JP2005231978A - Single crystal manufacturing method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a single crystal by vertical Bridgeman method that eliminates the turbulence of temperature at the proximity of solid-liquid interface, the deterioration of the product quality of crystal and the generation of boundaries due to convection of a melt within a crucible since the wall face temperature of the crucible is lower than the melt temperature at the lower part of the crucible, and the wall face temperature of the crucible and the temperature of the crucible itself are higher than the melt temperature at the upper part of the crucible. <P>SOLUTION: The apparatus for manufacturing the single crystal has the crucible to support the single crystal material, which is arranged within a furnace and comprises a conical part and a straight trunk part located at the upper part of the conical part, a flat sheet member arranged within the crucible so that it is movable up and down to the crucible and a supporting member to move the crucible up and down to the furnace. Upon the fall of the crucible, the flat sheet member is arranged at the position of boundary between the straight trunk part and the conical part while the solid-liquid interface is sweeping the conical part, and the flat sheet member is arranged at the upper position apart a predetermined space than the solid-liquid interface notwithstanding the fall of the crucible while the solid-liquid interface is sweeping the straight trunk part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a single crystal growth manufacturing method and apparatus, and more particularly to a single crystal manufacturing method by a vertical Bridgman method (VB method) for growing a fluorite single crystal used as a lens material of a semiconductor exposure apparatus, and The present invention relates to a single crystal manufacturing apparatus.

  In recent years, with the high integration of semiconductor integrated circuits, there is an increasing demand for the formation of ultrafine patterns. As a lithography apparatus for transferring a fine pattern onto a wafer, a reduction projection exposure apparatus is frequently used. In order to achieve high integration, it is necessary to increase the resolution of the projection lens. In order to increase the resolving power of the projection lens, it is necessary to use exposure light having a short wavelength and increase the numerical aperture of the projection lens (increase the aperture).

  The shortening of the exposure light wavelength has progressed to g-line (wavelength 436 nm), i-line (365 nm), KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), and in the future, F2 laser (157 nm). ) Is considered promising. In the wavelength range up to i-line, it was possible to use a conventional optical lens in the optical system, but in the wavelength range of KrF, ArF excimer laser, F2 laser light, the transmittance is low, It is impossible to use optical glass. For this reason, it is common to use quartz glass or fluorite with high transmittance of short wavelength light for the optical system of the excimer laser exposure apparatus, and fluorite is essential for the F2 laser exposure apparatus. It is said that.

  In addition, each lens constituting the projection lens is polished with very high surface accuracy, but if it is polycrystalline, the polishing speed varies depending on the crystal orientation, so it is difficult to ensure the surface accuracy of the lens. . Further, in the case of polycrystal, impurities are easily segregated at the crystal interface, and the uniformity of the refractive index is impaired, or fluorescence is emitted by laser irradiation. For these reasons, a large-diameter, high-quality single crystal fluorite is desired.

  Fluorite is usually produced by the vertical Bridgman method (VB method), and its production apparatus is described in US Pat. No. 2,214,976 (Patent Document 1). A schematic sectional view thereof is shown in FIG. In FIG. 5A, 1 is a furnace body, 2 is a heat insulating member that divides the inside of the furnace into a high temperature region 1a and a low temperature region 1b, 3a is an upper heater, 3b is a lower heater, and 4 is a bottom of the furnace body 1. A support rod 5 penetrating is a crucible attached to the upper end of the support rod 4. The raw material is put into this crucible 5, the inside of the furnace is evacuated, and the furnace temperature is raised to the melting point of fluorite or higher, usually 1390 to 1450 degrees Celsius and melted. FIG.5 (b) is a graph which shows the temperature along the perpendicular direction of the center part of a furnace. As shown in FIG.5 (b), the position of the heat insulation member 2 is set so that it may become melting | fusing point temperature T1. When crystal growth is performed, the crucible 5 is lowered from the high temperature region 1 a to the low temperature region 1 b at a speed of 0.1 to 5 mm / h, and the raw material is crystallized from the lower part of the crucible 5. FIG. 5 shows a state during the lowering of the crucible, where 6 is a melt, 8 is a solidified crystal, and 7 is a solid-liquid interface.

