JP2006052095A - Fluoride single crystal, its manufacturing method, aligner, and method for manufacturing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluoride single crystal which is excellent in optical characteristics such as refractive index uniformity, thereby it is free from the problem of the occurrence of a flare; and to provide a method for manufacturing the same. <P>SOLUTION: The fluoride single crystal having a plurality of subgrains partitioned by subboundaries, wherein the relative inclination angle of the crystal face orientation of the adjacent subgrain is ≤0.02° and the maximum inclination angle of the crystal face orientation of the subgrain is within 0.2°, is used for an optical element material. The residual RMS value, obtained by analyzing the in-plane distribution of the refractive index uniformity with the Zernike polynomial approximation and subtracting 1-36 term components, is ≤20 ppb. The method for manufacturing the fluoride single crystal, comprising manufacturing the single crystal from a raw material of a crystalline substance accommodated in a crucible, is characterized by including a step for forming a temperature gradient of ≤10°C/cm, a step for growing the crystal of the molten raw material by moving the crucible at a speed of ≤0.5 mm/h, and a step for gradually cooling the crystal grown in the previous growing step at a cooling speed of ≤5°C/h. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention generally relates to a fluoride single crystal and a manufacturing method thereof, and particularly 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 calcium fluoride (CaF ₂ ) crystal and a method for producing the crystal. The present invention is suitable, for example, for a crystal manufacturing method for manufacturing a crystal having a large diameter (a diameter of 200 mm or more).

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. Since the calcium fluoride (CaF ₂ ) single crystal has a high light transmittance (that is, internal transmittance) in such a wavelength region among glass materials, optical elements such as lenses and diffraction gratings used in exposure optical systems. It is 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 a calcium fluoride single crystal used in an exposure apparatus.

  Calcium fluoride single crystals are generally produced by the Bridgman-Stockburger method (also known as the “crucible descent method”). In this method, the raw material of the crystalline substance is filled in the crucible, and the crucible containing the melted raw material is lowered and cooled to crystallize. When a high-purity powder raw material made by chemical synthesis is used as a raw material, the loss of weight becomes severe due to the relationship between bulk specific gravity, so a proposal has been made to use a cullet-like material (see, for example, Patent Document 1). .)

  FIG. 14A shows the result of measuring the refractive index homogeneity for a calcium fluoride crystal having a diameter of 225 mm and a crystal plane orientation of (1 1 1) manufactured by a conventional crystal manufacturing method (that is, the above-described method). Shown in The measurement is performed with Mark III of Zygo, and the values obtained by removing only the Tilt component and the Power component at 6231 measurement points taken in by the CCD are shown. The display range is ± 200 ppb. The black portion represents a portion where the deviation from the average value is large on the plus side, and the white portion represents a portion where the deviation from the average value is large on the minus side. Moreover, the refractive index homogeneity calculated with 90% of the outer diameter as the effective diameter to eliminate the influence of the edge is 87.7 ppb in terms of RMS value (root mean square of deviation), PV value (maximum refractive index and minimum refractive index) The difference was 509.6 ppb.

  On the other hand, when the birefringence is measured with a He—Ne laser having a pitch of 2.5 mm and a wavelength of 633 nm, an average of + 2 × standard deviation is 1.14 nm / cm (average of 0.52, standard deviation of 0.31, number of measurement points) 6365 points).

  Calcium fluoride belongs to a cubic crystal, and its crystal structure is called fluorite type. As shown in FIG. 14A, the crystallinity when viewed from the crystal plane orientation of (1 1 1) is 3 Has symmetric symmetry. Such a property appears as a hexagon in the refractive index homogeneity distribution (see FIG. 14A) and represents a slip of the crystal.

  For example, there is a subboundary (subgrain boundary) that is a portion where dislocations are accumulated, which affects the refractive index homogeneity distribution. The image which image | photographed the calcium fluoride with a diameter of 260 mm which has a comparatively big crystal plane orientation inclination by reflection type X-ray topography is shown in FIG. Referring to FIG. 15, it can be seen that calcium fluoride produced by a conventional crystal production method is composed of a plurality of subgrain (sub-crystal grain) structures partitioned by subboundaries. In such a crystal, the refractive index homogeneity is remarkably deteriorated in a portion where the crystal plane orientation greatly changes, such as the region A and the region B.

Further, the concentration distribution of impurities contained in the crystal and the residual stress also affect the refractive index homogeneity. In addition, as a prior art which paid attention to refractive index homogeneity, calcium fluoride having a refractive index homogeneity of 5 ppm (that is, 5000 ppb) or less and a birefringence of 10 nm / cm or less (see, for example, Patent Document 2). In addition, there has been a proposal of using calcium fluoride (for example, see Patent Document 3) having a refractive index homogeneity of 3 ppm (that is, 3000 ppb) or less and a birefringence of 2 nm / cm or less for an exposure optical system. .
JP-A-4-349199 JP-A-8-5801 Japanese Patent Laid-Open No. 10-270351

  However, the conventional crystal manufacturing method cannot manufacture a crystal having high quality optical performance. That is, as a result of examination by the present inventor, it has been found that the calcium fluoride crystal as shown in FIG. 14A cannot be used as the lens glass material in the exposure optical system. Specifically, in the calcium fluoride crystal shown in FIG. 14A, the flare ratio changes depending on the opening area around the intended baking pattern, and the flare is small in the light shielding region and the flare is large in the opening region. This is because even if an attempt is made to burn the same pattern, a phenomenon in which the line width becomes narrower occurs if the opening area is large. Such a phenomenon occurs depending on the surface shape accuracy of the lens used in the exposure optical system, but basically, it is caused by high-order wavefront aberration, so that the refractive index homogeneity inherent in the lens glass material is inherent. It is difficult to correct higher-order components of the shape by shape.

