JPS62288193A - Method for pulling up single crystal - Google Patents

Abstract

PURPOSE:To produce high-quality single crystal having any diameter, by growing single crystal on seed crystal from a molded article partially immersed in raw material melt put in a crucible and forming a supercooled zone suitable for growth process. CONSTITUTION:Raw material melt is put in a crucible which is rising while being rotated through a supporting shaft. A molded article partially immersed in the melt is fixed by a bearer. The molded article has a small opening at the center and the part immersed in the melt consists of a slant side wall extending upward. Seed crystal is immersed in a supercooled zone of the melt in the molded article to attach crystal to the seed crystal, the seed crystal is pulled up, a shoulder part, a straight barrel part and a tail part of the growing single crystal are successively formed. In the above-mentioned single crystal pulling method, the crystal is pulled up while keeping the correlation shown by the formula S1<=S4<=S3<S2 when the relative velocity of the molded article based on the crucible is S1 in seeding process, S2 in shoulder forming process, S3 in straight barrel forming process and S4 in a tail forming process. Consequently, a proper supercooled zone is made corresponding to the diameter of formed single crystal to prevent dendrite formation.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for pulling single crystals, particularly GaAs,
Group IV compound semiconductor single crystals such as Gap and InP, II-Vl group compound semiconductor single crystals such as CdTe and ZnTe, semiconductor single crystals such as Si and Ge,
and B1.2SiO2o, LiNbO5, GdsGa
This invention relates to a method for pulling an oxide single crystal such as sOtg from a raw material melt in a molded body.

(Prior art) The conventional single crystal pulling method, in which a molded body is placed in a raw material melt and a seed crystal is immersed in the melt drawn through a small opening in the center of the molded body and pulled up, is described in, for example, Japanese Patent Publication No. Publication No. 188500/1982, Japanese Patent Publication No. 45712/1983, Japanese Patent Application Publication No. 58/1982
No. 15097, Japanese Unexamined Patent Publication No. 57-789'1, etc., both have a molded body floating on a melt, and the crystals are pulled up while the liquid level is always equal inside and outside the molded body. In other words, even in the seeding process and shoulder forming process,
There was no particular movement of the molded body during the process of forming the straight body part.

On the other hand, since the raw material melt is heated from around the crucible, when a molded body is used, the melt temperature inside the molded body is lower than that outside the molded body, and a supercooled state occurs at the solid-liquid interface of the crystal. It is formed. In particular, dendrite growth is likely to occur when the supercooled region within the compact is large during the seeding process or shoulder forming process, and in order to narrow the supercooled region, the size of the opening in the compact must be made small. However, as a result, the outer diameter of the pulled crystal becomes smaller.

(Problems to be Solved by the Invention) The present invention solves the drawbacks of the conventional single crystal pulling method using a compact, and by arbitrarily forming a supercooled region suitable for each step of the pulling method, The present invention aims to provide a single crystal pulling method that prevents dendrite growth, ensures diameter control of the pulled crystal, and enables production of high quality single crystals.

(Means for Solving the Problems) The present invention provides a molded body having at least a portion immersed in the melt having an upwardly extending inclined side wall and having a small opening in the center, disposed on the raw material melt, A step of immersing a seed crystal in the melt inside the molded body for seeding, a shoulder forming step of increasing the crystal diameter while pulling the seed crystal, and a straight body forming step of pulling the crystal while maintaining a predetermined diameter. In a single crystal pulling method comprising a step of forming a tail while decreasing the diameter, the relative movement speed of the compact with respect to the crucible containing the raw material melt is set at Sl during the seeding process, S2 during the shoulder forming process, and directly during the seeding process. As S3 during the trunk forming process and S4 during the tail forming process, Sl
This is a single crystal pulling method characterized by pulling a crystal while maintaining the following relationship: ≦54≦53<52.

(Function) FIG. 1 is a conceptual diagram of a single crystal pulling apparatus for carrying out the present invention. The crucible contains a raw material melt and a sealant (Bg
A heater for melting the raw material is placed around the crucible, and a heat insulating material is placed outside the crucible. An inverted cone-shaped molded body with a small opening at the tip is immersed in the raw material melt, and the surface of the raw material melt is maintained inside the molded body. Figure 2 shows the molded body.

