JP2006016259A - Method for manufacturing crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a crystal, by which the crystal having excellent optical characteristics such as internal transmittance can be manufactured with satisfactory reproducibility. <P>SOLUTION: The method for manufacturing the crystal from a crystalline substance is characterized by including a step for detecting the concentrations of impurities contained in a seed crystal being a base point for growing a single crystal, a step for receiving the seed crystal in which the concentrations of the impurities, detected in the detection step, are lower than those of the impurities contained in a raw material in a crucible, and a step for growing the single crystal through the seed crystal received in the crucible in the receiving step. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention generally relates to a crystal manufacturing method, and in particular, a calcium fluoride (CaF ₂ ) crystal suitable for various optical elements, lenses, 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.

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 is going from an 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 homogeneity (homogenity), birefringence, polishing (or processing) accuracy, and the like, and high quality is required for calcium fluoride crystals used in an exposure apparatus.

  Calcium fluoride single crystals are conventionally produced by the Bridgman method (also known as the “crucible descent method”). 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. At this time, by arranging a seed crystal having a plane orientation to be grown and serving as a starting point of growth at the lower part of the crucible, crystallization is prevented from starting from a plurality of positions in the crucible in the initial stage of growth. can do.

In addition, a manufacturing process for several months is required to manufacture a crystal having a large diameter (for example, a diameter of 200 mm or more) as required in recent years. In order to produce high-quality crystals efficiently in such a long-term process, it is essential to select crystals by sufficient crystal analysis, and in particular, analysis of impurities is important (see, for example, Patent Document 1). ).
JP 2001-72495 A

  However, conventional crystal manufacturing apparatuses and methods using seed crystals and crystal analysis have not been able to manufacture crystals having high-quality optical characteristics. For example, in a crystal manufacturing apparatus and method using a seed crystal, poor connection between the seed crystal and the grown crystal and polycrystallization, boundary, subboundary, etc. frequently occur from the connection surface with the seed crystal. These causes are caused by a steep impurity concentration gradient at the interface between the seed crystal and the grown crystal due to the segregation effect of the grown crystal during crystal growth when there are more impurities in the seed crystal, especially alkaline earth metals than the raw material. It is for producing. In addition, the seed crystal has an arbitrary crystal plane on the extreme surface. However, in actual crystal growth, a part of the seed crystal is melted, and the crystal orientation is continuously transferred from the interface as a base point. May cause crystal plane imperfections at the melting position.

  In addition, in the crystal manufacturing apparatus and method using crystal analysis, it is not sufficient to analyze impurities only in order to grow a high-quality crystal, and analysis with respect to crystal plane variations is extremely important. For example, in the growth of a large-diameter crystal, polycrystallization, boundary, subboundary, etc. frequently occur. Boundaries and the like can be easily confirmed using a birefringence meter or the like, but the sub-boundaries cannot be sufficiently observed. Then, the extreme concentration of the sub-bundle causes a polishing defect in the polishing process after the annealing process. Therefore, it is extremely important to properly grasp the crystal plane state of the crystal before annealing.

  Accordingly, an object of the present invention is to provide a crystal manufacturing method capable of manufacturing a crystal having excellent optical characteristics such as internal transmittance with good reproducibility.

  In order to achieve the above object, a crystal manufacturing method according to one aspect of the present invention is a crystal manufacturing method for growing a single crystal from a raw material of a crystalline substance, wherein the seed crystal serving as a starting point for the growth of the single crystal A step of detecting a concentration of impurities contained therein, a step of storing the seed crystal in the crucible in which the concentration of the impurity detected in the detection step is equal to or lower than the concentration of the impurity of the raw material; And growing the single crystal through the seed crystal stored in a crucible.

  According to another aspect of the present invention, there is provided a crystal manufacturing method comprising: a step of growing a single crystal of the raw material by melting and then solidifying the raw material of the crystalline substance; and the crystal of the single crystal grown in the growth step A step of measuring variation in plane orientation, a step of selecting the single crystal whose variation in crystal plane orientation measured in the measurement step is within a predetermined range, and heat-treating the single crystal selected in the selection step And a step of performing.

