JP4731844B2 - Crystal manufacturing method and apparatus - Google Patents

Description

The present invention generally relates to a crystal manufacturing method and apparatus, and in particular, is suitable for various optical elements, lenses, window materials, prisms, and exposure apparatuses used in a short wavelength range from a vacuum ultraviolet region to a far ultraviolet region. The present invention relates to a crystal manufacturing method and apparatus for calcium (CaF ₂ ) crystals.

In recent years, the demand for miniaturization of semiconductor elements mounted on electronic devices has been increasing due to the demand for smaller and thinner electronic devices, and various proposals have been made to increase the exposure resolution in order to satisfy such requirements. Yes. Since shortening the wavelength of the exposure light source is an effective means for improving the resolution, in recent years, the exposure light source has been changed from a KrF excimer laser (wavelength of about 248 nm) to an ArF excimer laser (wavelength of about 193 nm). The practical application of F ₂ laser (wavelength: about 157 nm) is also progressing.

On the other hand, with the shortening of the wavelength of the light source, most of the conventional glass materials cannot be used due to insufficient transmittance. Quartz glass (SiO ₂ ) can barely be used in the ArF excimer laser wavelength range, but even quartz glass cannot be used in the F ₂ laser wavelength range. Calcium fluoride (CaF ₂ ) single crystal has a high light transmittance (that is, internal transmittance) in such a wavelength region in a glass material, so that it is used for an optical element such as a lens or a diffraction grating used in an exposure optical system. Optimal as an optical material.

  Parameters for evaluating the optical properties of optical materials such as lenses include internal durability, laser durability indicating the change in transmittance when laser light is continuously received, and the refractive index of the lens is constant regardless of location. There are refractive index uniformity (homogenity), birefringence, polishing (or processing) accuracy, and the like, and high quality is required for calcium fluoride used in an exposure apparatus.

Calcium fluoride single crystals are generally produced by the crucible descent method (also known as “vertical Bridgman method”) (see, for example, Patent Documents 1 and 2). In this method, a raw material of a crystalline substance is filled in a crucible, and the raw material melted by heating with a heater or the like is crystallized by lowering the crucible and cooling. Calcium fluoride polycrystals are difficult to ensure the surface accuracy required for optical elements (lenses, etc.) constituting the exposure optical system, and impurities segregate at the grain boundaries. It is easy, and the refractive index uniformity is impaired, and the laser durability is problematic. Therefore, the crucible descent method was intended to produce a single crystal in which the entire grown crystal is aligned in one crystal orientation, that is, a so-called crystal grain boundary (hereinafter referred to as “grain boundary”) (for example, (See Patent Document 3).
U.S. Pat. No. 2,149,076 U.S. Pat. No. 2,214,976 Japanese Patent Laid-Open No. 10-265296

  However, when the entire crystal is grown as a single crystal without a grain boundary, the dislocation density increases, and a crystal having high-quality optical characteristics cannot be manufactured.

  Specifically, if the entire crystal is made into a single crystal during growth by using the crucible descent method, the resulting crystal has small regions slightly inclined with respect to the growth direction as a result of dislocations in the crystal and their regions. The boundary is a subgrain boundary (hereinafter referred to as “sub-boundary”). It is known that stress is concentrated on the subboundary formed by the accumulation of dislocations, resulting in optical degradation. Therefore, there is a demand for a method for producing a high-quality crystal that is required for an exposure optical system while suppressing the occurrence of subboundaries.

  Accordingly, an object of the present invention is to provide a crystal manufacturing method and apparatus that can suppress generation of subboundaries in a crystal and manufacture a crystal having excellent optical characteristics such as internal transmittance.

A crystal manufacturing method according to one aspect of the present invention is a crystal manufacturing method for manufacturing a calcium fluoride crystal in which generation of a subboundary is suppressed from a calcium fluoride raw material stored in a crucible, wherein the crucible is pulled down. a growth step of the molten the raw material to grow a crystal of calcium fluoride with a reduced occurrence of the sub-boundary by, said growth step, generating a grayed rain boundary Te process odor of growing host crystal from the raw material a first step of Ru is, the to expand the grain boundary, and a second step of growing a crystal of calcium fluoride with a reduced occurrence of the sub-boundary from the grain boundary, the in the first step In order to promote the generation of a grain boundary, the crucible is formed on the inner surface of the crucible containing the raw material. A conical portion having a convex conical shape with a conical angle of 70 ° to 110 ° sandwiching 90 ° between them, and in order to promote the expansion of the grain boundary in the second step, It is characterized in that the speed of pulling down the crucible after the generation is slower than before the generation .

