JPH0696480B2 - Crystal growth method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a crystal growth method for growing a single crystal of silicon or germanium used as a material for a semiconductor device, for example, without causing segregation of impurity components.

[Prior art]

As a method for growing a single crystal, all the raw materials charged in a conventional crucible are melted, a single crystal seed crystal is immersed in this melt, and then it is pulled upward to grow the single crystal at the lower end of the seed crystal. The so-called Czochralski method is widely known. In this method, for example, when a silicon single crystal is grown, impurities are often added to the melt of the silicon raw material before the pulling of the single crystal is started in order to adjust the electrical resistivity, electric conductivity type, etc. of the crystal. Impurities tend to segregate in the pulling direction of the crystal, and a crystal having a uniform electric resistivity cannot be obtained.

This segregation is the ratio of the impurity concentration at the start of solidification and the impurity concentration at the end of solidification at a certain point in the single crystal, in other words, the impurity concentration Cs in the single crystal at the melt / single crystal interface during crystal growth. It is related to the effective segregation coefficient Ke, which is the ratio Cs / Cl to the impurity concentration Cl in the melt. For example, in the case of Ke <1, as the single crystal is grown, the impurity concentration in the melt naturally increases and segregation of impurities occurs in the single crystal. The effective segregation coefficient Ke is Ke = 1 when the melt is completely stationary, and when the melt is subject to thermal convection or forced convection due to the magnetic field from the induction heating coil, the melt element of the impurity element Is a coefficient that changes toward the intrinsic equilibrium segregation coefficient Ko.

A melt layer method is a method for growing a single crystal while suppressing the occurrence of such segregation of impurities. FIG. 2 is a schematic view showing an implementation state of this melting layer method, in which the solid material charged in the crucible 1 is melted from the upper side to the lower side by the induction heating coil 2 provided so as to be able to move up and down, A method in which a melt layer 4 and a solid layer 5 are located above and below in a crucible 1 and a single crystal 7 is pulled up from the melt layer 4 while growing a single crystal 7 on the lower end of a seed crystal 6 as in the Czochralski method. [Journal of the
electro chemical society. Vol.105, No.7 393 ~ 395
page〕.

According to this method, regardless of the value of the effective segregation coefficient Ke, the induction heating coil 2 is moved downward along with the growth of the single crystal 7 to maintain the volume of the melt layer 4 constant, In order to suppress the impurity concentration change in the melt in the crucible 1 according to the reduction of the impurity concentration due to the newly generated melt, impurities are generally continuously added according to the amount of the melt in the crucible 1. Or, conversely, segregation can be suppressed by intentionally changing the volume of the melt layer 4 to maintain a constant impurity concentration.

[Problems to be Solved by the Invention]

By the way, in this melting layer method, as the solid material for the crystal initially charged in the crucible 1, it is desirable to use integrated polycrystalline silicon having the same shape as the inner shape of the crucible because it is necessary to increase the filling rate. Since it is difficult to manufacture polycrystalline silicon, it is usual to use agglomerate polycrystalline silicon.

Therefore, when the solid material is charged into the crucible 1, the filling rate is about 40 to 70%, and a large amount of voids are present. When the solid layer 5 is melted during crystal growth, a large void is reached. Due to the drop of the melt in the void, the melt layer 4 may oscillate, and abrupt level fluctuation may occur, resulting in crystal defects.

Furthermore, when the amount of solid material required from the volume of a single crystal to be obtained is charged into the crucible 1, the volume increases by the amount corresponding to the voids, so it is necessary to increase the size of the crucible 1 accordingly.

As a countermeasure, increase the filling rate when charging solid materials,
Also, it has been attempted to increase the depth of the crucible 1 to reduce the volume reduction ratio due to the voids, but there is a limit to the improvement of the filling rate of the solid material, and the crucible 1 and its peripheral equipment must be upsized. There were some problems that could not be avoided.

The present invention has been made in view of such circumstances, and an object of the present invention is to vibrate the melt and the level of the melt caused by the voids formed between the solid materials initially charged in the crucible. Another object of the present invention is to provide a crystal growth method capable of suppressing fluctuations and reducing the size of the crucible.

[Means for Solving the Problems]

The crystal growth method according to the present invention, the solid layer for melting the solid material for the crystal charged in the crucible is a solid layer in the lower part of the crucible, the melt layer in the state where the melt layer is positioned above the melt layer In the method for growing a crystal, prior to the start of the crystal growth, a solid material less than a predetermined amount is charged into the crucible so that voids do not remain between the solid materials in the charged crucible. At least a part of the solid material is melted from the upper side, and then the remaining solid material is replenished to the molten liquid layer in the upper part of the crucible so as to have the predetermined amount.

[Action]

In the method of the present invention, a solid material less than the required amount is charged into the crucible to melt at least a part of the crucible, and then the remaining solid material is replenished to melt the voids between the solid materials. It is filled with liquid and the gas in the voids is also discharged, preventing vibration of the melt due to the voids during crystal growth and increasing the filling rate of the material in the crucible, making it easy to replenish the remaining solid material. Therefore, the crucible can be downsized.

〔Example〕

FIG. 1 is a schematic diagram showing an implementation state of the method of the present invention, in which 1 is a crucible, 2 is a heater, 3 is a heat retaining cylinder, 4 is a molten layer of silicon, 5 is a solid layer of silicon, and 6 is a seed. Crystal, 7 is a single crystal, and 8 is a chamber.

