, the microprotrusions are substantially removed, but the smoothness is substantially the same as the textured surface after the rough etching and is not so high. FIG. 4 shows the surface state when the final etching is continued with buffered hydrofluoric acid and the etching amount is 3.5 μm. The microprotrusions are completely eliminated and the entire surface is smoother. Although small hillocks are generated, there is no practical problem, and no hillocks that are large enough to cause etch pits in the subsequent etching process to the tuning fork shape are recognized. .
[0028]
When the quartz wafer is etched with buffered hydrofluoric acid, the inventors of the present application conducted an experiment to measure the roughness of the wafer surface with respect to the etching amount. FIG. 5 shows the change of the surface roughness, that is, the maximum value (Rmax) of the unevenness with respect to the etching amount, and FIG. 6 shows the change of the average value (Ra) of the unevenness with respect to the etching amount. In addition, when the quartz wafer etched with buffered hydrofluoric acid is etched into a tuning fork shape in a later process, the inventor of the present application conducted an experiment to measure the generation of etch pits with respect to the etching amount. FIG. 7 shows the change in the number of etch pits per unit area (1 mm ² ) with respect to the etching amount. From these experimental results, it was found that it is preferable that the unevenness is the smallest, the number of etch pits is the smallest, and the variation is the smallest when the etching amount is in the range of about 1.5 to 4 μm.
[0029]
The quartz wafer that has been subjected to the rough etching and finish etching in this manner is rinsed off with an etchant and then etched into a tuning fork according to the process shown in FIG. First, a Cr film and an Au film are laminated on the front and back surfaces of the wafer by sputtering to form a corrosion resistant film. The Cr film and the Au film can also be formed by vacuum deposition. Next, after applying a resist film on the corrosion-resistant film and pre-baking it, both the front and back surfaces are simultaneously exposed using a photomask, developed, and post-baked at a predetermined temperature to obtain a predetermined tuning fork shape. Pattern. Using the resist film as a protective film, the corrosion-resistant film is etched and patterned into the tuning fork shape. According to the present invention, it is advantageous to form the resist film on the corrosion-resistant film to be thicker than usual, for example, to a thickness of about 1 to 2 μm. As a result, when the quartz wafer is etched into a tuning fork shape in the next step, the Cr film and the Au film at the hillocks and minute projections are protected by a thick resist film, thereby preventing the occurrence of etch pits. .
[0030]
Next, the quartz wafer is etched using hydrofluoric acid as an etchant to form a tuning fork shape. Further, when the resist film, Cr film and Au film remaining on the wafer are peeled off and washed, a quartz wafer having a desired tuning fork shape is obtained. Finally, a Cr layer and an Au layer are formed on each tuning-fork-shaped element piece by sputtering to form an electrode film, and predetermined electrodes and wiring patterns are formed using a photolithography technique as in the conventional case. Each crystal vibrating piece obtained in this way is mounted on a plug made of a hermetic terminal, and after adjusting the frequency, it is vacuum-sealed in a cylindrical metal case to complete a tuning fork type crystal resonator. .
[0031]
Although the present invention has been described in detail with reference to preferred embodiments thereof, as will be apparent to those skilled in the art, the present invention is implemented with various modifications and changes within the technical scope thereof. be able to. Naturally, the present invention is not limited to a tuning fork type crystal resonator, but also in the manufacture of various crystal devices such as a longitudinal vibration crystal resonator, a crystal oscillator, a crystal sensor, and a crystal filter. The same can be applied to the case where a crystal piece is manufactured by forming into a desired shape by etching. Furthermore, the present invention can be applied to various fields that require high-quality surface processing without the above-mentioned hillocks and microprojections, using quartz as a material, depending on the application. The cleaning performed after etching with hydrofluoric acid and before the final etching with buffered hydrofluoric acid, in addition to the above-described ultrasonic cleaning of pure water, depending on the processing conditions and applications of the crystal, impact pure water on the crystal surface as necessary. In particular, various cleaning methods such as a spraying method can be used.
[0032]
【The invention's effect】
Since this invention is comprised as mentioned above, there exists an effect as described below.
According to the quartz surface processing method of the present invention, the lapping-processed quartz material is etched with hydrofluoric acid, thereby removing the work-affected layer by lapping without further polishing, and without hillocks. A smooth pear ground is obtained. Furthermore, if necessary, finish etching with buffered hydrofluoric acid after etching with hydrofluoric acid eliminates nipple-like microprojections generated by hillock and hydrofluoric acid etching, and a smoother matte surface can be obtained. . In this way, according to the requirements of the quartz material application, usage conditions, etc., it is possible to obtain a surface state that satisfies this relatively easily, greatly reducing the time required for surface processing, reducing labor, and cost. Reduction can be achieved.
[0033]
In addition, according to the method for manufacturing a quartz piece of the present invention, after lapping the quartz wafer, the conventional polishing process can be omitted by etching to a desired thickness with hydrofluoric acid instead of the conventional NH4F aqueous solution. A surface that satisfies the smoothness required for etching processing to the desired tuning fork shape, etc. at the same time as removing the damaged layer by lapping and adjusting to the desired thickness by etching the quartz wafer. Therefore, the time required for wafer processing can be greatly shortened, the work can be simplified and labor can be reduced, and the yield can be improved and the manufacturing cost can be reduced.
[0034]
Further, according to the present invention, the quartz wafer etched with hydrofluoric acid is etched to the extent that hillocks are not generated with buffered hydrofluoric acid, and the finishing process is performed after cleaning, or by performing the finishing process after washing. The pear ground obtained by etching can be processed more flatly, and it is possible to prevent the occurrence of etch pits on the wafer surface in the subsequent etching process to a desired shape, so that the yield can be further improved.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a process of processing a quartz wafer by the method of the present invention.
FIG. 2A is a photograph in which the surface state of a quartz wafer after rough etching with hydrofluoric acid is magnified 3500 times, and FIG. 3B is a diagram simulating the surface state from the side.
FIG. 3 is a photograph of the surface state after etching 1.0 μm with buffered hydrofluoric acid on the quartz wafer of FIG. 2 enlarged 3500 times.
4 is a photograph of the surface state of the quartz wafer of FIG. 2 magnified 3500 times after etching with buffered hydrofluoric acid for 3.5 μm.
FIG. 5 is a diagram showing a change in the maximum value (Rmax) of the surface roughness with respect to the etching amount of the wafer by buffered hydrofluoric acid.
FIG. 6 is a diagram showing the change in the average value (Ra) of the surface roughness with respect to the etching amount of the wafer by buffered hydrofluoric acid.
FIG. 7 is a diagram showing the change in the number of etch pits per unit area with respect to the etching amount of the wafer by buffered hydrofluoric acid.
FIG. 8 is a flowchart showing a process of forming a tuning fork shape on a quartz wafer by the method of the present invention, following the process of FIG. 1;
FIG. 9 is a flowchart showing a process of processing a conventional quartz wafer.
FIG. 10A is a photograph of the surface state of a crystal wafer after rough etching with an NH 4 F aqueous solution enlarged 3500 times, and FIG. 10B is a diagram simulating the surface state from the side.
[Explanation of symbols]
1 Etching surface 2 Microprojection 3 Protrusion (hillock)

