WO1991017289A1

WO1991017289A1 - Silicon single crystal manufacturing apparatus

Info

Publication number: WO1991017289A1
Application number: PCT/JP1991/000547
Authority: WO
Inventors: Takeshi Kaneto; Yoshinobu Shima
Original assignee: Nkk Corporation
Priority date: 1990-04-27
Filing date: 1991-04-24
Publication date: 1991-11-14
Also published as: DE4190942T1; JPH0412084A; KR920702733A

Abstract

A silicon single crystal manufacturing apparatus for pulling at a high rate a silicon single crystal having a large diameter and stable composition according to the CZ method of the type in which a crucible is rotated. A crucible-type partition member is closely fitted to a bottom portion of the crucible, and the radius of curvature of a portion connecting a side and bottom of the crucible-type partition member is between 10mm and 50mm. Thus, a convection of molten silicon in a crystal growing section of the crucible is maintained in a condition suited for pulling at a high rate a silicon single crystal which is large in diameter and stable in composition.

Description

DESCRIPTION

Title of the Invention

SILICON SINGLE CRYSTAL MANUFACTURING APPARATUS

TECHNICAL FIELD

The present invention relates to an apparatus for manufacturing large-diameter silicon single crystals according to the Czochralski method. More particularly, the invention relates to a silicon single crystal manufacturing apparatus including a rotation-type quartz crucible containing molten silicon, an electric resistance heater for heating the quartz crucible from the side thereof, a quartz partition member arranged to divide the molten silicon into a single crystal growing section and a material melting section within the quartz crucible and having small holes for permitting the passage of the molten silicon therethrough, and starting material feed means for continuously feeding starting material silicon to the material melting section.

BACKGROUND ART In the field of LSIs, the diameter required for silicon single crystals has been increased year after year. At present, silicon single crystals of 6 inches in diameter are used for the latest devices. It is said that in the future silicon single crystals of over

10 inches in diameter, e.g., silicon single crystals of 12 inches in diameter will be needed.

In accordance with the Czochralski method (CZ method) which is known as a method of manufacturing large-diameter silicon single crystals, the amount of molten silicon in a crucible is decreased as a silicon single crystal is grown. Thus, as the silicon single crystal grows, the dopant concentration is increased and the oxygen concentration is decreased in the silicon single crystal. In other words, the properties of the silicon single crystal are varied in the direction of its growth. Since the quality required for silicon single crystals has been made severer year after year with increase in the level of integration of LSIs, this problem must be overcome.

As a means of solving this problem, a method is known in which as shown in Fig. 8, the interior of a quartz crucible 1 according to the ordinary CZ method is divided by a cylindrical quartz partition member 22 having small holes 12 for molten silicon 4 and a cylindrical silicon single crystal is grown on the inner side of the partition member 22 while continuously feeding starting material silicon 17 to the outer side of the partition member 22 from starting material feed means 14, and many patents have been disclosed (e.g., Patent Publication No. 40-10184, Laid-Open Patent No. 62- 241889, Laid-Open Patent No. 63-23092, Laid-Open Patent No. 63-319287, Laid-Open Patent No. 64-76992 and laid- Open Patent No.1-96087).

Where a silicon single crystal is manufactured by use of a double structure crucible incorporating therein a partition member on the basis of the prior art technique such as described above, the heat environment in the molten silicon is the very opposite to that in cases where the ordinary single structure crucible is used.

In the case of the CZ method employing the ordinary single structure crucible, the crucible side wall portion is higher in temperature than the crucible bottom portion. In other words, the amount of heat input through the crucible side wall portion is greater than the amount of heat supplied from the crucible bottom portion. As a result, it is said that the convection of the molten silicon within the quartz crucible is predominated by such flows as shown in Fig. 9. Where the pulling of a silicon single crystal is effected by the use of the double structure crucible, as compared with the case employing the single structure crucible, the proportion of the heat input from the crucible bottom portion becomes greater than the amount of heat applied to the single crystal growing section through the crucible side wall. This is due to the fact that the side portion of the partition member is remote from the heat source and that the temperature distribution in the molten silicon of the material melting section is higher in temperature in the bottom portion that the remainder. In such heat environment where the proportion of the heat input is from the bottom portion greater, the heat convection of the molten silicon within the single crystal growing section is predominated by such heat convection as shown in Fig. 10 in completely contrary to the case of Fig. 9. With such heat convection, the high temperature molten silicon in the crucible bottom portion is directly moved to the solid-liquid interface of the silicon single crystal. As a result, there is caused a problem of impeding the stable pulling of the silicon single crystal. The present invention has been made with a view to overcoming the foregoing problems. It is an object of the present invention to overcome the deficiencies of a silicon single crystal manufacturing apparatus employing the above-mentioned type of double crucible structure having a crucible-type partition member inserted therein by using the crucible type as the partition member and improving the heat environment of the molten silicon within the single crystal growing section, thereby attaining the table pulling of a silicon single crystal.

