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
  • 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
• • 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

Definitions

• the present invention relates to an apparatus for manufacturing large-diameter silicon single crystals according to the Czochralski method. More specifically, 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 adapted for dividing the molten silicon into a single crystal growing section and a material melting section and having a plurality of communication holes for permitting unidirectional passage of the molten silicon therethrough, a heat keeping cover for covering the partition member and the material melting section, starting material feed means for continuously feeding starting material silicon to the material melting section, and dopant feed means for feeding a dopant to the material melting section.
• silicon single crystals of 6 inches c in diameter are used for the latest devices. It is now said that in future silicon single crystals of 10 inches • or more in diameter, e.g., silicon single crystals of 12 inches in diameter will be needed.
• CZ Q method Czochralski method
• the rotation of the crucible and the electric resistance side heating produce a strong convection of molten silicon so that the molten silicon is stired vigorouly.
• This results in a molten silicon surface temperature distribution which is preferable for the growth of a large-diameter silicon single crystal or which is uniform and completely concentric with a silicon single crystal.
• the two methods also differ greatly from each other with respect to the functions of the internal components of the furnace.
• the two methods are entirely different from each other with respect to the concept for the growth of silicon single crystals.
• the ordinary CZ method the amount of the melt within the crucible is decreased with the growth of a silicon single crystal.
• the dopant concentration in the silicon single crystal is increased and the oxygen concentration is decreased.
• 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 becoming increasingly severe year after year along with the tendency toward increasing the level of integration of LSIs, this problem must be overcome.
• the heat in the molten silicon is transmitted as light through the partition member upwardly and it is dissipated from the portion of the partition member which is exposed on the molten silicon surface.
• the molten silicon temperature is decreased greatly in the vicinity of the partition member.
• the surface temperature of the molten silicon is not only uniform but also just above the solidifying point. Owing to the combination of these two facts, the molten silicon surface contacting with the partition member is in a condition having an extremely high tendency toward causing the occurrence of solidification.
• Laid-Open Patent No. 1-153589 is one proposing a method employing such partition member and adapted to prevent the occurrence of solification at the partition member.
• This laid-open patent propose to completely cover the partition member with a heat keeping member. By this method, the dissipation of heat from the partition member can be prevented and also the occurrence of solidification can be prevented.
• This invention further proposes to reduce the size of the molten silicon communication holes from the material melting section to the crystal growing section in such a manner that the molten silicon flows substantially in one direction from the former to the latter. Due to the synergetic effect of' .-this fact and the provision of the heat keeping member, the molten silicon temperature . in the material melting section can be maintained at a temperature sufficient for stably effecting the melting of starting material.
• the present invention proposes to overcome the foregoing problems in that in the CG-CZ furnace including the heat keeping member as in the case of Laid-Open Patent No. 1-153589, the cross-sectional area of the communication holes for molten silicon from the material melting section to the crystal growing section is made proper in " consideration of the balance with the feed rate of starting material.
• the operation of the present invention will now be explained by taking the case where the dopant is phosphorus with reference to Figs. 4, 5 and 6.
• the distribution coefficient of phosphorus is about 0.33.
• the liquid temperature- in B must substantially be equal to the solidifying point.
• the liquid temperature in A is also substantially equal to the solidifying point.
• the CC-CZ method cannot be materialized.
• the concentration distribution of the dopant is such that it is 1 in the silicon single crystal, 3 in B, 1 in A and 1 in the starting material system .
• the transfer of heat from A to B is so small that the provision of the heat keeping cover has the effect of easily increasing the liquid temperature in A to a temperature sufficient for melting the starting material.
• Fig. 5 shows schematically how the dopant concentration in various part ' s are varied.
• the subsidiary material is fed in an amount required for attaining the concentration of 6 in B and the concentration of 2 in A.
• the concentration in A- is increased rapidly.
• the transfer to B of the molten silicon of A which contains high-concentration dopant is limited to the feed rate of the starting material (the rate of grow of the crystal) and therefore the transfer of the dopant to B is very slow.
• the starting material (the concentration is 2) must be fed to A in an amount which is ten times the amount of molten silicon in A.
• the concentration in B becomes 6 and hence the concentration in the crystal attains the desired value of 2
• the crystal must be grown about ten times the amount of molten silicon in A.