  The generation of flare based on the rate of change in refractive index homogeneity is simply devised when the PV value or RMS value of refractive index homogeneity is reduced, the crystal plane orientation is changed, or the crystal is cut out. Therefore, even if only the distribution symmetry of refractive index homogeneity is suppressed, it cannot be solved.

  Therefore, the present invention solves the above problems, and uses a fluoride single crystal having good optical performance as a lens glass material in an exposure apparatus optical system, and a crystal excellent in optical characteristics such as refractive index homogeneity. It is an exemplary object to provide a crystal manufacturing method capable of manufacturing a crystal.

  In order to achieve the above object, a fluoride single crystal according to one aspect of the present invention is manufactured by purifying a raw material of a crystalline material, melting the purified crystalline material, and then growing the crystalline material. A plurality of subgrains partitioned by subboundaries, the relative tilt angle of the crystal plane orientation of the adjacent subgrains being within 0.02 degrees, and the subgrains The maximum tilt angle of the crystal plane orientation is within 0.2 degrees.

  The fluoride single crystal according to another aspect of the present invention is a fluoride single crystal produced by purifying a raw material of the crystalline material, melting the purified crystalline material, and then growing the crystalline material. The in-plane distribution of refractive index homogeneity is decomposed by Zernike polynomial approximation, and the residual RMS value obtained by subtracting the 1st to 36th term components is 20 ppb or less.

  According to still another aspect of the present invention, there is provided a crystal manufacturing method, wherein a plurality of heaters are disposed in a space in which a crucible moves, and a temperature gradient of 10 ° C./cm or less is formed across a crystal melting point; A step of growing the melted raw material crystal by moving the crucible at a speed of 5 mm / h or less, and a slow growth of the crystal grown in the growth step at a cooling rate of 5 ° C./h or less at room temperature. And a step of returning to step (1).

  An optical element as still another aspect of the present invention is manufactured from the above-described fluoride single crystal.

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

  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 irradiates the object to be processed through the optical system including the optical element described above. Then, the object to be processed is exposed.

  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 | crystallization excellent in optical characteristics, such as refractive index homogeneity, and its crystal manufacturing method can be provided.

  Hereinafter, with reference to the attached drawings, characteristics of a fluoride single crystal as one aspect of the present invention and a method for producing the crystal will be described. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  As a result of earnestly examining the occurrence of flare based on the rate of change of the refractive index homogeneity of the calcium fluoride crystal, the present inventor has obtained a higher-order component when the in-plane distribution of the refractive index homogeneity is decomposed by the Zernike polynomial approximation, We found that it must be below a certain value.

  FIG. 1 (a) decomposes the refractive index homogeneity of a calcium fluoride single crystal having a crystal plane orientation of (1 1 1), which best represents the characteristics of the present invention, by Zernike polynomial approximation, and converts the 1st to 36th term components. It is a figure which shows the residue distribution deducted. The calcium fluoride shown in FIG. 1A has a residual RMS value of 19.5 ppb, a crystal diameter of 225 mm, and a refractive index homogeneity calculated by 90% of the outer diameter as an effective diameter is 36.1 ppb in RMS value. The PV value was 247.5 ppb.

  On the other hand, the birefringence was measured with a He—Ne laser having a wavelength of 633 nm, and the average + 2 × standard deviation was 0.85 nm / cm (average 0.37, standard deviation 0.24).

  Here, FIG. 1A shows the residue distribution obtained by decomposing the refractive index homogeneity by Zernike polynomial approximation and subtracting the 1st to 36th term components as described above, and the details will be described below. . The Zernike polynomial Z_poly is represented by a mathematical general formula using a complex function as shown in the following formulas 1 and 2 when 0 ≦ ρ ≦ 1 and 0 ≦ θ ≦ 2π.

Here, I is an imaginary unit, n is an integer, and m is an integer defined only in two steps from -n to n. Also, practically, as m is positive, it is expressed as cos when it is positive, and as sin when it is negative, as shown in the following formulas 3 and 4, which are arranged in order and handled by numbers.

However, in the optical field, each term has a meaning and is represented side by side as shown in Table 1 below. Table 1 shows the first 36 terms.