The crystal manufacturing apparatus as still another aspect of the present invention includes a support unit for the crucible and a heater for heating the raw material stored in the crucible, and means for executing the above-described crystal manufacturing method. It is characterized by.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  ADVANTAGE OF THE INVENTION According to this invention, the crystal manufacturing method and apparatus which can manufacture the crystal | crystallization excellent in optical characteristics, such as internal transmittance, can be provided.

  Hereinafter, a crystal manufacturing method and apparatus as one aspect of the present invention will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted. In the present embodiment, the production of a calcium fluoride single crystal will be described as an example, but the present invention is not limited to the production of a calcium fluoride single crystal.

  First, in order to deepen the understanding of the crystal manufacturing method and apparatus of the present invention, the influence of grain boundaries on crystal quality will be described. The subboundary generated in the crystal is formed by agglomeration at a location where dislocations are energetically stable. In addition, when the dislocations aggregate to a certain extent, they change to a grain boundary and can move in the crystal.

  The grain boundary that has become movable within the crystal moves within the crystal while sweeping dislocations or subboundaries, and recrystallizes. In the process of recrystallization, the subboundary in the crystal is reduced, and the crystal is changed to a very high quality crystal.

  FIG. 6 is an X-ray topographic image of a cross section of a crystal cut out parallel to the growth direction. The crystal CR grows toward the top of the X-ray topographic image (FIG. 6). Referring to FIG. 6, in the crystal CR, a grain boundary GB is generated during the growth of the mother crystal MCR, and the subsequent region GBE (that is, inside the grain boundary GB) is less sub-boundary. It can be seen that the area has changed to a high quality area. Accordingly, the grain boundary GB is generated at the initial growth stage of the mother crystal MCR to remove the dislocation, and then the region GBE inside the grain boundary GB (in the following description, the region inside the grain boundary (that is, the grain boundary A crystal grown from the boundary) is also referred to as a grain boundary.) By cutting out the single crystal from the above, a high-quality single crystal can be obtained.

  As a result of intensive studies on the occurrence of grain boundaries, the present inventor has found that the shape of the crucible greatly affects the frequency of occurrence of grain boundaries. On the other hand, as a result of examining whether there is a factor related to the generation of grain boundary other than the shape of the crucible, the inventor of the present invention has a great influence on the frequency of occurrence of the grain boundary. I found out. That is, it has been found that if the crucible pulling speed is changed during crystal growth, grain boundaries are likely to occur.

  Hereinafter, the crystal production apparatus and method of the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view showing a configuration of a crystal manufacturing apparatus 100 of the present invention. The crystal manufacturing apparatus 100 melts the raw material ID in the crucible 110 and then cools the raw material ID to grow crystals. As shown in FIG. 1, the crystal manufacturing apparatus 100 includes a crucible 110, a support member 120, a crucible lifting / lowering unit 130, a heater 140, a thermocouple 150, a heat insulating member 160, and a housing 170.

  In the crystal manufacturing apparatus 100, a substantially cylindrical crucible 110 supported by a support member 120 is accommodated in a growth furnace CGF defined by a substantially cylindrical heat insulating member 160 and a casing 170, and the cylindrical surface of the crucible 110 is formed. It is heated by a heater 140 arranged along the periphery. The crystal manufacturing apparatus 100 also includes an exhaust device EM that exhausts the growth furnace CGF to a reduced pressure or vacuum environment.

The crucible 110 stores a raw material ID of a crystalline substance (in this embodiment, calcium fluoride). The crucible 110 melts, retains, and grows the crystalline material raw material ID, so that it does not react with the melt (liquid part) ID _a and has a low impurity content such as carbon, platinum, quartz glass, boron nitride. And the like. In addition, the crucible 110 preferably has a thermal conductivity that is about the same as that of the crystal to be grown, particularly about 1/2 to 2 times. This is because if the thermal conductivity is too high, the longitudinal heat conduction by the crucible 110 increases, and the longitudinal temperature gradient of the single crystal to be grown becomes small. Further, if the thermal conductivity is too small, the temperature distribution created by the heater 140 is not reflected in the raw material ID due to the heat insulating effect, and it becomes difficult to form a predetermined vertical temperature gradient in the single crystal to be grown.