  The crystal manufacturing method according to still another aspect of the present invention includes a step of growing a single crystal from a raw material of a crystalline substance through a seed crystal, and a step of heat-treating the single crystal grown in the growth step. The seed crystal used in the growth step has an impurity concentration equal to or less than the impurity concentration of the raw material, and the single crystal heat-treated in the heat treatment step has a crystal plane orientation distribution of 2 degrees or less on the surface. It is characterized by being.

  An optical element according to still another aspect of the present invention is manufactured from a single crystal manufactured from the above-described crystal manufacturing method.

  An exposure apparatus according to still another aspect of the present invention uses ultraviolet light, far ultraviolet light, and vacuum ultraviolet light as exposure light, and applies the exposure light to an object to be processed through an optical system including the above-described optical element. Irradiation is performed to expose the object to be processed.

  According to still another aspect of the present invention, there is provided a device manufacturing method comprising: exposing a target object using the above-described exposure apparatus; and developing the exposed target object.

  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 which can manufacture the crystal | crystallization excellent in optical characteristics, such as internal transmittance, with sufficient reproducibility can be provided.

  Hereinafter, a crystal manufacturing method 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. FIG. 1 is a flowchart for explaining a crystal manufacturing method 1000 of the present invention. In the present embodiment, the crystal production method 1000 will be described taking the production of a calcium fluoride single crystal as an example, but the present invention is not limited to the production of a calcium fluoride single crystal.

First, a synthetic raw material of high purity calcium fluoride is prepared as a raw material. A synthetic raw material of high-purity calcium fluoride is produced by reacting calcium carbonate (CaCO ₃ ) and hydrofluoric acid (HF) as shown in the following chemical formula 1. Although the present invention does not exclude a method of removing impurities (for example, SiO ₂ ) by treating calcium fluoride with hydrogen fluoride, high-purity calcium fluoride is powdered and bulky unlike raw stone. This is preferable because the density is very small (about 10 μm to about 20 μm).

  The calcium fluoride synthesized by the above reaction is preferably dried and then baked to remove moisture. Further, it is desirable that the calcium fluoride raw material obtained by the above reaction is vacuum packed so as not to be exposed to the atmosphere as much as possible in order to prevent moisture absorption.

  Next, the calcium fluoride raw material and the scavenger are mixed (step 1100). When mixing the calcium fluoride raw material and the scavenger, it is preferable to place the calcium fluoride raw material and the scavenger in a mixing container and rotate to ensure uniform mixing.

  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.

For example, zinc fluoride (ZnF ₂₎ scavenger, the following calcium oxide that occurred for CaF2 as shown in Formula 2 by the presence of moisture (CaO), as shown in the following chemical formula 3, the reduction in CaF ₂ To do.

  The more moisture, the more scavengers are required, and the unused scavenger residue becomes an impurity to the calcium fluoride crystals. For this reason, it is preferable to reduce the amount of moisture and scavenger. When the amount of the scavenger added is large, the refractive index homogeneity is reduced due to the residual amount of the scavenger, and the internal transmittance and the laser durability are lowered.

  The thus obtained mixture of calcium fluoride powder and scavenger is subjected to a purification treatment (step 1200). The purification process is a process for removing impurities (for example, carbonic acid) to make calcium fluoride highly purified, and includes dehydration, scavenging reaction, scavenger product removal, melting and solidification. In the refining process, the mixture is placed in a crucible of a refining furnace.

  Thereafter, the heater is energized to heat the mixture in the crucible and perform dehydration. In this way, dehydration is also performed during the purification process of step 1200. The purification furnace is evacuated to a vacuum by a vacuum evacuation system at a temperature at which the reaction is completed, and then the calcium fluoride raw material is completely melted. Subsequently, the crucible is lowered to remove the molten calcium fluoride material to grow crystals.

  The purpose of the refining process is to increase the bulk density and does not require temperature control as much as the single crystal growth process (step 1300) described later. Therefore, the resulting crystal may be polycrystalline or have grain boundaries. The upper part of the crystal thus obtained, that is, the last crystallized part with time is removed. Since this portion is a portion where impurities easily collect (that is, segregation), removing this portion removes impurities that adversely affect the optical characteristics. Again, this crystal is put in a crucible, and a series of steps of melting, crystallization, and top removal is repeated a plurality of times. The purified crystal (raw material) is put in a crucible of a crystal growth apparatus described later with reference to FIG.

