JPS63252989A - Production of semiconductor single crystal by pull-up method - Google Patents

Abstract

PURPOSE:To uniformize impurity concentration in a crystal with a simple apparatus, by solidifying a major part of a molten liquid containing doping impurity from below, starting the crystal growth from the upper liquid part and melting the solidified polycrystals in a manner to keep the volume of the molten liquid at a definite level. CONSTITUTION:A molten liquid 2 containing impurities is formed in a crucible 1. The molten liquid 2 is slowly solidified from the lower part of the crucible 1 to leave a molten part 4 above the solid or the molten liquid 2 is completely solidified and a part of the upper part of the solidified polycrystals 3 is melted to form a molten part 4. The crystal growth is started from the molten part 4 and the volume of the molten part 4 is maintained at a definite level by controlling a heating means. The impurity concentration in the polycrystals 3 abruptly decreases toward the lower part when the segregation coefficient K is sufficiently smaller than 1. Accordingly, no considerable change in the impurity concentration occurs in the molten part in the course of growing a crystal from the start of crystal growth. A similar crystal having uniform impurity concentration can be produced when the segregation coefficient is larger than 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a method for manufacturing a semiconductor single crystal doped with impurities by a pulling method.

[Prior Art] When a crystal is grown from a melt doped with impurities, the impurities are distributed in the crystal according to segregation theory. That is, C(g) = Co K (1-g)k-' In the above formula, C(g) is g (-W/W, iwO is the initial financial liquid amount, and W is the solidified amount.) Co indicates the impurity concentration in the crystal at a given position, Co indicates the impurity concentration in the initial melt, and K indicates the segregation coefficient.

Therefore, as is clear from FIG. 4, unless the crystal is K-1, the impurity concentration in the grown crystal changes as the melon solidifies, and therefore only a single crystal with non-uniform impurities can be obtained.

On the other hand, the double crucible method has been proposed as a method for obtaining single crystals with uniform concentration distribution [for example, Solid State Electronics (SOIidState El.
electronics), Volume 6, No. 2, No. 163
Pages 165 to 165].

This double crucible method uses an outer crucible connected by a capillary in addition to an inner crucible in which crystal growth occurs, and impurities in the melt are diffused and transferred between the inner crucible and the outer crucible. , to maintain a uniform impurity concentration in the melt in the inner crucible.

[Problems to be Solved by the Invention] In the conventional simple pulling method, as described above, the doping impurity concentration changes greatly as the crystal grows. Therefore, the impurity concentration range that can actually be used as a crystal is limited, resulting in a low crystal yield and a very high crystal cost.

On the other hand, the double crucible method described above requires complicated equipment such as an inner crucible and an outer crucible, and also requires complicated control work to keep the impurity concentration in the melt in the inner crucible constant. Therefore, the crystal cost would be quite high, and it could not be implemented industrially.

Therefore, an object of the present invention is to provide a method that makes it possible to obtain a semiconductor single crystal with a uniform impurity concentration at a low cost using relatively simple equipment.

[Means for Solving the Problems] The manufacturing method of the present invention includes the steps of generating a melt containing a predetermined amount of impurities in a crucible, and directing at least most of the melt from below in the -L direction. A step of solidifying to obtain a solidified polycrystal in which the upper part is in a molten state and doping impurities are distributed according to segregation from the bottom to the top, and crystal growth from the molten part in the -L direction. Start and weld 12
and growing the assimilated polycrystal while melting it so that the polycrystal is approximately constant.

The molten state portion formed above the assimilated polycrystal may be formed by once solidifying all of the melt in the crucible and then remelting the upper part; Most of the melt may be solidified from the bottom to the top, leaving a portion that will become the melt state.

[Effect] The principle of this invention will be explained with reference to FIG.

In the method shown in FIG. 1, the solidification described above is carried out so as to solidify all of the melt in the crucible, and then the upper part is reheated to form a melt.

That is, as shown in FIG. 1(a), a melt 2 with impurities on the gold side is produced in a crucible 1. Next, Figure 1(b)
As shown in FIG. 1, the melt 2 is slowly solidified from the lower side of the crucible 1, and the entire melt is solidified to obtain solidified polycrystals (see FIG. 1(, c)). Next, as shown in FIG. 1(d), a part of the upper part of the solidified polycrystal 3 is melted to form a melted part 4.
generate. From this melt state portion 4, crystal growth is started as shown in FIG. 1(e), and in this case, the amount of the melt state portion 4 is kept constant by controlling the heating means.

In the above process, the impurity concentration distribution in the vertical direction of the solidified polycrystalline 3 shown in FIG. 1(c) is shown in FIG. Note that the distribution shown here is an example when the segregation coefficient K is sufficiently smaller than 1. As is clear from FIG. 2, the concentration of impurities decreases rapidly toward the bottom of the crucible.

-1- Under the premise as shown in Figure 1(d)-(e)
When crystal growth proceeds according to the process, the impurity concentration in the melt state portion 4 at the time point is (the amount of impurities in the previous melt state portion) + (the impurity W(B) in the newly melted solidified polycrystal. )) - the amount of impurities incorporated into the solidified crystal as it grows (A)).