FIG. 2 (4) is a perspective view of the molded body, and FIG. 2 (03) is a sectional view. The inner diameter of the straight body part of the molded body is 70~80mm.1 The height of the straight body part is 1O~30B1.The diameter of the small opening is J~30-1.
The height of the inverted conical portion is approximately 10 to 20 B, but the straight body portion is not necessarily required. Although this molded body is fixed to the heat insulating material via a support in FIG. 1, it can also be fixed in other ways, or a vertical moving means may be attached to the molded body. The crucible is gradually raised by a support,
Rotation is applied as necessary to maintain the positional relationship with the heater so as to maintain the raw material melt at a predetermined temperature. Further, a seed crystal is fixed to the tip of the pulling shaft, and after the seed crystal is fully immersed in the supercooled raw material melt in the molded body, it is gradually pulled up while rotating. Figure 3 shows the state of the melt, compact, and pulled crystals in each pulling process. Figure 3 shows that seeding is a process, and the height of the melt level inside and outside the compact is shown in Figure 3. The difference is 8 to 12 degrees, and FIG. 3(B) shows the time when the relative movement speed of the molded body shows the largest value in the shoulder forming process, and the difference in liquid level height is 10 to 13 degrees. Figure 3 (C) shows the straight body part forming process, and the difference in liquid level height is between 12 and 16.
D) is the tail forming process, and the difference in liquid level height is 10~13tm.
It is. The difference in liquid level height inside and outside the molded body varies depending on the shape of the molded body and the size of the opening, but there can be a difference of 8 cm or more.

In this way, while the outside of the molded body is surrounded by hot melt, crystal growth occurs at a position lower than the outside liquid level.
The temperature distribution inside the compact is highest at the wall temperature of the compact,
Improves the heat retention of the pulled crystal. Furthermore, since the temperature of the wall of the molded body is the highest, it is possible to prevent the crystals from sticking to the molded body and to prevent the generation of growth nuclei from the wall of the molded body, allowing smooth crystal growth.

Next, Figures 4 and 5 show the following in relation to each pulling process.
The relationship between the length of the pulled crystal, the change in the relative moving speed of the molded body, and the change in the diameter of the surface of the raw material melt inside the molded body is shown.

The pulling process will be explained in order based on this relationship.

The melt introduced into the molded body forms a supercooled melt section, crystallizes in the upper part, and is pulled up. When seeding occurs, when the cross-sectional area of this supercooled melt portion is large, crystals grow rapidly from the outer diameter of the seed crystal.

Its outer diameter depends on the cross-sectional area of the supercooled melt section. In severe cases, dendrite growth occurs and becomes polycrystalline.

Therefore, during seeding, the cross-sectional area of the supercooled melt portion is made small, preferably to the extent that it has a diameter comparable to that of the seed crystal. Next, when forming the shoulder, the molded body is moved relative to the crucible and gradually immersed in the melt. This moving speed is higher than the rate at which the melt drops in the crucible, and since the molded body has a tapered shape that widens at the top, the cross-sectional area of the supercooled melt part formed inside the molded body is smaller than that of the crystal. It gradually increases as the crystal is pulled, and as a result, the outer diameter of the pulled crystal also gradually increases. This forms a shoulder. When the outer diameter of the crystal reaches the desired value, the relative movement speed of the molded body is made equal to the drop rate of the melt level in the crucible, and the cross-sectional area of the supercooled melt part formed inside the molded body is kept constant. The outer diameter of the crystal, which is regulated by this, is also constant, and a straight body portion is formed. Next, the relative movement speed is lowered to gradually reduce the crystal diameter and form a tail.

In other words, the outer diameter of the pulled crystal is regulated by the cross-sectional area of the supercooled melt formed inside the compact, and when using a tapered compact, seeding is carried out at the same time, shoulder formation is performed, and straight. By controlling the relative movement speed by changing the relative movement speed during the formation of the trunk and the tail, it is possible to obtain a high-quality single crystal without dendrite growth and with little variation in diameter.