  Next, the purified crystal of calcium fluoride is subjected to a single crystal growth process (crystal growth process) (step 1300). The crystal growth step is a step of growing a single crystal of calcium fluoride to improve the quality of the crystal (that is, adjusting the lattice arrangement).

  In the crystal growth process, it is known to use a seed crystal as a starting point of crystal growth, but it is difficult to simply use a seed crystal processed with an arbitrary crystal plane (that is, the crystal plane to be grown) as the surface. Quality crystals cannot be obtained. Therefore, in this embodiment, as shown in FIG. 2, seed crystals are selected. Referring to FIG. 2, first, the concentration of impurities contained in the seed crystal is detected (step 1310). The impurity to be detected is preferably an alkaline earth metal that is considered to have the most adverse effect when growing high-quality crystals. These impurities can be quantitatively detected by using inductively coupled high-frequency plasma spectroscopic mass spectrometry (ICP-MS). Here, FIG. 2 is a detailed flowchart of the crystal growth process of Step 1300.

  Next, it is determined whether or not the concentration of the seed crystal impurity detected in step 1310 is equal to or lower than the concentration of the purified calcium fluoride raw material impurity (step 1320). However, since the concentration of impurities in the calcium fluoride raw material may be high, for example, a seed crystal in which the concentration of strontium, which is at least one of the alkaline earth metals, is 300 ppm or less may be targeted. If the impurity concentration of the seed crystal is higher than the impurity concentration of the raw material, the process returns to step 1310 to detect the impurity concentration of another seed crystal.

  On the other hand, if the impurity concentration of the seed crystal is equal to or lower than the impurity concentration of the raw material, the variation in crystal plane orientation on the surface of the seed crystal is further measured (step 1330). For the measurement of the crystal plane orientation of the seed crystal, a diffraction phenomenon in the crystal plane of X-rays with respect to the surface and cross-sectional direction of the seed crystal is used. For example, there are a Laue method and an X-ray topography using a Laue measuring device having a two-dimensional detector such as an imaging plate.

  Next, it is determined whether or not the variation in crystal plane orientation of the seed crystal measured in step 1330 is within an allowable range (step 1340). Here, the allowable range depends on the quality required for the single crystal to be grown. For example, when a single crystal of calcium fluoride used for an optical element of an exposure apparatus is grown, the crystal plane of the seed crystal The variation in orientation is preferably set within 0.1 degree. This is because when the crystal plane orientation variation is large, distribution occurs in birefringence and refractive index. If the variation in crystal plane orientation of the seed crystal is outside the allowable range, the process returns to step 1310 and the process is repeated from the detection of the impurity concentration of another seed crystal.

  If the variation in crystal plane orientation of the seed crystal is within an allowable range, the seed crystal is stored in the lower part of the crucible (step 1350), a part of the seed crystal is melted, and a single crystal is grown through the seed crystal. Do. Specifically, the calcium fluoride raw material in the crucible is heated to about 1390 ° C. to about 1450 ° C. to completely melt the raw material. Thereafter, the crucible is gradually lowered (for example, 0.1 mm / h to 5.0 mm / h), and the molten calcium fluoride raw material is cooled to grow a single crystal based on the seed crystal. During the growth of the single crystal, the crystal plane orientation at the melting position of the seed crystal is maintained at 2 degrees or less with respect to the crystal plane orientation on the surface of the seed crystal. Further, it is preferable that the single crystal to be grown is grown so that the crystal plane orientation is 2 degrees or less with respect to the crystal plane orientation at the position connected to the seed crystal. By realizing a good connection with the seed crystal, the plane orientation at the melting position is transferred, and thereafter, the crystal grows stably, so that it can be within the specified range with respect to the plane orientation at the seed connection position. As a result, a crystal with good optical properties and high integrity can be obtained.

  As described above, in this embodiment, the seed crystal having a lower concentration of impurities (for example, alkaline earth metal) than the calcium fluoride raw material is selected, and an arbitrary crystal plane of the seed crystal (ie, The surface on which the single crystal is to be grown is kept at the melting position of the seed crystal. This prevents a steep impurity concentration gradient at the interface between the seed crystal and the single crystal to be grown and imperfection of the crystal plane at the melting position of the seed crystal, resulting in poor connection between the seed crystal and the growing single crystal. It is possible to suppress the occurrence of polycrystallization, boundary, subboundary, etc. from the connection surface with the seed crystal.

