JP2005132675A - Single crystal production apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the temperature gradient at a cone part becomes considerably small in comparison with that at the face of a heater when the cone part of the bottom part of a crucible is arranged at a position corresponding to melting point of the surface of the heater, and when the temperature gradient becomes small, the position of the solid-liquid interface becomes unstable by heat disturbance and the crystal defects are liable to occur for a single crystal production apparatus. <P>SOLUTION: In the single crystal production apparatus, the temperature distribution of the surface of the heater is transferred to the bottom part of the crucible, a temperature gradient is formed along the bottom face of the crucible, and it becomes possible to gradually move the melting position to the peripheral direction from a seed crystal, and further, in the bottom part of the crucible, it becomes possible to fixedly maintain the temperature gradient in the vicinity of the solid-liquid interface and crystal growth speed similarly to the constant diameter part by providing a plurality of fins protruding in the obliquely downward direction in the symmetricity to the axis at the bottom part of the crucible. Resultingly, it becomes possible to produce a large diameter, high quality single crystal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a single crystal growth technique, and more particularly to an apparatus for manufacturing a single crystal by a vertical Bridgman method (VB method) for growing a fluorite single crystal used as a lens material of a semiconductor exposure 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 excimer laser, ArF excimer laser, and F2 laser light, the transmittance was low, and the conventional optical lens was used. It is impossible to use glass. For this reason, it is common to use quartz glass or fluorite having high transmittance of short wavelength light for the optical system of the excimer laser exposure apparatus. In particular, in the F2 laser exposure apparatus, fluorite is essential. Has been.

  In addition, each lens constituting the projection lens is polished with the ultimate surface accuracy. However, if the lens is polycrystalline, the polishing speed varies depending on the crystal orientation, so that 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 manufactured by the vertical Bridgman method (VB method) as shown in US Pat. No. 2,214,976 (Patent Document 1), and the manufacturing apparatus has a configuration as shown in FIG. ing. In FIG. 4A, 1 is a furnace body, 2 is a heat insulating member that divides the inside of the furnace body 1 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 furnace body 1. A support bar 5 penetrating the bottom is a crucible attached to the upper end of the support bar 4. A seed single crystal 9 is placed at the lower end of the crucible 5 and a raw material is placed thereon. Then, the furnace is evacuated to raise the furnace temperature and melt the raw material. FIG. 4B is a graph showing the temperature distribution along the vertical direction of the upper heater 3 a and the lower heater 3 b of the furnace body 1. The vertical axis represents the position of the furnace body 1, and the horizontal axis represents the temperature distribution. As shown in FIG. 4B, the position of the heat insulating member 2 is set to the melting point temperature T1. The position of the crucible 5 at the start of crystal growth is a position where the upper part of the seed single crystal 9 is melted. When the crystal is grown, the crucible 5 is lowered from the high temperature region 1a to the low temperature region 1b at a rate of about 0.1 to 5 mm / hour, and the seed single crystal 9 is used as a starting point for crystallization from the lower part. FIG. 4 shows a state in the middle of the crucible lowering, where 6 is a melt, 8 is a solidified crystal, and 7 is a solid-liquid interface.
U.S. Pat. No. 2,214,976

  However, in the above-mentioned conventional vertical Bridgman method, it has been very difficult to produce a high-quality single crystal when it becomes a large-diameter fluorite, for example, a fluorite having a diameter of 300 mm or more, which has been increasingly demanded in recent years. . In particular, there is a problem in that crystal defects are likely to occur in the process of gradually widening the crystal surface from the crystallization starting point (seed single crystal 9) along the cone portion 5b on the bottom surface of the crucible 5 to reach the maximum diameter.

