JP2006117442A - Method and apparatus for producing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a high quality single crystal by decreasing crystal defects introduced into the upper end part of a seed crystal, and an apparatus therefor. <P>SOLUTION: In the method for producing a single crystal by the vertical Bridgman process comprising placing a seed crystal on the low end of a crucible, melting a raw material in the crucible and gradually solidifying the melt liquid starting from the seed crystal to grow a columnar single crystal, the upper end of the seed crystal is melted before melting the raw material so that the melt liquid does not come into direct contact with unmelted seed crystal so as to alleviate thermal shock. Further, even if a scavenger mixed in the raw material drips, an adverse effect as an impurity is mitigated because it is diluted by the melt liquid at the upper end of the seed crystal. As a result, crystal defects introduced into the upper end part of the seed crystal are decreased and propagation of the crystal defects into the growing crystal is prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus and method for manufacturing a single crystal by a vertical Bridgman method (VB method), and more particularly to a single crystal growth technique 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 ultra fine pattern formation. As a lithography apparatus that transfers 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 resolution of the projection lens, it is necessary to use exposure light having a short wavelength.

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, F ₂ laser light (157 nm) Use is 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 light, F ₂ laser light, the transmittance is low, It is impossible to use optical glass. Therefore, the optical system of excimer laser exposure apparatus, and the transmittance of short-wavelength light using a high silica glass or fluorite become common as optical element material, in F ₂ laser exposure apparatus, firefly Stone is required.

  Optical requirements for fluorite used in such projection lenses are extremely high. In particular, laser transmittance durability, stress birefringence, and refractive index uniformity are important. Therefore, a uniform single crystal fluorite with few crystal defects is desired.

  Fluorite is usually produced by the vertical Bridgman method (VB method) as disclosed in Patent Documents 1 and 2 below.

  FIG. 4 is a view showing a crystal manufacturing apparatus according to a conventional vertical Bridgman method.

In FIG. 4, 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, 4 is a support rod that penetrates the bottom of the furnace body 1, Reference numeral 5 denotes a crucible attached to the upper end of the support bar 4. A seed crystal 9 is placed at the lower end of the crucible 5 and a fluorite raw material (calcium fluoride (CaF ₂ )) is put on the crucible 5, and then the furnace is evacuated to raise the furnace temperature and melt the raw material. The graph on the left side of FIG. 4 shows the temperature distribution along the vertical direction of the heater surface portion of the furnace. As shown in the graph, 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 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 speed of about 0.1 to 5 mm / hour through the support rod 4 by a vertical movement mechanism, Crystallize from. 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.
US Patent 2,214,976 JP 2002-308692 A

  However, the conventional vertical Bridgman method as described above has a problem that it is difficult to produce a high-quality single crystal as recently required. When the grown crystal is observed, even if a single crystal having a low defect is used as a seed crystal that is the starting point of crystallization, a crystal defect is generated at the upper end portion of the seed crystal and is propagated in the grown crystal. It was solved.

One of the causes of the introduction of defects at the upper end portion of the seed crystal is a thermal shock generated when a high-temperature melt is dropped into contact with the upper portion of the seed crystal when the raw material is melted before the start of crystal growth. Another cause is a scavenger (antioxidation fluoride additive) mixed in a small amount in the fluorite raw material. This is a metal fluoride added to remove CaO produced by the reaction of the raw material (CaF ₂ ) with moisture or the like and impurities originally present in the raw material. For example, a ZnF ₂ scavenger reacts with CaO to form CaF ₂ and itself is removed as ZnO or the like during crystal melting. As a result, CaO as an impurity is removed, and a fluoride crystal having excellent transmittance characteristics is obtained. However, since the scavenger has a lower melting point than fluorite, it is melted and dripped before the fluorite raw material to contact the seed crystal and give a thermal shock, and the high concentration scavenger directly contacts the seed crystal and has an adverse effect as an impurity. And causes crystal defects at the upper end of the seed crystal.

  An object of the present invention is to provide a single crystal manufacturing method and apparatus capable of manufacturing a high quality single crystal by reducing crystal defects introduced into the upper end portion of the seed crystal in this way.

  In order to solve the above problems, the method for producing a single crystal according to the present invention comprises placing a seed crystal at the lower end of the crucible to melt the raw material in the crucible, and gradually solidifying the melt starting from the seed crystal to form a columnar single crystal. In the method for producing a single crystal by the vertical Bridgman method for growing a crystal, the upper end portion of the seed crystal is melted before the raw material is melted.

  Further, the single crystal production apparatus of the present invention is a vertical type in which a seed crystal is placed at the lower end of the crucible, the raw material in the crucible is melted, and the melt is gradually solidified starting from the seed crystal to grow a columnar single crystal. An apparatus for producing a single crystal by the Bridgman method has a local heating means for locally heating and melting the upper end portion of the seed crystal.

  According to the present invention, the upper end portion of the seed crystal is melted before the raw material is melted, so that the melt does not directly contact the unmelted seed crystal and the thermal shock is alleviated. Moreover, even if the scavenger mixed with the raw material is dropped, it is diluted with the melt at the upper end of the seed crystal, so that the adverse effect as an impurity is reduced. As a result, it is possible to reduce the crystal defects introduced into the upper end portion of the seed crystal, prevent the crystal defects from propagating in the grown crystal, and manufacture a high-quality single crystal.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a cross-sectional view of a single crystal manufacturing apparatus according to a first embodiment of the present invention.