(Example 1) <111 by LEC method (liquid encapsulation Czochralski method)
> direction of GaAs single crystal pulling. 4
An inch quartz crucible was charged with 1.5KF of GaAs raw material, 240P of B2011 was used as a sealant, and the molded body shown in FIG. 2 was used. The temperature distribution has a longitudinal temperature gradient of 10°C/cy and a radial temperature gradient of 1°C/cy.
It was set as n. The relative movement speed of the molded body is 0/H1 for seeding.
1.8a/H when forming the shoulder part, 1.25M/H when forming the straight body part
, the tail was formed at 0.5 elbow/H, and the pulling rate was 5 IuL.
/H. The crystal had an outer diameter of 50 mm, no dendrite growth, and little variation in diameter.

Increases and decreases occurred repeatedly.

(Example 2) A ZnTe single crystal was pulled by the LEC method. 1.4 ml of ZnTe raw material in a 4-inch diameter quartz crucible
In this case, B2O3 was used as a charge and a sealant. A molded article having the same shape as in Example 1 was used.

The temperature distribution in the longitudinal direction was 100° C./cfn1, and the temperature distribution in the radial direction was 10° C./c1n. The moving speed of the molded body was 0.2 IuL/H for seeding, 1.2 mx/H for shoulder formation, 0.6 IuL/H for straight body formation, 0.3 mx/H for tail formation, and the pulling speed was Bat. /H. The obtained crystal had a straight body diameter of 40 am, a length of 3 Qm, and was of good quality, containing several grain boundaries, without Puntrian growth.

If the compact is not actively moved as described above, dendrites will occur immediately after seeding, or crystals will be cut from the melt during pulling, making stable crystal pulling impossible.

(Effects of the Invention) By adopting the above configuration, the present invention forms a supercooled region suitable for each step of the pulling method, thereby easily controlling the formation of the shoulder and straight body of a single crystal. In addition, we were able to pull a high-quality single crystal that does not contain dendrite growth.

[Brief explanation of drawings]

Fig. 1 is an overall view of a pulling device for carrying out the present invention, Fig. 2 (4) and (B) are perspective views and cross-sectional views of a molded body used in the device shown in Fig. 1, and Fig. 3 (4). - (9) are enlarged views showing the relationship between the melt of the compact and the pulled crystals in each step of the pulling method;
FIG. 4 is a diagram showing the relationship between the pulled crystal length and the relative moving speed of the molded body, and FIG. 5 is a diagram showing the relationship between the pulled crystal length and the change in the surface diameter of the raw material melt in the molded body. Fig. 1 (A) Fig. 2 - I pot or 1 Monho - N Momme I cap, each 4S Shizushima

Claims (3)

[Claims] (1) A molded body having sloped side walls with at least the part immersed in the melt expanding upward and a small opening in the center is placed on the raw material melt, and the melt in the molded body is seeded with seed crystals. a shoulder formation process that increases the crystal diameter while pulling the seed crystal; a straight body formation process that pulls the crystal while maintaining a predetermined diameter; and a tail formation process that reduces the diameter. In the single crystal pulling method, the relative movement speed of the compact with respect to the crucible containing the raw material melt is set at S_1 during the seeding process, S_2 during the shoulder forming process, S_3 during the straight body forming process, and S_3 during the tail forming process. As S_4, S
A single crystal pulling method characterized by pulling the crystal while maintaining the relationship _1≦S_4≦S_3<S_2. (2) The relative movement speed S_2 of the molded body during the shoulder forming process is set to be higher than the liquid level drop rate of the melt in the crucible accompanying crystal pulling, and the relative movement speed S_3 during the straight body forming process is set to The method for pulling a single crystal according to claim 1, wherein the relative movement speed S_4 during the tail forming step is set to be approximately equal to the surface lowering speed and smaller than the liquid level lowering speed. (3) Pulling a single crystal according to claim 1 or 2, characterized in that a liquid sealant is disposed on the surface of the raw material melt and the crystal is pulled by the Czochralski method. Upper method.