Therefore, crystal growth progresses, and FIGS. 1(d) and (e)
) The amount of impurities mixed in at the time of melting decreases as the melt state portion 4 moves toward the lower side of the crucible 1. Furthermore, the amount of impurities in the melt state portion is reduced by the amount of impurities that are incorporated into the crystals generated as the crystal grows. Further, as described above, the amount of melt in the melt state portion 4 is controlled to be approximately constant. Therefore, it can be seen that the impurity concentration in the melt in the melt state portion 4 does not change significantly from the start of crystal growth until the crystal growth continues.

In other words, the present invention maintains a constant amount of melt in the molten portion, and adjusts the change in the amount of impurities mixed in from the solidified raw material polycrystal, whose impurity concentration changes according to segregation, into the grown crystal. This buffers the change in the amount of impurities taken into the cliff liquid, thereby making the change in impurity concentration in the cliff liquid state almost constant.

Note that the above explanation is for the case where the segregation coefficient K is sufficiently smaller than 1, but even when the segregation coefficient K is larger than 1, a crystal with a uniform impurity concentration can be similarly obtained by the method of the present invention. Furthermore, as described above, the molten portion can be formed by solidifying the initial melt by solidifying only most of it and leaving part of it as the molten portion. That is, solidification is stopped from the state shown in FIG. 1(b) to the state shown in FIG. 1(d),
Crystal growth may be started in this state.

[Example Description] In a pBN crucible with a diameter of 10.16 cm (4 inches), 1 kg of GaAs polycrystal, a predetermined amount of In, and about 2
After filling with 00g of 8203, it was set in the furnace. This was evacuated, pressurized using N2 gas, and then heated to produce a melt.

Next, the crucible position was moved and assimilation was started from below the crucible. Assimilation was made to proceed at a sufficiently slow rate and continued until the entire volume was solidified.

Next, by adjusting the crucible position and heating means, only the upper 20% of the solidified polycrystal is melted again, and then a seed crystal is brought into contact with this molten part, and then the seed crystal is pulled up while rotating. , grew crystals.

During crystal growth, the crucible position was adjusted so that the surface of the molten portion was always at the same position. In addition, the melt is
Approximately the same amount (approximately 20% of the initial financial liquid volume) was always present while the solidified polycrystals remained.

When the distribution of the In concentration of the grown crystal was measured in the length direction, the results shown by the solid line in FIG. 3 were obtained. As is clear from Figure 3, the impurity concentration was uniform, and there was only a difference of about 20% between g-0 and g-0,8 (
In addition, in the usual pulling method, doping is performed according to the segregation theory as shown by the broken line in FIG. 3, so the concentration at g-0, 8 is more than four times that at the g-0 position. ).

The crystal grown according to this example was g-
All crystals up to 0.8 were high quality crystals with low dislocation densities.

Note that the impurity concentration increases significantly from g-0.8 onwards, but this is because the solidified polycrystals disappear at this point.
This is because the amount of melt decreased and crystals grew according to the normal segregation theory.

[Effect of the invention] As described above, in this invention, compared to the conventional pulling method,
Since the impurity concentration in the crystal can be made uniform in a uniform manner, the quality of the crystal can be made uniform. Furthermore, since the yield of good crystals is significantly improved, semiconductor single crystals can be obtained at low cost.

In particular, when growing a low-dislocation-density crystal by doping In as an impurity, a high In concentration causes cell growth, polycrystalline formation, and a decrease in yield. Since it is possible to obtain a crystal that does not cause cell growth until the In concentration becomes high, the yield improvement and cost reduction effects are significant.

[Brief explanation of drawings]

FIG. 1 is a process diagram for explaining the present invention in detail, FIG. 2 is a diagram showing the impurity concentration distribution in the solidified polycrystal, and FIG. 3 is a diagram showing the impurity concentration distribution in the solidified polycrystal. FIG. 4 is a diagram showing the impurity concentration distribution in a single crystal, and FIG. 4 is a diagram for explaining the impurity concentration distribution due to segregation. In the figure, 1 is a crucible, 2 is a melt, 3 is a solidified polycrystal, and 4 is a portion in a melt state. Patent applicant: Sumitomo Electric Industries, Ltd.
The force is 1'lrun

Claims (3)

[Claims] (1) a step of generating a melt containing a predetermined amount of impurities in a crucible, and solidifying at least a large portion of the melt from the bottom to the top, with the upper part being in a melt state; and a step of obtaining a solidified polycrystal in which doping impurities are distributed according to segregation from the bottom to the top, and crystal growth is started from the upper melt state portion, and the amount of melt in the melt state portion is almost constant. A method for manufacturing a semiconductor single crystal by a pulling method, which comprises a step of growing a solidified polycrystal while melting it so that the solidified polycrystal is grown. (2) The solidification is performed so as to solidify all of the melt in the crucible, and the upper part of the melt is formed by remelting after solidification.
A method for manufacturing a semiconductor single crystal by the pulling method described in . (3) A method for manufacturing a semiconductor single crystal by a pulling method according to claim 1, wherein the solidification is performed so as to leave a portion in a molten state above.