DISCLOSURE OF INVENTION

With a view to overcoming the foregoing problems, in accordance with the present invention there is provided a silicon single crystal manufacturing apparatus including a rotation-type quartz crucible containing molten silicon an electric resistance heater for heating the quartz crucible from the side thereof a quartz partition member arrange to divide the molten silicon into a single crystal growing section and a material melting section within the quartz crucible and having small holes for permitting passage of the molten silicon therethrough and starting material feed means for continuously feeding starting material silicon to the material melting section, and the apparatus is characterized in that the partition member is in the form of a crucible type, that the outer surface of the bottom of the crucible-type partition member is closely fitted to the bottom of the quartz crucible and that the portion connecting the side of the crucible-type partition member and the bottom surface of the partion member has a radius of curvature in the range from 10mm to 50mm .

The inventors, etc., have conducted the below mentioned tests and made the present invention on the basis of the knowledge resulting from the tests. In order to overcome the foregoing problems of the double structure crucible in which the cylindrical partition member is arranged within the quartz crucible, it is conceivable to use a crucible of the double structure in which the thickness of the quartz at the bottom of a single crystal growing section is increased as shown in Fig. 5.

By increasing the thickness of the quartz at the bottom of the single crystal growing section , it is possible to reduce the amount of heat introduced through the bottom in the single crystal growing section. As a result, the amount of heat input through the side of the single crystal growing section can be increased and thus it is possible to obtain the equivalent heat convection as in the case where the ordinary single structure crucible is used. In this case, however, the manufacture of such crucible in which the various parts are not uniform in thickness involves a problem from the production cost point of view.

Thus, the inventors, etc., have considered that in order to construct a double structure crucible in which the quartz thickness at the bottom of its single crystal growing section is increased as mentioned above, the equivalent effect may be possibly obtained by arranging inside a quartz crucible a crucible-type partition member which is smaller than the bore of the quartz crucible.

Then, where a double structure crucible is constructed through the assembly of two quartz crucibles having different bores, the following problems are caused. In other words, as shown in Fig. 6, the shape of the ordinary quartz crucible is determined by a bore D, a crucible bottom radius of curvature R- a radius of curvature R_? of the portion connecting the bottom and side portions of the crucible. For instance, the following conditions hold: R =300mm and R_=80mm in the case of a quartz crucible of 12 inches in diameter (D=300mm) ;

R_. =400mm and R_?=90mm in the case of a quartz crucible of 16 inches in diameter (D=400mm) ; and R =500mm and R_?=120mm in the case of a quartz crucible of 20inches In diameter (D=500mm) .

Thus, generally the radius of curvature R_. of the crucible bottom is increased with increase in the bore D of the crucible. Where two quartz crucible of different bores are assembled to construct a double structure crucible, as shown in Fig. 7, a space corresponding to the difference between the radiuses of curvature is formed between the quartz crucible inner surface and the crucible-type partition member bottom outer surface. For instance, when a double structure crucible is constructed in which a quartz crucible having a bore of 14 inches and adapted for crucible- type partition member is arranged with a quartz crucible 1 of 20 inches in diameter, a space of about 30mm at the maximum is formed between the bottom of the crucible-type partition member 11 and the quartz crucible inner surface. Where the double structure crucible of such shape is used, the amount of heat input through the bottom still amoμnts to a greater proportion in the amount of heat applied to the single crystal growing section. This is due to the fact that the space is formed between the bottom outer surface of the crucible-type partition member 11 and the inner surface of the quartz crucible 1. In other words, the temperature distribtion of the molten silicon in the material melting section is higher in temperature in "the molten silicon bottom that the remainder so that the high-temperature molten silicon is present in the bottom of the crucible-type partition member and the proportion of the heat input through the bottom is increase. In accordance with the foregoing, the method of constructing the double structure crucible for stably pulling a silicon single crystal is such that the partition member 11 is formed into a crucible type and arranged in such a manner that the bottom outer surface of the crucible-type partition member is closely fitted to the bottom of the quartz crucible and the radius of curvature of the portion connecting the side and the bottom of the crucible-type partition member is from 10 to 50mm.

