JPS59203792A - Process for growing single crystal - Google Patents

Abstract

PURPOSE:To reduce crack generation in the slow cooling stage due to introduction of failure part into the shoulder or barrel part of a single crystal in the pulling method for growing a single crystal by changing the temp. gradient in the pulling direction at immediately above the melt surface for the growing stage of the shoulder part and for the growing stage of the barrel part. CONSTITUTION:A switch 10 which can be turned on/off so as to control the quantity of heat rays passing through a peeping hole 7 of a single crystal growing apparatus is provided to the outside of the peeping hole 7. For example, a seed crystal 5 is pulled up while rotating a single crystal 6 around a Z axis of LiTaO3 to open the switch 10 during the growing stage of the single crystal 6, but it is closed during the stage for growing the barrel part of the crystal. In this way, a temp. gradient in the pulling direction just above the melt 4 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a single crystal growth method, and particularly to temperature control during growth.

[b) Background of the technology Single-crystal wafers are often used for semiconductor devices, but in recent years, electronic components that utilize the physical properties of single crystals by using wafers as substrates and forming film patterns on their surfaces have been put into practical use. It's coming.

An example of this is the use of single crystal wafers such as tantalum oxide (LiTaOJ) and niobium oxide (LiNbO3) as substrates for surface acoustic wave filters and resonators, but these single crystals are expensive. Since these components account for a large proportion of the production cost, it is desired to improve the yield in growing them.

(C) Prior art and problems Figure 1 (al) Figure 1 (bl is a diagram showing the configuration of the growth apparatus and its temperature gradient, Figure 2 is a side view of the grown single crystal, ■ is a container , 2 Haruha, 3 is a high frequency coil, 4 is a melt, 5 is a seed single crystal, 6 is a single crystal, 7 and 7a are viewing windows, 8
9 indicates the shoulder portion, and 9 indicates the torso portion.

In Fig. 1 (al), a crucible 2 is placed inside a container 1, and a high-frequency coil 3 is placed outside the container 1 so as to surround the crucible 2. The melt 4 is heated by the high frequency coil 3.
It becomes. A seed single crystal 5 is immersed in the melt 4 and pulled while rotating to grow a single crystal, and the figure shows the single crystal 6 during growth. In order to monitor this growth state, a viewing window 7 is provided in the container 1 through which the vicinity of the boundary between the melt 4 and the single crystal 6 can be seen.
It is provided on the side.

The temperature gradient in the pull direction inside the single crystal growth apparatus with this configuration during single crystal 6 growth is shown in the graph on the right side of Figure 1 (al), where the vertical axis indicates the position in the height direction of the apparatus. The horizontal axis shows temperature.

The temperature rises and the temperature gradient becomes larger as we move downward from the top, but the temperature drops above the 4th surface of the melt and rises again, so the temperature gradient reverses twice and immediately above the 4th surface of the melt As shown in the figure, the temperature gradient is the largest.

Figure 1 (bl is a single crystal growth apparatus without a viewing window 7, but instead provided with a viewing window 7a at the top of the container 1; the temperature gradient in this case is simple as it goes downward without the above-mentioned reversal. 'I'm rising two times.

FIG. 2 shows a grown single crystal, which is grown from a seed single crystal 5 and consists of a shoulder part 8 where it grows to a predetermined thickness and a body part 9 which maintains that thickness. Figure 1 (al.
When the conventional equipment shown in Figure 1 (bl) is used, even if the temperature control is set to the optimal state, cracks are less likely to occur during slow cooling due to defects introduced in the shoulder 8 or body 9 during growth. There is no problem.

(dl) Purpose of the Invention In view of the above-mentioned conventional problems, it is an object of the present invention to provide a single crystal growth method that reduces the occurrence of cracking during slow cooling due to the introduction of defects in the shoulder or body portion during the growth.

(el) Structure of the Invention The above object is achieved by making the temperature gradient in the pulling direction at a point directly above the single crystal raw material melt surface different between when growing the shoulder portion and when growing the body portion of the single crystal.

