JPH0699227B2 - Single crystal manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a single crystal, and particularly to a method for growing a single crystal by the Czochralski method (including the liquid-encapsulated Czochralski method). Regarding technology.

[Prior Art] One of the methods for growing a compound semiconductor single crystal such as GaAs or InP is to put a raw material in a crucible, heat and melt it, and bring a seed crystal into contact with the surface of the melt, and then gradually pull it up. There is a Czochralski method for growing a single crystal with a uniform crystal orientation.

In the crystal growth by the Czochralski method, if the temperature of the melt surface at the start of pulling the seed crystal 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 melt temperature and the pulling timing during seeding.

To accurately know the melt surface temperature during seeding, contact the thermocouple with the melt surface.By inserting the thermocouple, convection of the melt is disturbed and the temperature distribution in the melt changes. Then, it becomes impossible to grow the single crystal.

It is also possible to measure the temperature of the melt surface in a non-contact manner using an optical thermometer, but in this case, there is an influence of the atmospheric gas in the furnace and its convection, and the window material of the furnace, It has not been possible to measure the temperature of the melt surface with good reproducibility.

Therefore, conventionally, the pulling start timing is visually determined by observing the state of the contact portion between the seed crystal and the melt through the sight window provided in the furnace body.

[Problems to be Solved by the Invention] However, in the above-mentioned method of visually measuring the seeding temperature, it is difficult to accurately determine the temperature, and many years of experience and skill are required. There was a problem that the shape was different for each growth, the reproducibility was not sufficient, and crystal defects were likely to occur.

The present invention has been made in view of the above problems, and in the single crystal growing step by the Czochralski method, it is possible to grow a single crystal with few crystal defects and variation in shape with good reproducibility. The purpose is to be able to.

[Means for Solving the Problem] The inventors of the present invention repeated pulling while changing the melt temperature, and investigated the rate of change of the crystal weight at that time. As a result, as shown in FIGS. 2 (a) to 2 (c), it was found that the trajectory of the rate of change of the crystal weight was different depending on the melt surface temperature Tint. That is, as the melt surface temperature is raised from the higher state, the locus becomes gentler as shown in FIG.
The locus becomes steeper as it is pulled up from a lower state. Furthermore, it was found that if the trajectory of the rate of change of the weight coincides with the trajectory when the temperature is raised from the optimum temperature for at least 20 to 30 minutes after the pulling is started, sufficiently reproducible crystal growth can be performed. .

This invention has been made based on the above knowledge, the weight measuring device is connected to the single crystal pulling shaft to start pulling of the single crystal, and then the weight of the crystal is detected based on the detection signal from the weight measuring device. The melt surface temperature at the start of pulling was determined so that the locus of the change falls within a preset allowable range for at least 20 minutes after the start of pulling.

[Operation] According to the means described above, crystal growth with good reproducibility becomes possible by pulling a single crystal while keeping the change rate of weight change dw / 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 closed cylindrical high-pressure vessel 3 is provided with a substantially cylindrical heater 4. At the center of the heater 4, a crucible 5 made of pBN and having a diameter of about 6 inches is arranged. The melt 6 is put in the crucible 5, and the upper surface of the melt 6 is covered with a liquid sealant layer 7 made of B ₂ O ₃ . The crucible 5 is rotatably and vertically movable by a support shaft 8 fixed to its lower end. Reference numeral 9 denotes a support shaft rotation / vertical drive mechanism provided at the lower end of the support shaft 8. Reference numeral 11 denotes a heat insulating member arranged so as to surround the outer circumference of the heater 4.

On the other hand, from above the crucible 5, a crystal pulling shaft 12 is hung in the high-pressure vessel 3 so as to be rotatable and movable up and down. A seed crystal is held at the lower end of the crystal pulling shaft 12 to melt the melt in the crucible 5. The surface of 6 can be contacted. Reference numeral 13 denotes a pulling shaft rotation / vertical drive mechanism provided at the upper end of the crystal pulling shaft 12. Also, the crystal pulling shaft 12
A weight sensor 14 capable of measuring the weight of the crystal is attached.

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 the lower part of the side wall is connected to
A gas discharge pipe 16 for discharging the Ar gas to the outside of the high pressure container 3 is connected. These gas inlet pipe 15 and gas exhaust pipe
It is possible to pressurize and depressurize the inside of the high-pressure container 3 via 16 to bring the internal pressure to a predetermined pressure.

An example of growing an InP single crystal by the LBC method using the single crystal pulling furnace having the above structure will be described below.

First, prepare InP polycrystal as a raw material, and use this for crucible 5.
insert.

Next, B ₂ O ₃ is put into the crucible 5 as a sealant, the crucible 5 is installed inside the heater 4, and then 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 operated to lower the pulling shaft 12 first, and the seed crystal held at the lower end thereof is brought into contact with the surface of the raw material melt 6 in the crucible 5.

After the pulling of the single crystal is started, the weight change rate dw / d is obtained from the weight change ΔW detected by the weight measurement by the weight sensor 14.
Calculate t, and the trajectory of the rate of change is the third for at least 20 minutes.
The melt surface temperature at the start of pulling is determined so as not to deviate from the allowable range shown by the diagonal lines in the figure. If it is out of the allowable range, the melt surface temperature is adjusted again to pull up the single crystal.

The present inventors confirmed that the locus of the weight change rate immediately after the start of pulling is within the hatched line in FIG. 3 according to the above-mentioned example, and then continued to grow the InP single crystal ingot by manual control. As a result, it was confirmed that an InP single crystal having the same shape and few defects could be obtained with good reproducibility.

[Effects of the Invention] As described above, according to the present invention, the weight measuring device is connected to the single crystal pulling shaft to start pulling of the single crystal, and thereafter, the change of the crystal weight based on the detection signal from the weight measuring device. The melt temperature at the start of pulling is determined so that the locus of the change rate is within a preset allowable range for at least 20 minutes after the start of pulling. There is an effect that it is possible to grow a single crystal with less reproducibility with good reproducibility.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing an example of a single crystal pulling furnace used for carrying out the present invention, and FIGS. 2 (a), (b), and (c) are melting at the start of pulling. FIG. 3 is a graph showing the difference in the trajectory of the rate of change of weight when the liquid surface temperature is changed, and FIG. 3 shows the allowable range of change in the rate of change of weight immediately after the start of pulling when growing an InP single crystal according to the present invention. It is a graph. 3 ... high-pressure container, 4 ... heater, 5 ... crucible, 6 ...
Raw material melt, 7 ... Liquid sealant layer, 8 ... Support shaft, 12 ...
Crystal pulling shaft, 14 …… Weight sensor, 15 …… Gas inlet tube,
16 …… Gas discharge pipe.

Claims (1)

[Claims] 1. A weight measuring device is connected to a single crystal pulling shaft to start pulling of a single crystal, and thereafter, a rate of change in crystal weight is sequentially calculated based on a detection signal from the weight measuring device, and at least pulling is started. 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 falls within a preset allowable range for the next 20 minutes.