  The crucible 110 has a storage part 114 for storing the seed crystal SC in the lower part 112. The storage portion 114 is formed such that a conical portion 116 described later is connected to the inside of the crucible 110. The crucible 110 is connected to the support member 120 at the lower portion 112 and is installed at the center of the growth reactor CGF.

  The crucible 110 has a conical portion 116 having a convex conical shape at the bottom 112 where crystal growth starts. It is important that the conical portion 116 has a conical shape on the inner surface for storing the raw material ID, and the outer surface shape of the lower portion 112 of the crucible 110 is not necessarily a conical shape as shown in FIG. Absent. The outer surface shape of the lower portion 112 of the crucible 110 may be a shape that does not affect the heat radiation space, such as a cylindrical shape. The conical part 116 has a cone angle AG (cone vertex angle) of 70 to 110 degrees. As a result, a grain boundary is likely to occur in the lower portion 112 of the crucible 110.

  Here, the relationship between the cone angle AG of the conical part 116 of the crucible 110 and the occurrence of the grain boundary will be described. In this embodiment, the conical angle 116 of the conical part 116 is set to 60 degrees, 90 degrees, and 120 degrees, and conditions other than the conical angle AG of the conical part 116, such as temperature control of the growth reactor CGF, the filling amount of the raw material ID, the seed The experiment was conducted under the same conditions for the crystal SC orientation, the crucible 110 pull-down speed, and the like. In the temperature distribution simulation, it has been confirmed that there is no significant difference in the temperature distribution of crystals between the crucibles.

  When the crystal manufactured by the crucible 110 having the conical angle 116 of the conical part 116 of 60 degrees, 90 degrees, and 120 degrees is evaluated, the crystal manufactured by the crucible 110 having the conical angle 116 of the conical part 116 of 60 degrees and 120 degrees is obtained. Grain boundary did not occur at all (2 times for each experiment), whereas all the crystals produced from crucible 110 with conical angle AG of 90 degrees of conical part 116 had grain boundary (number of experiments). 3 times). Accordingly, it can be understood that the grain boundary can be easily generated by setting the conical angle AG of the conical portion 116 to 70 degrees to 110 degrees including 90 degrees.

Further, in order to investigate the relationship between the grain boundaries generated and the crystal orientation of the mother crystal, when classified according to the concept of Coincident Site Lattice (CSL), one of the relationships is Σ11 (Eulerian angle (φ ₁ , Φ, φ ₂ ) = (33.68, 79.53, 33.68)).

  On the other hand, when the preferential growth orientation of calcium fluoride was examined, it was found that in the growth without the seed crystal SC, a crystal orientation close to <0, 1, 1> tends to appear. Therefore, an angle Δθ formed between the normal line of the conical part 116 of the crucible 110 and the preferential growth direction of calcium fluoride in Σ11 (the preferential growth direction is (0.083, 0.600, 0.796)) is calculated. The results are shown in FIG. In FIG. 2, the cone angle AG / 2 of the conical portion 116 is adopted on the horizontal axis, and the angle Δθ is adopted on the vertical axis.

  Referring to FIG. 2, it is considered that the grain boundary is more likely to occur as the angle Δθ is smaller. The calculation is performed every 5 degrees with respect to the conical angle AG of the conical portion 116. In addition, 24 preferential growth directions equivalent to each cone angle AG of the conical portion 116 are plotted. As can be seen from FIG. 2, the angle Δθ is a small value when the cone angle AG of the conical portion 116 of the crucible 110 is in the range of 70 degrees to 110 degrees, as in the experiment described above.

  From the above, it can be concluded that the occurrence frequency of the grain boundary is closely related to the cone angle AG of the conical portion 116 of the crucible 110. In particular, the cone angle AG of the conical portion 116 is 70 degrees to 110 degrees. It was found that the frequency of occurrence was high in the range.

The support member 120 penetrates the bottom of the housing 170, and the top reaches the growth reactor CGF. The support member 120 supports the crucible 110 and the weight of the melt in the crucible 110 and is driven by the crucible lifting / lowering unit 130 to move the crucible 110 up and down. Further, the support member 120 is configured to be able to rotate the crucible 110 by being driven by a rotation mechanism (not shown). The rotation of the crucible 110 by the support member 120 is performed in order to make the temperature of the crucible 110 uniform.