  Refractive index homogeneity is approximated by a Zernike polynomial, and higher-order components of 36 terms or more shown in Table 1 are hereinafter referred to as Zernike residues. In the calcium fluoride crystal shown in FIG. 1A, the Zernike residue is 20 ppb or less as described above. The upper limit of 20 ppb is obtained by calculating the flare rate from the optical simulation and as an upper limit allowable for the exposure apparatus. Therefore, if there is a Zernike residue of 20 ppb or more, the flare rate increases, and there arises a problem that the line width varies greatly depending on the pattern to be baked.

  On the other hand, the refractive index homogeneity of the conventional calcium fluoride crystal shown in FIG. 14A represents the influence of the slip surface of the crystal even in the Zernike residue component, as shown in FIG. 14B. Referring to FIG. 14B, the value of the Zernike residue of the conventional calcium fluoride crystal is 43.6 ppb. When such a calcium fluoride crystal is used for the lens glass material of the exposure optical system, it depends on the flare. Deterioration of the exposure performance cannot be avoided.

  Here, conditions for a calcium fluoride single crystal having a small Zernike residue will be described. Calcium fluoride single crystal with small Zernike residue has a relative inclination angle of each adjacent subgrain crystal plane orientation within 0.02 degrees and a maximum inclination angle of the subgrain crystal plane orientation of the entire crystal is 0.2 degrees. Is within. In order to improve higher-order wavefront aberrations clarified in this embodiment, it is necessary to define the crystal structure.

  An X-ray topographic image of a calcium fluoride single crystal having a diameter of 30 mm is shown in FIG. Referring to FIG. 2, it can be seen that this calcium fluoride single crystal is composed of six subgrain structures. In such a small-diameter calcium fluoride single crystal, the relative inclination angle of the crystal plane orientation of each subgrain can be easily reduced.

  In the calcium fluoride single crystal shown in FIG. 2, the relative inclination angles of all the subgrain crystal plane orientations in the imaging plane obtained by measuring the rocking curve of each subgrain are within 0.02 degrees. . In addition, the variation in the inclination angle of the entire plane including subgrains that are not adjacent to each other is also within 0.2 degrees.

  However, in the case of a large-diameter calcium fluoride crystal, the displacement of the relative tilt angle is very small in many regions, but the relative tilt is relatively large as in the regions A and B of the calcium fluoride crystal shown in FIG. There is a partial region where the corners are shifted. Therefore, unless such a region is defined, a calcium fluoride single crystal suitable for the lens glass material of the exposure optical system cannot be obtained. Of course, it is satisfactory if it is a crystal that does not have a region where the relative inclination angle is greatly shifted, such as region A and region B, but it is very difficult to realize it with a large-diameter calcium fluoride single crystal. . The relative inclination angle between the region A and the region B of the calcium fluoride crystal shown in FIG. 15 is 0.27 degrees, which is larger than the other regions. Such a value is considerably larger than the surrounding region, and when viewed as a Zernike residue having a refractive index homogeneity, the value becomes large in this region and is not suitable as an exposure optical system.

  On the other hand, the calcium fluoride single crystal shown in FIG. 1 (a) has a large contrast as compared with the conventional calcium fluoride single crystal (FIG. 15), as shown in FIG. 1 (b). Some areas are not recognized. In the calcium fluoride single crystal shown in FIG. 1 (a), the relative tilt angle of the subgrain structure is within 0.02 degrees and the maximum tilt angle is within 0.2 degrees in any region, and the Zernike residue The effect is not seen. In other words, the tilt angle that does not affect the Zernike residue is a partial tilt due to the presence of the subgrain, and the relative tilt angle of the crystal plane orientation of the subgrain is within 0.02 degrees, and the curvature of the lattice plane As a whole, the maximum inclination angle of the crystal plane orientation of the subgrain is within 0.2 degrees. By selecting such a calcium fluoride single crystal as the lens glass material of the exposure optical system, it is possible to guarantee exposure performance free from flare.

  In addition, the reflection X-ray topography image was used for the definition of the above-mentioned subgrain structure. X-ray topography is a method of acquiring an image by making X-rays incident under the condition that diffraction occurs on a crystal plane and recording the diffraction intensity two-dimensionally. When the crystal plane orientation is inclined in a structural unit such as a subgrain, the diffraction conditions change, and as shown in FIG. 1 (b), a shaded image is obtained.

  In addition, since the diffraction condition of Bargg is used, it is affected by the expansion and contraction of the crystal lattice due to the strain existing in the crystal. However, the X-ray topography in which the Zernike residue is 20 ppb or less by the examination described later. It was found that it can be defined as an image. That is, for the calcium fluoride crystal in which the (1 1 1) plane appears as the crystal plane orientation, measurement was performed on the (4 4 0) plane. A Cu target Kα ray (wavelength 0.15405 nm) is used as the X-ray source, and the crystal plane orientation of each subgrain in the obtained X-ray topography image is measured by a rocking curve. Thereby, the relative inclination angle of the crystal plane orientation of the subgrain can be accurately defined. The maximum tilt angle of the subgrain crystal plane orientation of the entire crystal may be compared with the crystal plane orientation measured by the rocking curve of the darkest and lightest regions in the X-ray topography image.

