EP0483365A1

EP0483365A1 - Silicon single crystal manufacturing apparatus

Info

Publication number: EP0483365A1
Application number: EP91908635A
Authority: EP
Inventors: Yoshinobu Nkk Corporation Shima; Hiroshi Nkk Corporation Kamio; Makoto Nkk Corporation Suzuki
Original assignee: NKK Corp; Nippon Kokan Ltd
Current assignee: JFE Engineering Corp
Priority date: 1990-04-27
Filing date: 1991-04-24
Publication date: 1992-05-06
Also published as: JPH0412087A; JP2670548B2; KR920702735A; WO1991017288A1; CN1056136A

Abstract

L'invention se rapporte à un appareil de fabrication de monocristaux de silicium, qui sert à produire par tirage à une vitesse élevée un monocristal de silicium ayant un grand diamètre et une composition stable, en fonction de la technique CZ du type utilisant un creusé mis en rotation. En maintenant correctement les équilibres thermiques de la périphérie externe d'un monocristal de silicium, et de la surface libre du silicium en fusion sur la face interne d'un élément de cloison, on peut produire par tirage un monocristal de silicium de grand diamètre à une vitesse élevée. Les conditions devant être satisfaites sont les suivantes: O4 = 18 ~ 24 pouces; O3/O4 = 0.75 ~ 0,84; O2 - O1 = 30 ~ 50mm; alpha = 15 ~ 25°; et h = 10 ~ 30mm. O1 représente le diamètre du monocristal de silicium; O2 représente le diamètre de l'ouverture au niveau de l'extrémité inférieure de la partie latérale cylindrique d'un couvercle de conservation thermique; O3 représente le diamètre de l'élément de cloison; O4 représente le diamètre du creusé; et h représente la distance entre la surface du silicium en fusion et la partie de O2.The invention relates to an apparatus for manufacturing silicon single crystals, which is used to produce by drawing at high speed a silicon single crystal having a large diameter and a stable composition, according to the CZ technique of the type using a hollow in rotation. By correctly maintaining the thermal equilibria of the external periphery of a silicon single crystal, and of the free surface of the molten silicon on the internal face of a partition element, it is possible to produce by drawing a large diameter silicon single crystal with high speed. The conditions to be met are as follows: O4 = 18 ~ 24 inches; O3 / O4 = 0.75 ~ 0.84; O2 - O1 = 30 ~ 50mm; alpha = 15 ~ 25 °; and h = 10 ~ 30mm. O1 represents the diameter of the silicon single crystal; O2 represents the diameter of the opening at the lower end of the cylindrical side part of a thermal preservation cover; O3 represents the diameter of the partition element; O4 represents the diameter of the excavation; and h represents the distance between the surface of the molten silicon and the part of O2.

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 a plurality of small holes for permitting the passage of the molten silicon therethrough, a heat keeping cover for covering the inner side of the partition member and above the material melting section, and starting material feed means for continuously feeding starting material silicon to the material melting section. BACKGROUND ART

In the field of LSIs, the required diameter for silicon single crystals has been increasing 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 10 inches or more in diameter, e.g., silicon single crystals of 12 inches in diameter will be needed.

The silicon single crystal manufacturing methods according to the Czochralski method (CZ method) are divided into two types. Namely, one in which the crucible is rotated and another in which the crucible is not rotated. Today, the manufacturing methods of all the silicon single crystals used for LSIs are such that they are manufactured by the methods of the type in which the crucible and a silicon single crystal are rotated in the opposite directions and the crucible is heated by an electric resistance heater generally surrounding the side of the crucible. In spite of various attempts, silicon single crystals of 5 inches or more in diameter have not been manufactured up to date by the methods which do not rotated the crucible or by use of the heating methods other than the electric resistance heater and they will not be manufactured in the future. The reason is that where the crucible is not rotated, where the magnetic induction heating or I the electric resistance heating from the crucible bottom is used and so on, it is not possible to obtain a temperature distribution which is completely concentric with the growing silicon single crystal. The growth of 5 a silicon single crystal is extremely sensitive to the temperature.

In the CZ method which rotates the crucible (hereinafter referred to as the ordinary CZ method) , a strong convection of the molten silicon is caused due to 0 the rotation of the crucible and the side heating by the electric resistance heater and the molten silicon is stired excellently. These facts are. desirable for the growing of large-diameter silicon single crystals of 5 inches or more in diameter. In other words, it is 5 possible to obtain a molten silicon surface temperature distribution which is uniform and completely concentric with a silicon single crystal. Therefore, the present invention is based on the ordinary CZ method.