  The crucible lifting / lowering unit 130 includes a motor 132 connected to the support member 120 and a power source 134 that energizes the motor 132. By controlling the energization of the motor 132 by the power supply 134, the crucible 110 can be moved from the heating region of the heater 140 to the non-heating region, and the temperature of the crucible 110 can be gradually lowered.

  Here, the speed at which the crucible lifting / lowering unit 130 pulls down the crucible 110 (that is, the vertical movement speed) will be described. In this embodiment, the crucible lifting / lowering unit 130 has a function of changing the pulling-down speed of the crucible 110 during the crystal growth. The crucible lifting / lowering unit 130 can, for example, change the pulling speed of the crucible 110 steeply from 1 mm / h to 0.25 mm / h during the growth. Thereby, a grain boundary can be generated from a location where the pulling speed of the crucible 110 is changed. Moreover, by pulling down the crucible 110 at a low speed of 0.25 mm / h, the entire crystal can be expanded without reducing the grain boundary. Note that the pulling-down speed of the crucible 110 is preferably 0.5 mm / h or less while the solid-liquid interface SLI of the raw material ID passes through the conical portion 116, and is preferably 1 mm / h or less in other regions. This has been confirmed by the inventors' experiments.

  Note that it is possible to generate a grain boundary by changing the speed at which the crucible 110 is pulled down regardless of the cone angle AG of the conical portion 116 of the crucible 110. This is confirmed by the experiment used.

  The heater 140 is arranged in a ring shape with respect to the cylindrical surface of the crucible 110, heats the raw material ID together with the crucible 110, and melts it. The heater 140 heats the crucible 110 with a uniform heating force along the vertical direction of the crucible 110. In the present embodiment, the heater 140 is made of graphite.

As shown in FIG. 1, the heater 140 includes multiple stages of an upper heater 142 and a lower heater 144, and can accurately control the temperature in the growth furnace CGF. Specifically, the upper heater 142 is suitable for maintaining the temperature of the melt IDa, and the lower heater 144 is suitable for maintaining the grown crystal (solid portion) ID _b . Set to temperature. Further, in the vicinity of the middle between the upper heater 142 and the lower heater 144, the inside of the crucible 110 is adjusted to be the melting point temperature of the raw material ID.

  The thermocouple 150 is disposed on the central outer side surface of the upper heater 142 and the lower heater 144, and detects the temperature of the upper heater 142 and the temperature of the lower heater 144. The temperature distribution of the upper heater 142 and the lower heater 144 is thermally designed to have a substantially uniform temperature distribution in order to control the distribution of the current inside the upper heater 142 and the lower heater 144. It varies in the range.

  The heat insulating member 160 is disposed adjacent to the inner surface of the growth furnace CGF so as to surround the heater 140. The heat insulating member 160 is made of carbon whose inner surface is well polished, and protects the housing 170 from the heat of the heater 140.

  The case 170 blocks the atmosphere in the growth furnace CGF from the outside air during crystal growth, and maintains a reduced pressure or vacuum environment in the growth furnace CGF. In the present embodiment, the housing 170 is configured by arranging a heat insulating material (not shown) in the double cylinder using a stainless steel double cylinder or the like.

Calcium fluoride was manufactured using the crystal manufacturing apparatus 100 shown in FIG. Hereinafter, the crystal manufacturing method 1000 according to one aspect of the present invention will be described together with the operation of the crystal manufacturing apparatus 100. FIG. 3 is a flowchart for explaining the crystal manufacturing method 1000 of the present invention.

In the present embodiment, a graphite crucible 110 having a diameter of 300 mm is prepared, and the conical angle AG of the conical portion 116 is set to 80 degrees. Note that the cone angle AG of the conical portion 116 changes depending on the material and size of the crystal to be grown, and is not limited to the cone angle of the present embodiment. Moreover, as calcium fluoride used for the raw material ID, high purity calcium fluoride powder chemically synthesized by treating CaCO ₃ with hydrofluoric acid instead of raw stone (natural fluorite) was once melted and solidified ( That is, the refined pulverized product is used. This is because high-purity calcium fluoride has a large volume reduction when melted, and the size of crystals obtained with respect to the size of the crucible 110 is remarkably reduced.