However, with the vertical Bridgman method described in the above-mentioned US Pat. No. 2,214,976, it becomes difficult to produce a high-quality single crystal when the diameter becomes large as recently required, for example, 300 mm or more. The convection which arises in a melt can be mentioned as the cause. This convection is pointed out in Japanese Patent Application Laid-Open No. 5-124877 (Patent Document 2). Japanese Patent Application Laid-Open No. 5-124487 describes a method in which a convection is interrupted by providing a region having a temperature gradient of 0 ° C./cm directly above the solid-liquid interface so that the solid-liquid interface is not affected by the convection.
U.S. Pat. No. 2,214,976 JP-A-5-12487

  However, in Japanese Patent Laid-Open No. 5-124887, since the temperature gradient is 0 ° C./cm in the vicinity of the solid-liquid interface, it is considered that the location other than the solid-liquid interface becomes the melting point temperature and the position of the solid-liquid interface becomes unstable with respect to the furnace. . Therefore, there is a need for a method for suppressing convection while maintaining a temperature gradient.

  Since the crucible 5 is heated from the outside, a temperature difference occurs between the radial direction of the melt 6 or between the crucible wall surface and the melt 6 and radial convection occurs. In FIG. 4, arrow 9 shows a typical convection pattern. The mechanism by which such convection occurs is explained as follows. First, if there is a temperature difference in the radial direction of the melt 6, a radial density difference is caused and convection is induced. As a result, the melt 6 is soaked. On the other hand, since the temperature of the wall surface of the crucible 1 is gradually increased upward from the solid-liquid interface portion 7, the following situation is obtained when the wall surface temperature of the crucible 5 and the melt temperature are compared. That is, the wall surface temperature of the crucible 1 is lower than the melt temperature in the lower part (near the solid-liquid interface 7), and the crucible 5 and the wall surface temperature are higher than the melt temperature in the upper part. As a result, the melt becomes a downward flow along the wall surface at the lower portion and an upward flow along the wall surface at the upper portion. The convection generated in this way increases as the crucible 5 becomes larger and the temperature difference in the radial direction and the temperature gradient of the crucible wall surface increase. This convection disturbs the temperature in the vicinity of the solid-liquid interface, causing deterioration in crystal quality and generating a boundary.

  An object of the present invention is to provide a single crystal manufacturing method and apparatus capable of manufacturing a large-diameter and high-quality single crystal without the influence of the convection of the melt.

  In order to solve the above-mentioned problems, a method for producing a single crystal according to the present invention comprises a crucible disposed inside a furnace, comprising a conical portion and a straight body portion located above the conical portion, and holding a single crystal material, and a crucible And a support member that moves the crucible up and down relative to the furnace, and the flat plate member has a conical solid-liquid interface as the crucible descends. Is placed at the boundary position between the straight body part and the conical part while sweeping the part, and while the solid-liquid interface is sweeping the straight body part, a predetermined distance from the solid-liquid interface regardless of the descending of the crucible It is characterized by being arranged above.

  The apparatus for producing a single crystal according to the vertical Bridgman method of the present invention includes a crucible disposed inside a furnace, comprising a conical portion and a straight body portion located above the conical portion, and holding a single crystal material, and the interior of the crucible A flat plate member arranged to move up and down with the crucible, a support member for moving the crucible up and down with respect to the furnace, the flat plate member as the crucible descends from the furnace, the solid-liquid interface sweeps the conical part Control is placed at the boundary between the straight body and the conical part while the solid-liquid interface is swept across the straight body part, and placed above the solid-liquid interface by a predetermined distance regardless of the crucible descending. Means.

  By adopting such a configuration, it is possible to prevent convection of the single crystal material below the flat plate member. The crucible and the furnace, and the crucible and the flat plate member may be configured so as to be relatively movable up and down.

  According to the present invention, the flat plate member is disposed horizontally in the melt in the crucible, and the flat plate member is held at a small distance from the solid-liquid interface, whereby the flat plate member and the solid-liquid interface are separated. As a result, there is no convection between them, and as a result, the temperature in the vicinity of the solid-liquid interface is stabilized, and a large-diameter and high-quality single crystal can be produced.

  According to the present invention, a flat plate member is horizontally disposed in the melt in the crucible, and the flat plate member is held upward with a small distance from the solid-liquid interface. In this case, convection is eliminated, the temperature near the solid-liquid interface is stabilized, and a large-diameter and high-quality single crystal can be produced. The details will be described below with reference to the drawings.

