JPS638291A - Apparatus for producing semiconductor single crystal - Google Patents

Abstract

PURPOSE:To produce a semiconductor single crystal having excellent electrical uniformity, by placing a heater contacting with or slightly immersed in molten liquid of a semiconductor raw material over the whole liquid surface. CONSTITUTION:A desired semiconductor raw material is charged into a molten liquid tank 42 and melted to molten liquid 51 of a specific temperature or thereabout by electrifying an electric heater 52 and raising the temperature in the molten liquid tank 42. The electric heater 52 is switched off and the space formed by the molten liquid tank 42 and a partition wall 43 is evacuated with a vacuum pump through a line 44 to form a heat-insulation part 45 which prevents the increase of the temperature of the molten liquid 51 near the side wall of the molten liquid tank 42. Separately, an electric heater block 61 of a liquid surface heating apparatus 60 is electrified to keep the upper layer of the molten liquid 51 to a predetermined temperature in high accuracy. A semiconductor crystal 58 is pulled up and grown from the upper layer of the molten liquid 51 by slowly lifting a rotary shaft 55 under rotation keeping the above state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor single crystal manufacturing apparatus that pulls a crystal from an upper layer of a semiconductor material melt stored in a melt tank.

[Prior Art] Generally, this type of manufacturing apparatus, for example, a single crystal manufacturing apparatus for a compound semiconductor such as GaAS, has an airtight container 11 as shown in FIG. Inside the container 11 is a melt tank 12.
A tank 12 is provided with a melted liquid (semiconductor material melt) 2 on its outer wall by melting the semiconductor material filled in the tank 12 at high temperature.
1, an electric heater 22 is provided. The melt 21 is stored in the lower part of the tank 12, and the melt 21 is stored above it.
A cover liquid 23 is stored to prevent gasification of the liquid.

The device of FIG. 2 further has a rotation axis 24.25.

The rotating shaft 24 passes through the bottom of the container 11 via a shaft seal groove 26, and its upper end is fixed to the bottom of the melt tank 12. Further, a rotating shaft (pulling shaft) 25 passes through the upper part of the container 11 via a shaft sealing mechanism 27.

The rotating shaft 25 rotates while moving upward at a low speed, with the solidified semiconductor crystal 28 attached to its lower end and the tip of the crystal 28 contacting the center portions of the two liquid surfaces of the melt 21. As a result, the melt 21 is gradually pulled up from the liquid surface 29 of the melt 21, cooled, and crystallized.

[Problems to be Solved by the Invention] The semiconductor crystal 28 manufactured by the single crystal manufacturing apparatus shown in FIG. 2 has a slight striped structure. These stripes are concentration unevenness caused by impurities, and therefore, the semiconductor crystal 28 having this kind of striped structure has a problem in terms of electrical uniformity. The present inventor believes that the above-mentioned striped structure occurs due to convection occurring within the melt tank 12 (subject to crystal growth).
It has been recognized that this is caused by non-uniformity or fluctuations in the liquid temperature in the upper layer of the melt 21. Furthermore, the inventor
It has also been recognized that the above-mentioned convection generation is caused by the temperature distribution of the melt 21. That is, in the apparatus shown in FIG. 2, the temperature of the melt 21 is high near the side wall of the melt tank 12. Therefore, the melt 21 heated by the electric beater 22 (near the side wall of the melt tank 12) rises along the inner wall of the melt tank 12. The upward flow along the inner wall of the melt tank 12 is
In the upper layer of the melt 21, the flow is radial toward the central axis 30 of the melt tank 12, and this radial flow becomes a downward flow near the central axis 30.

As a result, convection as shown by the broken line in FIG. 2 occurs within the melt tank 12.

Therefore, in this invention, it is possible to prevent the generation of convection caused by the generation of localized high-temperature parts of the semiconductor material melt near the side walls of the melt tank, thereby producing semiconductor single crystals with good electrical uniformity. The technical problem to be solved is to make it possible.