  Subsequently, the surface of the grown calcium fluoride single crystal is ground to remove excess deposits, and the crystal plane distribution (crystal surface orientation variation) of the grown single crystal is measured (step 1400). . In this embodiment, the crystal plane distribution is measured as shown in FIG. FIG. 3 is a detailed flowchart of the crystal plane distribution measurement in step 1400.

  Referring to FIG. 3, first, a single crystal grown on a sample stage is fixed, and the crystal plane orientation at an arbitrary point of the single crystal is measured using, for example, a Laue measurement device (step 1410). Next, an arbitrary crystal plane suitable for X-ray topography is selected based on the crystal plane orientation measured in step 1410, and the crystal plane distribution of the entire surface of the single crystal is measured by X-ray topography with respect to such crystal plane. (Step 1420).

  If there is a portion in which the crystal plane orientation clearly differs from the X-ray topograph in the grown single crystal, the crystal plane orientation of the portion is measured again, and the deviation of the crystal plane orientation is quantified (step 1430). By performing steps 1410 to 1430 on the top surface and the bottom surface with respect to the growth direction of the single crystal, the variation in crystal plane orientation of the grown single crystal can be found.

  Then, a single crystal having a crystal plane distribution within a predetermined range is selected (step 1440), and heat treatment (annealing process) is performed in an annealing furnace (step 1500). Here, the predetermined range depends on the quality required for the single crystal to be grown. For example, when a single crystal of calcium fluoride used for an optical element of an exposure apparatus is grown, the crystal plane distribution is 2 It is preferable to set within a degree. However, it is needless to say that the crystal plane distribution of the entire single crystal need not be 2 degrees or less, and the crystal plane distribution on the surface of the portion used as the optical element may be 2 degrees or less.

  As described above, in this embodiment, the crystal plane state of the grown single crystal is measured before the annealing process, and the single crystal delivered to the annealing process is selected, thereby preventing polishing defects in the polishing process after the annealing process. can do.

  The annealing step is a step of heat-treating the grown calcium fluoride single crystal to remove strain that causes crystal cracking. Specifically, in the annealing step, the crucible of the annealing furnace is heated uniformly to about 900 ° C. to about 1300 ° C. to remove the strain of the calcium fluoride single crystal while remaining solid. A heating temperature of about 1140 ° C. or higher is not preferable because it causes structural changes and the like. The heating time is about 20 hours or more, more preferably about 20 hours to about 30 hours. In the annealing step, crystal dislocations are reduced through annealing. And the temperature of a calcium-fluoride single crystal is returned to room temperature, maintaining the state from which distortion was lost.

  Thereafter, a calcium fluoride single crystal is formed on the required optical element (step 1600). 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. An exposure apparatus for photolithography is configured by combining various laser light sources, an optical system having a lens made of calcium fluoride obtained from the crystal manufacturing method 1000 of the present invention, and a stage capable of moving the wafer. Can do.

  As described above, according to the crystal manufacturing method 1000 of the present invention, by selecting the seed crystal and the grown single crystal, a crystal having excellent quality such as internal transmittance and laser durability is reproducible. Can be manufactured well.

  FIG. 4 is a schematic cross-sectional view showing the configuration of the crystal manufacturing apparatus 100 used in step 1300 described above. The crystal manufacturing apparatus 100 melts the raw material ID of calcium fluoride in the crucible 110, and then cools the raw material ID to grow crystals. As shown in FIG. 4, the crystal manufacturing apparatus 100 includes a crucible 110, a support member 120, a heater 130, a heat insulating member 140, a housing 150, and a control unit 160.