  1 is a cross-sectional view of a single crystal manufacturing apparatus according to Embodiment 1 of the present invention. In FIG. 1A, 1 is a furnace body, 2 is a heat insulating member that divides the inside of the furnace into a high temperature region 1a and a low temperature region 1b, 3a is an upper heater, 3b is a lower heater, and 4 is a bottom of the furnace body 1. It is a support rod that penetrates. 5 is a crucible attached to the upper end of the support rod 4, 5a is a straight body part, 5b is a conical part. The crucible 5 moves up and down by moving the support bar 4 up and down by means (not shown). 6 is a melt which is a single crystal material, 7 is a solid-liquid interface, and 8 is a solidified crystal. An arrow 9 indicates the convection pattern of the melt 6. Reference numeral 10 denotes a flat plate member disposed inside the crucible 5, and 11 denotes a column that serves as a holding means for the flat plate member 10. Since the flat plate member 10 has low wettability and is required to be usable in a very high temperature environment, it is desirable to use high purity carbon. The support 11 penetrates the upper surface of the crucible 5, the upper end penetrates the furnace body 1, and a weight 12 is attached to the tip. The flat plate member 10 moves up and down by moving the column 11 up and down by means (not shown). When the flat plate member 10 is lowered, the lowering of the flat plate member 10 is stopped by the weight 12 coming into contact with the upper surface of the furnace body 1.

  FIG.1 (b) is a graph which shows the temperature along the perpendicular direction of the center part of a furnace. The horizontal axis indicates temperature, and the vertical axis indicates the position in the vertical direction of the single crystal manufacturing apparatus. As shown in FIG. 1B, the heaters 3a and 3b are controlled so that the position of the heat insulating member 2 becomes the melting point temperature T1. Next, the crucible 5 is lowered from the high temperature region 1 a to the low temperature region 1 b by lowering the support rod 4, and is crystallized sequentially from the bottom of the crucible 5.

  Next, a single crystal manufacturing method using the single crystal manufacturing apparatus of this embodiment will be described with reference to FIG. First, the single crystal raw material is put into the crucible 5 and melted in the high temperature region 1a as shown in FIG. At this time, the position of the furnace serving as the solid-liquid interface 7 is located at the lowermost end of the crucible 5. At this time, the distance between the upper surface of the furnace body 1 and the lower surface of the weight 12 is h, and this value is a value obtained by adding a predetermined minute distance d to the height of the conical portion 5b of the crucible 6. However, when the lowermost end of the crucible 5 is disposed above the position corresponding to the solid-liquid interface 7 of the furnace body, it is necessary to increase the distance h by that distance.

  Next, after the single crystal raw material is completely melted to become the melt 6, the crucible 6 is slowly lowered. The speed at this time is generally 0.5 mm / Hr to 5.0 mm / Hr. FIG. 2B shows a state where the solid-liquid interface is growing the crystal on the conical portion 5b. While the solid-liquid interface 7 sweeps the conical part 5b, the flat plate member 10 moves downward together with the crucible 5, so that it is disposed at the boundary position between the conical part 5b and the straight body part 5a.

  Next, the crucible 6 is further lowered. FIG. 2C shows a state in which the solid-liquid interface is growing the crystal on the straight body portion 5a. When the flat plate member 10 is moved by the distance h relative to the furnace body 1, the bottom surface of the weight 12 comes into contact with the upper surface of the furnace body 1 and stops. The length of the column 11 is adjusted in advance so that the distance between the flat plate member 10 and the solid-liquid interface 7 becomes a minute distance d when the furnace body 1 is stopped. The position of the solid-liquid interface 7 is fixed at a substantially constant position by the above temperature distribution, and the distance between the solid-liquid interface 7 and the flat plate member 10 is set to a minute distance when the straight body portion 5a is grown by adjusting the length of the support 11. d can be held.

  In the straight body portion 5 a where the distance between the flat plate member 10 and the solid-liquid interface 7 is a minute distance d, the melt 6 is divided up and down by the flat plate member 10. Convection 9 is generated in the melt 6 above the flat plate member 10, but this convection does not affect the solid-liquid interface 7. Rather, the flat plate member 10 is soaked by convection, and the convection of the melt 6 below the flat plate member 10 can be suppressed.

  The minute distance d on the lower side of the flat plate member 10 can reduce the increment of the melt temperature with the solid-liquid interface 7 with respect to the melting point temperature by making the value as small as possible. It means a reduction in convection drive energy and suppresses convection. When the influence of convection on the solid-liquid interface 7 is eliminated, the temperature in the vicinity of the solid-liquid interface 7 is stabilized. Further, since the temperature gradient at the solid-liquid interface 7 is maintained regardless of the presence or absence of the flat plate member 10, the stability of the solid-liquid interface position against temperature disturbance is also maintained.