• the present invention is based on the discovery that by properly adjusting the cross-sectional area of the communication holes to balance with the feed rate of starting material, it is possible to realize a condition which substantially constitutes a mixed system with respect to the dopant and which substantially constitutes a unmixed system with respect to -heat. As regards the heat, this can be realized since the flow of heat without passing through the communication holes 10 is extremely large between the regions -A- and B. The concept for realizing the above-mentioned situation will now be described.
• the molten silicon flows completely unidirectionally from A to B (the unmixed system).
• the heat practically all the heat is introduced through the crucible bottom and the partition member and it is dissipated from the molten silicon surface. Only a small portion of the heat is introduced by being entrained on the molten silicon flowing from A into B through the communication hole. If the former is 100, then the later is less than 0.5.
• the dopant the whole amount is introduced through the communication holes as a matter of course.
• Fig. 4 shows the manner in which the dopant concentration is varied in the various parts when the operation of increasing the dopant concentration in such a system by two times is performed. Due to the presence of the mixing, in the steady state the dopant concentration in A substantially equal to that in B. In other words, it is 3 before the time T and it is 6 after the time T».
• the increase in the amount of the subsidiary starting material at the time I. represents the required amount for increasing the concentration in the whole molten silicon from 3 to 6. Then, consider the manner in which the heat flows. Stating the conclusion first, the heat flow is substantially the same with that in the unmixed system. Note B first.
• the flows of the heat in A and B are substantially the same as in the case of the unmixed system.
• the stable melting of the starting material is made possible and thus the CC-CD method is materialized.
• the degree of mixing is increased gradually.
• the unmixed system is changed to the mixed system with respect to the dopant and to a condition of substantially the unmixed system with respect to the heat, and (b) the unmixed system is changed to the mixed system with respect to the two.
• the lower limit to the cross-sectional area of the communication holes is the change point of (a) .
• the upper limit is the change point of (b) .
• the temperature difference between A and B becomes less than 10 C.
• the flow -from A to B is increased with increase in the feed rate of starting material.
• the mixing between the molten silicon in A and the molten silicon in B tends to become difficult.
• Fig. 3 shows the proper range of the communication holes (the range of the present invention) determined in consideration of the foregoing facts.
• the lower limit of 30 g/min- for the starting material feed rate is determined from the standpoint of the prosecutive of a single crystal. While this feed rate corresponds to the pulling of a crystal of 5 inches in diameter at about lmm/min, to make the rate of crystallization less than ' this free rate is not desirable from the productivity point of view.
• the upper limit of 130 g/min corresponds to the pulling of a crystal of 10 inches in diameter at a rate of 1.1 - m/min. The reason for determining this upper limit reside in that it is impossible to grow a crystal " at any rate of crystalization higher than that.
• the range of Fig. 3 can exist only in cases where there exists a metal heat keeping member for preventing -the occurrence of solidification at the partition member.
• Fig.l is a sectional view of an apparatus-, used in an embodiment .
• Fig. 2 is a graph showing the relation between the crystal lengthwise direction and the electric resistance value in the embodiment
• Fig. 3 is a graph showing the relation between the starting material feed rate and the total sum of the cross-sectional areas of the communication holes according to the present invention
• Fig. 4 is a schematic diagram for explaining the ' principle of the present invention.
• Fig. 5 is a graph showing the relation between the dopant concentration ratio and the time in a conventional unmixed system
• Fig. 6 is a graph showing the relation between the dopant concentration ratio and- the time in a mixed system according to the present invention.
• 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 furnace heat insulating member, 7 molten silicon, 8 a partition member, 9 a heat keeping cover, 10 communication holes, 12 the lower end of the heat keeping cover, 14 starting material feed means, 15 openings in the heat keeping cover, 16 a chamber upper cover, 20 a pull chamber, 21 a starting " material, 22 a subsidiary material, A a material melting section, and B a crystal growing section.
• Embodiment 1 confirmed the effects of the present invention in cases where the amount of addition of the dopant (electric resistance value) was changed in the course of the pulling. Tests were made in such a manner that in the course of the pulling the resistance value was changed from 20 ⁇ cm to 10 ⁇ cm and further a change from 10 ⁇ cm to 5 ⁇ cm was effected.
• the kind of the dopant was phosphorus and the crystal diameter was 6 inches.
• the cross-sectional areas of the communication holes used for effecting the crystal growth were the following four levels.
• 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 coupled to an electric motor on the outer side of the furnace and it serves to impart a rotational motion (10 rpm) to the graphite crucible 2.
• Numeral 7 designates molten silicon contained in the crucible 1.
• a silicon single crystal 5 of a cylindrical shape is pulled from the molten silicon 7 at a pull rate of 1.4 mm/min while being rotated (20 rpm) .