  Referring to FIG. 3, first, seed crystal SC having a {1 1 1} plane on the upper surface is stored in storage portion 114 of crucible 110 (step 1002). Next, the crucible 110 is filled with the crushed material ID and scavenger (step 1004). The amount of the scavenger is preferably 0.01 wt% or more and 0.1% or less with respect to the amount of the raw material ID. In this embodiment, a scavenger of 0.01 wt% is attached to the raw material ID.

  Here, the scavenger has a function of reducing calcium oxide (CaO) generated by the presence of water to calcium fluoride to calcium fluoride. As the scavenger, zinc fluoride, cadmium fluoride, manganese fluoride, bismuth fluoride, sodium fluoride, lithium fluoride, and the like that are more easily bonded to oxygen and more easily decomposed and evaporated than the growing fluoride are desirable. . A substance that reacts with the oxide mixed in the fluoride raw material and becomes an easily vaporized oxide is selected, and zinc fluoride is particularly preferable.

Next, the growth furnace CGF is maintained at a vacuum degree of about 10 ⁻³ Pa to 10 ⁻⁴ Pa by operating the exhaust device EM, and the heater 140 is energized to heat the calcium fluoride raw material ID in the crucible 110. Then, the raw material ID filled in the crucible 110 is completely melted (step 1006). Specifically, the temperature of the growth furnace CGF was controlled so that a part of the seed crystal SC and the raw material ID were melted, and the melted state was maintained for 2 days.

After that, the crucible 110 was gradually pulled down (lowered) to cool the molten (dissolved) raw material ID of calcium fluoride, and a single crystal was grown (generated) (step 1008). That is, the crystal grows by further depositing a melt on the surface of the crystal grown near the melting temperature. In the present embodiment, the temperature distribution of the entire growth furnace CGF is fixed, and the pulling-down speed of the crucible 110 is 0.25 mm / h while the solid-liquid interface SLI of the raw material ID passes through the conical part 116, In other areas, the rate was 1 mm / h. That is, a grain boundary is generated in the initial stage of crystal growth, and then the grain boundary is expanded. In other words, the pulling-down speed of the crucible 110 after the grain boundary is generated is slower than the pulling-down speed of the crucible 110 before the grain boundary is generated. The length of the grown calcium fluoride crystal was 100 mm to 300 mm, and it was grown over a period of about 400 hours to 1500 hours.

  Subsequently, the crystal-grown fluoride single crystal is heat-treated in an annealing furnace (annealing step) (step 1010). The annealing step is a step of heat-treating the grown calcium fluoride single crystal to remove strain that causes crystal cracking. The grown single crystal is put in a crucible housed in an annealing furnace. In the annealing step, the crucible is heated to about 1080 ° C. so as to remove the distortion of the calcium fluoride crystal while it remains solid.

  Thereafter, a single crystal is cut out from the grown calcium fluoride crystal (step 1012). It is cut from the grain boundary, not from the grown calcium fluoride mother crystal. FIG. 4 is a diagram showing the crystallinity of a single crystal cut out from the grain boundary of the grown calcium fluoride crystal. Referring to FIG. 4, it can be seen that calcium fluoride having high crystallinity and excellent optical performance is obtained. Note that the single crystal obtained from the crystal manufacturing apparatus 100 has a crystal orientation (for example, (1 1 0)) different from a predetermined crystal orientation (for example, (1 1 1) plane) of the seed crystal SC (mother crystal). However, at the time of cutting, a crystal having a size (for example, a diameter of 300 mm) and an orientation (for example, (1 1 1) plane) necessary for lens design may be obtained. Cutting out in the direction) has no problem in terms of optical characteristics. Even if the orientation of the crystal is different from that of the mother crystal, as described above, if a desired crystal can be cut out from a grain boundary having no sub-boundary where stress is accumulated, a high-quality crystal can be obtained in terms of optical characteristics. Can be obtained.

  As described above, the crystal manufacturing apparatus 100 and the crystal manufacturing method 1000 are configured so that the shape of the crucible 110, specifically, the cone angle AG of the conical portion 116 is set to 70 degrees to 110 degrees, so that the grain boundary is obtained at the initial stage of crystal growth. The grain boundary is enlarged by changing the pulling-down speed of the crucible 110 during growth, and then a single crystal is cut out from the grain boundary to produce a crystal having excellent optical characteristics such as internal transmittance. be able to.