As mentioned hereinabove, there is a great o difference in the flow of molten silicon between the ordinary CZ method and the other CZ method. This difference results in great variations of the growing condition of silicon single crystals. As a result, the two methods differ greatly from each other with respect 5 to the functions and effects of the furnace components (e.g., the hot zone, the crucible and the partition member) . In other words, the two methods are entirely different with respect to the concept of growing a silicon single crystal.

In accordance with the ordinary CZ method, the molten silicon in the crucible is decreased as a silicon single crystal grows. 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 vary relative to the direction of the crystal growth. Since the quality required for silicon single crystals has become severer year after year with increase in the level of integration for LSIs, this problem must be overcome. As a means of overcoming this problem, there is known a method (e.g. ,Patent Publication No. 40-10184, P2, L12 - L16) in which the interior of a quartz crucible according to the ordinary CZ method is divided by a cylindrical quartz partition member having small holes for molten silicon and a cylindrical silicon single crystal is grown on the inner side of the partition member while feeding starting material silicon to the outer side of the partition member. However, as pointed out in Laid-Open Patent No. 62-241889 (P2, L12 - L16) , the serious problem of this method is that solidification of the molten silicon tends to occur on the inner side of the partition member with the partition member as a starting point. The cause for this is as follows. As will be seen from the fact that quartz is used for optical fibers, etc. , the quartz partition member efficiently transmits heat by radiation. In other words, the heat in the molten silicon is transmitted as light upwardly through the partition member and it is dissipated from the portion of the partition member which is exposed on the surface o the motlen silicon. As a result, the molten silicon temperature is greatly reduced in the vicinity of the partition member. Further, in accordance with the ordinary CZ method, due to the vigorous agitation of the molten silicon, the surface temperature of the molten silicon is not only uniform but also slightly higher than the solidifying point. Thus, due to the combination of these two facts, the molten silicon surface contacting with the partition member is in a condition having a very high tendency to cause solidification. In order to avoid this problem, Laid-Open Patent No. 62- 241889 proposes a method which uses no partition member. In this method, however, the material melting section is so narrow that the starting material melting capacity is extremely small and it is not put in practical use as yet.

Laid-Open Patent No. 1-153589 is one proposing a method in which a partition member is used and also the occurrence of solidification at the partition member is prevented. This patent proposes to completely cover the partition member by a heat keeping cover. The dissipation of heat from the partition member can be prevented by this method. Thus, the occurrence of solidification at the partition member can be prevented. However, to effect for example the growing of a large- diameter silicon single crystal of 5 inches or more in diameter at a silicon single crystal solidification rate of over 45g/min (e.g., a high pull rate of over 1mm/ min) over a long period of time stably, this invention is still not adequate.

As the results of various studies made, it has been found out that where the conventional heat keeping cover is used, there are the following factors which impede the growth of a silicon single crystal.

(1) Where the shape of the heat keeping cover is not proper, any attempt to increase the pull rate of a silicon single crystal causes some deformation of the silicon single crystal.

(2) Even if the pull rate of the silicon single crystal could be increased by improving the heat keeping cover, if the melting rate of the continuously fed starting material silicon in the material melting section were not sufficient, an unbalance between the rate of solidification of the silicon single crystal and the starting material silicon feed rate would be caused.

An object of the present invention is such that when growing a silicon single crystal while continuously feeding starting material silicon, the occurrence of solidification at a partition member is prevented and also the growing of a silicon single crystal of 5 inches or more in diameter is effected stably at a silicon single crystal solidifying rate of over 45g per minute (corresponding to the pulling of a crystal of 6 inches in diameter at a rate of over 1mm per minute) over a long period of time.

DISCLOSURE OF INVENTION

A silicon single crystal manufacturing apparatus according to the present invention is one comprising 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, a heat keeping cover for covering the inner side of the partition member and above the material melting section, and starting material feed means for continuously feeding starting material silicon to the material melting section, and the apparatus is characterized in that the quartz crucible has a diameter ranging from 18 to 24 inches, that the ratio of the diameter of the partition member to the diameter of the quartz crucible is from 75 to 84%, that the diameter of the opening at the lower end of the cylindrical side portion of the heat keeping cover which keeps the heat of the partition member is greater than the diameter of a silicon single crystal by 30 to 50mm, that the angle formed by a straight line connecting the edge of the opening at the upper end of the cylindrical side portion of the heat keeping cover covering the partition member and the edge of the opening at the lower end of the cylindrical side portion and a vertical line is between 15 and 25 degrees, and that the distance b from the edge of the opening at the lower end of the cylindrical side portion of the heat keeping cover covering the partition member to the molten silicon surface is between 10 and 30 mm.