• Numeral 3 designates an electric resistance heater surrounding the graphite crucible.
• the pressure in the furnace (within a chamber 16) is 0.01 to 0.03 atmosphere.
• Numeral 8 designates a partition member made from a high-purity silica glass and arranged within the crucible 1 to be concentric therewith. Its diameter is 40cm.
• the partition member 8 is formed with communication holes 10 that the molten starting material in a material melting ' section flows into a single crystal growing section through the communication holes. In this embodiment, concerning the communication holes, the crystal growth -is effected by using the previously mentioned four- kinds of conditions.
• the lower edge portion of the partition member is preliminarily fused to the crucible 1 or fused to it by the heat produced when melting the silicon starting material.
• the amount of molten silicon is 20 Kg in total, that is, 5 Kg in the material melting section and 15 Kg in the crystal growing section.
• the amount of addition of the dopant in each of the two regions is such that at the start the resistance value of the crystal becomes 20 ⁇ cm (4.5 ppba) . Even in the condition of (a) , due to the diffusion of the dopant through the communication hole dopant contents of the two regions are inevitably made equal to each other.
• Numeral 14 designates starting material feed means having an opening above the material melting section and granular silicon starting material is supplied to the material melting section through the feed means.
• the feed rate is equal to the rate of crystallization, i.e. , 65 g/min.
• the starting material feed means 14 is connected to a starting material storage chamber (not shown) provided externally of the chamber upper cover 16, thereby feeding the starting material continuously.
• the feed rate of subsidiary material is calculated in accordance with the desired resistance value and the starting material feed rate. In accordance with the present embodiment, in the course of the pulling the feed rate of the subsidiary material is changed twice in order to change the resistance value as mentioned previously.
• Numeral 9 designates a heat keeping cover made from a tantalum sheet of 0.2mm in thickness. This has the effect of reducing the dissipation of heat from the partition member 8 and the material melting section. In accordance with the present invention, the presence of the proper range of the cross-sectional areas of the communication holes is due to the presence of the partition member.
• Numeral 15 designates openings formed in the upper part of the heat keeping member 9.
• the opening having an area of 100 cm is formed at each of four locations.
• Ar gas introduced into a pull chamber 20 is passed through the openings 15 first land then through the space between the resistance heater 3 and a furnace heat . insulating member 6 and it is discharged from the bottom of the furnace.
• Fig. 2 shows the changes of the resistance value in the lengthwise direction of the pulled crystal under the previously mentioned four kinds of conditions of the communication holes.
• (a) shows the case where the cross-sectional area of the communication holes is less than the lower limit of the present invention. Firstly, during the initial period of the pulling the resistance value is changed and also it becomes lower than the desired value. At some other intermediary points of 60 cm and 140 cm, respectively, the response characteristic with respect to the changes in the amount of the dopant is extremely bad. Practically, the desired resistance value is obtained at no point throughout the whole length.
• the reason is that in order that the steady state may be attained in this system, it is necessary to supply the starting material in an amount which is at least ten times the amount of the molten silicon in the .material melting section ( " 5 Kg) , that is, about 108cm of the crystal in terms of the crystal length must be pulled.
• the response characteristic with respect to the changes in the amount of the dopant is quite excellent.
• the transition regions of the resistance value are less than 10cm in terms of the crystal length.
• the CC-CZ method is well suited for the growth of long crystals involving no composition variation and also the application . of the present invention causes the CC-CZ method to become a crystal growing method suitable cope with small-lot production. In the case of (d) , the melting of the starting material is not satisfactory and the CC-CZ operation is not possible.
• Embodiment 2 is a diagrammatic representation of Embodiment 1 :
• the present invention is not only applicable as an apparatus for manufacturing silicon single crystals of 10 inches or more in diameter but also as an apparatus for manufacturing single crystal of any other material than silicon single crystals while maintaining the stable composition and quality.

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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
  • 1990-04-13 JP JP2098583A patent/JP2585123B2/ja not_active Expired - Fee Related
• 1991
  • 1991-04-11 KR KR1019910701827A patent/KR920702732A/ko not_active Application Discontinuation
  • 1991-04-11 EP EP91906975A patent/EP0484538A1/en not_active Withdrawn
  • 1991-04-11 WO PCT/JP1991/000477 patent/WO1991016476A1/en not_active Application Discontinuation
  • 1991-04-13 CN CN91102532A patent/CN1056135A/zh active Pending

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