JP4393555B2 - Single crystal growth method - Google Patents

Description

  The present invention relates to a single crystal growth apparatus and a single crystal growth method for silicon used as a semiconductor material.

  Conventionally, the Czochralski method (CZ method) has been widely used as a silicon single crystal growth method for semiconductors. In particular, the CZ method is excellent in growing large-diameter crystals and has been widely used. However, as mass production progresses, further improvement in crystal yield is desired, and from the viewpoint of resource saving and energy saving, it has become necessary to improve the crystal yield of the CZ method, which consumes a large amount of power.

For example, Patent Document 1 of a silicon single crystal pulling apparatus and a silicon single crystal pulling method describes a single crystal pulling apparatus and a silicon single crystal pulling method with a high crystal yield and operating rate.
The raw material polycrystal supply apparatus is described.
Further, in Patent Document 2 of a method for producing a silicon single crystal, a magnetic field is applied to suppress deterioration of the inner surface of the quartz crucible, extend the life of the crucible, and prevent dislocation due to the deterioration of the crucible. Is described.
Further, Patent Document 3 regarding a method for growing a single crystal and an apparatus used for the method describes a method for obtaining a single crystal with a high yield by keeping the interface between the solid layer and the molten layer flat, making the resistivity uniform. Is described.

JP 2004-338978 A JP2000-247788 JP 09-208374 A In the above-described conventional example, for example, Patent Document 1 describes a raw material polycrystal supply apparatus as a single crystal pulling apparatus or a silicon single crystal pulling method with a high crystal yield and operating rate. There are no written countermeasures such as problems of twin crystals due to polycrystallization or fall of foreign matter. Patent Document 2 describes a method of applying a magnetic field during pulling of a single crystal to suppress the deterioration of the inner surface of the quartz crucible, extend the life of the crucible, and prevent dislocation due to the deterioration of the crucible. However, the method for preventing the dislocation due to the atmosphere in the furnace is not described, and the problem with respect to the basic problem of the transition is not solved.

Further, Patent Document 3 describes a growth direction distribution of resistivity and a yield improvement method, but it is not a measure for a product with a large resistivity width, such as a crystal for a solar cell.
Thus, what is important in improving the crystal yield is to take measures against the crystal growth or transition of the grown crystal first.

  An object of the present invention is to improve the rate of polycrystallization of a grown crystal during the process of growing a silicon single crystal using the CZ method, for example, in the single crystal growth method. At the same time, moisture is adsorbed to the internal parts of the furnace when the furnace is opened, which causes the carbon parts to become exhausted, and the effects of changes in the furnace over time, the incorporation of carbon into the crystal, and the reaction between molten silicon and carbon. Then, the purpose is to solve problems such as the generation of SiC, which is taken into the growing crystal and transformed.

In order to achieve the above object, the present invention prevents the adsorption of moisture to the furnace body capable of maintaining a high vacuum and the components in the furnace, chemically reacts the residual adsorbate, detoxifies, and vacuums by venting to prevent chromatic transition of silicon in the grown single crystal, there is provided a single crystal growth method that obtain a high-quality crystal at high yield.

In the single crystal growth method according to the present invention, a vacuum constituting the crystal growth furnace is provided in a crystal growth furnace having a vacuum sealing material capable of maintaining the ultimate vacuum in the furnace and performing crystal growth at normal pressure, reduced pressure, or in a vacuum atmosphere. The chamber has a water-cooled jacket structure, and warming water having a temperature higher than room temperature is passed through the water-cooled jacket to perform a pull-up preparation process. Thereafter, the initial vacuum achievement is reduced to 10 by a vacuum exhaust device for raising the degree of vacuum in a short time while flowing an inert gas mixed with 0.01% to 3% monosilane gas or silane gas into the furnace. In the stage where the replacement with the inert gas has progressed to the fourth power torr or lower, the in-furnace parts and the raw material crystals existing in the vacuum chamber are heated by a preheating device surrounding the in- furnace parts and the raw material crystals , and the adsorbed moisture Remove. In order to reduce vacuum leakage, it is effective to improve the accuracy of the flange, and for the vacuum seal material, for example, to use a magnetic fluid seal or the like for the seal of the rotary shaft, thereby reducing the vacuum leakage. In addition, moisture adsorption can be reduced.

