Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With pretreatment or preparation of a base
Reexamination Certificate
1999-12-08
2001-11-20
Utech, Benjamin L. (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With pretreatment or preparation of a base
Reexamination Certificate
active
06319314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and a device for manufacturing semiconductors. More particularly, the present invention relates to a method and a device for manufacturing spherical semiconductor crystals.
2. Description of the Prior Art
Conventionally, spherical semiconductor crystals are manufactured by buoying small pieces of semiconductor material with the aid of electromagnetic floating coils and at the same time heating them to obtain liquid drops. The liquid drops are solidified during free fall, and spherical semiconductor crystals are thus obtained. A method for manufacturing spherical semiconductor crystals has been disclosed in U.S. Pat. No. 4,322,379. In this patent, bar-shaped or scrap material for producing spherical semiconductor crystals is fed into a quartz tube that is provided with a nozzle at its distal end. After the bar-shaped or scrap material is melted through a coil-heating process, liquid drops are forced to drop down from the distal end of the nozzle by applying a gas pressure. Then, the liquid drops are solidified during free fall, and spherical semiconductor crystals are thus obtained.
However, the following problems remain unsolved in the above-described methods. In the process of buoying and heating small pieces of semiconductor material, a plurality of small pieces of semiconductor material are supplied into a region above the electromagnetic floating coils for heating. However, this process still takes too much time to produce spherical semiconductor crystals. Moreover, the quartz tube employed in the '379 patent deteriorates after several operations. This will cause a hindrance to uninterrupted production of spherical semiconductor crystals. Furthermore, under this process it is required to heat the quartz tube so as to melt the material. The above heating process will fuse the quartz tube and impurities contained in quartz will blend into the liquid drops. Therefore, it is quite difficult to maintain the purity of the produced semiconductor crystals.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and a device for manufacturing spherical semiconductor crystals capable of solving the above-mentioned problems and performing continuous production of spherical semiconductor crystals whose purity is maintained. In addition, the deterioration of the device can be prevented.
To achieve the above-mentioned object, in the method for manufacturing spherical semiconductor crystals according to this invention, the melt portion of a buoying semiconductor material is heated to melt so as to obtain spherical semiconductor crystals by solidifying the drops during free fall, and the semiconductor material is conducted to descend toward its melt portion in response to the amount of the semiconductor material dropped. During the preliminary stage of the heating-and-melting process, the semiconductor material is preheated. The semiconductor material is in the shape of a bar. The lower end of the semiconductor material is sharpened. The semiconductor material is driven to rotate at a preset speed while being heated and melted. Dopants are blended into the semiconductor material in a preset proportion. Doping gas is mixed in a preset proportion into the surroundings of the liquid drops melted from the semiconductor material. Alternatively, a solution containing subject impurities is spread over an unblemished semiconductor material, in which no subject impurities are contained.
According to this invention, the device for manufacturing spherical semiconductor crystals comprises: A supporting member for supporting semiconductor material in a manner capable of ascending/descending at a preset speed; a heater disposed in a manner such as not to be in contact with the semiconductor material, the heater being used for melting the semiconductor material to allow the melted liquid to drop down; a manufacturing room for allowing the liquid drops to solidify during free fall; and a controller for conducting the semiconductor material to descend toward the heater with the aid of the supporting member in response to the amount of the semiconductor material dropped. Furthermore, the lower portion of the manufacturing room is provided with an impact absorbing member used for absorbing the impact of the falling spherical semiconductor crystals solidified from the liquid drops and for retaining them. The semiconductor material is in the shape of a bar. Moreover, the lower end of the semiconductor material is sharpened. The lower end of the heater is devised as a melting portion and is sharpened in the same way as the lower end of the semiconductor material, and the upper section of the melting portion is employed for preheating the semiconductor material. Moreover, the clamping portion of the supporting member is made of carbon-fiber-reinforced carbon material having a melting point higher than that of semiconductor material or metals with high melting points. Moreover, the heat-emission body in the melting portion of the heater has a double-spiral shape. Moreover, the supporting member is provided with a rotation mechanism capable of rotating the semiconductor material at a preset speed. A doping gas source is communicated with the manufacturing room.
In the above-described structure, the semiconductor material, made, for example, of silicon, is connected to the supporting member and is conducted to descend at a preset speed. Then, the heater melts the surface of the semiconductor material to form liquid drops. The liquid drops accumulate at the lower end of the semiconductor material and drop down by their own weight. The liquid drops cool down within the manufacturing room during free fall and become solid spheres without deformation. Moreover, the semiconductor material is conducted to descend toward the heater by the controller, and spherical semiconductor crystals can be continuously produced by melting the semiconductor material and dropping liquid drops. Therefore, there is no need to store liquid drops temporarily and puff them out from the distal end of the nozzle by applying a gas pressure, as in the conventional method. Moreover, quartz storage parts or graphite susceptors are no longer required and cost can thus be reduced. Moreover, the semiconductor material is melted through a non-contact process, therefore spherical semiconductor crystals of high purity can be produced. Moreover, because there is no need of quartz storage parts, it is possible to eliminate the possibility of breakdown induced by deterioration of quartz members in the spherical semiconductor crystal-manufacturing device.
Furthermore, preheating the semiconductor material in the preliminary stage of the heating-and-melting process can prevent breakage of the semiconductor material induced by heat expansion. Therefore, spherical semiconductor crystals can be continuously produced.
Furthermore, damage of spherical semiconductor crystals can be avoided by absorbing the impact of the falling spherical semiconductor crystals with the aid of an impact absorbing member installed within the lower portion of the manufacturing room.
Furthermore, compared with small pieces of semiconductor material, the surface of bar-shaped semiconductor material is smaller. Because bar-shaped semiconductor material is used, the semiconductor material can be maintained in an uncontaminated state and spherical semiconductor crystals can be continuously produced.
Furthermore, the lower ends of the semiconductor material and the heater are sharpened, therefore the liquid drops can be collected at a determined site and can then be conducted to drop down onto a predetermined locality. Moreover, melted liquid will accumulate at the distal end of the bar-shaped material and then convert into liquid drops during the melting process, therefore melted liquid drops of the same shape can be continuously produced. Consequently, spherical semiconductor crystals can be continuously and directly produced from semiconductor material.
Furthermore
Anderson Matthew A.
Komatsu Electronics Co., Ltd.
Powell Goldstein Frazer & Murphy LLP
Utech Benjamin L.
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