Claims (11)

The process of lapping the surface of the quartz material, the process of etching the lapped surface of the quartz material with hydrofluoric acid, and the surface of the quartz material etched with hydrofluoric acid at an etching amount of 1.5 to 4 μm with buffered hydrofluoric acid A method of surface processing of quartz, comprising a step of etching . In the etching process by hydrofluoric acid, the surface processing method of the crystal of claim 1, wherein the use of hydrofluoric acid containing a surfactant to the etchant. A process of lapping a quartz wafer of a predetermined size, a process of etching the lapped crystal wafer to a desired thickness with hydrofluoric acid, and etching the crystal wafer etched with hydrofluoric acid to 1.5 to 4 μm with buffered hydrofluoric acid A method for producing a crystal piece, comprising: a step of etching by a quantity; and a step of forming the crystal wafer etched by buffered hydrofluoric acid into a desired shape by etching. 4. The method for manufacturing a crystal piece according to claim 3 , further comprising a step of cleaning the crystal wafer etched with hydrofluoric acid before etching with the buffered hydrofluoric acid. The method for producing a crystal piece according to claim 4, wherein the cleaning is ultrasonic cleaning using pure water. 6. The method for manufacturing a crystal piece according to claim 3 , wherein in the etching process using hydrofluoric acid, etching is performed while rocking the crystal wafer in hydrofluoric acid. 7. The method for manufacturing a crystal piece according to claim 3 , wherein hydrofluoric acid added with a surfactant is used as an etching solution in the etching process using hydrofluoric acid. 8. The method for producing a crystal piece according to claim 3 , wherein an electrode and a wiring pattern are formed on the surface of the crystal wafer formed into the desired shape by using a photolithography technique. 9. The method for manufacturing a crystal piece according to claim 3 , wherein the desired shape is a tuning fork shape of a tuning fork type crystal vibrating piece. The step of forming the crystal wafer into the desired shape includes a step of forming a corrosion-resistant film composed of a Cr film formed on the surface of the crystal wafer and an Au film laminated thereon. The manufacturing method of the crystal piece in any one of Claim 3 thru | or 9 . 11. The method for manufacturing a crystal piece according to claim 10 , wherein a thick photoresist film is formed on the corrosion-resistant film in the step of forming the crystal wafer into the desired shape.

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