  The rocking curve angle resolution that can be measured by the apparatus used in this embodiment is 0.0002 degrees. However, looking at the image of the subgrain structure of the entire crystal, when the full scale ± 0.5 degree is displayed as a monochrome image of 256 gradations, it is about 0.004 degree. The lateral resolution is 0.05 mm (50 μm). By evaluating the crystal with such a resolution, it has sufficient resolution to define the angle from the density of the X-ray topography image without measuring the rocking curve of all subgrains, and has a large aperture. The characteristics of calcium fluoride can be defined.

  The relationship between the relative tilt angle of the crystal plane orientation of subgrains and the Zernike residue will be described. FIG. 3 is a diagram showing an X-ray topographic image of a (1 1 1) -oriented calcium fluoride single crystal having a relatively large subgrain crystal plane orientation relative tilt angle. FIG. 4 is a graph showing the results of measuring the crystal plane orientation of the calcium fluoride single crystal shown in FIG. 3 at a number of measurement points. The horizontal axis represents the position in the diameter direction of unit mm, and the vertical axis represents the deviation of the subgrain crystal plane orientation measured in unit degrees from the (1 1 1) plane orientation.

  Since the calcium fluoride single crystal has a variation in crystal plane orientation, as shown in FIG. 3, there is a large difference in light and shade as an X-ray topographic image, and the crystal plane orientation is plotted as shown in FIG. The graph is uneven. The calcium fluoride single crystal shown in FIG. 4 has a relative inclination angle of the crystal plane orientation of adjacent subgrains of 0.05 degrees and a maximum inclination angle of 0.3 degrees or more. Actually, when Zernike residue was measured, it was 28.0 ppb.

  FIG. 5 is a view showing an X-ray topographic image of a calcium fluoride single crystal having a (1 1 1) plane orientation with a curved crystal lattice plane and a relative tilt angle of a large subgrain crystal plane orientation. FIG. 6 is a graph showing the results of measuring the crystal plane orientation of the calcium fluoride single crystal shown in FIG. 5 at a number of measurement points. The horizontal axis represents the position in the diameter direction of unit mm, and the vertical axis represents the deviation of the subgrain crystal plane orientation measured in unit degrees from the (1 1 1) plane orientation. As shown in FIG. 6, when the least square approximation line of the plot points is shown, it becomes a substantially monotonous change, and it can be seen that the lattice plane of this crystal is curved.

  Referring to FIGS. 5 and 6, a radial subgrain structure is observed, the relative tilt angle of the crystal plane orientation of adjacent subgrains is 0.5 degrees or more, and the maximum tilt angle is 1.5 degrees or more. I understand that. As shown in FIG. 5, the X-ray topography image is missing white because the angle difference is too large to satisfy the X-ray diffraction conditions. Actually, when the Zernike residue was measured, it was 36.0 ppb.

  As described in the above two examples, the Zernike residue, the relative inclination angle and the maximum inclination angle of the crystal plane orientation of the subgrain have a correlation, and the subgrain satisfying the Zernike residue of 20 ppb is the crystal plane of the subgrain. The relative tilt angle of the orientation is within 0.02 degrees, and the maximum tilt angle of the crystal plane orientation of the subgrains is within 0.2 degrees as a whole due to the curvature of the lattice plane.

  Further, as shown in FIG. 7, there is a calcium fluoride single crystal having a very fine subgrain structure even if the relative inclination angle of the crystal plane orientation of each adjacent subgrain is small. As shown above, the entire subgrain structure must be measured and the relative tilt angle of each subgrain crystal plane orientation and the maximum tilt angle of the subgrain crystal plane orientation within the effective diameter used as the lens glass material for the exposure optical system must be specified. Therefore, the exposure performance cannot be guaranteed. Here, FIG. 7 is a diagram showing an X-ray topography image of a calcium fluoride single crystal having a fine subgrain structure.

  The Zernike residue, which is a higher-order wavefront aberration component targeted in the present invention, is also affected by the stress state inside the fluoride (calcium fluoride) single crystal. However, it is very difficult to directly measure the stress inside the fluoride single crystal. However, the fluoride single crystal has a unique piezoelectric optical coefficient, and the birefringence is uniquely determined by the product with the stress. Since both refractive index homogeneity and birefringence distribution are evaluated by transmission through thick crystals, it is difficult to obtain a quantitative correlation at the microscopic level, but when the rate of change in birefringence is large, the refractive index changes. Zernike residue, which is a higher-order component, tends to be larger. In order to reduce the Zernike residue to 20 ppb or less as the residual stress inside the crystal, the standard deviation of the in-plane distribution of birefringence needs to be 0.3 nm / cm or less.

  Further, when a scavenger, which is an organic fluoride or metal fluoride added for the purpose of removing impurities, remains in the crystal after crystal growth, it has a refractive index distribution. As the remaining scavenger, zinc (Zn) or lead (Pb) can be considered. According to the study of the present inventor, the residual amount is 1 ppm or less, and if the Zernike residue is affected if a sufficient stirring process is performed, the Zernike It is possible to use as a lens glass material of an exposure optical system without affecting the residue and securing a sufficient transmittance.