[Means for Solving the Problems] The present invention provides a heating device for maintaining the upper layer of the semiconductor material melt stored in the melt tank at the highest temperature over almost the entire range of the surface of the melt. The melt tank is provided so as to be almost in contact with the liquid surface or slightly immersed in the liquid, and the sides and bottom of the melt tank have a heat insulating structure.

[Function] The heat insulating structure and heating device described above prevent the melt from reaching a high temperature near the side wall of the melt tank and make the temperature distribution of the melt substantially uniform, thereby preventing the generation of convection. In addition, since the @ above the melt is kept at the highest temperature by the heating device, even if convection occurs in the lower part of the melt, the movement of the melt in the upper layer of the melt that is used for clear crystal formation will not be possible. Therefore, the temperature of the upper layer of the melt can be made more uniform.

[Embodiment] FIG. 1 shows a semiconductor single crystal manufacturing apparatus according to an embodiment of the present invention, and 41 is an airtight container.

The pressure inside the container 41 is maintained at about several tens of 9/ctAg. A cylindrical melt tank 42 with a bottom is provided within the container 41 . Inside the melt tank 42, there is provided a cylindrical partition wall 43 with a bottom and a larger diameter at its upper end. The upper edge of this partition wall 43 is fixed to the inner wall of the intermediate portion of the melt tank 42 . Melt tank 42 and partition wall 4
The space closed by 3 is a pipe 44 that penetrates the container 41.
The insulating part 4 is connected to a vacuum pump (not shown), and is maintained in a vacuum state by evacuation by the pump.
form 5. Note that it is also possible to form the heat insulating portion 45 by filling this space with a heat insulating member having excellent heat insulation properties. An electric heater 52 that melts the semiconductor material filled in the melt tank 42 at high temperature to form a melt (semiconductor material melt) 51 is provided in the heat insulating section 45 so as to surround the partition wall 43 . The melt 51 is stored in the lower part of the melt tank 42, and above it is stored a cover liquid 53 such as a low melting point glass liquid that prevents the melt 51 from being gasified.

54 and 55 are rotation axes. The rotating shaft 54 passes through the bottom of the container 41 via a shaft sealing mechanism 56, its upper end is fixed to the bottom of the melt tank 42, and its lower end is connected to a rotating shaft drive mechanism (not shown). On the other hand, the rotating shaft 55 passes through the upper part of the container 41 via a shaft seal 1 structure 57, and its upper end is connected to a rotating shaft drive mechanism (not shown). The rotating shaft 55 is used as a pulling shaft for growing a semiconductor crystal 58 at its lower end and lifting the crystal 58 above the liquid level 59 of the melt 51.

In order to keep the temperature of the upper layer of the melt 51 uniform and at the highest temperature, the liquid surface 59 of the melt 51 (excluding the central part where the semiconductor crystal 58 is grown) covers almost the entire range. This is a liquid level heating device provided. The liquid surface heating device 60 includes an annular electric heater block 61 and this electric heater block 61.
It has an annular temperature equalization block 62 fixed to the bottom surface of the holder. The temperature equilibrium block 62 has a two-layer structure, for example, with a tA plate having excellent thermal conductivity as an upper layer and a heat-resistant plate made of the same material as the melt tank 42 as a lower layer. The liquid surface heating device 60 further includes a cylindrical heat shield block 63 surrounding the semiconductor crystal 58. This heat shield block 63
is for preventing the semiconductor crystal 58 from being unnecessarily heated by the electric heater block 61, and is made of a heat insulating material, and its lower outer wall is connected to the electric heater block 61.
It is fixed to the inner wall of 1.

Now, in this embodiment, the temperature equilibrium block 62 is
1 or slightly immersed in the melt 51. However, since the liquid level 59 of the melt 51 decreases as the amount of the melt 51 decreases due to the growth of the semiconductor crystal 58, the liquid level heating device 60
The structure must be such that it can move following the drop in the liquid level in step 1. For this purpose, for example, the liquid level heating device 60 may be configured to be movable in the vertical direction, and the amount of movement thereof may be controlled by a program or in accordance with the detection of the position of the liquid surface 59, or the liquid surface heating device 60 may be controlled by itself. A relatively simple means of creating a floating structure may be applied. Note that this type of means for making it movable following the drop in the liquid level is well known, so detailed explanation will be omitted.