Where the growing of a silicon single crystal of 5 inches or more in diameter is effected at a rate of silicon single crystal solidification higher than 45 grams per minute (corresponding to the pulling of a silicon single crystal of 6 inches in diameter at a rate higher than 1mm per minute) as mentioned previously, if the shape of the heat keeping cover is not proper, the silicon single crystal is deformed. This is due to the following two causes.

(I) Referring to Fig. 8, where molten silicon 7 has a large surface area between a silicon single crystal 5 and the cylindrical side portion lower end 17 of a heat keeping cover 15 as in (a) , the dissipation of heat from this portion is so large that as shown in (c), the radial temperature gradient of the molten silicon in the vicinity of the surface of the silicon single crystal 5 is decreased and the silicon single crystal 5 is deformed. Thus, the power of the electric resistance heater cannot be decreased to decrease the molten silicon temperature and it is impossible to effect a high-rate pulling requiring a large amount of feed material .

(II) As shown in Fig. 8(b), if the opening at the cylindrical side portion upper end 18 of the heat keeping cover 15 is small in radius, the dissipation of heat from the silicon single crystal is decreased. While the temperature of the molten silicon must be decreased in order to increase the growth rate of the silicon single crystal, if the temperature is decreased, as shown in (c) , the radial temperature gradient of the molten silicon is decreased and the silicon single crystal is deformed. Although not shown, if the distance h from the cylindrical side portion lower end 17 of the heat keeping cover 15 to the molten silicon surface is increased, the dissipation of heat from the silicon single crystal is also decreased. Therefore, in order to pull the silicon single crystal at a high rate while preventing deformation of the silicon single crystal, it is necessary that the heat radiation from the molten silicon surface is reduced as shown in Fig. 9(a) and simultaneously conditions for promoting the dissipation of heat from the silicon single crystal are set as shown in (b) , thereby increasing the radial temperature gradient of the molten silicon in the vicinity of the silicon single crystal surface as shown in Fig. 9(c) . Therefore, it is only necessary to grasp the radial temperature gradient of the molten silicon when the silicon single crystal is deformed. However, it is extremely difficult to measure the radial temperature gradient of the molten silicon. The reason is that it is impossible to except an accuracy of less than 1 C in the high temperature region of over 1420 C. Thus, experiments were conducted on the characteristics of heat keeping cover shapes under the below-mentioned single crystal growing conditions .

The parameters used in the discussion to follow will be defined with reference to Fig. 10. The angle a is an angle formed by the straight line connecting the lower end 17 of the cylindrical side portion covering the partition member 8 and the cylindrical side portion upper end 18 and a vertical line, φ designates the diameter of a silicon single crystal, φ_? designates the diameter of the opening at the cylindrical side portion lower end of the heat keeping cover, φ_ designates the diameter of the partition member, φ. designates the diameter of the quartz crucible, and h designates the distance from the lower end of the cylindrical side portion of the heat keeping cover to the molten silicon surface.

