JPH0243718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a structure of a crucible for crystal growth that can suppress thermal convection of a melt.

(b) Background of technology Current semiconductor integrated circuits use crystal substrates (wafers) cut from single crystal semiconductors such as silicon (Si) or compound semiconductors such as gallium arsenide (GaAs) and indium phosphide (InP). It is formed by

Here, the method of growing single crystals is the pulling method (abbreviated as
There are two methods: the CZ method) and the floating zone method (abbreviated as the FZ method), but CZ is suitable for growing large crystals with large diameters.

The present invention relates to the structure of a crucible used for crystal growth by the CZ method.

(c) Conventional technology and problems Crucibles used to grow single crystals are made of various materials, such as platinum (Pt), quartz (SiO ₂ ), and boron nitride (BN), depending on the material to be melted.

The present invention relates to a structure of a crucible that is effective in suppressing convection of melt, and will be explained below using Si as an example, which is currently used to pull crystals with the largest diameter and is greatly affected by thermal convection.

A crucible made of quartz is used as a crucible for growing Si single crystals, and there is also one that is further lined with silicon nitride (Si ₃ N ₄ ), which is used to grow crucibles with a diameter of 4
[inch] or 5 [inch] lengths of about 1 [m] are manufactured by the pulling method.

FIG. 1 is a diagram showing the state around the crucible in which a Si single crystal is pulled using such a crucible 1 made of quartz. To grow a huge single crystal as shown above, the diameter is approximately
Approximately 20 [Kg] in a crucible of 300 [mm] and thickness of approximately 5 [mm]
The crucible is filled with high-purity Si polycrystals, and a carbon heater 2 provided surrounding the crucible 1 is energized in an inert atmosphere such as argon (Ar) to heat and melt the Si polycrystals to form a melt 3.

Next, the seed crystal 4 fixed to the pulling shaft is immersed in the melt 3, but at this time, the melt 3 is maintained at a temperature such that the tip of the seed crystal 4 is slightly melted.
While maintaining an equilibrium state, the temperature of the melt 3 is gradually lowered to thicken the crystal 5 to the required diameter, and the pulling shaft is gradually pulled up to grow a straight-shaped single crystal 5. .

Here, since the melting point of Si is 1410 [℃], the temperature of the melt 3 at the bottom of the crucible is several tens of degrees [℃] higher than that.
Further, since the diameter and depth of crucible 1 are large, thermal convection as shown by arrow 6 occurs from the bottom of crucible 1 along the inner wall.

However, since this thermal convection is not steady but accompanied by turbulence, the heat fluctuates greatly, resulting in growth stripes with different impurity concentration distributions along the growth direction of the crystal 5. To solve this problem, the pulling shaft and crucible 1 are rotated at low speeds in opposite directions to create a lateral forced flow, thereby suppressing thermal convection. In the case of , the sufficient effect is not realized because the flow rate is large.

(d) Purpose of the Invention The purpose of the present invention is to provide a crucible structure capable of suppressing thermal convection and obtaining a high-quality single crystal.

(e) Structure of the Invention The object of the present invention is to provide a crucible for crystal growth, characterized in that the inside of the crucible is cylindrical, has a plurality of protrusions on the upper and lower outer edges, and has partition walls that float in the melt. This can be achieved by using

(f) Embodiment of the Invention FIG. 2 is a side view A of a crucible having a structure in which a partition wall according to an embodiment of the present invention for suppressing thermal convection is movable up and down depending on the liquid level of the melt. They are a top view B and a perspective view C of the partition wall.

The present invention focuses on the fact that thermal convection occurs along the side walls of the crucible due to the temperature difference between the surface and bottom of the melt in the crucible, and provides partition walls along the side walls.

That is, in FIG. 2, the partition wall 1 according to this embodiment
7 forms a concentric circle with the crucible 11, and its inner diameter is set to be sufficiently large so as not to become an obstacle during crystal growth. It is sufficiently shallow. The partition wall 17 is made of the same material as the crucible 11, and in this embodiment is made of quartz (SiO ₂ ), the same as the crucible. The conditions for this partition wall 17 are that it does not react with or be eroded by the melt 13, and that the specific gravity is lower than that of the melt 13.
It is necessary to float smaller.

In the case of this embodiment, the specific gravity of Si is 2.33, while the specific gravity of SiO ₂ is 2.20, and the partition walls 17 are always floating on the melt 13. Next, on the periphery of the partition wall 17, a plurality of (four in this embodiment) protrusions 18 are provided on the upper and lower sides.
18' serves as a stopper or positioning of the floating partition wall 17. Particularly, by providing the protrusion 18' at the lower part of the partition wall 17, it is possible to suppress the partition wall 17 from moving up and down in the left and right directions.

The crystal size to be grown is 4 [inches] or 5 [inches].
The diameter of the crystal is pulled up from the center of the crucible 11, that is, the center of the area surrounded by the partition wall 17. During this crystal growth, it is necessary to observe the meniscus line where the crystal grows through the viewing window of the device, and in this case, the presence of the partition wall 17 must be observed. must not obstruct the view.

To give a specific example, when pulling a Si single crystal of 4 [inches] or 5 [inches] using a straight body crucible with a diameter of 12 [inches] and a height of about 250 [mm], the partition wall 1
The width W of the projections 18, 18' of No. 7 may be set to 50 [mm] or less.

Further, the thickness of the partition wall 17 may be about half the thickness of the crucible, and in this embodiment, it is about 3 mm.

When such a partition wall 17 is used, as the growth of the single crystal progresses, the liquid level decreases and the partition wall 17 finally bottoms out in the crucible 11, and it seems that the effect of preventing thermal convection is lost. Since the influence of thermal convection disappears in proportion to , there is no problem even if it hits the bottom. In this embodiment, since the partition wall 17 is removable, the crucible 11
Another advantage is that the partition wall 17 can be easily cleaned.

(g) Effects of the Invention By carrying out the present invention, it was possible to grow a single crystal without growth striations, and the quality of the crystal could be improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining crystal growth, FIGS. 2A and B are cross-sectional views and plan views showing the structure of a crucible according to an embodiment of the present invention, and FIG. 2 C is a cross-sectional view for explaining the crystal growth. FIG. 3 is an external perspective view showing the configuration of a partition plate. In the figure, 1 and 11 are crucibles, 2 is a carbon heater, 3 and 13 are melts, 5 is crystals, 17 is a partition wall, 1
8 and 18' are protrusions.

Claims (1)

[Claims] 1. A crucible that holds a melt for crystal growth and is used to immerse a seed crystal in the melt and gradually pull it up to grow the crystal. A crucible for crystal growth characterized by having a plurality of protrusions on the upper and lower outer edges and a melt wall that floats in the melt.