JP4493486B2 - Crystal forming substrate - Google Patents

Description

  The present invention relates to a crystal forming substrate used in a manufacturing method obtained by epitaxially growing a desired crystal layer on a crystal forming substrate cut out from a crystal body, and more particularly to crystal forming using crystal as a material constituting the crystal forming substrate. Regarding the substrate.

  As a piezoelectric element mounted on an electronic component such as a vibrator, an oscillator, or a surface acoustic wave element, a crystal element plate processed into a flat plate shape is widely used. As a method for producing this quartz base plate, a method of cutting and polishing a quartz single crystal obtained by a hydrothermal synthesis method to form a flat plate has been conventionally used. A so-called “gas phase transport method” has been developed.

  This "vapor phase transport method" means that epitaxial growth is performed on a crystal forming substrate or a buffer layer formed on this substrate by a reaction between an inexpensive silicon alkoxide raw material and oxygen at atmospheric pressure without using a vacuum apparatus. In this method, a quartz crystal layer is formed using an atmospheric pressure vapor phase epitaxial growth method (AP-VPE).

  More specifically, in the apparatus of the schematic diagram as shown in FIG. 2, under atmospheric pressure, silicon alkoxide is vaporized and introduced onto a crystal-forming substrate in an electric furnace, and the introduced silicon alkoxide is oxygen and Alternatively, a silicon thin film layer is deposited on the crystal forming substrate by reacting silicon alkoxide with hydrogen chloride separately introduced as a reaction accelerator for oxygen.

  In this method, when the crystal thickness is formed on the substrate for crystal formation on the crystal formation substrate at a growth rate of about several μm and the crystal layer is formed to the approximate thickness excited at the desired frequency, the crystal is formed from the device. Take out the entire board. The quartz crystal layer is cut into a desired outer size with a crystal forming substrate by dicing or the like, and then the quartz crystal layer and the crystal forming substrate are separated, so that a plurality of quartz base plates mounted on each electronic component can be simultaneously formed. Make it.

  The following literature is disclosed about the manufacturing method of the above-mentioned quartz crystal layer.

JP 2002-80296 A

  In addition, the applicant has not found any prior art documents related to the present invention by the time of filing of the present application other than the prior art documents specified by the above prior art document information.

  In the above-described method for manufacturing a quartz crystal layer, a sapphire crystal substrate is used as a crystal formation substrate because of physicochemical stability in a crystal formation environment. However, the sapphire crystal substrate has a higher hardness than the crystal crystal layer to be formed, and it takes time for the dicing cutting process, so the workability is remarkably deteriorated, and the dicing blade is consumed greatly. Furthermore, it is difficult to balance the cutting force at the time of the cutting process in order to perform the cutting process on the crystals having different hardnesses. Further, since sapphire crystals are expensive, there is a high possibility that the cost of the finally produced quartz base plate will be increased.

  Even if crystal is used as the material of the crystal forming substrate, the linear expansion coefficient in each crystal axis direction of the crystal constituting the crystal forming substrate depends on the cut angle when the crystal forming substrate is made of this crystal. If the anisotropy and the high-temperature treatment during epitaxial growth are performed at a crystal transition point (573 ° C.) or higher, cracks may occur in the crystal crystal layer formed on the crystal forming substrate.

The present invention has been made for the purpose of solving the above-mentioned problems, and a crystal forming substrate is disposed in an electric furnace in a high temperature state, and a crystal raw material gas and a catalyst gas are allowed to flow into the electric furnace, In a crystal forming substrate used in an artificial crystal forming method capable of epitaxially growing a crystal crystal layer on a crystal substrate,
The crystal forming substrate is a rectangular substrate using quartz as a material, and the cut angle of this crystal substrate is the crystal axis of the crystal body, the electrical axis is + X axis, the optical axis is + Z axis, and + X and + Z When a right-handed Cartesian coordinate system is configured with the mechanical axis as the + Y axis perpendicular to the axis, it rotates in the angular range of +33 degrees to +38 degrees or +142 degrees to +147 degrees around the + X axis from the + Z axis , and then + Z This is a crystal forming substrate having a cut angle rotated by +45 degrees around the + Y 'axis from the' axis .

  By using the crystal forming substrate disclosed in the present invention, the hardness is lower than that of the conventional sapphire crystal substrate, the dicing cutting process can be performed in a short time, the workability is remarkably improved, and the consumption of the dicing blade is reduced. In addition, since a crystal in which crystals having the same hardness are overlapped is cut, the balance of the cutting force during cutting is good. Further, since the quartz crystal is very cheap compared to the sapphire crystal, the cost of the quartz base plate to be manufactured can be reduced.