When the bottom of the crucible-type partition member is fitted closely to the bottom of the quartz crucible, the amount of heat input to the single crystal growing section through the side of the crucible- type partition member is increased with decrease in the radius of curvature R_? of the portion connecting the bottom and side of the crucible-type partition member. In other words, the heat convection of the molten silicon is brought into the desired condition for effecting the growing of a silicon single crystal. The reason for setting the upper limit of R„ to 50mm is that if the upper limit is higher, the heat put through the bottom of the crucible is increased and the condition of the heat convection of the molten silicon becomes as shown in Fig.9. For example, where it is selected so that the bore of the crucible-type partition member is 350mm (14 inches in diameter) and R₂= 50mm, the area of the double wall structure formed by the close fitting of the crucible-type partition member to the quartz crucible is about 50% of the total area of the bottom of the crucible-type partiton member. In other words, if the valve of R„ is greater, the closely fitted area becomes less than one half the total area of the bottom of the crucible-type partition member and the effect of reducing the amount of heat input through the bottom is also decreased. The reason for setting the lower limit of R_? to 10mm resides in that it is impossible to industrially produce a smaller one.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a diagram schematically showing a quartz double crucible in an embodiment of the present invention, Fig. 2 is a sectional view showing a silicon single crystal manufacturing apparatus employing a quartz double crucible such as shown in Fig. 1, Fig.3 is a graph showing the relation between the radius of curvature of the bottom of the crucible-type partition member and the yield of single crystal growth, Fig. 4 is a graph showing the relation between the radius of curvature of the portion connecting the side and bottom of the partition member and the yield of single crystal growth, Fig. 5 is a diagram schematically showing a double structure crucible in which the bottom of a single crystal growing section is increased in thickness Fig. 6 is a diagram, showing schematically the shape of the ordinary quartz crucible, Fig. 7 is a diagram showing schematically the quartz crucible and the crucible-type partition member, Fig. 8 is a diagram showing schematically a conventional silicon single crystal manufacturing apparatus employing the conventional double structure crucible, Fig. 9 is a diagram schematically showing the convection of the molten silicon in a case where a single structure crucible is used, and Fig. 10 is a diagram schematicaly showing the convection of the molten silicon in a case where the conventional double structure crucible is used.

In the drawings, numeral 1 designates a quartz crucible, 2 a graphite crucible, 4 molten silicon, 5 a silicon single crystal, 6 a heater, 8 a chamber, 11 a crucible-type partition member, 12 small holes, 14 starting material feed means, 17 starting material silicon, and 22 a cylindrical partition member.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 is a sectional view of a quartz double crucible in an embodiment of the present invention. In the Figure, numeral 1 designates a quartz crucible, and 11 a crucible-type partition member. The crucible-type, partition member 11 is arranged within the quartz crucible 1 to be concentric therewith. Numeral 12 designates small holes formed through the crucible-type partition member so that during the growing of a silicon single crystal the molten silicon is supplied from the outer side of the partition member to the inner side of the partition member. In the present embodiment, the quartz crucible 1 comprises a quartz crucible having an inner diameter, 484mm; an outer diameter, 500mm; a bottom inner surface radius of curvature, 500mm; and a crucible height, 200mm; and the crucible-type partition member 11 has an inner diameter, 336mm; an outer diameter, 350mm; a bottom outer surface radius of curvature, 500mm; a radius of curvature of the portion connecting the bottom and side of the crucible-type partition membr, 10mm; and a crucible-type partition member height, 250mm. The radius of curvature of the portion connecting the bottom side of the crucible-type partition member is selected 10mm on the ground that it has been impossible to manufacture a quartz crucible of smaller radius of curvature for use as a crucible-type partition member.

Fig. 2 is a sectional view showing a silicon single crystal manufacturing apparatus employing a quartz double crucible such as shown in Fig. 1. Numeral 1 designates a quartz crucible which is set in a graphite crucible 2, and the graphite crucible 2 is supported on a pedestal 3 so as to be vertical movably and rotatable. Numeral 4 designates molten silicon contained in the crucible 1 and a silicon single crystal 5 grown into a cylindrical shape is pulled from the molten silicon 4. Numeral 6 designates an electric resistance heater surrounding the graphite crucible 2, and 7 a hot-zone heat insulating member surrounding the electric resistance heater 6. Numeral 14 designates starting material feed means, and 17 starting material silicon.