The crucible 1 is located in the center of the chamber 8, the outer periphery of which is provided with a heater 2 which is arranged up and down and is composed of an induction heating coil and the like, and a heat insulating cylinder 3 is provided outside thereof. The depth of the melt layer 4 and the thickness of the solid layer 5 in the crucible 1 can be relatively adjusted by adjusting the relative upper and lower positions of the crucible 1 and the heater 2.

The crucible 1 has a double structure in which a quartz container 1b is arranged inside a graphite container 1a, and a shaft 1c for rotating and ascending / descending the crucible 1 is provided at the bottom of the graphite container 1a. The shaft 1c allows the crucible 1 to be rotated and / or moved up and down.

A pulling shaft 6a is provided above the crucible 1 through a pull chamber 9 provided in an upper portion of a chamber 8 so as to rotate and ascend and descend, and a seed crystal 6 is detachably attached to a lower end thereof by a chuck 6b. By immersing the lower end of the seed crystal 6 in the melt layer 4 and then raising it while rotating it,
The single crystal 7 is grown on the lower end of the seed crystal 6.

Further, a supply device 10 for supplying a solid crystal raw material to the crucible 1 is installed above the chamber 8. Supply device
10 is a hopper 10a, a feeder 10b with a weighing machine, and a feeder 10
It is equipped with a charging pipe 10c for supplying the material from the discharge end of b to the crucible 1, and the solid material supplied into the hopper 10a is fed by the feeder 1
It is dropped on 0b, transferred by a feeder 10b, weighed, and supplied into the crucible 1 by a charging pipe 10c.

Thus, in such a method of the present invention, first, in the crucible 1, polycrystalline silicon in the form of lumps or granules as a solid material is slightly smaller than the required amount obtained from the volume of the single crystal to be pulled. After charging, the heater 2 is lowered while melting the solid material from the upper side, and melting control is performed so that the molten liquid enters the voids of the solid material and almost all of the voids are filled with the molten liquid. In this state, the voids between the solid materials are filled with the molten liquid, and the gas in the voids is also discharged to the outside, which causes the molten liquid to fall into the voids during the crystal growth process, and the gas in the voids to the outside. It is possible to prevent the occurrence of crystal defects such as polycrystallization by reducing the vibration of the melt and the fluctuation of the melt level due to the jetting. In this state, the molten liquid layer 4 is present in the upper part of the crucible 1 and the solid layer 5 is present in the lower part thereof. At this time, all of the solid material charged into crucible 1 may be melted.

The solid material is then replenished from the feeder 10 until the predetermined required amount is reached. The replenished solid material may float on the surface of the melt layer 4, so the heater 2 is set at this position to melt it.

After that, by controlling the temperature of the heater 2 and / or its position, the molten liquid layer 4 is present in the upper part of the crucible 1 and the solid layer 5 is present in the lower part thereof at a required depth or thickness, respectively. After immersing the seed crystal 6 in the layer 4, the seed crystal 6 is pulled while rotating, and the single crystal 7 is grown at the lower end thereof.

Compared with the case where the solid material is charged into the crucible 1 at a time by charging the solid material into the crucible 1 separately before and after the process of melting at least a part of the solid material from the upper end, Then, the filling rate of the solid material in the crucible is increased, and the substantial amount of the solid material charged into the crucible 1 is increased.
The crucible 1 can be downsized.

When all the solid material initially charged in the crucible 1 is melted, the temperature control and / or the position control of the heater 2 thereafter solidifies the molten liquid at the bottom of the crucible 1 to solidify the solid material having a predetermined thickness. Allow the layers to form.

Although the induction heating coil is used for heating the molten liquid, the present invention can be applied to a resistance heating type heater.

〔The invention's effect〕

As described above, in the method of the present invention, the solid material initially charged in the crucible is melted at least partly from the upper end to fill the voids between the solid materials with the molten liquid, and the gas in the voids. Is discharged, the molten liquid falls into the voids during the subsequent crystal growth process, and vibration of the molten liquid when the gas in the voids is discharged and fluctuations in the molten liquid level can be reduced, and crystal defects are generated. In addition, the filling rate of the material into the crucible can be greatly increased, and the remaining solid material can be easily filled, and the crucible can be downsized, and the peripheral equipment can be downsized. The present invention has excellent effects so that the productivity can be improved and the productivity is not reduced.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an implementation state of the method of the present invention,
FIG. 2 is a schematic vertical sectional view showing a state of implementation of the conventional method. 1 ... crucible, 2 ... heater, 3 ... heat insulation cylinder 4 ... melt layer, 5 ... solid layer, 6 ... seed crystal, 7 ... single crystal, 8 ... chamber, 9 ... pull chamber, 10 ... ... Supply device

Claims (1)

[Claims] Claim: What is claimed is: 1. A solid material for a crystal charged in a crucible is melted to grow a crystal from the melt layer in a state where a solid layer is located in the lower part of the crucible and a melt layer is located in the upper part. In the method, prior to the start of the crystal growth, a fixed material less than a predetermined amount set in advance is charged into the crucible, and the solid material is formed so that voids do not remain between the solid materials in the charged crucible. A method for growing a crystal, characterized in that after melting at least a part from the upper side, the remaining solid material is replenished to the molten liquid layer in the upper part of the crucible in the predetermined amount.