JPH02204388A - Production of single crystal - Google Patents

Abstract

PURPOSE:To grow the single crystal having lessened crystal defects with good reproducibility by measuring the change rate of the crystal weight within the specific time right after the start of pulling up at the time of pulling up the single crystal by a Czochralski method, comparing the measured value and a preset reference and determining the surface temp. of the melt at the time of starting the pulling up. CONSTITUTION:A weight measuring instrument 14 is connected to a single crystal pulling-up shaft 12 and the pulling-up of the single crystal is started; thereafter, the change range of the crystal weight is successively calculated in accordance with the detection signal from the weight measuring instrument 14. The surface temp. of the melt at the start of the pulling-up is so determined that the locus of the change rate enters the preset permissible range in at least 20 minutes after the start of the pulling up.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a single crystal, and in particular to a method for growing a single crystal by the Czochralski method (including the liquid confinement Czochralski method). Regarding technology.

[Prior Art] One of the methods for growing compound semiconductor single crystals such as GaAs and InP is to place raw materials in a crucible and heat and melt them.
There is the Czochralski method, in which a seed crystal is brought into contact with the surface of the melt and then gradually pulled up to grow a single crystal with uniform crystal orientation.

In crystal growth by this Czochralski method, if the temperature of the melt surface at the start of seed crystal pulling is too high, the seed crystal will melt and the crystal will not grow, and if it is too low, crystal defects will occur. Therefore, in the Czochralski method, it is very important to determine the temperature of the melt during seeding and the timing of pulling.

To accurately determine the melt surface temperature during seeding, it is sufficient to place a thermocouple in contact with the melt surface, but inserting a hot couple disrupts the convection of the melt and The temperature distribution changes, making it impossible to grow a single crystal.

It is also possible to measure the temperature of the melt surface non-contact using an optical thermometer, but in this case, it is affected by the atmospheric gas in the furnace, its convection, and the furnace window material, making it difficult to accurately measure the temperature. It has not yet been possible to measure the temperature of the melt surface with good reproducibility.

Therefore, conventionally, the state of the contact area between the seed crystal and the melt was observed through a viewing window provided in the furnace body, and the pulling start timing was determined visually.

[Problem M to be Solved by the Invention] However, when the above-mentioned visual seeding is a temperature measurement method, it is difficult to accurately determine the temperature.

This method requires many years of experience and skill, has large variations from one operator to another, and has a different shape each time the single crystal is grown, resulting in insufficient reproducibility and the problem of crystal defects being likely to occur.

This invention was made in view of the above-mentioned problems, and it is possible to grow single crystals with fewer crystal defects and less variation in shape with good reproducibility in the single crystal growth process using the Czochralski method. The purpose is to make it possible.

[Means for Solving the Problems] The present inventors repeatedly carried out pulling while changing the melt temperature, and investigated the rate of change in crystal weight at that time. As a result, as shown in FIGS. 2(a) to 2(c), it was found that the locus of the rate of change in crystal weight differs depending on the melt surface temperature T int. That is, as the melt surface temperature is raised from a high state, the trajectory becomes gentler, as shown in FIG. 2(a), and as the melt surface temperature is raised from a lower state, the trajectory becomes steeper. Furthermore, they found that if the trajectory of the weight change rate matches the trajectory when the temperature is lifted from the optimum temperature for at least 20 to 30 minutes after the start of pulling, crystal growth can be achieved with sufficient reproducibility. .

This invention was made based on the above-mentioned knowledge, and a weight measuring device is connected to the single crystal pulling shaft to start pulling the single crystal, and then, based on the detection signal from the above-mentioned type 1'J measuring device, The rate of change in crystal weight was calculated sequentially, and the surface temperature of the melt at the start of pulling was determined so that the trajectory of the rate of change fell within a preset tolerance range for at least 20 minutes after the start of pulling.

[Operation] According to the above-described means, crystal growth with good reproducibility can be achieved by pulling a single crystal while keeping the change rate of 1 weight dv/dt within a certain range.

[Embodiment] FIG. 1 shows a single crystal pulling furnace used in an embodiment of the present invention, in which a substantially cylindrical heater 4 is disposed in a closed high-pressure vessel 3.