  Hereinafter, a crystal manufacturing apparatus 100A, which is a modification of the crystal manufacturing apparatus 100, will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view showing the configuration of the crystal manufacturing apparatus 100A. The crystal manufacturing apparatus 100A has the same configuration as that of the crystal manufacturing apparatus 100, but further includes a measuring device 180 that measures the moving distance of the crucible 110. The crystal manufacturing apparatus 100 </ b> A can control the pulling speed (moving speed) of the crucible 110 based on the moving distance of the crucible 110 measured by the measuring apparatus 180.

  In this embodiment, the measurement device 180 is attached to the support member 120 and includes a measurement unit 182 and a control unit 184. The measuring unit 182 measures the moving distance of the crucible 110 by monitoring the moving distance of the support member 120.

  The control unit 184 takes in the moving distance of the crucible 110 measured by the measuring unit 182. In addition, the control unit 184 stores in advance a relationship between the position of the solid-liquid interface SLI and the movement distance of the crucible 110 obtained from an experiment or a growth simulation. Thereby, the control part 184 can calculate the position of the solid-liquid interface SLI from the moving distance of the crucible 110, and can control the pulling-down speed of the crucible 110 according to the position of the solid-liquid interface SLI.

  For example, in order to generate the grain boundary at a position 30 mm from the lower end of the conical part 116 of the crucible 110, the control unit 184 is 1 mm / h until the solid-liquid interface SLI passes the position 30 mm from the lower end of the conical part 116. Thereafter, the crucible 110 is controlled to move at a speed of 0.25 mm / h. Thereby, a grain boundary can be generated at the initial stage of growth, and the grain boundary can be expanded. As a result, it becomes possible to secure a crystal size necessary for cutting out a single crystal having a high quality and a large diameter. Note that the speed of the crucible 110 varies depending on the material and size of the crystal to be grown, and is not limited to the speed of the present embodiment.

  By cutting out the single crystal from the grain boundary of the crystal manufactured from the crystal manufacturing apparatus 100A, a high-quality single crystal can be obtained in the same manner as the crystal manufacturing apparatus 100 (crystal manufacturing method 1000).

  As described above, according to the crystal manufacturing apparatuses 100 and 100A and the crystal manufacturing method 1000 of the present invention, the grain boundary is positively generated in the initial stage of growth, thereby suppressing the subboundary in the crystal, Crystals having excellent quality such as transmittance and laser durability can be produced with good reproducibility.

  The calcium fluoride crystals obtained by the crystal manufacturing apparatuses 100 and 100A and the crystal manufacturing method 1000 of the present invention are formed on the required optical elements. Optical elements include lenses, diffractive elements, optical film bodies and their composites, such as lenses, multi-lenses, lens arrays, lenticular lenses, fly-eye lenses, aspherical lenses, diffraction gratings, binary optics elements and their Includes complex. The optical element includes an optical sensor (for example, for focus control) in addition to a single lens. If necessary, an antireflection film may be provided on the surface of the optical component of calcium fluoride crystal. As the antireflection film, magnesium fluoride, aluminum oxide, or tantalum oxide is preferably used, and these can be formed by vapor deposition by resistance heating, electron beam vapor deposition, sputtering, or the like. Since the optical element obtained by the present invention is excellent in quality such as internal transmittance and laser durability, the optical performance is improved as compared with the conventional optical element.

If the optical elements of the present invention are combined in various ways, a projection optical system and illumination optical system suitable for ArF excimer laser and F ₂ laser can be configured. Then, various laser light sources, an optical system having a lens made of calcium fluoride obtained from the crystal manufacturing apparatuses 100 and 100A and the crystal manufacturing method 1000 of the present invention, and a stage capable of moving the wafer are combined for photolithography. The exposure apparatus can be configured.

  Hereinafter, an exemplary exposure apparatus 500 of the present invention will be described with reference to FIG. Here, FIG. 7 is a schematic block diagram showing the configuration of the exposure apparatus 500 of the present invention. As shown in FIG. 7, the exposure apparatus 500 includes an illumination apparatus 510 that illuminates a reticle 520 on which a circuit pattern is formed, a projection optical system 530 that projects diffracted light generated from the illuminated reticle pattern onto a plate 540, and a plate And a stage 545 for supporting 540.

