Patent Application
20130263785
1. Field of Invention
The present invention relates to a crucible and, more particularly, to a crucible to provide a dense thermal gradient in thermal radiation for growing crystals.
2. Related Prior Art
Physical Vapor Transport (“PVT”) and physical vapor deposition (“PVD”) are often used to grow of silicon carbide crystals and mass produce chips. For example, as disclosed in U.S. Pat. No. 5,746,827, silicon carbide crystals are grown in a PVT process. Several problems are encountered in the PVT process. For example, the heat gradient is large. The pressure of the protective gas is low. It is difficult to control the temperature of the seed crystal and the pressure of the sublimation gas. The PVT process is unstable. The yield of the growth of the crystals is poor. Microtubules (or “thermal decomposition pores”) or polycrystalline occurs to fail the PVT process.
As disclosed in U.S. Pat. No. 7,316,747, a thermal radiation process is used to grow quality silicon carbide crystals. The thermal radiation process however suffers some problems. The thermal field is uneven. Thus, the rate of the decomposition of the powder source varies. Hence, the concentrations of the gases in the growth chamber are unstable. Accordingly, the partial pressures in the growth chamber vary. Therefore, it is difficult to control Single polytype.
As disclosed in U.S. Pat. No. 6,824,611, a process is used to control and improve the growth of silicon carbide crystals. However, the silicon reacts with the graphite used in the container so that excessive carbon or silicon is produced to change the compositions of the gases in the sublimation. In addition, the silicon attacks the interior of the container made of the graphite and produces carbon debris which becomes impurity in the silicon carbide crystals and affects the quality of the silicon carbide crystals.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.
It is the primary objective of the present invention to provide a crucible to provide a dense thermal gradient in thermal radiation for growing crystals.
To achieve the foregoing objectives, the crucible includes a growth chamber for containing a material source, a holder attached to an upper internal portion of the growth chamber for holding a seed crystal, a reflector placed around the holder for reflecting thermal radiation, and a gas-guiding device placed on a lower internal portion of the growth chamber for guiding gas produced by sublimation of the material source.
In another aspect, the gas-guiding device includes needles arranged in groups extending along concentric circles around an axis of the growth chamber.
In another aspect, the gas-guiding device includes rods arranged in groups extending along concentric circles around an axis of the growth chamber.
In another aspect, the gas-guiding device includes gas-guiding elements in the form of concentric annular sheets extending around an axis of the growth chamber.
In another aspect, the gas-guiding device includes a single gas-guiding element in the form of a spiral sheet.
Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings.
The present invention will be described via detailed illustration of four embodiments referring to the drawings wherein:
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The growth chamber 10 is used to contain the seed crystal 90 and the material source 91 to grow crystals therein. The growth chamber 10 stands high temperature, and receives heat from an external heat source. The heat is used to grow crystals. The growth chamber 10 includes a cylindrical wall extending about an axis between a ceiling and a floor.
The holder 20 is used to hold the seed crystal 90. The holder 20 is attached to the ceiling of the growth chamber 20.
The reflector 30 is used to reflect thermal radiation L to the gas-guiding device placed in the growth chamber 20. The reflector 30 is attached to the ceiling of the growth camber 20. The reflector 30 is preferably an annular element extending around the holder 20. The reflector 30 is made of a high-temperature metal carbide or the same material as the material source 91. The reflector 30 stands high temperature in a range of 1500° C. to 3000° C. or a larger range. The angle A of a lower face of the reflector 30 is changeable in a range of 0 to 30 degrees or a larger range. The angle A of the lower face of the reflector 30 is changeable to change the thermal field, reduce the distribution of temperature in a region influenced by the thermal gradient, and reduce microtubules.
In the first embodiment, the gas-guiding device includes many gas-guiding elements 40 attached to the floor of the growth chamber 10. The gas-guiding elements 40 are divided into several groups extending along evenly distributed concentric circles around the axis of the growth chamber 10. The groups get shorter in a direction toward the cylindrical wall of the growth chamber 10 from the axis of the growth chamber 10. The gas-guiding elements 40 are made of a same height in each group. All of the gas-guiding elements 40 extend higher than the material source 91. The gas-guiding elements 40 are made of a high-temperature metal carbide or the same material as the material source 91. The gas-guiding elements 40 are needles with a dimension of smaller than 2 millimeters.
In operation, heat is introduced into the growth chamber 10 from the external heat source. The material source 91 gets heated and sublimated into gas. The gas ascends, reaches the seed crystal 90, and becomes crystals on the seed crystal 90. The heating, sublimation and crystallization continue so that the material source 91 is completely turned into crystals on the seed crystal 90.
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The present invention has been described via the detailed illustration of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.