  Further, in the cut angle of the crystal forming substrate using the crystal according to the present invention, the linear expansion coefficient in each crystal axis direction of the crystal forming substrate is close to isotropic, so that the high temperature treatment during epitaxial growth is the crystal transition point (573 ° C.). ) Even when the above is performed, the possibility of cracks occurring in the quartz crystal layer formed on the crystal forming substrate is very low.

  Therefore, by using the crystal forming substrate of the present invention, there is an effect that it is possible to provide a quartz base plate that is highly workable and inexpensive, and further excellent in characteristics.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an apparatus for using a crystal forming substrate according to the present invention to perform epitaxial growth of a crystal crystal layer and a buffer layer on a crystal forming substrate mounted therein. FIG. 2 is a view showing an embodiment of a cut angle when a rectangular crystal forming substrate is cut out from a crystal body. FIG. 3 is a diagram showing another form of a cut angle when a rectangular crystal forming substrate is cut out from a crystal body. FIG. 4 is a view showing one form of a cut angle when a circular crystal forming substrate is cut out from a crystal body. FIG. 5 is a partial cross-sectional view showing a form in which the crystal forming substrate disclosed in FIGS. 2 to 4 is used and a crystal crystal layer is formed by the apparatus shown in FIG.

  In each figure, a part of the structure is not shown for the sake of clarity. Each dimension is also partially exaggerated, and the same reference numerals in the drawings indicate the same object.

In FIG. 1, the epitaxial growth of quartz under atmospheric pressure uses silicon alkoxide (Si (OC ₂ H ₅ ) ₄ ) as a raw material, which is evaporated by heating and crystal layer forming furnace 1 using a carrier gas such as nitrogen. The crystal crystal layer 3 is formed by being transported onto the crystal forming substrate 2 and reacting with oxygen gas on the crystal forming substrate 2. As a heating source (not shown) of the silicon alkoxide, a heater such as a high frequency induction heater or a resistance heater can be used.

  By heating silicon alkoxide, which is a raw material, a part of the alkoxide is supplied as a vapor phase to the growth section. Generally, the heating temperature is about 25 to 120 ° C. in consideration of the vapor pressure of silicon alkoxide. The carrier gas for supplying a part of the raw material to the growth part may be an inert gas, and nitrogen, argon, helium, etc. can be used, but nitrogen is preferable from the viewpoint of low cost. is there.

  The silicon raw material does not need to have a high purity (for example, 3N or 5N) used as a target for laser ablation, and a purity of about 99.5% is sufficient, but the higher the purity, the more the crystal And crystal quality can be improved.

On the other hand, oxygen for reacting with the silicon alkoxide to form the quartz crystal layer 3 is supplied as a gas to the growth section together with the carrier gas. When the amount of oxygen supplied is large, the crystal crystal layer 3 to be obtained has a high growth rate and tends to improve crystallinity, and conversely when the amount of oxygen is small, the reverse tendency is exhibited. This is thought to be due to the small equilibrium constant of the reaction for obtaining crystals from silicon alkoxide and oxygen. Accordingly, the amount of oxygen to be supplied is preferably excessive with respect to the alkoxide of silicon. If this amount is expressed as an oxygen partial pressure, it varies depending on the amount of silicon alkoxide to be evaporated, but generally 0.1 to 0. The amount is about 3 atm. Further, by supplying hydrogen chloride (HCl) to the reaction between silicon alkoxide and oxygen, the growth rate of crystal increases. This is considered that hydrogen chloride has a catalytic effect in the reaction of silicon alkoxide with oxygen. If this amount is expressed as an oxygen partial pressure, it varies depending on the amount of silicon alkoxide to be evaporated, but generally 0.001 to 0.003 atm.
The amount is about.

As the crystal forming substrate 2 used in such a manufacturing method, a crystal plate cut out from the artificially formed crystal crystal body by a cut angle shown in FIGS. To do. That is, in FIG. 2, the crystal forming substrate 1 is a rectangular flat crystal plate used in the crystal layer forming furnace of FIG. As the crystal axis of the crystal body, the + X axis is the electric axis of the crystal single crystal, the + Y axis is the mechanical axis of the crystal, the + Z axis is the optical axis of the crystal, and the above three axes of + X, + Y and + Z axes are A right-handed orthogonal coordinate system is formed as a whole. In such a coordinate system, the cut angle at which the crystal forming substrate 2 is cut out first rotates within the range of angle φ1 from +33 degrees to +38 degrees (counterclockwise is the + direction) from the + Z axis to the + X axis, and further to + Z This is an angle rotated by an angle θ1 of +45 degrees around the + Y ′ axis that is shifted from the + Y axis due to its rotation from the 'axis . Such a form is a so-called double rotation form. As a result, in FIG. 2, each orientation of the quartz substrate 21 is such that the short side is the + X ′ axis, one side of the long side is the + Z ″ axis, and one side of the thickness is the + Y ′ axis.