In FIG. 1, 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, 4 is a support rod that penetrates the bottom of the furnace body 1, 5 is a crucible attached to the upper end of the support bar 4, 5 a is a seed crystal storage section at the lower end of the crucible 5, 10 is a crystal raw material (CaF ₂ ), 11 is a seed crystal, and 20 is disposed near the seed crystal storage section 5 a. The local heater 21 is a heat receiving fin attached to the upper part of the seed crystal storage 5a.

  Moreover, FIG. 2 is a figure which shows the state which the seed crystal upper end part of FIG. 1 fuse | melted.

  In FIG. 2, 11a is a molten seed crystal and 11b is an unmelted seed crystal.

  In the configuration of FIG. 1, the crystal is grown as follows. First, the seed crystal 11 is placed in the seed crystal storage portion 5a at the lower end of the crucible 5, and the raw material is put thereon, and then the inside of the furnace is evacuated. Next, the heat receiving fins 21 are heated by the local heater 20. The upper end portion of the seed crystal 11 is heated and melted by the heat conduction of the heat receiving fins 21. FIG. 2 shows the state at this time. Next, the furnace temperature is raised by the heaters 3a and 3b to melt the raw material. The graph on the left side of FIG. 2 shows the temperature distribution along the vertical direction of the heater surface of the furnace. As shown in the graph, 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 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 speed of about 0.1 to 5 mm / hour through the support rod 4 by a vertical movement mechanism, Crystallize from. The local heater 20 is fixed to the crucible 5 side, but may be retracted to the outside when the crucible 5 is attached to the furnace body 1 side so as to be movable left and right. Further, in order to monitor the temperature of the upper end portion 11a of the seed crystal 11, a temperature detector such as a thermocouple may be attached to the upper portion of the seed crystal storage portion 5a.

When the raw material is melted in the above process, the scavenger (ZnF ₂ ) is first melted and then the raw material is melted and dropped. At this time, since the seed crystal upper end portion 11a has already melted, it does not directly contact the unmelted seed crystal 11b, and the thermal shock is alleviated by the melt 11a. Further, since the dropped scavenger is diluted with the melt 11a, the adverse effect as an impurity is reduced. As a result, it is possible to reduce the crystal defects introduced into the upper end portion of the seed crystal, restrict the propagation of crystal defects in the grown crystal, and manufacture a high-quality single crystal.
(Second embodiment)
FIG. 3 is a cross-sectional view of the single crystal manufacturing apparatus according to the second embodiment of the present invention.

  In FIG. 3, the local heater 20 is being fixed to the location of the heat insulation member 2 of 1st Embodiment with the heat | fever reflecting plate 22 and the heat insulation members 2a and 2b.

  In the configuration of FIG. 3, the local heater 20 is disposed outside the moving region so as not to hinder the movement of the crucible 5, and heats the heat receiving fins 21 by radiation.

  In the first embodiment, when the crucible 5 moves, the local heater 20 needs to move together with the crucible 5 or retreat to the outside of the movement region of the crucible 5. In the second embodiment, The structure is simple because it is not necessary.

  In addition to calcium fluoride, fluorides such as magnesium fluoride, barium fluoride, neodymium fluoride, lithium fluoride, and lanthanum fluoride are known as glass materials suitable for optical element materials of semiconductor exposure apparatuses. The present invention is also applicable to the production of these fluoride crystals.

Sectional drawing of the single-crystal manufacturing apparatus which concerns on 1st embodiment of this invention The figure which shows the state which the seed crystal upper end part of FIG. 1 fuse | melted Sectional drawing of the single-crystal manufacturing apparatus which concerns on 2nd embodiment of this invention Sectional view of conventional single crystal manufacturing equipment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Furnace main body 1a ... High temperature area | region 1b ... Low temperature area | region 2 ... Heat insulation member 2a ... Heat insulation member 2b ... Heat insulation member 3a ... Upper heater 3b ... Lower heater 4 ... Support rod 5 ... Crucible 5a ... Seed crystal storage part 6 ... Melt 7 ... solid-liquid interface 8 ... crystal 9 ... seed crystal 10 ... raw material 11 ... seed crystal 11a ... molten seed crystal 11b ... unmelted seed crystal 20 ... local heater 21 ... heat receiving fin 22 ... heat reflector

Claims (5)

In the method for producing a single crystal by the vertical Bridgman method in which a seed crystal is placed at the lower end of the crucible and the raw material in the crucible is melted, and the column crystal single crystal is grown by gradually solidifying the melt starting from the seed crystal.
A method for producing a single crystal, comprising melting an upper end of the seed crystal before melting the raw material.   The single crystal manufacturing method according to claim 1, wherein the single crystal is manufactured using calcium fluoride as the raw material. In a single crystal manufacturing apparatus by the vertical Bridgman method for placing a seed crystal at the lower end of the crucible and melting the raw material in the crucible, and gradually solidifying the melt starting from the seed crystal to grow a columnar single crystal,
An apparatus for producing a single crystal, comprising a local heating means for locally heating and melting the upper end portion of the seed crystal.   4. The single crystal according to claim 3, wherein the local heating means includes a local heater arranged near the seed crystal storage unit at the lower end of the crucible and a heat receiving fin attached to the upper part of the seed crystal storage unit. Manufacturing equipment.   The local heating means includes a local heater disposed outside the crucible moving region corresponding to the seed crystal storage unit at the lower end of the crucible, and a heat receiving fin attached to the top of the seed crystal storage unit. The single crystal manufacturing apparatus according to claim 3.

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