JPH0798715B2 - Method for producing silicon single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a silicon single crystal used in, for example, a semiconductor material.

(Prior Art) There are several methods for growing a single crystal, and one of them is a pulling method (also called Czochralski method). In this method, as shown in FIG. 1, a raw material M is charged into a crucible 2 (made of quartz inside and made of carbon outside, hereinafter referred to as a crucible) arranged in a pulling device 1 to load a heater. After melting in 3, the melt 6 is pulled up by the wire 5 to which the seed crystal 4 is attached, and solidified and grown to produce the single crystal 7.

When a single crystal for semiconductor is grown by the above-mentioned pulling method, an impurity (for example, P, B, etc.) may be added before pulling up the melt in order to adjust its electric resistance and electric conductivity type. However, in general, during single crystal growth, the ratio of the impurity concentration Ce in the melt to the impurity concentration Cs of the single crystal, that is, the effective segregation coefficient Ke (= Cs / Ce) is smaller than 1,
The impurity concentration during melting increases as the single crystal grows. As a result, there is a problem that the impurity concentration in the single crystal changes and segregation occurs, and a single crystal having a uniform electric resistance cannot be obtained.

The melt layer method is a method for preventing such segregation and growing a uniform single crystal.

In this method, as shown in FIG. 2, the lower solid layer M _s is reduced by the amount of the melt 6 reduced while the wire 5 with the melt 6 suspended from the seed crystal 4 is pulled up and the single crystal 7 is grown. Is melted to keep the volume of the melt 6 constant, and impurities are continuously added from the chute 8 as the single crystal 7 is pulled up to make the impurity concentration in the melt layer uniform (Japanese Patent Publication No. -8242, JP-B-62-880), or by intentionally changing the volume of the melt layer to keep the impurity concentration in the melt constant without adding impurities during crystal pulling. (Japanese Patent Laid-Open No. 61-205691).

The melt layer method solved the problem that the segregation of impurities was improved and the electric resistance of the silicon single crystal was significantly changed.

However, the melt layer method has the following problems that prevent single crystallization.

(A) Foreign matter floating on the surface of the molten liquid is taken into the crystal body being pulled up, resulting in deterioration of quality and polycrystallization.

(B) The liquid surface vibrates due to the gas generated from the melt,
Polycrystals are formed and normal pulling cannot be performed.

(C) The generated gas is recrystallized in the upper part of the crucible, the seed chuck, etc., and this is dropped into the melt and melted to be mixed in the single crystal.

The present inventors considered that a homogeneous single crystal could not be grown unless the generation of the above-mentioned foreign matter and gas was prevented, and investigated their identities and their causative substances.

As a result, it was found that the foreign matter floating on the surface of the melt was silicon oxide, and the gas generated from the melt was also silicon oxide. Then, it was revealed that the causative substance of the floating foreign matter was the oxide film covering the surface of the silicon raw material, and the generated gas was the oxide film of the silicon raw material of the lower solid layer.

Therefore, as a result of further research on the method of removing the oxide film covering the surface of the silicon raw material, the present inventors have found that if the raw material silicon is heat-treated at an appropriate temperature, the oxide film (oxygen) can be relatively easily removed. The present invention has been completed and the present invention has been completed.

That is, the gist of the present invention is "a method for producing a silicon single crystal by a molten layer method, which is characterized by using a silicon solid material from which a surface oxide film is removed" and "a molten layer." There is a method for manufacturing a silicon single crystal by the method, after charging the raw material into the pulling device and reducing the pressure inside the device or making it an inert gas atmosphere or a reducing atmosphere, the raw material is kept at a temperature of 1,000 to 1,400 ° C. And a heat treatment step are performed.

(Operation) The method for producing a silicon single crystal of the present invention is characterized by using a silicon solid material from which a surface oxide film is removed.
Except for the oxide film, no foreign matter or gas is generated due to the oxide film, so that a homogeneous silicon single crystal can be stably grown.

The surface oxide film of the raw material is removed by depressurizing the silicon solid raw material,
Alternatively, it can be performed by heat treatment in which the temperature is maintained at 1,000 to 1,400 ° C. for 1 to 3 hours under an inert gas atmosphere or in a reducing atmosphere.

In the above heat treatment, the heating temperature is 1,000 ° C to 1,400 ° C. The reason is that if the temperature is lower than 1,000 ° C., heat treatment for a long time is required and the oxide film removing effect is small. On the other hand, when the temperature exceeds 1,400 ° C., the melting point of Si is 1414 ° C., so that melting is likely to occur and the oxide is taken into the molten layer. Further, it is desirable to keep the heating time for 1 to 3 hours. This is because oxide removal is incomplete in less than 1 hr, and power consumption increases if retained for longer than 3 hr. The pressure for reducing the pressure is preferably 1 to 20 torr, and Ar gas or He gas is used as the inert gas.