In the center of this heater 4 is a pBN with a diameter of about 6 inches! 2
A crucible 5 is arranged. A melt 6 is placed in this crucible 5, and the upper surface of the melt 6 is B20.
．． It is covered with a liquid sealant N7 consisting of. Further, the crucible 5 is rotatably and vertically supported by a support shaft 8 fixed to its lower end. Reference numeral 9 denotes a support shaft rotation and vertical movement mechanism provided at the lower end of the support N8. In addition, 1
Reference numeral 1 denotes a heat insulating member disposed so as to surround the outer periphery of the heater 4 .

On the other hand, a crystal pulling shaft 12 is suspended from above the crucible 5 into the high pressure container 3 so as to be able to rotate and move vertically. It is possible to contact the surface of 6. Reference numeral 13 denotes a pulling shaft rotation/-E lowering mechanism provided at the upper end of the crystal 9 lifting shaft 12. In addition, the crystal pulling shaft 12 has a

A weight sensor 14 is attached that can measure the weight of the crystal.

Furthermore, a gas introduction pipe 15 for introducing high-pressure Ar gas is connected to the upper part of the side wall of the high-pressure container 3, and a gas exhaust pipe 16 for discharging the Ar gas to the outside of the high-pressure container 3 is connected to the lower part of the side wall. has been done.

The interior of the high-pressure container 3 can be pressurized or depressurized through the gas introduction pipe 15 and the gas discharge pipe 16 to maintain the internal pressure at a predetermined constant pressure.

Hereinafter, an example will be described in which an r n P 4Ji crystal is grown by the LEC method using the single crystal pulling furnace configured as described above.

First, InP polycrystal is prepared as a raw material and placed in a crucible S.

Next, B, O, and the like are placed in a crucible 5 as a sealant, and the crucible 5 is placed inside the heater 4. High-pressure Ar gas is introduced into the high-pressure container 3, and the heater 4 is heated. The raw material in the crucible 5 is melted.

Next, the pulling shaft rotation/vertical drive mechanism 13 is activated to first lower the pulling fi 12 to bring the seed crystal held at its lower end into contact with the surface of the raw material melt 6 in the crucible 5.

After starting to pull the single crystal, the weight is measured by the weight sensor 14, and the weight change rate d is determined from the detected weight change ΔW.
w/dt is calculated, and the trajectory of its rate of change is at least 20
The melt surface temperature at the beginning of pulling σa is determined so as not to fall within the allowable range indicated by diagonal lines in FIG. If it is outside the allowable range, adjust the melt surface temperature again and pull the single crystal.

The inventors of the present invention confirmed that the trajectory of the weight change rate immediately after the start of pulling fell within the hatched area in FIG. 3 according to the above-mentioned example, and then continued to grow an InP single crystal ingot under manual control.

As a result, it was confirmed that an InP single crystal with the same shape and fewer defects could be obtained with good reproducibility.

[Effects of the Invention] As explained above, the present invention connects a weight measuring device to the single crystal pulling shaft to start pulling the single crystal, and then measures changes in the weight of the crystal based on the detection signal from the ff1ffi measuring device. The melt temperature at the 11th time of pulling is determined so that the trajectory of the rate of change falls within a preset tolerance range for at least 20 minutes after the start of pulling, so even if the shape is the same, there will be no defects. This method has the effect of being able to grow single crystals with good reproducibility.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing an example of a single crystal pulling furnace used in the implementation of the present invention, and Figures 2 (a,), (b), and (c) show cases in which the melt surface temperature at the start of pulling was changed. FIG. 3 is a graph showing the permissible range of the weight change rate immediately after the start of pulling when growing an InP single crystal according to the present invention. 3... High pressure container, 4... Heater, 5... Crucible. 6... Raw material melt, 7... Liquid sealed MM, 8...
...Support shaft, 12...Crystal pulling shaft, 14...
Weight sensor, 15... Gas inlet pipe, 16... Gas exhaust No. 1 exit pipe. Figure Moment (minutes) To>Tb>TC (Sunny weather)

Claims (1)

[Claims] (1) Connect a weight measuring device to the single crystal pulling shaft to start pulling the single crystal, and then sequentially calculate the rate of change in crystal weight based on the detection signal from the weight measuring device, at least 20 minutes after the start of pulling. A method for producing a single crystal, characterized in that the melting point surface temperature at the start of pulling is determined so that the locus of the rate of change per minute falls within a preset tolerance range.