The single crystal growth method according to the present invention includes a water-cooled jacket structure of a vacuum chamber as a structure for keeping the inner wall of the furnace at room temperature or higher so as not to cause condensation or adsorption on the inner wall of the chamber when the furnace is opened. That is, usually, the cooling water is often lower than room temperature, and condensation may occur on the inner wall of the chamber constituting the furnace. However, by supplying warm water inside the water cooling jacket of the furnace chamber and keeping the inner wall of the furnace at room temperature or higher, when the temperature control system is dismantling the furnace or when the inner surface of the furnace is exposed to the atmosphere in the preparation process, It never occurs condensation on the inner wall of the chamber, can reduce the adsorption of moisture.

Further, in the single crystal growth method according to the present invention, heated inert substitution gas is flowed into the furnace to remove adsorbed moisture. That is, the adsorbed moisture in the gas passage is removed. Furthermore, the in-furnace parts are heated by a preheating device to remove adsorbed moisture. Perform preliminary overheating of the insulation tube .

Furthermore, when a small amount of monosilane gas or silane gas is used during the inert supply, the moisture adsorbed on the in-furnace parts and silicon raw materials is converted into other substances by the following chemical reaction formulas 1 or 2, and single crystal growth Water can be effectively removed from the atmosphere in the furnace.
      SiH ₄  + 2H ₂ O = SiO ₂  + 4H ₂                      -1
      SiClH ₃  + 2H ₂ O = SiO ₂  + HCl + 3H ₂       -2

In single crystal growth method according to the present invention, when performing vacuuming by the vacuum exhaust device, wherein increasing the temperature of the hot water flows through the water-cooling jacket, a vacuum may be I line Do.
At the same time as evacuation, the temperature of the furnace wall is raised than during exposure to the atmosphere to remove adsorbed moisture.

Further, the heating control of the inert feed gas, and hot water temperature control in the water cooling jacket, and the preliminary heating device, may be controlled in accordance with the heater main heating source vacuum level, respectively. The temperature is raised including the main heater to remove the adsorbed moisture.

  According to the present invention, it is possible to improve the vacuum level, reach a high degree of vacuum in a short time, and to reliably remove moisture and the like as an adsorbent, so that prevention of transition during single crystal growth, Since it is possible to reliably prevent polycrystallization, the crystal yield can be improved.

According to the present invention, air, moisture, and hydrocarbon compounds remaining in the furnace are removed before the start of pulling of the single crystal, and these substances that easily react with silicon are removed before the silicon melting step. Therefore, the generation of foreign matter such as silicon carbide and oxide that hinders the growth of the single crystal is eliminated, thereby obtaining the effect of improving the yield of crystal growth. Further, conventionally, when there is moisture, the carbon parts in the furnace are converted to hydrocarbons, resulting in shape deterioration. Further, although there was a problem that carbon dioxide gas was generated by residual oxygen and the life of carbon parts was shortened, the effect of realizing long life was obtained by removing residual gas and residual moisture according to the present invention. In addition, since the amount of carbon taken into the growing crystal can be reduced, it is possible to reduce carbon-induced oxygen precipitation that occurs during the subsequent heat treatment of the wafer process.
Furthermore, since the present invention does not further deteriorate the in-furnace parts, it has been possible to suppress the change with time of the conventional process conditions, so that the effect of stabilizing the quality was obtained.

  The best mode for carrying out the present invention will be described below based on examples.

An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic view of a single crystal growth apparatus according to the present invention.
It is.
In the figure, the vacuum chamber 1 has a water cooling jacket structure and shields heat during heating in the furnace, but the cooling water is routed and cooled by the cooling water coupling pipe 2 in the water cooling jacket. . An inert gas such as argon gas or helium gas is used as the atmospheric gas. The inert gas is supplied into the furnace via the gas flow meter 3. Conventionally, the inert gas has been supplied at a substantially normal temperature, but in the present invention, the inert gas is supplied to the furnace via the temperature raising heat exchanger 4 and the gas valve 5 through the control of the supply gas.

  The main controller manages all sections of the single crystal pulling process, and in the pulling preparation process, that is, when the inner wall of the chamber is exposed to air, instead of cooling water, the temperature rises through the hot water valve 7. Hot water heated by the exchanger 9 is supplied into the water-cooled jacket. The temperature of the hot water is monitored by the thermometer 6, and the hot water is heated to a temperature of 5 ° C. or higher compared to room temperature. After the furnace is closed and the air and moisture are completely replaced, the process enters the step of melting the raw material polycrystal. Then, the cold water valve 8 is opened, and the cooling water is pumped from the cooling water tank 14 by the pump 21 and passed through the chamber Is done. In general, when cooling water for cooling of a plurality of furnaces is used, the cooling water having a high temperature from the furnace heated to warm water during operation of the furnace may be reused.