  In the present embodiment, as a crystal plane orientation, it is easy to produce a seed crystal by cleavage, and the (1 1 1) plane in which the crystal plane orientation is determined based on the crystal plane orientation is described as an example. However, a fluoride single crystal having a (1 0 0) plane obtained by cutting a seed crystal on the (1 0 0) plane and growing the crystal is also used to suppress the occurrence of flare due to the rate of change in refractive index homogeneity. It goes without saying that the provisions of the invention are valid. In the exposure optical system, a crystal having a crystal plane orientation of (1 1 1) having a small birefringence is usually used because of its characteristics, but has a crystal plane orientation of (1 0 0) for aberration correction or the like. Crystals may also be used. In this case, since the crystal having the crystal plane orientation of (1 1 1) and the crystal having the crystal plane orientation of (1 0 0) are also arranged on the same axis, the provisions of the present invention for high-order wavefront aberration are also effective. It becomes.

  Fluoride single crystals that can be used in short-wavelength exposure optical systems from the vacuum ultraviolet region to the far ultraviolet region include calcium fluoride, magnesium fluoride, barium fluoride, and lithium fluoride. Suitable for the lens glass material of the exposure optical system is a cubic crystal, which is calcium fluoride or barium fluoride which is stable at room temperature. A tetragonal crystal such as magnesium fluoride has a large difference in refractive index depending on the orientation, and if it is deliquescent like lithium fluoride, it is difficult to use as a lens glass material. Accordingly, preferred fluorides for applying the present invention to the exposure apparatus are calcium fluoride and barium fluoride.

  Hereinafter, the above-described calcium fluoride having a large diameter (200 mm or more) (that is, the in-plane distribution of refractive index homogeneity is decomposed by the Zernike polynomial approximation, and the residual RMS value obtained by subtracting the 1st to 36th term components is 20 ppb or less. (Calcium fluoride whose relative tilt angle of crystal plane orientation of a certain calcium fluoride or adjacent subgrain is within 0.02 degrees and whose maximum tilt angle of subgrain crystal plane orientation is within 0.2 degrees) A crystal manufacturing method and apparatus will be described. FIG. 8 is a flowchart for explaining a crystal manufacturing method 1000 according to one aspect of the present invention.

  In the crystal manufacturing method 1000, crystallization is performed by moving a crucible housed in a furnace having a constant temperature environment downward. The crystal manufacturing method 1000 is not limited to the manufacture of a calcium fluoride single crystal having a diameter of 200 mm or more.

  Referring to FIG. 8, first, a calcium fluoride raw material and a 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 than the fluoride to be grown and that are easily decomposed and evaporated are desirable. . For example, a zinc fluoride (ZnF ₂ ) scavenger, as shown in the following chemical formula 1, shows calcium oxide (CaO) generated due to the presence of moisture with respect to calcium fluoride (CaF ₂ ) as shown in the following chemical formula 2. Thus, it is reduced to calcium fluoride (CaF ₂ ).

  The mixture of the calcium fluoride raw material and scavenger thus obtained 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.

  Next, a single crystal growth process is performed on the purified calcium fluoride crystals (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). Here, the crystal growth process will be described in detail with reference to FIG. FIG. 9 is a detailed flowchart of the crystal growth process in step 1300.

Referring to FIG. 9, first, the calcium fluoride purified in step 1200 is stored in a crucible and melted (step 1310). Next, the calcium fluoride is held in a molten state for a sufficiently long time (step 1320). The scavenger reacts with calcium oxide (CaO), which is an impurity contained in calcium fluoride, to be reduced to calcium fluoride (CaF ₂ ), and is itself removed as an oxide when calcium fluoride is melted. At this time, if the scavenger is lead fluoride (PbF ₂ ), lead oxide (PbO) is held, and if the scavenger is zinc fluoride (ZnF ₂ ), zinc oxide (ZnO) holds calcium fluoride in a molten state. However, it remains in the crystal if there is not enough time. In the crystal manufacturing process, it is preferable that the time is short, and therefore it is necessary to set an optimal time. For this purpose, it is indispensable to grasp the responsiveness of the crystal manufacturing apparatus and to add time for removing impurities to the time constant of the apparatus. In the production of calcium fluoride having a diameter of 200 mm or more according to the present embodiment, the time constant of the crucible temperature is 3 hours to 6 hours, although it varies slightly depending on the position of the crucible and the amount of raw material stored in the crucible. 10 hours and a total of 40 hours or more of 30 hours or more are required as the impurity removal time. In other words, what is necessary is just to hold | maintain for 40 hours or more in the state which melted calcium fluoride. Needless to say, as the size (diameter and depth) of the crucible increases, it is necessary to set a longer time to give a sufficient impurity removal time. Thereby, it can be set as the stable temperature environment.