  Important parameters that affect crystal defects include a temperature gradient G in the vicinity of the solid-liquid interface and a crystal growth rate V, and these values need to be managed constant in order to obtain a high-quality single crystal. Therefore, conventionally, a temperature distribution having a temperature gradient on the heater surface is created by the upper and lower heaters 3a and 3b, and this temperature distribution is transferred to the wall surface of the crucible 5 by radiation to obtain a constant temperature gradient G. Also, the crystal growth rate V was controlled to be constant by controlling the crucible pulling rate constant.

  As can be seen from FIG. 4, the straight body portion 5a of the crucible 5 faces the heater surface and has a small interval, so that the temperature distribution created on the heater surface is transferred almost directly to the position facing the straight body portion 5a. Therefore, when the straight body 5a of the crucible is at the melting point temperature position as shown in FIG. 4, the temperature gradient G and the crystal growth rate V can be kept constant.

  However, the bottom cone portion 5b of the crucible 5 does not face the heater surface, and as the diameter of the crucible increases, the distance to the heater surface also increases, so that the radiation field of view increases and any arbitrary surface on the outer surface of the cone portion 5b increases. Radiation from a wide range affects the minute surface and is averaged. Therefore, when the crucible cone portion 5b is placed at the melting point temperature position of the heater surface as shown in FIG. 5, the temperature gradient G of the cone portion 5b is considerably smaller than the temperature gradient on the heater surface. When the temperature gradient G becomes small, the position of the solid-liquid interface 7 becomes unstable due to thermal disturbance, and crystal defects are likely to occur.

  The object of the present invention is to eliminate such a decrease in temperature gradient at the bottom of the crucible, increase the temperature gradient along the bottom surface, and gradually move the melting point position from the seed single crystal 9 to the peripheral direction. An object of the present invention is to provide a single crystal production apparatus capable of producing a high quality single crystal with a caliber.

  In order to solve the above-mentioned problems, the single crystal production apparatus of the present invention is a single crystal production by a vertical Bridgeman method in which a melt obtained by melting raw materials in a crucible is gradually solidified from the lower end to grow a columnar single crystal. The apparatus is characterized in that a plurality of fins which are axially symmetrical and project obliquely downward are arranged on the bottom surface of the crucible.

  Furthermore, when the inclination angle of the bottom surface of the crucible with respect to the vertical axis is θ and the inclination angle of the fin with respect to the horizontal plane is α, α ≧ θ / 2.

  According to the present invention, the temperature distribution of the heater surface is transferred to the bottom surface of the crucible along the bottom surface of the crucible by providing the bottom surface of the crucible with a plurality of fins that are axially symmetrical and projecting obliquely downward. It is possible to gradually move the melting point position from the seed single crystal to the peripheral direction with the temperature gradient in the vicinity of the solid-liquid interface at the bottom part of the crucible as well as the straight body part, It becomes possible to manage the crystal growth rate at a constant level. As a result, a large-diameter and high-quality single crystal can be manufactured.

  Further, the temperature transferred from the heater surface to the cone portion 5b is set to α ≧ θ / 2, where θ is an inclination angle of the bottom inner surface of the crucible with respect to the vertical axis and α is an inclination angle of the fin with respect to the horizontal plane. The gradient can be increased, and more stable crystal growth is possible.

  According to the present invention, the temperature distribution of the heater surface is transferred to the bottom cone portion 5b of the crucible by providing a plurality of fins which are axially symmetrical and projecting obliquely downward on the bottom portion of the crucible, and the bottom surface of the crucible The melting point position can be gradually moved from the seed single crystal 9 to the peripheral direction along the rim, and the cone portion 5b at the bottom of the crucible is also fixed in the same manner as the straight body portion 5a. The temperature gradient G and the crystal growth rate V in the vicinity of the liquid interface can be managed constant. As a result, a large-diameter and high-quality single crystal can be manufactured.

  Further, the temperature transferred from the heater surface to the cone portion 5b is set to α ≧ θ / 2, where θ is an inclination angle of the bottom inner surface of the crucible with respect to the vertical axis and α is an inclination angle of the fin with respect to the horizontal plane. The gradient can be increased, and more stable crystal growth is possible.