  The exposure apparatus 500 is a projection exposure apparatus that exposes a plate 540 with a circuit pattern formed on the reticle 520 by, for example, a step-and-scan method or a step-and-repeat method. Such an exposure apparatus is suitable for a lithography process of sub-micron or quarter micron or less, and in the present embodiment, a step-and-scan type exposure apparatus (also referred to as “scanner”) will be described as an example. Here, the “step and scan method” means that the wafer is continuously scanned (scanned) with respect to the reticle to expose the reticle pattern onto the wafer, and the wafer is stepped after completion of one shot of exposure. The exposure method moves to the next exposure area. The “step-and-repeat method” is an exposure method in which the wafer is stepped and moved to the exposure area of the next shot for every batch exposure of the wafer.

  The illumination device 510 illuminates a reticle 520 on which a transfer circuit pattern is formed, and includes a light source unit 512 and an illumination optical system 514.

As the light source unit 512, for example, an ArF excimer laser having a wavelength of about 193 nm, a KrF excimer laser having a wavelength of about 248 nm, or the like can be used as the light source. However, the type of the light source is not limited to the excimer laser. A 153 nm F ₂ laser or a YAG laser may be used, and the light source and the number thereof are not limited. For example, if two solid-state lasers that operate independently are used, there is no mutual coherence between the solid-state lasers, and speckle caused by the coherence is considerably reduced. Further, the optical system may be swung linearly or rotationally to reduce speckle. When a laser is used for the light source unit 512, a light beam shaping optical system that shapes a parallel light beam from the laser light source into a desired beam shape and an incoherent optical system that makes a coherent laser light beam incoherent are used. Is preferred. The light source that can be used for the light source unit 512 is not limited to the laser, and one or a plurality of lamps such as a mercury lamp and a xenon lamp can be used.

  The illumination optical system 514 is an optical system that illuminates the reticle 520, and includes a lens, a mirror, an optical integrator, a stop, and the like. For example, a condenser lens, a fly-eye lens, an aperture stop, a condenser lens, a slit, and an imaging optical system are arranged in this order. The illumination optical system 514 can be used regardless of on-axis light or off-axis light. The optical integrator includes an integrator configured by stacking a fly-eye lens and two sets of cylindrical lens array (or lenticular lens) plates, and may be replaced with an optical rod or a diffractive element. An optical element manufactured from the calcium fluoride crystal of the present invention can be used as an optical element such as a lens of the illumination optical system 514.

  The reticle 520 is made of, for example, quartz, on which a circuit pattern (or image) to be transferred is formed, and is supported and driven by a reticle stage (not shown). Diffracted light emitted from the reticle 520 passes through the projection optical system 530 and is projected onto the plate 540. The reticle 520 and the plate 540 are optically conjugate. Since the exposure apparatus 500 of this embodiment is a scanner, the pattern of the reticle 520 is transferred onto the plate 540 by scanning the reticle 520 and the plate 540 at a speed ratio of the reduction magnification ratio. In the case of a step-and-repeat type exposure apparatus (also referred to as a “stepper”), exposure is performed with the reticle 520 and the plate 540 being stationary.

  The projection optical system 530 is an optical system that projects light that reflects a pattern on the reticle 520 that is the object plane onto the plate 540 that is the image plane. The projection optical system 530 includes an optical system composed only of a plurality of lens elements, an optical system (catadioptric optical system) having a plurality of lens elements and at least one concave mirror, a plurality of lens elements, and at least one kinoform. An optical system having a diffractive optical element such as an all-mirror optical system can be used. When correction of chromatic aberration is required, a plurality of lens elements made of glass materials having different dispersion values (Abbe values) can be used, or the diffractive optical element can be configured to generate dispersion in the opposite direction to the lens element. To do. An optical element manufactured from the calcium fluoride crystal of the present invention can be used as an optical element such as a lens of the projection optical system 530.

  The plate 540 is a wafer in this embodiment, but widely includes a liquid crystal substrate and other objects to be processed. The plate 540 is coated with a photoresist. The photoresist coating process includes a pretreatment, an adhesion improver coating process, a photoresist coating process, and a prebaking process. Pretreatment includes washing, drying and the like. The adhesion improver coating process is a surface modification process for improving the adhesion between the photoresist and the base (that is, a hydrophobic process by application of a surfactant), and an organic film such as HMDS (Hexmethyl-disilazane) is used. Coat or steam. Pre-baking is a baking (baking) step, but is softer than that after development, and removes the solvent.