  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 casing 150 and a heat insulating member 140, and the cylindrical surface of the crucible 110 and Heated by a heater 130 disposed along the upper surface. In addition, the crystal manufacturing apparatus 100 includes an exhaust device (not shown) that maintains the growth furnace CGF in 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 is made of a material that does not react with the melt and has a low impurity content, for example, carbon, platinum, quartz glass, boron nitride, etc., in order to melt, hold, and grow the crystal material ID. It is preferable. The material of the crucible 110 is preferably about the same as the thermal conductivity 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 is not reflected in the raw material 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 portion 112 for storing the seed crystal SC on the bottom surface. The storage portion 112 is formed such that a taper portion (not shown) is continuous with the inside of the crucible 110. The taper portion increases as the growth region from the seed crystal SC installed in the storage portion 112 grows. The crystal plane orientation to be grown can be controlled by arranging the seed crystal SC in the storage portion 112 with an orientation in an arbitrary direction. The crucible 110 is connected to the support member 120 in the storage portion 112 on the bottom surface and is arranged at the center of the growth reactor CGF.

  The support member 120 penetrates the bottom of the casing 150 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 has a crucible lifting / lowering mechanism (not shown). The crucible elevating mechanism is composed of, for example, a motor connected to the support member 120, a power source for energizing the motor, and a control mechanism for controlling the power source, and the control mechanism controls energization by the power source to support the motor. The temperature of the crucible 110 can be gradually lowered by moving the crucible 110 from the heating region of the heater 130 to the non-heating region via the member 120. Further, the support member 120 may have a rotation mechanism (not shown) so that the crucible 110 can be rotated via the rotation mechanism. 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 heater 130 is arranged in a ring shape with respect to the cylindrical surface of the crucible 110 and covers the upper surface of the crucible 110, and heats the raw material ID together with the crucible 110 to melt it. The heater 130 of the present embodiment heats the crucible 110 with a uniform heating force along the vertical direction of the crucible 110. In addition, the temperature in the growth furnace CGF can be precisely controlled by providing the heater 130 with a multi-stage configuration.

  The heat insulating member 140 is disposed adjacent to the inner surface of the growth furnace CGF so as to surround the heater 130. The heat insulating member 140 is made of carbon whose inner surface is well polished, and protects the inner surface of the housing 150 from the heat of the heater 130.

  The case 150 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. The housing 150 is configured by arranging a heat insulating material (not shown) in the double cylinder using, for example, a stainless steel double cylinder.

  The control unit 160 controls the operation of each unit of the crystal manufacturing apparatus 100. In this embodiment, the control unit 160 maintains the crystal plane orientation at the melting position of the seed crystal SC at 2 degrees or less with respect to the crystal plane orientation on the surface of the seed crystal SC, and the crystal plane orientation of the single crystal is The crystal growth is controlled so as to be 2 degrees or less with respect to the crystal plane orientation at the position connected to the seed crystal SC. Specifically, crystal growth is controlled by reducing the temperature gradient at the time of connecting the seed crystal and controlling the crucible pulling speed at 1 mm / h or less.

  First, high-purity calcium fluoride serving as a raw material ID was generated. After calcium carbonate and hydrofluoric acid were reacted to form powdered calcium fluoride, scavenger zinc fluoride was added to the calcium fluoride and mixed until both were uniform. Next, this mixture was placed in a crucible of a refining furnace, heated, and then cooled to obtain high-purity calcium fluoride serving as a raw material ID.

  Next, the raw material ID was stored in the crucible 110 of the crystal manufacturing apparatus 100 shown in FIG. On the other hand, the seed crystal SC stored in the storage unit 112 of the crucible 110 has an impurity concentration lower than that of the raw material ID, and the crystal surface falls within one degree from the (1 1 1) plane by the Laue method and X-ray topography. A seed crystal having a crystal plane orientation distribution within 0.1 degree is used. Furthermore, the crystal plane orientation distribution of the cross section of the seed crystal SC was measured, and a seed crystal having the same crystal plane orientation at least 20 mm from the surface was used.

  Next, the growth furnace CGF was brought into a vacuum atmosphere by an exhaust device (not shown), and the temperature of the growth furnace CGF was raised from room temperature to the melting point of calcium fluoride or more by the heater 130 to melt the raw material ID. Then, the crucible 110 was gradually lowered, and a calcium fluoride single crystal was grown using the seed crystal SC as a base point. When the grown calcium fluoride was observed by the Laue method and X-ray topography, good bonding between the seed crystal SC and the grown crystal (calcium fluoride single crystal) was confirmed.