Referring now to Fig. 11 showing the results of the experiments conducted by the inventors, etc. , there is illustrated the relation among the diameter φ_? of the opening, the angle a of the cylindrical side portion of the heat keeping cover which determines the cooling rate of the silicon single crystal and the maximum pull rate which permits the pulling without any deformation of the silicon single crystal in the case of the silicon single crystal of 6 inches in diameter. Note that the ratio of the partition member diameter to the quartz crucible diameter is 0.8. When the angle a of the cylindrical side portion of the heat keeping cover exceeds 15 degrees, if the difference between the diameter φ„ of the opening and the diameter φ of the silicon single crystal is less than 50mm, the maximum pull rate of the silicon single crystal is increased to as high as over 1mm per minute (the solidification rate of the silicon single crystal is over 45g/min) . While the Figure does now show cases where the difference between the diameter φ_ of the opening and the diameter φ- of the silicon single crystal is less than 30mm, the reason for this is that if the heat keeping cover is brought closer to the silicon single crystal, there is the danger of the silicon single crystal 5 and the heat keeping cover 15 contacting with each other. This maximum pull rate of the silicon single crystal is increased further with increase in the angle c of the cylindrical side portion of the heat keeping cover. If the angle a exceeds 30 degrees, however, the silicon single crystal is cooled excessively and the rate of occurrence of dislocation due to the thermal stress is increased. Therefore, the angle o! should preferably be less than 25 degrees. On the other hand, if the distance h from the cylindrical side portion lower end 17 to the surface of the molten silicon 17 is lower than 30mm, the heat input to the silicon single crystal from the surface of the molten silicon 7 is increased and the maximum pull rate is decreased. However, if the distance between the cylindrical side portion lower end 17 and the surface of the molten silicon 7 becomes less than 10mm, there is the danger of causing the heat keeing cover 15 to change its properties or to contact with the molten silicon surface. This is not realistic. Then, as mentioned previously, even if the pull rate of the silicon single crystal is increased greatly, where the melting rate of the continuously fed starting material silicon is not sufficient, an unbalance is caused between the solidification rate of the silicon single crystal and the feed rate of the starting material silicon. Also, such a condition is not preferable for the pulling of the silicon single crystal at high rates and for the temperature distribution of the molten silicon in the single crystal growing section. The fact that the melting capacity of the starting material silicon is low means that the molten silicon temperature in the material melting section is low. This is not desirable for the purpose of increasing the temperature gradient of the molten silicon in the vicinity of the silicon single crystal.

Also, in Laid-Open Patent No. 1-153589, the heat keeping cover is arranged above the material melting section so as to ensure that starting material silicon is melted fully. In fact, however, the provision of the heat keeping cover alone is not sufficient in cases where a large amount of the starting material silicon is supplied in correspondence to a high pull rate of the silicon single crystal. The inventors, etc. , have conducted various experiments and found out the following results. While a considerable part of the starting material silicon supplied is deposited on the outer surface of the partition member due to the flow of the molten silicon, the vicinity of the partition member is the lowest-temperature portion in the material melting section and therefore an unmelted residue of the starting material silicon is caused. To prevent this, it is possible to provide a special heater to facilitate the melting. However, this is not an effective method since the construction is complicated and the occurrence of contamination is caused. The inventors have discovered a method of increasing the temperature in the vicinity of the partition member without providing any special heater. Firstly, the quartz crucible must be greater than 18 inches. The reason is that the crucible wall is more separated from the silicon single crystal (solidification point temperature) with increase in the diameter of the crucible and the outer peripheral temperature is increased, thus promoting the melting of the starting material silicon. However, quartz crucibles of over 24 inches are not easily available and not practical.

Referring now to Fig. 12, there is illustrated the relation between the ratio of the diameter φ„ of the partition member to the diameter φ. of the quartz crucible and the maximum melting rate of the starting material silicon in cases where the heat keeping cover is provided. At this time, the heat keeping cover is shaped so that the angle at its cylindrical side portion lower end is 20 and its diameter at the cylindrical side portion lower end is greater than the diameter of the silicon single crystal by 45mm. Also, the amount of molten silicon is between 20 and 40 Kg. Where the diameter of the partition member is in the range from 75 to 84% of the diameter of the quartz crucible, the maximum melting rate is attained. Where the ratio is less than 15% , the partition member is apart from the high-temperature side electric resistance heater so that the temperature of the molten silicon becomes somewhat lower and the melting rate of the material is rapidly decreased. On the other hand, if the ratio is greater than 84% , the melting capacity of the material melting section is also decreased. The reason is that there is an increase in the ratio of the floating area on the molten silicon in the material melting section of the starting material silicon which is much greater in rate of heat radiation than the molten silicon. In other words, if the ratio of the floating area of the starting material silicon is increased, the heat radiation from the surface of the molten silicon in the material melting section is increased.

As a result, the optimum ratio fo the diameter of the partition member to the diameter of the quartz crucible is in the range from 75% to 84%.

As described hereinabove, in accordance with the silicon single crystal manufacturing apparatus which employs the heat keeping cover and continuously feeds the starting material silicon, it is possible to stably manufacture a silicon single crystal of 6 inches in diameter at a solidification rate of over 45g per minute

(a pull rate of higher than 1mm per minute) only when the conditions such as the shapes of the crucible, the partition member and the heat keeping cover are within the extremely limited ranges of conditions.