  The stage 545 supports the plate 540. Since any structure known in the art can be applied to the stage 545, detailed description of the structure and operation is omitted here. For example, the stage 545 can move the plate 540 in the XY directions using a linear motor. For example, the reticle 520 and the plate 540 are synchronously scanned, and the positions of the stage 545 and the reticle stage (not shown) are monitored by, for example, a laser interferometer, and both are driven at a constant speed ratio. The stage 545 is provided on a stage surface plate supported on a floor or the like via a damper, for example, and the reticle stage and the projection optical system 530 have a damper on a base frame placed on the floor or the like, for example. It is provided on a lens barrel surface plate (not shown) that is supported via the cable.

In exposure, a light beam (exposure light) emitted from the light source unit 514 illuminates the reticle 520 with, for example, Koehler illumination by the illumination optical system 514. Light that passes through the reticle 520 and reflects the reticle pattern is imaged on the plate 540 by the projection optical system 530. The illumination optical system 514 and the projection optical system 530 used by the exposure apparatus 500 include an optical element manufactured from calcium fluoride according to the present invention, and transmit ultraviolet light, far ultraviolet light, and vacuum ultraviolet light with high transmittance. Therefore, it is possible to provide a device (semiconductor element, LCD element, imaging element (CCD, etc.), thin film magnetic head, etc.) with high throughput and high economic efficiency.

  Next, an embodiment of a device manufacturing method using the above-described exposure apparatus 500 will be described with reference to FIGS. FIG. 8 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by the lithography technique of the present invention using the mask and the wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4. The assembly process (dicing, bonding), packaging process (chip encapsulation), and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 9 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 500 to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer. According to this device manufacturing method, it is possible to manufacture a higher quality device than before. Thus, the device manufacturing method using the exposure apparatus 500 and the resulting device also constitute one aspect of the present invention.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the method of cooling the melted raw material may be any method other than the Bridgeman method, such as a method of pulling up the heater while fixing the crucible, a method of gradually decreasing the heater output, or any other known method.

It is a schematic sectional drawing which shows the structure of the crystal manufacturing apparatus as one side surface of this invention. It is a graph which shows the relationship between the priority growth direction with respect to the conical part of a crucible, and the angle which a conical part makes. It is a flowchart for demonstrating the crystal manufacturing method as 1 side surface of this invention. It is a figure which shows the crystallinity of the single crystal cut out from the grain boundary of the grown calcium fluoride crystal. It is a schematic sectional drawing which shows the structure of the crystal manufacturing apparatus which is a modification of the crystal manufacturing apparatus shown in FIG. It is a figure which shows the crystallinity of the grain boundary which generate | occur | produced in the crystal | crystallization, and a mother crystal. It is a schematic block diagram which shows the structure of the exposure apparatus as 1 side surface of this invention. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 9 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 8.

Explanation of symbols

100 and 100A Crystal manufacturing apparatus 110 Crucible 112 Lower crucible 114 Storage section 116 Conical section 120 Support member 130 Crucible lifting section 140 Heater 142 Upper heater 144 Lower heater 150 Thermocouple 160 Heat insulation member 170 Housing 180 Measuring apparatus 182 Measuring section 184 Control Part ID Raw material SC Seed crystal CGF Growth furnace EM Exhaust device 500 Exposure device 510 Illumination device 514 Illumination optical system 530 Projection optical system

Claims (3)

A crystal production method for producing a calcium fluoride crystal in which generation of subboundaries is suppressed from a raw material of calcium fluoride stored in a crucible,
A growth step of growing a calcium fluoride crystal that suppresses generation of the subboundary from the raw material melted by pulling down the crucible;
The growth step includes a first step of generating a grain boundary in the process of growing a mother crystal from the raw material;
Expanding the grain boundary, and growing a calcium fluoride crystal that suppresses the occurrence of the subboundary from the grain boundary;
In order to promote the generation of the grain boundary in the first step, the crucible has a downwardly convex shape with a cone angle of 70 degrees to 110 degrees sandwiching 90 degrees at the lower part of the inner surface of the crucible containing the raw material. Having a conical conical part,
In order to promote the expansion of the grain boundary in the second step, the crystal manufacturing method is characterized by slowing down the crucible after the generation of the grain boundary rather than before the generation of the grain boundary.   2. The crystal according to claim 1, further comprising a step of cutting a crystal having a desired crystal orientation from a calcium fluoride crystal that suppresses the generation of the subboundary grown from the grain boundary in the second step. Production method.   A crystal manufacturing apparatus, comprising: a support unit for the crucible; and a heater for heating the raw material stored in the crucible, and means for executing the crystal manufacturing method according to claim 1.