Classifications

• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
  • C30B15/14—Heating of the melt or the crystallised materials
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
  • C30B15/10—Crucibles or containers for supporting the melt
  • C30B15/12—Double crucible methods
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/06—Silicon

Definitions

• 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 BACKGROUND ART
• silicon single crystals 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 are divided into two types. Namely, one in which the crucible is rotated and another in which the crucible is not rotated.
• 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.
• 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 present invention is based on the ordinary CZ method.
• 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) .
• the two methods are entirely different with respect to the concept of growing a silicon single crystal.
• the molten silicon in the crucible is decreased as a silicon single crystal grows.
• the dopant concentration is increased and the oxygen concentration is decreased in the silicon single crystal.
• 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.
• a method e.g. ,Patent Publication No.
• 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.
• the molten silicon temperature is greatly reduced in the vicinity of the partition member.
• the surface temperature of the molten silicon is not only uniform but also slightly higher than the solidifying point.
• the molten silicon surface contacting with the partition member is in a condition having a very high tendency to cause solidification.
• 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.
• this invention is still not adequate.
• 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.
• a silicon single crystal manufacturing apparatus 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
• 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
• ⁇ designates the diameter of a silicon single crystal
• ⁇ ? designates the diameter of the opening at the cylindrical side portion lower end of the heat keeping cover
• ⁇ _ designates the diameter of the partition member
• ⁇ . designates the diameter of the quartz crucible
• h designates the distance from the lower end of the cylindrical side portion of the heat keeping cover to the molten silicon surface.
• Fig. 11 showing the results of the experiments conducted by the inventors, etc. , there is illustrated the relation among the diameter ⁇ ? 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.
• the ratio of the partition member diameter to the quartz crucible diameter is 0.8.
• the angle a of the cylindrical side portion of the heat keeping cover exceeds 15 degrees, if the difference between the diameter ⁇ critique of the opening and the diameter ⁇ 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 ⁇ _ of the opening and the diameter ⁇ - 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.
• the heat keeping cover is arranged above the material melting section so as to ensure that starting material silicon is melted fully.
• 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.
• 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.
• quartz crucibles of over 24 inches are not easily available and not practical.
• Fig. 12 there is illustrated the relation between the ratio of the diameter ⁇ critique of the partition member to the diameter ⁇ . of the quartz crucible and the maximum melting rate of the starting material silicon in cases where the heat keeping cover is provided.
• 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.
• the amount of molten silicon is between 20 and 40 Kg.
• 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.
• 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.
• 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.
• 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%.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• Numeral 14 designates starting material feed means so that the granular starting material silicon
• 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.
• 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.
• 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.
• numeral 22 designates cutouts formed in the heat keeping cover to provide flow passages for an atmosphere gas.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• molybdenum may be used as the material for the heat keeping cover 15 in addition to tantalum used in the present embodiment .
• 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) .
• 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.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Liquid Deposition Of Substances Of Which Semiconductor Devices Are Composed (AREA)

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• 1990
  • 1990-04-27 JP JP2114522A patent/JP2670548B2/ja not_active Expired - Fee Related
• 1991
  • 1991-04-24 WO PCT/JP1991/000546 patent/WO1991017288A1/en not_active Ceased
  • 1991-04-24 KR KR1019910701968A patent/KR920702735A/ko not_active Withdrawn
  • 1991-04-24 EP EP91908635A patent/EP0483365A1/en not_active Withdrawn
  • 1991-04-27 CN CN91102923A patent/CN1056136A/zh active Pending

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