  After holding calcium fluoride in a molten state, a temperature gradient is formed in the space (growth furnace) in which the crucible moves (step 1330). As described above, the crystal manufacturing method 1000 of the present invention performs crystallization by moving a crucible housed in a furnace having a constant temperature environment downward. This method is characterized in that a single crystal is produced by moving a crucible containing a raw material of a crystalline substance through a furnace having a temperature gradient across the melting point. In this embodiment, the temperature gradient described later is set small. The temperature gradient is generally set to 15 ° C./cm or more in order to prevent growth due to rapid polycrystallization due to the generation of natural nuclei, but in this embodiment, it is set to 10 ° C./cm or less. However, along with this, the crystal growth process becomes vulnerable to disturbances such as the generation of natural nuclei. Therefore, it is necessary to circulate cooling water whose temperature is adjusted to ± 1 ° C. in the growth furnace to minimize the influence of outside air.

  After forming the temperature gradient, the crucible is gradually pulled down and the molten calcium fluoride is gradually cooled to grow a single crystal (step 1340). In the present embodiment, the speed at which the crucible is pulled down is set to 0.5 mm / h or less. In order to grow a high-quality single crystal, it is better that the crucible is pulled down slowly, and about 2 mm / h is sufficient to stably obtain a single crystal having a diameter of 200 mm. However, since the temperature inside the growth furnace becomes lower as it goes downward, if the crucible pulling speed is high, a large thermal stress is applied to the solidified portion after crystal growth, causing dislocation for stress relaxation. To do. Since such a dislocation accumulates to form a subgrain structure, it is necessary to sufficiently reduce the pulling-down speed. For this reason, if productivity is ignored, the lower the crucible pulling speed, the better the crystallinity. However, in practice, it is important to determine the minimum crucible pulling speed. According to the study of the present inventor, when a temperature gradient of 5 ° C. to 10 ° C./cm was formed during crystal growth, it was necessary to set the crucible pulling speed to 0.5 mm / h or less. When the crucible pulling speed is increased, the relative tilt angle of the crystal plane orientation of the adjacent subgrain structure frequently increases, and the thermal stress applied to the grown crystal increases, resulting in slipping. The birefringence increases.

  Next, the grown single crystal is gradually cooled (step 1350). In this embodiment, the slow cooling rate after crystal growth is reduced. Although a temperature gradient is necessary for crystal growth, if a temperature gradient exists after crystal growth, it becomes thermal stress and becomes a cause of dislocations. Since a subboundary is formed by a large number of dislocations, control of the slow cooling rate after crystal growth is important. If it takes about 20 hours to cool from the temperature near the melting point after crystal growth to room temperature, it is possible to gradually cool the crystal without applying thermal stress enough to cause cracks, but that alone deteriorates the quality of the crystal. End up. According to the study of the present inventor, it was necessary to cool at a cooling rate of 5 ° C./h or less in order to perform slow cooling without deteriorating the quality of the crystal. As a result, the average value of the birefringence immediately after crystal growth and the standard deviation value of the birefringence caused by temperature unevenness during slow cooling can also be reduced.

  By performing the crystal growth process (step 1300) as in steps 1310 to 1350, the in-plane distribution of refractive index homogeneity is decomposed by Zernike polynomial approximation, and the residual RMS value obtained by subtracting the 1st to 36th term components is 20 ppb. Calcium fluoride or calcium fluoride having a relative tilt angle of crystal plane orientation of adjacent subgrains of 0.02 degrees or less and a maximum tilt angle of subgrain crystal plane orientation of 0.2 degrees or less. Can be manufactured.

  Subsequently, the crystal-grown calcium fluoride is heat-treated (annealing process) (step 1400). The annealing step is a step of heat-treating the grown calcium fluoride to remove strain that causes crystal cracking. In the annealing step, the crucible is heated uniformly to about 1000 ° C. to about 1300 ° C. to remove the distortion of the calcium fluoride crystal while it remains solid. The soaking time is 20 hours or more, more preferably about 40 hours to about 80 hours. In the annealing step, crystal dislocations are reduced through annealing. Thereafter, the temperature of the calcium fluoride crystal is returned to room temperature while maintaining the state in which distortion is eliminated.

  Thereafter, a calcium fluoride single crystal is formed on the required optical element (step 1500). 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 refractive index homogeneity and internal transmittance, the optical performance is improved as compared with the conventional optical element.

By combining various optical elements thus obtained, a projection optical system and an 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.

  FIG. 10 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 in the crucible 110 and then cools the raw material ID to grow crystals. As shown in FIG. 10, the crystal manufacturing apparatus 100 includes a crucible 110, a support member 120, a heater 130, a thermocouple 140, a heat insulating member 150, and a housing 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 heat insulating member 150 and a housing 160, and the cylindrical surface of the crucible 110 is Heated by a heater 130 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 has an openable / closable lid 118 that prevents evaporation of the raw material ID, and stores the raw material ID of the crystalline substance (calcium fluoride in this embodiment). The size (diameter) of the raw material ID stored in the crucible 110 is 0.9 to 0.95 times the size (diameter) of the crucible 110, that is, the size (diameter) of the purified raw material ID. ) And the size (inner diameter) of the crucible 110 is preferably 1: 1.05 to 1: 1.1. Thereby, the refined raw material ID can be stored in the crucible 110 without being crushed. Further, the surface area can be remarkably reduced as compared with the pulverized raw material, and the mixing of water adhering to the surface of the raw material ID can be reduced. Therefore, the amount of scavenger added to the raw material ID in the crystal growth step can be reduced, and the residual scavenger can be reduced.