The second feature of the present invention resides in that the material of the heat keeping cover is a metal sheet. Graphite, ceramics and metals can be conceived as heat keeping cover materials. With the heat keeping coves made from graphite and ceramics, however, it is impossible to ensure the desired melting capacity for starting material silicon and the desired molten silicon temperature distribution for pulling a silicon single crystal at a high pull rate. The graphite and ceramic heat keepig covers are high in radiation rate and hence low in heat keeping effect. The metal sheet is low in radiation rate and hence is capable of allowing the heat keeping cover to exhibit its function fully. The third feature resides in the presence ^' of cutouts in the heat keeping cover. The cutouts have the function of adjusting the gas flow within the chamber so that fine particles of SiO produced within the chamber are prevented from impeding a silicon single crystal.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a longitudinal sectional view of a silicon single crystal manufacturing apparatus according to the present invention, Figs. 2a and 2b are longitudinal sectional views of heat keeping covers in another embodiments of the present invention with Fig.

2a showing the heat keeping cover of the single step type and Fig. 2b showing the heat keeping cover of the multiple step type, Fig. 3 is a schematic diagram of the gas flows according to the present invention; Fig. 4 is a schematic diagram of the gas flow according to a conventional technique, Fig. 5 is a first perspective view showing the cutouts in the heat keeping cover of the embodiment of the present invention, Fig. 6 is a second perspective view showing the cutouts in a heat keeping cover of another embodiment of the present invention, Fig. 7 is a third perspective view showing the cutouts in a heat keeping cover of still another embodiment of the present invention, Fig. 8a is a schematic diagram of a heat keeping cover shape having a low temperature gradient representing a case in which the heat radiation from the molten silicon is high, Fig. 8b is a similar diagram representing a case in which the heat radiation from the molten silicon is low, Fig. 8c is a graph showing the relation between the distance from the quartz crucible inner wall and the molten silicon temperature in a case where the temperature gradient is low, Fig. 9a is a schematic diagram of a heat keeping cover shape having a high temperature gradient representing a case in which the heat radiation from the molten silicon is low, Fig. 9b is a similar diagram representing a case in which the heat radiation from the silicon single crystal is high, Fig. 9c is a graph showing the relation between the distance from the quartz crucible inner wall and the molten silicon temperature in a case where the temperature gradient is high.

Fig. 10 is a schematic diagram showing the definitions of the parameters used with the present invention, Fig. 11 is a graph showing the relation between the maximum pull rate of a silicon single crystal classified b the inclination of the cylindrical side portion of the heat keeping cover and the difference between the diameter at the heat keeping cover side portion lower end and the diameter of the silicon single crystal, Fig. 12 is a graph showing the relaton between the maximum melting rate of the starting material silicon classified by the amount of molten silicon and the ratio of the diameter of the partition member to the diameter of the quartz crucible and Fig. 13 is a diagram showing a region in whcih a silicon single crystal is grown stably in relation with the difference X between the diameter of the heat keeping cover side portion lower end and the diameter of the silicon single crystal, the inclination a of the heat keepig cover side portion and the ratio Y of the partition member diameter to the quartz crucible diameter. In the drawings:

Numeral 1 designates a quartz crucible, 2 a graphite crucible, 3 an electric resistance heater, 4 a pedestal, 5 a silicon single crystal, 6 a heat insulating member, 7 molten silicon, 8 a partition member, 9 starting material silicon, 10 small holes, 11 a material melting section, 12 a single crystal growing section, 14 starting material feed means, 15 a heat keeping cover, 16 a chamber upper cover, 17 a cylindrical side portion lower end, 18 a cylindrical side portion upper end, 20 a pull chamber, 22 cutouts, A the flow of an atmosphere gas passing through the cutouts in the heat keeping cover, B the flow of an atmosphere gas passing through the cutouts in the heat keeping cover, S. the region in which the heat radiation from the single crystal is so high that the crystal changes to a dislocation-containing state, S_? the region in which the heat keeping cover has possiblity of contacting the single crystal, S, and S. the regions in which any attempt to obtain a single crystal solidification rate of over 45 g/min results in deformation of the crystal, and S_j. the region in which the maximum melting rate of the starting material is no longer obtainable. BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described with reference to the drawings. Fig. 1 is a sectional view of a silicon single crystal manufacturing apparatus showing an embodiment of the present invention.