The inventor is tantalate tume (LiTaO3) ・
Through our experience in growing single crystals such as niobium oxide (LiNb03), we have learned that by separating the temperature gradients during the growth of the shoulder and the body during single crystal growth, defects in the shoulder and body can be eliminated. In addition, tantalum oxide (LiTaOs) and niobium oxide (LiN) can be individually reduced to reduce the occurrence of cracking during slow cooling.
In the case of a bO3) single crystal, it has been found that it is effective if the temperature gradient during shoulder growth is larger than that during body growth.

However, in the conventional devices shown in FIG. 1 (al) and FIG. 1 (bl), although it is possible to control the temperature in either case, the temperature gradient tends to be In order to separate them, it is necessary to change the configuration of the device.

(fl　Embodiments of the invention An embodiment of the present invention will be described below with reference to the drawings.

The same reference numerals indicate the same objects throughout the figures.

Figure 3 fat is a partial configuration diagram of a single crystal growth apparatus for carrying out the method according to the present invention, Figure 3 (bl, Figure 3 (C1
1 is a diagram showing the temperature gradient when the switch is opened and closed in the device, and 10 indicates the switch.

In order to carry out the method according to the present invention, a switch 1 which can be opened and closed as shown in FIG.
0 was added to the outside of the viewing window 7.

Figure 3 fbl shows the temperature gradient in the device shown in Figure 3 (al) when the switch 10 is open, according to the expression in Figure 1 (al); Figure 3 (C1 is the same case when the switch IO is closed, and it is similar to Figure 1 fbl, and the temperature gradient directly above the melt 4 is as shown in Figure 3 (bl). Therefore, by adjusting the opening and closing of the switch 10, the temperature gradient in this part can be adjusted within the range from the case shown in FIG. 3 (bl) to the case shown in FIG. 3 (C1).

Using the apparatus described above, a single crystal of tantalate (LiTaO3) was grown along the Z axis.
By opening the switch 10 during the growth of the shoulder portion 8 shown in the figure and closing the switch 10 during the growth of the body portion 9, the occurrence of cracks was reduced to about two-thirds of the conventional level. Furthermore, substantially similar results were obtained when growing niobium oxide (LiNb03) along the Z axis.

(g) Effects of the Invention As explained in ``Effects of the Invention'', the configuration according to the present invention can reduce the occurrence of cracks during slow cooling due to the introduction of defects in the shoulder or body portion during single crystal growth, thereby improving the yield. This has the effect of making it possible to reduce the production cost of electronic components using expensive single-crystal substrates to 1.

[Brief explanation of drawings]

Figure 1 (81/Figure 1 fbl is a diagram showing the structure of the growth apparatus and its temperature gradient, Figure 2 is a side view of the grown single crystal, Figure 3 (al is a diagram showing the structure of the growth apparatus) Partial configuration diagram of the single crystal growth apparatus for
1 is a diagram showing the temperature gradient when the switch is opened and closed in the device. In the drawings, 1 is a container, 2 is a high-frequency coil, 4 is a melt, 5 is a seed single crystal, 6 is a single crystal, 7 and 7a are viewing windows, 8 is a shoulder part, and 9 is a body part , 1° indicate the switch, respectively. 567

Claims (3)

[Claims] (1) A seed single crystal is immersed in a melt of a single crystal raw material and pulled up while being rotated to grow a shoulder portion that grows the single crystal to a predetermined thickness, and then to maintain the predetermined thickness. In growing a single crystal by a pulling method for growing a body part of the single crystal, if the temperature gradient in the pulling direction immediately above the melt surface is different between when growing the shoulder part and when growing the body part of the single crystal. A single crystal growth method characterized by (2) Claim (1) characterized in that the temperature gradient is varied by opening and closing a viewing window provided on the side of the single crystal growth apparatus used for the growth. Single crystal growth method described. (3) In making the temperature gradient different, when growing single crystals of lithium cuntarate (LiTaOi) and lithium niobate (LiNb03), the temperature gradient during the shoulder growth is made larger than the temperature gradient during the body growth. A method for growing a single crystal according to claim (1).