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 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 114 of the lower portion 112 and is arranged 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 does not necessarily have a conical shape. 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. In the present embodiment, the conical portion 116 has a cone angle AG (angle of cone apex) of 120 degrees or less, more preferably 60 degrees or more and 90 degrees or less. This is because the crystal grows from the seed crystal SC along the inner surface of the crucible 110, but if the cone angle AG of the conical portion 116 is large, the latent heat at the time of solidification of the crystal rapidly increases, so that the latent heat is stably excluded. This is because stable crystal growth in proportion to the speed at which the crucible 110 is pulled down cannot be performed. On the other hand, if the conical angle 116 of the conical portion 116 is small, it takes a long time to lower the crucible 110 until it reaches a portion having a large diameter, which is disadvantageous for manufacturing a crystal having a large diameter. The cone angle AG is also important for the subgrain structure. By reducing the cone angle AG, the stress during crystal growth can be relieved and a fine structure can be prevented.

  The support member 120 penetrates the bottom of the casing 150 and the top reaches the growth reactor CGF. The support member 120 is connected to the crucible 110 through a carbon joint member 122. 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, heats the raw material ID together with the crucible 110, and melts it. The heater 130 heats the crucible 110 with a uniform heating force along the vertical direction of the crucible 110. As shown in FIG. 10, the heater 130 is composed of multiple stages of a first heater 130a, a second heater 130b, a third heater 130c, and a fourth heater 130d, and controls the temperature in the growth reactor CGF. It can be controlled precisely. Specifically, the melting point of the raw material ID is set between the second heater 130b and the third heater 130c, the temperature of the second heater 130b is set higher than the melting point, and the temperature of the third heater 130c is Set lower than the melting point. A temperature gradient is obtained by dividing the temperature difference between the second heater 130b and the third heater 130c by the distance between the second heater 130b and the third heater 130c. Further, the temperature of the fourth heater 130d is set close to the temperature of the third heater 130c. Thereby, rapid cooling when the crucible 110 descends can be prevented. Further, annealing can be performed by controlling the temperature of the first heater 130a to the fourth heater 130d.

  The thermocouple 140 is disposed on the central outer side surface of the first heater 130a to the fourth heater 130d and detects the temperature. As the thermocouple 140, a sample taken from the same rod strand is used, and the thermocouple 140 is periodically calibrated, and the cause of the temperature measurement error is minimized.

  The heat insulating member 150 is disposed adjacent to the inner surface of the growth reactor CGF so as to surround the heater 130. The heat insulating member 150 is made of carbon whose inner surface is well polished, and protects the housing 160 from the heat of the heater 130.

  The case 160 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 160 is configured by arranging a heat insulating material (not shown) in the double cylinder using a double cylinder made of stainless steel or the like.

The operation of the crystal manufacturing apparatus 100 will be described. After storing the raw material ID of calcium fluoride in the crucible 110, the crucible 110 is heated by the heater 130. At this time, the seed crystal SC is installed in the storage portion 114 of the crucible 110, and all the raw material ID of calcium fluoride is melted, but the crucible 110 is fixed at a position where a part of the seed crystal SC is not melted. Thereafter, the growth furnace CGF is exhausted to about 10 ⁻³ Pa to 10 ⁻⁴ Pa by the exhaust device EM, and the output of the heater 130 is gradually increased to melt the raw material ID.

  The melting temperature from the upper end of the seed crystal SC to the raw material ID may be equal to or higher than the melting point of calcium fluoride, but is preferably set to 1410 ° C. to 1450 ° C. Below 1410 ° C., it takes a long time until the raw material ID is completely melted, and productivity cannot be improved. Moreover, at 1450 degreeC or more, the vaporization of calcium fluoride raw material ID is intense, and the fall of productivity by loss of raw material ID cannot be avoided.

  The temperature of the growth furnace CGF is adjusted by adjusting the output of the heater 130 to form a temperature gradient of 10 ° C./cm or less, which is higher in the upper direction and lower in the lower direction as described in the crystal manufacturing method 1000 described above. The crystal growth is performed through the seed crystal SC by pulling down the crucible 110. When the crucible 110 is slow, the productivity is poor when it is slow, and when it is too fast, the temperature change is so rapid that it tends to be polycrystalline, and fine subgrains are generated. Set.

