JP2005213113A - Apparatus for growing oxide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the quality of a growing crystal in a growth vessel is degraded by thermal stress because the temperature gradient during descending of the growth vessel and at the time of completion of the descending becomes large relatively when the temperature gradient is made large at the solid-liquid interface position in a conventional apparatus, in the growth of the oxide single crystal by a vertical Bridgman method. <P>SOLUTION: In the growth apparatus, a cylindrical heat insulating part is arranged at a part lower than the lowest part of the growth vessel at the position at the time of completion of descending of the growth vessel in a furnace core tube. Thereby, the temperature gradient is made small during descending of the growth vessel and at the time of completion of the descending without changing the temperature gradient at the solid-liquid interface position, and the high quality crystal can be grown. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an oxide single crystal growth apparatus. More specifically, the present invention relates to a growth apparatus for lithium tetraborate single crystal, which is a borate-based oxide crystal.

  A lithium tetraborate single crystal, which is one of oxide single crystals, is used as a substrate crystal of a surface acoustic wave device, and optical applications have been reported. As a method for artificially growing such a lithium tetraborate single crystal, the Czochralski method and the vertical Bridgman method are known, and various single crystal growing apparatuses have been invented in accordance with the manufacturing method.

  FIG. 4 shows a part of an apparatus for growing an oxide single crystal using the conventional vertical Bridgman (VB) method. In the growth furnace 41, a space in which a later-described growth vessel 44 can be arranged and moved in the vertical direction is provided in the core tube 42. Further, the inside of the furnace core tube 42 is replaced with an inert atmosphere or an oxidizing atmosphere. A support base 45 that supports the growth container 44 is provided at the bottom of the outer side of the growth container 44, and a drive device that moves the growth container 44 and the support base 45 up and down in the core tube 42 is connected to the support base 45. ing.

  The inside of the reactor core tube is heated by a heater 43 disposed in the growth furnace 41, the temperature is set so that the upper part in the furnace core tube is higher than the melting point temperature of the oxide single crystal and the lower part is lower than the melting point temperature. Then, the growth vessel 44 containing the seed crystal 46 and the oxide single crystal raw material 47 to be grown thereon is inserted so that the upper portion of the seed crystal 46 is at a temperature equal to or higher than the melting point. Thereafter, the growth vessel 44 is moved downward in the growth furnace at an optimum speed, so that the single crystal is gradually formed from the raw material lower portion to the upper portion of the seed crystal upper portion.

  The following documents are disclosed about the apparatus for growing an oxide single crystal as described above.

JP 2001-106597 A Japanese Patent Laid-Open No. 9-20596

  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 vertical Bridgman method growth, temperature control at the temperature position that becomes the solid-liquid interface in the core tube is important for growing high-quality oxide crystals. If the temperature gradient at the solid-liquid interface is small, cell growth, light scatterers, etc. occur and the quality of the grown crystal is degraded. To obtain high-quality crystals, it is necessary to increase the temperature gradient at the solid-liquid interface. There is.

  However, in the conventional growth apparatus, if the temperature gradient at the solid-liquid interface position is increased, the temperature gradient in the furnace tube at the position where the growth crystal is lowered and the temperature of the entire growth crystal reaches the temperature below the melting point becomes relatively large. The temperature difference between the upper part and the lower part of the grown crystal is increased, and the thermal stress associated therewith is increased. Further, cracks occurred when the thermal stress exceeded the limit value.

  In order to reduce the temperature gradient during the descent of the growth vessel and at the end of the descent without changing the temperature gradient at the solid-liquid interface position, it is possible to divide the heater in the vertical direction and control it individually. However, there is a limit to the minimum length per heater for subdivision of the heater, and the furnace core tube made of a good thermal conductivity material is inside the divided heater. It is actually difficult to change the gradient partly.

  In order to solve the above-mentioned problems of the prior art, the present invention has arranged a growth vessel in a reactor core tube in which the upper part is set to a temperature higher than the melting point and the lower part is set to a temperature lower than the melting point by a heater. In an oxide single crystal growth apparatus using the vertical Bridgman method in which a growth vessel is positioned on the top and the raw material is melted, and then the growth vessel is lowered to grow crystals, the growth vessel is lowered and the entire crystal is melted. An apparatus for growing an oxide single crystal, characterized in that a cylindrical heat insulating portion is disposed in a reactor core tube below a lowermost portion of a grown crystal at a position where the following temperature is reached.

  Further, the growth apparatus is characterized in that lithium tetraborate is grown as the oxide single crystal.

  If a cylindrical heat insulating part is disposed in the furnace core tube below the lowest part of the growing crystal at the position where the entire crystal reaches a temperature below the melting point as in the present invention, the position at which the solid-liquid interface is formed Without changing the temperature gradient, it is possible to reduce only the temperature gradient in the grown crystal during and after the descent. As a result, the thermal stress in the grown crystal can be made extremely small, and a high quality grown crystal can be obtained.

  Also, in the growing apparatus, it is possible to configure a growing apparatus that is inexpensive and not complicated without increasing the number of heaters.