With this apparatus, the use of such quartz crucible of the double structure as shown in Fig. 1 has the effect of reducting the heat input through the bottom within the single crystal growing section and conversely increasing the amount of heat input through the side; thus ensuring the stable growing of a silicon single crystal. The results of experiments conducted by the inventors, etc., to confirm this effect are shown in Figs. 3 and 4. Fig. 3 is a graph showing the relation between the radius of curvature of the bottom of the crucible-type partition member and the yield of single crystal growth.

Here, the term yield of single crystal growth represents a percentage of the production of a silicon single crystal of over 1mm in length when the growing of a single crystal, i.e. , a silicon single crystal of 6 inches in diameter is effected at a pull rate of about Imm/min. In the apparatus of Fig. 2, after 25 Kg of silicon starting material has been heated and melted in the crucible 1, the crucible 1 is rotated at 10 rpm and the silicon single crystal 5 is rotated at 20 rpm in opposition to the crucible, thereby growing the silicon single crystal of 6 inches in diameter at a ^"pull rate of about lmm/min while feeding the starting material silicon 17 into the material melting section from the starting material feed means 14. Also, the double crucible is constructed by using the crucible-tγpe partition member in which the radius of curvature of the portion connecting the bottom and side portion is uniform at about 10mm and the radius of curvature of the bottom portion is different. As will be seen from Fig. 3, the yield of single crystal growth is decreased with increase in the difference between the radius of curvature of the bottom outer surface of the crucible type partition member and the radius of curvature of the bottom inner surface of the quartz crucible.

As shown in the embodiment of the present invention in Fig. 1, by closely fitting the outer surface of the crucible-type partition member to the inner surface of the crucible bottom, it is possible to increase the yield of single crystal growth to the maximum.

Fig. 4 is a graph showing the results obtained by conducting the similar experiments as Fig. 3 by using a double structure crucible constructed by use of a crucible-type partition member which is closely fitted to a crucible with the radius of curvature of the crucible-type partition member bottom outer surface and the radius of curvature of the outer crucible inner surface having the same value of 500mm and the radiuses of the portions connecting the side and bottom portions of the partion member and the crucible being different from each other.

As will be seen from Fig. 4, if the radius of curvature of the portion connecting the bottom and side portions of the crucible-type partition member is selected greater than 50mm, the yield of single crystal growth is decreased.

In order to construct a double structure crucible of the type shown by the embodiment of Fig.l, it is not always necessary to use the method of preparing a crucible type partition member within the scope of the present invention. In other words, in order to accomplish the stable pulling of a silicon single crystal, it is sufficient that the partition member attains a crucible shape within the scope of the invention during the growing of the silicon single crystal. This can be accomplished by devising a way of introducing heat during the heating and melting of starting material silicon in such a manner that the bottom portion of the crucible-type partition member is softened and deformed, thereby providing the desired double structure crucible according to the invention.

Since the silicon single crystal manufacturing apparatus according to the present invention is constructed as described hereinabove as compared with the amount of heat input through the crucible bottom portion within the single crystal growing section, the amount of heat input through the side portion of the crucible-type partition member is increased so that the resulting heat environment of the molten silicon is equivalent to the heat environment within the ordinary single structure crucible and the amount of heat input through the bottom portion of the crucible within the single crystal growing section is reduced, thus increasing the amount of heat input through the side portion of the crucible-type partition member and thereby ensuring the stable pulling of a long silicon single crystal. L

INDUSTRIAL APPLICABILITY

The silicon single crystal manufacturing apparatus of the present invention is not only applicable to the j manufacture of single crystals of silicon material but also applicable to the manufacture of single crystals of other materials than silicon.

Claims

1. A silicon single crystal manufacturing apparatus including a rotation-type quartz crucible containing molten silicon, an electric resistance heater for heating said quartz crucible from the side thereof, a quartz partition member arranged so as to divide said molten silicon into a single crystal growing section and a material melting section within said quartz crucible and having small holes for permitting passage of said molten silicon therethrough, and starting material feed means for continuously feeding starting material silicon to said material melting section, characterized in that said partition member is in the form of a crucible type, that an outer surface of a bottom portion of said crucible-type partition member is closely fitted to a bottom portion of said quartz crucible, and that a portion connecting the side and bottom portions of said crucible-type partition member is composed of an R portion having a radius of curvature.

2 . A silicon single crystal manufacturing apparatus as set forth in claim 1, wherein said radius of curvature is in the range from 10mm to 50mm.