  Next, the crucible 6 is further lowered. FIG. 2D shows a state in which the melt 6 in the crucible 5 is all solidified crystal 8. At this time, the flat plate member 10 is located in the gap between the upper portion of the crucible and the crystal and does not touch the crystal. The single crystal manufactured in this way. It is slowly cooled and removed from the crucible 5.

  The distance between the solid-liquid interface 7 and the flat plate member 10 is the same as the height of the conical portion 5b at the crucible lowering start position in FIG. 1 (a), and when the flat plate member 10 is lowered together with the crucible 5, FIG. Thus, the distance between the flat plate member 10 and the solid-liquid interface 7 becomes a minute distance d that can suppress convection. In addition, since the distance can be maintained, even a crucible with a small conical angle can produce a high-quality single crystal with a large diameter in the straight body portion 5a. The conical portion is also advantageous because the convection volume of the crucible 5 can be reduced by the flat plate member 10.

  The distance d is preferably as small as possible. However, in view of the position variation of the solid-liquid interface 7 in the process of lowering the crucible 5, the support column is provided so that the solid-liquid interface 7 and the flat plate member 10 do not contact each other. It is necessary to set a length of 11. This value can be determined by experiment or simulation. According to the examination results of the inventors, it is preferable that d = 10 to 150 mm for a crucible having an inner diameter of 250 to 350 mm. If it is 10 mm or less, the possibility of being involved in crystal growth increases, and if it is 150 mm or more, the effect of suppressing convection is reduced.

  Further, the melt 6 above and below the flat plate member 10 must be able to flow. Therefore, a gap is provided between the outer diameter of the flat plate member 10 and the inner diameter of the straight body portion 5 a of the crucible 5. The gap value should be as narrow as possible. For a crucible having an inner diameter of 250 to 350 mm, it is preferable to be 50 mm or less on one side. If it is 50 mm or more, it will be affected by convection. Moreover, you may provide one or more small holes in the flat plate member 10 as another method of ensuring a distribution channel.

  Further, it is desirable that the flat plate member 10 is stationary, but as long as the temperature of the melt 6 is not disturbed, the tip of the column 11 is rotated or slightly moved up and down by installing a driving means instead of a weight. It doesn't matter. By rotating or slightly raising and lowering the flat plate member 10, it is possible to promote soaking of the flat plate member and reduce convection drive energy.

  FIG. 3 is a cross-sectional view of a single crystal manufacturing apparatus according to Embodiment 2 of the present invention. In FIG. 3, 20 is a flat plate member, 21 is a column for holding the flat plate member 20, 22 is a temperature sensor fixed to the plate member 20, 23 is a column driving means for driving the column 22 up and down, and 24 is a temperature sensor. The calculation means outputs the drive amount to the column drive means 23 in response to the signal 22. The other parts are the same as those in FIG. In the configuration of FIG. 3, the temperature sensor 22, the calculation means 24, and the column drive means 23 form a feedback control system and are controlled as follows.

  The temperature sensor 22 detects the temperature of the melt 6 immediately below the flat plate member 20, and the column driving means 23 holds the flat plate member 20 together with the crucible 5 until the temperature detected by the temperature sensor 22 reaches the melting point temperature + α (α is a minute temperature). Lower. When the temperature detected by the temperature sensor 22 reaches the melting point temperature + α (α is a minute temperature), the calculation means 24 calculates the drive amount so that the temperature sensor 22 detects the melting point temperature + α (α is a minute temperature). Then, the value is output to the column driving means 23. Since there is a positive temperature gradient in the vicinity of the solid-liquid interface 7, the flat plate member 20 is maintained slightly above the solid-liquid interface 7. As a result, the convection of the melt between the flat plate member 20 and the solid-liquid interface 7 is suppressed, the temperature in the vicinity of the solid-liquid interface is stabilized, and a large-diameter and high-quality single crystal can be manufactured. In the second embodiment, the position of the flat plate member 20 is automatically corrected with respect to the position variation of the solid-liquid interface 7 in the process of lowering the crucible 5, so there is little risk of contact between the solid-liquid interface 7 and the flat plate member 20. . Further, since the temperature of the movement of the flat plate member 20 accompanying the lowering of the crucible 5 is controlled, it is not necessary to perform an experiment for adjusting the length of the support column 22, and the operability of the apparatus is improved.