Next, the operation of the configuration shown in FIG. 1 will be explained. First, after filling the melt tank 42 with a desired semiconductor material, the electric heater 52 is energized to raise the temperature in the melt tank 42 to melt the semiconductor material into a melt 51, which is then heated to a predetermined temperature. shall be. After this, the power supply to the electric heater 52 is stopped,
A heat insulating portion 45 is formed by evacuating the space closed by the melt tank 42 and the partition wall 43 through the piping 44 using a vacuum pump (not shown). This prevents the temperature of the melt 51 from becoming high near the side wall of the melt tank 42. On the other hand, liquid surface heating device eoI71
The electric heater block 61 is activated to accurately maintain the upper layer of the melt 51 at a predetermined temperature. Thereafter, in this state, the rotating shaft 55 is rotated while moving upward at a low speed, thereby pulling and growing the semiconductor crystal 58 from the upper layer of the melt 51.

Now, in the state where the semiconductor crystal 58 is grown by pulling,
The temperature distribution of the melt 51 in the melt tank 42 is such that the upper layer maintains a high temperature due to the heating operation by the electric heater block 61 of the liquid surface heating device 60, and the middle layer maintains a high temperature.

The temperature in the lower layer is approximately the same or slightly lower, and the temperature distribution within each layer is approximately constant. Therefore, convection of the melt 51 hardly occurs within the melt tank 42, and even if it occurs, it is weak. Furthermore, in this embodiment, since the upper layer of the melt 51 is kept at the highest temperature as described above, even if convection occurs in the lower layer of the melt 51, the melt 51 in the upper layer There is no movement of the melt 51, and there is no possibility that the lower layer convection will affect the semiconductor crystal growth at the center of the upper layer of the melt 51. In this way, according to this embodiment, it is possible to prevent the occurrence of convection over the entire liquid layer as shown by the broken line in FIG. Can be manufactured.

Further, in this embodiment, since the liquid surface heating device 60 is brought into contact with the liquid surface 59 of the melt 51, there is no fluid interface between the liquid surface 59 and the cover liquid 53, and the upper layer of the melt 51 is This prevents convection phenomena caused by surface tension from occurring in the area. Furthermore, in this embodiment, the liquid surface heating device 60
The temperature equilibrium block 62 forming the bottom of the melt 51 can further equalize the temperature of the upper layer of the melt 51. As a result of the above, the electrical uniformity of the semiconductor crystal 58 can be further improved. In addition, in this invention whose main purpose is to prevent the occurrence of convection over the entire liquid layer, the temperature equilibrium block G2 is not necessarily required.

Further, since the liquid surface heating device 60 is for keeping the upper layer of the melt 51 at the highest temperature, it is sufficient to provide it only in the vicinity of the liquid surface 59.

[Effect of the invention 1] According to the present invention, the temperature of the semiconductor material melt is prevented from becoming high near the side wall of the melt tank, and the temperature distribution is made uniform, and the temperature of the upper layer of the melt is raised to the highest temperature. Therefore, it is possible to prevent the occurrence of convection throughout the liquid layer, and it is possible to manufacture a semiconductor crystal with good electrical uniformity and no striped structure.

FIG.

42... Melt tank, 43... Partition wall, 45... Heat insulation part, 51... Melt (semiconductor material melt), 52...
Electric heater, 54, 55...Rotating shaft, 58...Semiconductor crystal, 60...Liquid surface heating device, 61...Electric heater block, 62...Temperature equilibrium block, 63...
heat shield block.

Applicant Sub-Agent Patent Attorney Suzue Takehiko Figure 1

Claims (1)

[Claims] In a semiconductor single crystal production device that pulls a crystal from the upper layer of a semiconductor material melt stored in a melt tank, a heating device for keeping the upper layer of the melt at the highest temperature is installed over almost the entire surface of the melt. A semiconductor single crystal production apparatus characterized in that the melt tank is provided so as to be substantially in contact with the liquid surface or slightly immersed in the liquid, and the sides and bottom of the melt tank have a heat insulating structure.