  The evacuation from the furnace is evacuated by the vacuum pump 11 via the evacuation valve 10. However, when crystal growth is performed while maintaining a reduced pressure state, the evacuation valve 10 is used as a pressure adjustment valve and is necessary. Adjust the pressure to a reduced pressure state. The valve 12 is a control valve that controls replacement gas supply from the replacement gas source 13. For example, before substitution with an inert gas, substitution with moisture or residual oxygen in the furnace can be performed by substitution with dry nitrogen gas. The cooling water path for cooling the furnace is supplied from the cooling water tank 14 through the cooling water valve 8 to the cooling water measured by the thermometer 6 to the vacuum chamber 1 and from the upper chamber to the main chamber by the cooling water coupling pipe 2. Then, it is supplied to the lower chamber and returned to the cooling water tank 14 again. When the water temperature of the cooling water tank 14 rises, it is cooled by a heat exchanger such as a chiller, and a certain range of temperature is maintained.

  In the process of cleaning the furnace and charging the raw material when the furnace is open to the atmosphere, the cold water valve 8 is closed, the hot water valve 7 is opened, and hot water having a temperature higher than room temperature is supplied from the pump 22 via the temperature rising heat exchanger 9 to the chamber. To prevent condensation on the inner wall of the chamber.

FIG. 2 is a schematic diagram of the preliminary overheating function of the heat insulating cylinder in the present invention.
In the figure, the heat retaining ring 15 is used to shield heat from the heater and keep the inside of the furnace at a high temperature. In the present invention, the preheater 18 is heated by the electric power from the in-furnace component preheating power source 16 to promote the replacement of the adsorbed moisture. The insulating material 17 is an insulating material for preventing electricity when the heat retaining ring 15 is a conductive carbon fiber.

FIG. 3 is a gas supply path diagram of the single crystal growth apparatus in the present invention.
As the inert gas, helium gas or argon gas is used. Here, an example of using argon gas is shown. The argon gas is usually used while vaporizing liquid argon. The argon gas supplied to the vacuum chamber 1 is supplied from an argon gas valve 19. The supplied argon gas outdoor is at a level of minus 80 ° C. and does not contain moisture, but the furnace components adsorb some moisture by being left in the atmosphere. The supplied argon gas is first heated through the temperature raising heat exchanger 4 and supplied from the gas valve 5 to the vacuum chamber 1. Even in this state, the substitution amount of the adsorbed water amount is greatly improved as compared with the conventional method. However, a monosilane gas (SiH ₄ ) is further added from the monosilane gas valve 20 to about 0.01% to 3%, When heated by the preheating device 18 for in-furnace parts and heated to 100 ° C. or higher, moisture can be rapidly exhausted.

FIG. 4 is a flow chart of a single crystal growth process in the present invention.
In the figure, the automatic control unit of the furnace measures the environmental temperature for each process and performs control so that the temperature of the cooling water flowing into the vacuum chamber 1 through the water cooling jacket is not lower than the environmental temperature. That is, when the cooling water temperature is lower than room temperature, condensation may occur on the inner wall of the vacuum chamber 1. Therefore, the automatic control unit for the furnace wall performs cooling water temperature rise control higher than room temperature (STEP-1).

Next, the furnace is opened to the atmosphere, and raw materials are charged for the next crystal growth. When the crystal growth is completed, the grown crystal is first taken out. After that, the furnace cleaning and raw material charging work are continued. Here, the powder and deposits generated during crystal growth are removed from the furnace. During these operations, during the corresponding time and raw material incorporation operation time, the chamber inner wall surface is exposed to the atmosphere, and moisture adsorption on the chamber wall occurs.
Thereafter, when the furnace is assembled and evacuation is performed, moisture adsorption on the chamber wall is a detrimental effect for quickly reaching a predetermined degree of vacuum. (STEP-2).
Therefore, when the furnace is opened to the atmosphere, it is necessary to increase the temperature of the chamber furnace wall to reduce moisture adsorption.

Next, the furnace is assembled, the furnace is sealed, and vacuum roughing is started. (STEP-3).
Furthermore, in order to quickly remove the adsorbed moisture on the chamber furnace wall surface, the cooling water temperature is further increased. Further, after the inside of the furnace is depressurized, the replacement gas is supplied and the operation of evacuation is repeated to increase the replacement rate.
Further, a high-temperature replacement gas is supplied into the furnace, and the adsorbed moisture on the surface of the in-furnace parts is replaced with gas, and exhausted and evacuated so as to quickly reach the target vacuum level (STEP-4).