  FIG. 4 is a cross-sectional view of a single crystal manufacturing apparatus according to Example 3 of the present invention. In FIG. 4, 30 is a flat plate member, 31 is a column holding the flat plate member 30, 32 is a distance sensor fixed to the plate member 30, 33 is column driving means for driving the column 32 up and down, and 34 is a distance sensor 32. Is an arithmetic means for receiving the signal and outputting a driving amount to the column driving means 33. The other parts are the same as those in FIG. In the configuration of FIG. 4, the distance sensor 32, the calculation means 34, and the column driving means 33 form a feedback control system and are controlled as follows.

  The distance sensor 32 detects the distance between the flat plate member 30 and the solid-liquid interface 7, and the column driving means 33 lowers the flat plate member 30 together with the crucible until the detection value of the distance sensor 32 becomes a minute distance d. When the detection value of the distance sensor 32 reaches the minute distance d, the calculation means 34 calculates the driving amount so that the detection value of the distance sensor 32 maintains the minute distance d, and outputs the value to the column driving means 33. . In the third embodiment, the position of the flat plate member 30 is automatically corrected with respect to the position fluctuation of the solid-liquid interface 7 in the process of lowering the crucible 5, so that there is little risk of contact between the solid-liquid interface 7 and the flat plate member 30. . Further, since the interval d is directly detected, the value can be set minutely. As a result, convection of the melt between the flat plate member 30 and the solid-liquid interface 7 is suppressed, the temperature in the vicinity of the solid-liquid interface is stabilized, and a large-diameter and high-quality single crystal can be manufactured. Further, since the movement of the flat plate member 30 accompanying the lowering of the crucible is controlled by the distance sensor 32, it is not necessary to perform an experiment for adjusting the length of the support column, and the operability of the apparatus is improved.

1 is a cross-sectional view of a single crystal manufacturing apparatus according to Example 1. FIG. 3 is a cross-sectional view showing a manufacturing process of a single crystal manufacturing apparatus according to Example 1. FIG. 6 is a cross-sectional view of a single crystal manufacturing apparatus according to Example 2. FIG. 6 is a cross-sectional view of a single crystal manufacturing apparatus according to Example 3. FIG. It is sectional drawing of the conventional single crystal manufacturing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace body 1a High temperature area | region 1b Low temperature area | region 2 Heat insulation member 2a Upper heater 3b Lower heater 4 Support rod 5a Straight trunk | drum 5b Conical part 6 Melt 7 Solid-liquid interface 8 Crystal 9 Convection 10, 20, 30 Flat plate member 11, 21, 31 Strut 12 Weight 22 Temperature sensor 32 Distance sensor 23, 33 Drive unit 24, 34 Arithmetic unit

Claims (6)

  In a method for producing a single crystal by the vertical Bridgman method, a crucible arranged inside a furnace and comprising a conical portion and a straight body portion located above the conical portion and holding a single crystal material, and the crucible inside the crucible And a support member for moving the crucible up and down relatively with respect to the furnace, and as the crucible is lowered relative to the furnace, The flat plate member is disposed at the boundary position between the straight body portion and the conical portion while the solid-liquid interface sweeps the conical portion, and the crucible is lowered while the solid-liquid interface sweeps the straight body portion. Regardless of the solid-liquid interface, the single crystal manufacturing method is characterized by being disposed above a predetermined distance.   The single crystal manufacturing method according to claim 1, wherein the predetermined distance is 10 to 150 mm.   In an apparatus for producing a single crystal by the vertical Bridgman method, a crucible is disposed inside a furnace and includes a conical portion and a straight body portion located above the conical portion and holds a single crystal material, and the crucible is disposed inside the crucible. A flat plate member arranged so as to be relatively movable up and down, a support member that moves the crucible up and down relatively with respect to the furnace, and the flat plate member as the crucible is lowered relative to the furnace. When the solid-liquid interface sweeps the conical part, it is placed at the boundary between the straight body part and the conical part, and while the solid-liquid interface sweeps the straight body part, the solid-liquid interface is solid regardless of the descending of the crucible. And a control unit arranged above the liquid interface by a predetermined distance.   The single crystal manufacturing apparatus according to claim 3, wherein the predetermined distance is 10 to 150 mm.   The temperature sensor is attached to the flat plate member, and the flat plate member is controlled by the control means so as to be located at the predetermined distance from the solid-liquid interface according to a value of the temperature sensor. 3. The single crystal manufacturing apparatus according to 3.   A distance sensor is attached to the flat plate member, and by measuring the distance between the flat plate member and the solid-liquid interface based on the value of the distance sensor, the flat plate member moves from the solid-liquid interface to the predetermined distance. The single crystal manufacturing apparatus according to claim 3, wherein the control is performed by the control means.

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