Numeral 1 designates a quartz crucible of 20 inches in diameter and it is set in a graphite crucible 2. The graphite crucible 2 is supported on a pedestal 4. The pedestal 4 is connected to an electric motor externally of the furnace and it serves the function of imparting rotary motion (10 rpm) to the graphite crucible 2. Numeral 7 designates the molten silicon contained in the crucible 1. A cylindrical silicon single crystal 5 is pulled from the molten silicon 7 at a rate of 1. Imm/min while being rotated (20 rpm) oppositely to the crucible 1. Numeral 3 designates an electric resistance heater surrounding the graphite crucible.

The pressure within the furnace (within a chamber 16) is between 0.01 and 0.03 atmosphere.

Numeral 8 designates partition member which is made from a high-purity cellular silica glass and arranged within the crucible 1 to be concentric therewith. Its diameter is 16 inches amounting to 80% of the diameter of the 20-inch quartz crucible. The partition member 8 is formed with small holes therethrough so that the molten silicon 7 in a material melting section 11 flows into a single crystal growing section 12 through the small holes 10. The lower edge portion of the partition member is preliminarily fused to the crucible

I of fused to it by the heat produced when melting starting material silicon 9.

Numeral 14 designates starting material feed means so that the granular starting material silicon

9 is supplied from above the material melting section

II to it through the feed means. The feed rate is such that the starting material silicon is fed in an amount equal to the silicon single crystal growth rate, i.e., about 48 g/min. The starting material feed means 14 is connected to a starting material feed chamber (not shown) arranged externally of the chamber upper cover 16, thereby feeding the starting material silicon continuously. Numeral 15 designates a heat keeping cover which is made from a tantalum sheet of 0.2mm in thickness. Its purpose is to reduce the dissipation of heat from the partition member 8 and the material melting section 11. Also, by modifying its shape, it is possible to adjust the heat radiation from the surface of the molten silicon 7 and silicon single crystal. In the present embodiment, the opening at the lower end 17 of the cylindrical side portion of the heat keeping cover 15 has a diameter of 200mm, and the cylindrical side portion is constructed so that it is increased in diameter toward its upper end and the angle formed by the straight line connecting the cylindrical side portion lower end 17 and the cylindrical side portion upper end 18 and a vertical line is 20 degrees.

Also, even if the heat keeping cover side portion has a shape as shown in the sectional view of Fig.^' 2a or Fig. 2b, it is sufficient if the angle a formed by the straight line connecting the side portion upper end 18 covering the partition member and the side portion lower end and a vertical line is in the range from 15 to 25 degrees. In this case, the thickness is 0.2mm.

In Fig. 1, numeral 22 designates cutouts formed in the heat keeping cover to provide flow passages for an atmosphere gas.

In the case of the invention stated in Laid-Open Patent No. 1-153589 in which the heat keeping for the partition member 8 and the material melting section 11 is provided by the use of the heat keeping cover 15, there is the danger of the single crystal growth being impeded by the occurrence of dislocations in the crystal. This is due to the fact that there are cases where the flow of the furnace atmosphere gas (argon)) is not proper. In Laid-Open Patent No. 1-153589 the heat keeping cover 15 is provided. A shown at B in Fig. 4, practically all the atmosphere gas flow is passed through the space between the cylindrical side portion lower end 17 of the heat keeping cover 15 and the surface of the molten silicon 7 and discharged through a gas discharge port 13. Since the atmosphere gas is introduced at the room temperature into a pull chamber 20, when passing by in the vicinity of the molten silicon surface, the gas is mixed with an SiO vapor evaporated from the molten silicon surface and the evaporated SiO vapor is cooled. As a result, fine particles of SiO are produced in the vicinity of the molten silicon surface. The fine particles are aggregated so that they fall onto the molten silicon surface and are deposited on the sold-liquid interface of the silicon single crystal thereby causing disintergration of the silicon single crystal.

On the other hand, Fig. 3 shows a schematic diagram of the gas flowing in the case of the present embodiment where there was provided the cutouts 22 of a sufficient size. A large part of the atmosphere gas flows, as shown by a gas stream A, through the cutouts 22 and enters the spaced near the upper end of the electric resistance heater 3. Contrary to the case of Laid-Open Patent No. 1-153589, practically there is no flow just above the molten silicon surface. Fig. J5 shows a first embodiment of the heat keeping cover.