At the stage where the replacement gas has advanced, the process enters the in-furnace component preheating step (STEP-5).
For example, preliminary overheating of a heat insulating cylinder, which is a porous heat insulating material in the furnace, is performed in the furnace. The temperature is increased from 100 ° C. to 200 ° C., and moisture or residual gas is replaced by supplying an inert gas or supplying a heated inert gas.

  When the replacement of the residual gas is completed, the supply of the inert gas is stopped, and the ultimate vacuum is confirmed by evacuation. When the ultimate vacuum is 10E-4 Torr or less, it is assumed that there is no vacuum leakage, and the process proceeds to the crystal growth process (STEP-6).

Next, preheating of the in-furnace parts is stopped (STEP-7).
The preheating device is basically for the purpose of promoting the evaporation of adsorbate by raising the temperature of the porous insulation material in the furnace. It stops in the single crystal growth process, but in some cases, it is used to improve the temperature distribution in the furnace. It is also possible to do.

Next, the process proceeds to a single crystal growth process (STEP-8).
In the single crystal growth process, first the melting of the polycrystalline raw material and the growth of the seed crystal are followed by the target single crystal growth step. When the single crystal growth process is completed, the furnace is disassembled and the crystal is taken out through the cooling step. It will be repeated work from the first state.

If the vacuum process does not proceed smoothly, vacuum seal maintenance work is performed (STEP-9).
When there is a leak in the so-called vacuum furnace where the vacuum holding state is poor, maintenance work such as replacement of the vacuum seal material and tightening of the flange fitting portion is performed. When there is a very small amount of leakage, the monosilane gas (SiH ₄ ) added to the inert gas reacts with air and moisture and is discharged out of the furnace, which is effective in improving the yield of crystals.

In this invention, there exists an advantage which improves a single crystal yield in this way.
In the description of the present invention, a silicon single crystal is described. However, the technique for removing adsorbed substances such as moisture and oxygen in the present invention improves the quality during the production of silicon polycrystals and other inorganic single crystals / polycrystals. Needless to say, it can be applied to yield improvement. In addition to crystal manufacturing, vacuum chambers are used to manufacture inorganic and organic thin films by vacuum deposition, chemical vapor deposition, molecular beam epitaxy, etc. The present invention can be applied to the removal of adsorbed gas and moisture to improve quality and yield.

The schematic diagram of the single-crystal growth apparatus in this invention is shown. The schematic diagram of the preliminary overheating function of the heat insulation cylinder in this invention is shown. The gas supply path figure of the single crystal growth apparatus in this invention is shown. The single-crystal growth process flowchart in this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Cooling water coupling piping 3 Gas flow meter 4 Temperature rising heat exchanger 5 Gas valve 6 Thermometer 7 Hot water valve 8 Cold water valve 9 Temperature rising heat exchanger 10 Vacuum exhaust valve 11 Vacuum pump 12 Valve 13 Replacement gas source 14 Cooling water tank 15 Heat retaining ring 16 Pre-heating power source for furnace parts 17 Insulating material 18 Pre-heating heater 19 Argon gas valve 20 Monosilane gas valve 21 Pump 22 Hot water pump

Claims (3)

In a crystal growth furnace having a vacuum sealing material capable of maintaining the ultimate vacuum in the furnace and performing crystal growth at normal pressure, reduced pressure or in a vacuum atmosphere, the vacuum chamber constituting the crystal growth furnace has a water cooling jacket structure, and the water cooling jacket After warming up warm water at a temperature higher than room temperature, the preparation process for pulling up was performed, and then the degree of vacuum was reduced in a short time while flowing an inert gas mixed with 0.01% to 3% monosilane gas or silane gas into the furnace. The initial vacuum degree is reduced to 10 minus 4 torr or less by a vacuum exhaust device for raising the temperature, and when the replacement with the inert gas proceeds, the in- furnace parts and the raw material crystals contained in the vacuum chamber are placed inside the furnace. A single crystal growth method characterized by removing adsorbed moisture by heating with a preheating device surrounding the product and the raw crystal .   The single crystal growth method according to claim 1, wherein when evacuation is performed by the evacuation apparatus, the temperature of the hot water flowing through the water cooling jacket is increased to perform evacuation. Wherein the heating control of the inert gas, and hot water temperature control in the water-cooling jacket, the preheating device and, single crystal according to the heater of the main heating source in claim 1 or 2 controlled in accordance with respective vacuum levels Growth method.

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