  Next, the crystal plane distribution of the grown calcium fluoride single crystal was measured, and a calcium fluoride single crystal having a crystal plane distribution of 2 degrees or less was placed in a crucible of an annealing furnace. Then, the annealing furnace was evacuated and the temperature of the crucible was raised to 1100 ° C. and held for 50 hours. Thereafter, the temperature was gradually lowered and cooled to room temperature. The calcium fluoride single crystal thus obtained was polished to form an optical element. As a result, an optical element having desired optical characteristics could be produced without causing polishing defects.

  Hereinafter, an exemplary exposure apparatus 500 of the present invention will be described with reference to FIG. Here, FIG. 5 is a schematic block diagram showing the configuration of the exposure apparatus 500 of the present invention. As shown in FIG. 5, 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 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 the exposure, the light beam 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. 6 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. 7 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 flowchart for demonstrating the crystal manufacturing method as 1 side surface of this invention. It is a detailed flowchart of the crystal growth process of step 1300 shown in FIG. It is a detailed flowchart of the crystal plane distribution measurement of step 1400 shown in FIG. It is a schematic sectional drawing which shows the structure of the crystal manufacturing apparatus used by step 1300 shown in FIG. 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.). 7 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Crystal manufacturing apparatus 110 Crucible 120 Support member 130 Heater 140 Heat insulation member 150 Case 160 Control part SGF Growth furnace ID Raw material SC Seed crystal 500 Exposure apparatus 510 Illumination apparatus 514 Illumination optical system 530 Projection optical system

Claims (15)

A crystal manufacturing method for growing a single crystal from a raw material of a crystalline substance,
Detecting a concentration of impurities contained in a seed crystal serving as a base point for growth of the single crystal;
Storing the seed crystal in which the concentration of the impurity detected in the detection step is equal to or less than the concentration of the impurity of the raw material in the crucible;
And a step of growing the single crystal through the seed crystal housed in the crucible in the housing step.   The crystal manufacturing method according to claim 1, wherein the impurity is an alkaline earth metal. Measuring a variation in crystal plane orientation on the surface of the seed crystal;
2. The crystal manufacturing method according to claim 1, wherein the storing step stores the seed crystal whose variation in crystal plane orientation measured in the measuring step is within 0.1 degrees.   4. The crystal manufacturing method according to claim 3, wherein the measuring step uses Laue method or X-ray topography.   4. The crystal manufacturing method according to claim 3, wherein the growth step maintains the crystal plane orientation of the melting position of the seed crystal at 2 degrees or less with respect to the crystal plane orientation on the surface of the seed crystal. .   4. The crystal manufacturing method according to claim 3, wherein in the growth step, the single crystal is grown so that a crystal plane orientation thereof is 2 degrees or less with respect to a crystal plane orientation at a position connected to the seed crystal. . Growing a single crystal of the raw material by melting the raw material of the crystalline substance and then solidifying;
Measuring a variation in crystal plane orientation of the single crystal grown in the growth step;
A variation of the crystal plane orientation measured in the measuring step, the step of selecting the single crystal within a predetermined range;
And a step of heat-treating the single crystal selected in the selection step.   8. The crystal manufacturing method according to claim 7, wherein the selecting step selects the single crystal having a crystal plane orientation distribution of 2 degrees or less on the surface.   The crystal manufacturing method according to claim 7, wherein the measuring step uses an X-ray diffraction phenomenon on a crystal plane of the single crystal. Growing a single crystal from a raw material of a crystalline material through a seed crystal;
Heat-treating the single crystal grown in the growth step,
The seed crystal used in the growth step has an impurity concentration equal to or lower than the impurity concentration of the raw material,
The crystal manufacturing method, wherein the single crystal heat-treated in the heat treatment step has a surface crystal plane orientation distribution of 2 degrees or less.   The crystal production method according to claim 1, wherein the raw material is calcium fluoride.   An optical element manufactured from a single crystal manufactured from the crystal manufacturing method according to claim 1.   13. The optical element according to claim 12, wherein the optical element is one of a lens, a diffraction grating, an optical film body, and a composite thereof.   Using ultraviolet light, far ultraviolet light, and vacuum ultraviolet light as exposure light, irradiating the object to be processed through the optical system including the optical element according to claim 11 or 12 to irradiate the object to be processed An exposure apparatus for performing exposure. Exposing a workpiece using the exposure apparatus according to claim 14;
And developing the exposed object to be processed.