(Example)
Fig.1 (a) is sectional drawing of the single-crystal manufacturing apparatus in connection with embodiment of this invention. In FIG. 1A, 1 is a furnace body, 2 is a heat insulating member that divides the inside of the furnace body 1 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 furnace body 1. A support rod penetrating the bottom, 51 is a crucible attached to the upper end of the support rod 4, 51a is a straight body portion of the crucible 51, 51b is a bottom cone portion of the crucible 51, and 52 is a fin attached to the bottom cone portion 51b. .

  In the configuration of FIG. 1A, the crystal is grown as follows. First, the seed single crystal 9 is placed at the lower end of the crucible 51, and the raw material is put thereon. Then, the furnace body 1 is evacuated to raise the furnace temperature and melt the raw material. FIG. 1B shows the temperature distribution along the vertical direction of the heater surface portion of the furnace body 1. FIG. 1B is a graph showing the temperature distribution along the vertical direction of the upper heater 3 a and the lower heater 3 b of the furnace body 1. The vertical axis represents the position of the furnace body 1, and the horizontal axis represents the temperature distribution. As shown in FIG.1 (b), the position of the heat insulation member 2 is set so that it may become melting | fusing point temperature T1. The position of the crucible 51 at the start of crystal growth is a position where the upper part of the seed single crystal 9 is melted. When the crystal is grown, the crucible 51 is lowered from the high temperature region 1a to the low temperature region 1b at a speed of about 0.1 to 5 mm / hour, and the seed single crystal 9 is used as a starting point for crystallization from the lower part. FIG. 1 shows a state where the crystal surface gradually expands along the cone part 5b on the bottom of the crucible and reaches the maximum diameter in the middle of the crucible descent, 6 is a melt, 8 is a solidified crystal, 7 Is a solid-liquid interface.

  FIG. 2 is an enlarged cross-sectional view of a portion of the crucible 51 shown in FIG. Hereinafter, how the temperature distribution of the heater surface portion is transferred to the bottom cone portion 51b of the crucible 51 by the action of the fins 52 will be described with reference to FIG. In FIG. 2, B1 indicates a base portion of the fin 52 on the cone portion 51b, and B2 indicates a portion between the fins on the cone portion 51b. F <b> 1 indicates a tip portion of the fin 52. A hatched surface HS represents a heater surface facing the crucible 51, H1 is a portion facing the F1 at a point portion on the heater surface HS, and H2 is a point entering the field of view from B2 at a point on the heater surface HS. . Transfer of heat energy between the heater surface HS and the crucible 51 is performed by radiation. The tip end portion F1 of the fin 52 mainly receives and transfers radiant energy with the surface near H1 facing F1. Since the field of view near the portion B2 between the fins is blocked by the fins, radiation energy is exchanged with the surface near the point H2 that mainly enters the field of view. In a furnace having a high temperature, the temperature difference between the two surfaces to which radiant energy is transferred is reduced. The reason is that the radiant energy is proportional to the fourth power of the absolute temperature, so the equivalent thermal resistance between the two surfaces where the radiant energy is transferred is inversely proportional to the third power of the average absolute temperature of the two surfaces. This is because the thermal resistance between the two surfaces becomes minute. Therefore, the temperature at the point F1 is close to the temperature at the point H1, and the temperature at the point B2 is close to the temperature at the point H2. Further, the temperature of the point B1 becomes close to the temperature of the point F1 due to the heat conduction action of the fins.

  The temperature distribution on the heater surface is transferred to the cone portion 51b by the visual field limiting action and heat conduction of the fins 52 as described above. Actually, the temperature distribution on the heater surface is not transferred as it is due to the effects of heat conduction on the crucible wall surface, heat radiation from the support rod 4, radiation radiation from the bottom surface of the fin 52, etc. This increases the tendency of temperature transfer.