  Since the linear expansion coefficient of the crystal in each axis direction of the crystal forming substrate 2 cut out at such a cut angle is about 12.011, and the error between the axes is 0.01% or less, epitaxial growth is performed. Even when the high temperature treatment is performed at a crystal transition point (573 ° C.) or higher, the crystal forming substrate 2 expands isotropically in each axial direction, so that the crystal crystal formed on the crystal forming substrate 2 The possibility of cracking in the layer is very low.

In the case of a rectangular crystal forming substrate, the cut angle that exhibits the above effects is rotated in the range of an angle φ2 from +142 degrees to +147 degrees around the + Z axis from the + Z axis , as shown in FIG. and + in the crystal forming a substrate cut from a quartz crystal in Z 'from the axis + Y' cutting angle rotated by an angle θ2 about the axis to +45 degrees, a similar effect. Further, when the outer shape of the crystal forming substrate 2 is a circular flat plate shape, as shown in FIG. 4, the cut angle is only rotated within an angle φ3 from +142 degrees to +147 degrees around the + X axis from the + Z axis. A cut (so-called single rotation) crystal forming substrate has the same effect. These substrates are heated and kept at a constant growth temperature.

  The orientation of the crystal forming substrate 2 with respect to the flow of the raw material gas in the crystal layer forming furnace shown in FIG. 1 may be parallel to or perpendicular to the flow of the raw material gas, and is arranged at an angle. May be.

  In addition, the epitaxial growth of the crystal crystal layer 3 on the crystal forming substrate 2 may be performed directly on the crystal forming substrate 2, but a buffer layer having a thickness of about 25 to 80 nm is formed on the crystal forming substrate 2. The crystallinity of the quartz crystal layer 3 is further improved by providing and further epitaxially growing the quartz crystal layer 3 thereon. In FIG. 5, the crystal forming substrate 2 disclosed above is used, and the buffer layer is formed on the crystal forming substrate 2 and the crystal crystal layer 3 is formed on the buffer layer by the apparatus shown in FIG. This configuration is illustrated using a partial cross-sectional view.

FIG. 1 is a schematic diagram of an apparatus for performing epitaxial growth of each crystal layer and buffer layer on a crystal forming substrate placed inside a crystal layer forming furnace, in which the crystal forming substrate according to the present invention is used. FIG. FIG. 2 is a diagram showing an embodiment of a cut angle when a rectangular crystal forming substrate according to the present invention is cut out from a crystal crystal. FIG. 3 is a view showing another form of the cut angle when the rectangular crystal forming substrate in the present invention is cut out from the crystal body. FIG. 4 is a diagram showing an embodiment of a cut angle when a circular crystal forming substrate according to the present invention is cut out from a crystal body. FIG. 5 is a partial cross-sectional view showing a form in which the crystal forming substrate disclosed in FIGS. 2 to 4 is used and a crystal crystal layer is formed by the apparatus shown in FIG.

Explanation of symbols

1. Crystal layer forming furnace 2. Crystal forming substrate 3. Crystal crystal layer

Claims (1)

A crystal used in an artificial crystal forming method in which a crystal forming substrate is disposed in a high temperature electric furnace, a crystal raw material gas and a catalyst gas are allowed to flow into the electric furnace, and a crystal crystal layer can be epitaxially grown on the crystal substrate. In the forming substrate,
The crystal forming substrate is a rectangular substrate using quartz as a material, and the cut angle of the crystal forming substrate is such that the crystal axis of the crystal crystal body is the electrical axis + X axis, the optical axis is + Z axis, When a right-handed Cartesian coordinate system is configured with the mechanical axis as the + Y axis perpendicular to the + X and + Z axes, the angle range from the + Z axis to the + X axis is +33 degrees to +38 degrees, or +142 degrees to +147 degrees. A crystal forming substrate, which is a cut angle that is rotated and further rotated at an angle of +45 degrees around the + Y ′ axis from the + Z ′ axis .

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