When such a heat treatment is applied to the silicon solid raw material, the reactions of the following formulas (1) to (3) occur.

_{SiO 2 → Si + O 2 ↑} ... (1) 2SiO 2 → 2SiO + O 2 ↑ ... (2) 2SiO → 2Si + O 2 ↑ ... (3) oxide film of the silicon solid material surface by these reactions (Si
O ₂ ) is removed. Then, the above reaction occurs rapidly at a high temperature of 1,000 ° C. or higher, and progresses more smoothly under reduced pressure.

By the way, the most preferable embodiment of the present invention is to perform the above heat treatment in a pulling apparatus. Then, the raw material after the heat treatment can be melted as it is to grow a single crystal. However, if the heat treatment requires a long time,
From the viewpoint of improving the operation rate of the pulling device, it is preferable to perform the treatment in a separately provided heat treatment furnace (vacuum heat treatment furnace, inert gas atmosphere furnace, etc.). In this case, in order to prevent re-oxidation of the heat-treated raw material, it is necessary to take measures such as storing in a container filled with an inert gas such as Ar.

(Example 1) In this example, a silicon solid raw material was heat-treated at different temperatures to examine the degree of removal of oxygen in the raw material. The heat treatment of the raw material was performed using the pulling apparatus 1 shown in FIG. After charging the raw material M _s into the crucible 2, 10 to
Reduce the pressure to rr to create an Ar atmosphere, and set the raw material _Ms to 950 ° C and 1,000
The temperature was raised to 1,200 ° C, 1,400 ° C.

The results are shown in FIG. In the figure When the raw material temperature is 950 ℃, △ is 1,000 ℃, ○ is 1,20
0 ℃, ● is the case when the temperature is raised to 1,400 ℃.

As is clear from FIG. 3, when the temperature is out of the temperature range specified by the present invention at 950 ° C., the difference in oxygen concentration before and after the heat treatment is small and the effect is small. The effect begins to appear when the processing temperature exceeds 1,000 ° C, and only 1 at 1,400 ° C.
It has decreased from 12ppm to 2ppm with the processing of time.

(Example 2) In this example, a silicon single crystal having a diameter of 50 mm was produced using a raw material that was heat treated and a raw material that was not heat treated, and the length of the single crystal was investigated.

The melting of the raw materials and the pulling up of the molten liquid were performed by the pulling device 1 shown in FIG. The heat treatment raw material used was one that was depressurized to 10 torr, then heated to 1,300 ° C. in an Ar atmosphere and held for 1 hour.

The results are shown in FIG. In the figure, ⋄ is the case of using a raw material that has not been heat treated, and ◆ is the case of using a raw material that has been heat treated. As can be seen from this figure, in the case of the raw material which is not heat-treated, the length of the single crystal is short and the length is largely varied. It is considered that this is due to vibration of the molten liquid surface due to floating foreign matter or gas generated by the raw material oxide film (oxygen). On the other hand, in the case of the heat-treated raw material, the oxide film of the raw material is removed in advance and no foreign matter or the like is generated, so that the length of the single crystal is long and its variation is very small.

(Effects of the Invention) As described above, since the method of the present invention uses the silicon solid raw material having a low oxygen content, no foreign matter or gas of silicon oxide is generated even when melted. Therefore, a high quality silicon single crystal can be manufactured with high yield. Oxygen in the raw material can be easily removed in the heat treatment furnace, so that the cost does not increase so much.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the growth of a single crystal by the pulling method, FIG. 2 is a diagram for explaining the growth of a single crystal by the melt layer method, and FIG. 3 is a heat treatment time of a silicon solid raw material and FIG. 4 is a diagram showing the relationship with the oxygen concentration. FIG. 4 is a comparison of the lengths of the single crystals in the case of the heat-treated raw material and the non-heat-treated raw material. Crystal, 5 is wire, 6 is melt, 7 is single crystal, and 8 is chute.

Continuation of the front page (56) References JP 59-92993 (JP, A) JP 58-49518 (JP, B2) JP 62-880 (JP, B2)

Claims (2)

[Claims] 1. A method for producing a silicon single crystal by a melt layer method, which comprises using a silicon solid material from which a surface oxide film has been removed. 2. A method for producing a silicon single crystal by a melt layer method, which comprises charging a raw material into a pulling apparatus, reducing the pressure in the apparatus or making it an inert gas atmosphere or a reducing atmosphere, and then changing the raw material to 1,000. A method for producing a silicon single crystal, which comprises a step of heat-treating while maintaining a temperature of up to 1,400 ° C.