Next, in the ideal state where the temperature distribution on the heater surface is directly transferred to the cone portion 51b by the action of the fins 52, a condition for the temperature gradient of the cone portion to be larger than the temperature gradient of the heater surface is obtained. FIG. 3 is a cross-sectional view for showing the relationship between the temperature gradient of the heater surface and the temperature gradient of the crucible bottom, and the reference numerals are the same as those in FIGS. In FIG. 3, θ is an inclination angle of the bottom cone portion 51b of the crucible with respect to the vertical axis, α is an inclination angle of the fin 52 with respect to the horizontal plane, β is an inclination angle of the fin 52 with respect to the vertical axis (α + β = π / 2), A Is the point at the base of the fin, B is the point at the tip of the fin, and C is the point where the straight body part 51a and the cone part 51b intersect. In the ideal state, the temperature of the heater surface facing the line segment BC is transferred onto the line segment AC. In this ideal state,
(Cone temperature gradient) ≥ (heater surface temperature gradient)
Is when AC ≦ BC.

Considering the triangle ABC, the condition for AC ≦ BC is ∠A ≧ ∠B.
∠A = π−θ−β ∠B = β α + β = π / 2
Therefore, the condition for satisfying ∠A ≧ ∠B is α ≧ θ / 2.

Therefore, in the ideal state, when α ≧ θ / 2 (cone temperature gradient) ≧ (heater surface temperature gradient)
It becomes.

  As described above, the temperature distribution on the heater surface is transferred to the bottom cone portion 51 b of the crucible 51 by the action of the fins 52. Then, by creating a temperature gradient along the bottom surface of the crucible 51 and lowering the crucible 51, the melting point position can be gradually moved from the seed single crystal 9 to the peripheral direction, and at the cone portion 5b on the bottom surface of the crucible. However, similarly to the straight body portion 5a, the temperature gradient G and the crystal growth rate V in the vicinity of the solid-liquid interface can be managed to be constant. As a result, a large-diameter and high-quality single crystal can be manufactured.

  Further, when the inclination angle of the bottom inner surface of the crucible 51 with respect to the vertical axis is θ, and the inclination angle of the fin 52 with respect to the horizontal plane is α, α ≧ θ / 2 is set, so that the surface is transferred from the heater surface to the cone portion 51b. The temperature gradient can be increased, and more stable crystal growth is possible.

  Note that the inclination angle α of the fin 52 with respect to the horizontal plane need not be constant, and the inclination angle may be different between the upper stage and the lower stage. The temperature gradient can be changed by changing the inclination angle.

  Further, it is desirable that the thermal conductivity of the fins 52 be larger than the thermal conductivity of the crucible 51. By increasing the heat conduction of the fins 52 and reducing the heat conduction of the crucible 51, it is possible to reduce the decrease in the temperature gradient at the bottom of the crucible.

It is sectional drawing of the single-crystal manufacturing apparatus in connection with embodiment of this invention. It is an expanded sectional view of the part of the crucible 51 of FIG. Sectional drawing which shows the relationship between the temperature gradient of a heater surface, and the temperature gradient of a crucible bottom part. 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 3a Upper heater 3b Lower heater 4 Support rod 5 Crucible 5a Straight body part 5b Cone part 6 Melt 7 Solid-liquid interface 8 Crystal 9 Seed single crystal 51 Crucible 51a Straight body part 51b Cone part 52 Fin

Claims (2)

  In a single-crystal manufacturing apparatus based on the vertical Bridgeman method in which a melt obtained by melting the raw material in the crucible is gradually solidified from the lower end to grow a columnar single crystal, the bottom part of the crucible is axially symmetrically projected downward. A single crystal manufacturing apparatus characterized by arranging a plurality of fins.   2. The single crystal manufacturing apparatus according to claim 1, wherein θ ≧ θ / 2, where θ is an inclination angle with respect to a vertical axis of the bottom surface of the crucible and α is an inclination angle with respect to a horizontal plane of the fin.

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