While in this embodiment, the cutout 22 having an area

2 of 90 cm is provided at each of four locations with the

2 total area amounting to 360 cm , the area of cover 50

2 cm produces a sufficient exhaust effect. On the contrary, the area of over 1000 mm causes the cutouts to be excessively open and the essential heat keeping effect of the heat keeping cover is lost. Also, it is desirable that the height-direction positions of the cutouts 22 are as high as possible, i.e. , they are at least higher than the upper end portion of the heater. The reason is that in the upper part the gas stream at A tends to flow easily, that is, this is effetive in preventing the stream at B in Fig. 4. While the disintegration of silicon single crystals occurred frequently without the cutouts 22, after the provision of the cutouts it is possible to stably grow silicon single crystals of over 1m in length. There is no particular limitation to the number of the cutouts 22. However, in order to improve the symmetry with respect a silicon single crystal, it is desirable t provide the cutouts at two locations than at a single location. This is due to the fact that in order to stabilize the growing of a silicon single crystal, it is desirable to improve the symmetry of the heat environment with respect to the silicon single crystal. Fig. 6 shows a second embodiment of the cutouts 22. The cutout 22 is formed at each of eight locations in the flange portion of the heat keeping cover. In this case, the eight cutouts 22 are formed between the heat insulating member 6 which supports the heat keeping cover. On the other hand, Fig. 7 shows a third embodiment in which eight cutouts 22 are additionally formed in the upper part of the side portion in the embodiment of Fig. 6.

Also, molybdenum may be used as the material for the heat keeping cover 15 in addition to tantalum used in the present embodiment .

As described hereinabove, by limiting the angle of the heat keeping cover cylindrical side portion and the ratios of the diameter of the cylindrical side in portion lower end and the partition member diameter to the quartz crucible diameter to the region shown in Fig. 3 thereby ensuring the optimization, it is possible to simultaneously satisfy the melting capacity of starting material and prevention of the occurrence of deformation and dislocations in a single crystal for the first time. A silicon single crystal can be stably grown over a long period of time at a silicon single crystal solidification rate for 45g per minute (a pull rate of over 1mm per minute in the case of a 6-in single crystal) .

Here, it has been confirmed that even the case of an 8-in single crystal and 10-in single crystal, it is possible to grow over a long period of time the silicon single crystal having a single crystal solidification rate of up to to 75g per minute by effecting the growing through the use of a quartz crucible of 20 to 24 inches for the former and a quartz crucible of 22 to 24 inches for the latter and a heat keeping cover and a partition member of the shapes which satisfy the region of Fig. 13.

By working the present invention, it is now possible to pull a large-diameter silicon single crystal of over 5 inches in diameter at a high rate of over 1mm per minute while feeding starting material silicon at a rate corresponding to the growth rate of the silicon single crystal .

INDUSTRIAL APPLICABILITY

As described hereinabove, the present invention is not only applicable to a silicon single crystal manufacturing apparatus capable of pulling a large- diameter silicon single crystal of over 5 inches in diameter at a high rate of over 1mm per minute but also applicable to a manufacturing apparatus for pulling single crystals of any other starting materials than silicon.

Claims

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 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, heat keeping cover for covering the inner side of said partition member and above said material melting section, and starting material feed means for continuously feeding starting material silicon to said material melting section, characterized in that said quartz crucible has a diameter ranging from 18 to 24 inches, that the ratio of a diameter of said partition member to the diameter of said quartz crucible is between 75 and 84%, that an opening at a cylindrical side portion lower end of said heat keeping cover for keeping heat of said partition member has a diameter greater than a diameter of a silicon single crystal by 30 to 50mm, that an angle formed by a straight line connecting an edge of an opening at an upper end of the cylindrical side portion of said heat keeping cover for covering said partition member and an edge of the opening at said cylindrical side portion lower end and a vertical line is in the range from 15 to 25 degrees, and that the distance from the opening edge of the cylindrical side portion of said heat keeping cover for covering said partition member to a surface of said molten silicon is in the range from 10 to 30mm.

2. A silicon single crystal manufacturing apparatus as set forth in claim 1, characterized in that the material of said heat keeping cover is a metal sheet .

3. A silicon single crystal manufacturing apparatus as set forth in claim 2 , characterized in that said heat keeping cover is formed with a plurality of cutouts

2 having a total area ranging from 50 to 1000 cm , and that positions of said cutouts are at least higher than an upper end of said electric resistance heater.