  Therefore, by using the growth apparatus according to the present invention, there is an effect of providing an inexpensive and high quality oxide single crystal.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing a state at the end of growth of a growth apparatus used for growing a lithium tetraborate single crystal which is one of oxide single crystals in the present invention.
FIG. 2 is a graph showing the tube temperature at an arbitrary position of the core tube.
FIG. 3 is a perspective view showing a heat insulating portion arranged in the core tube.
In FIG. 1 and FIG. 3, a part of the structure is not shown for clarity of explanation, and some dimensions in the figure are also exaggerated.

  That is, the core tube 12 constituting the growth furnace 11 is formed in a cylindrical shape and arranged in the vertical direction. A heater 13 is disposed outside the core tube 12, and the temperature inside the core tube 12 can be set by the heater 13. Further, the inside of the furnace core tube 12 is an inert atmosphere or an oxidizing atmosphere.

  A growth vessel 14 for growing a lithium tetraborate single crystal is disposed in the core tube 12. The growth container 14 is made of ceramics such as alumina. A support device 15 is disposed at the bottom of the growth container 14. A driving device 19 for moving the growth vessel 14 and the support device 15 up and down in the core tube 12 is provided below the support device 15.

  In this reactor core tube 12, a growth vessel 14 is lowered, and a cylindrical heat insulating portion 17 is arranged in the reactor core tube below the bottom of the growth vessel 14 at a position where the entire crystal has reached a temperature equal to or lower than the melting point. The heat insulating portion 17 is formed of ceramic bricks or ceramic fibers, and has thermal and chemical stability in a growing environment, and has no outer gas. A support device 15 passes through a hole penetrating the central portion of the heat insulating portion 17.

  Next, a single crystal growth method using the growth apparatus of the present invention will be disclosed. First, a plate-like lithium tetraborate seed crystal is placed in the growth vessel 14, and a high-purity four-crystal is formed above the lithium tetraborate seed crystal. After the lithium borate raw material is contained in the lid, the lid 18 is placed.

  The driving vessel 19 is used to raise the growth vessel 14 and the support device 15 in the core tube 12 set to a temperature gradient necessary for growth by the heater 13, and the lithium tetraborate raw material in the growth vessel 14 is melted. FIG. 2 is a graph showing the temperature at each position in the core tube. A curve α is a temperature distribution curve in the conventional growing apparatus, and a curve β is a temperature distribution curve in the present embodiment in which the heat insulating portion 17 is arranged.

  Next, when the lithium tetraborate seed crystal upper portion in the growth vessel 14 inserted and raised in the reactor core tube 12 reaches a temperature equal to or higher than the melting point, the drive device 19 is stopped and the growth vessel 14 is moved to the position for a certain time. Hold on.

  Thereafter, the growth container 14 is lowered at 0.3 to 2.0 mm / h by the driving device 19 and moved to a temperature position lower than the melting point, whereby a lithium tetraborate single crystal is gradually crystallized on the lithium tetraborate seed crystal. And the descent was terminated at the position in the tube where the upper portion of the grown crystal reached a temperature lower than the melting point temperature (point a in FIGS. 1 and 2). The position of the growth container in the apparatus shown in FIG. 1 is the container position at the end of the growth container descent. The temperature gradient in the grown crystal at this time was made to be a temperature gradient less than half of the conventional temperature gradient by the action of the heat insulating portion 17 in accordance with the furnace temperature distribution curve of FIG.

  Thereafter, after gradually cooling to a temperature close to room temperature, the grown crystal is taken out from the growth container. The grown crystal is a high quality lithium tetraborate single crystal with no cracks and no minute light scatterers.

  In the above examples, the case where a lithium tetraborate single crystal is grown as an oxide single crystal is exemplified, but the present invention is not limited to the growth of lithium tetraborate, but has a thermal conductivity such as lithium niobate or langasite. Even if the present invention is implemented in an apparatus for growing small oxide single crystals, the same effect is obtained, and the present invention can also be used as an apparatus for growing these oxide single crystals.

FIG. 1 is a schematic sectional view showing a growth apparatus used for growing an oxide single crystal in the present invention. FIG. 2 is a graph showing the tube temperature at each position of the core tube. FIG. 3 is a perspective view showing a heat insulating portion provided in the growing apparatus according to the present invention. FIG. 4 is a schematic view showing an oxide single crystal growth apparatus in the prior art.

Explanation of symbols

11, growth furnace 12, furnace core tube 13, heater 14, growth vessel 15, support fixture 16, oxide single crystal (lithium tetraborate single crystal)
17, heat insulation part 18, lid 19, drive device

Claims (2)

  A growth vessel is placed in a reactor core tube whose upper part is set to a temperature higher than the melting point and lower part is set to a temperature lower than the melting point by a heater. The growth vessel is filled with seed crystals and raw materials. In the apparatus for growing an oxide single crystal by a vertical Bridgman method in which the growth vessel is lowered and the raw material is gradually solidified from below to above in the growth vessel to grow a crystal by gradually solidifying the raw material. An apparatus for growing an oxide single crystal, characterized in that a cylindrical heat insulating portion is disposed in a furnace core tube below a growth crystal lowermost portion at a position where the growth vessel is lowered and the whole raw material reaches a temperature equal to or lower than a melting point. .   The growth apparatus according to claim 1, wherein the oxide single crystal is a lithium tetraborate single crystal.

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