The slow cooling rate to room temperature of the crucible 110 after crystal growth is 5 ° C./h or less. A more detailed setting method of the heater 130 will be described. Since the crystal immediately after growth has a temperature gradient in the furnace, the temperature gradient is 10 ° C./cm between the upper part of the crystal (ie, the part solidified last) and the vicinity of the lower seed crystal (ie, the part first solidified). When the axial thickness of the crystal is thick, a temperature difference of several hundred degrees is generated. Therefore, even if the temperature of each heater 130 is simply lowered at 5 ° C./h, thermal stress is generated in the crystal due to the temperature distribution based on this non-uniform temperature difference. As a result, slip occurs, and the in-plane distribution of refractive index homogeneity is decomposed by Zernike polynomial approximation, and the residual RMS value obtained by subtracting the 1st to 36th term components is 20 ppb or less, and the crystals of adjacent subgrains. It has not always been possible to produce calcium fluoride having a relative tilt angle of the plane orientation within 0.02 degrees and a maximum tilt angle of the crystal plane orientation of subgrains within 0.2 degrees. Of course, if the cooling is performed at a slower cooling rate, the thermal stress is reduced accordingly, so that the crystal quality is improved, but the efficiency is not sufficient. Therefore, the present inventor conducted experiments on generation of slip in the crystal by the difference in the growth furnace heat transfer simulation and the slow cooling process, and reached the following knowledge. First, all the heater set temperatures are matched to a temperature of 1000 ° C. or more over 100 hours, and then returned to room temperature. Usually, in the fluoride single crystal, the annealing temperature for performing sufficient strain removal is 1000 ° C. or higher. First, it is necessary to eliminate the above-mentioned temperature difference in the crystal in this temperature range. At this time, if the values are set so as to coincide too rapidly, for example, immediately after the growth, the heaters 130a and 130b set to a temperature higher than the crystal melting point have zero output, and the temperature distribution temporarily increases, resulting in thermal stress in the crystal. Will become bigger. Considering heat transfer characteristics such as the time constant of a crystal manufacturing apparatus for manufacturing a crystal having a large diameter (200 mm or more), which is the main target of the present invention, a slip reduction effect can be obtained by taking 100 hours or more. did it. Secondly, after all the set temperatures of the heater 130 are matched at a temperature of 1000 ° C. or higher, a step of maintaining a constant temperature for 20 hours or more may be further added. Sufficient strain removal can be achieved by taking the soaking time according to the annealing process described above.
As described above, according to the crystal manufacturing method 1000 and the crystal manufacturing apparatus 100, a crystal having excellent optical characteristics such as refractive index homogeneity (that is, an in-plane distribution of refractive index homogeneity is decomposed by Zernike polynomial approximation, The relative inclination angle of the crystal plane orientation of calcium fluoride or the adjacent subgrain with the RMS value of the residue after subtracting the items 36 to 36 is 20 ppb or less, and the maximum inclination of the crystal plane orientation of the subgrain Calcium fluoride whose angle is within 0.2 degrees can be produced.

  Hereinafter, an exemplary exposure apparatus 500 of the present invention will be described with reference to FIG. Here, FIG. 11 is a schematic block diagram showing the configuration of the exposure apparatus 500 of the present invention. As shown in FIG. 11, 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 emit ultraviolet light, far ultraviolet light, and vacuum ultraviolet light without generating flare. Therefore, a device (semiconductor element, LCD element, imaging element (CCD, etc.), thin film magnetic head, etc.) can be provided with high throughput and good 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. 12 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. 13 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 figure which shows the refractive index homogeneity (Zernik residue) and X-ray topography image of the calcium fluoride single crystal of this invention. It is a figure which shows the X-ray topography image of a small-diameter calcium fluoride single crystal. It is a figure which shows the X-ray topography image of the calcium fluoride single crystal which has the relative inclination | tilt angle of the crystal plane orientation of a comparatively big subgrain. It is a graph which shows the result of having measured the crystal plane orientation of the calcium fluoride single crystal shown in FIG. 3 at many measurement points. It is a figure which shows the X-ray topography image of the calcium fluoride single crystal which the crystal lattice plane curves and has the relative inclination angle of the crystal plane orientation of a big subgrain. It is a graph which shows the result of having measured the crystal plane orientation of the calcium fluoride single crystal shown in FIG. 5 at many measurement points. It is a figure which shows the X-ray topography image of the calcium fluoride single crystal which has a fine subgrain structure. 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 schematic sectional drawing which shows the structure of the crystal manufacturing apparatus used with the crystal manufacturing method of this invention. 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.). 13 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 12. It is a figure which shows the refractive index homogeneity of a typical calcium fluoride manufactured by the conventional crystal manufacturing method, and a Zernike residue. It is a figure which shows the X-ray topographic image of the calcium fluoride which has a comparatively big crystal plane orientation inclination.

Explanation of symbols

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

Claims (12)

A fluoride single crystal produced by purifying a raw material of a crystalline substance, melting the purified crystalline substance and then growing the crystalline substance,
Having a plurality of subgrains partitioned by subboundaries;
A fluoride single crystal having a relative tilt angle of crystal plane orientation of adjacent subgrains within 0.02 degrees and a maximum tilt angle of crystal plane orientation of subgrains within 0.2 degrees . A fluoride single crystal produced by purifying a raw material of a crystalline substance, melting the purified crystalline substance and then growing the crystalline substance,
A fluoride single crystal characterized in that an in-plane distribution of refractive index homogeneity is decomposed by Zernike polynomial approximation, and a residual RMS value obtained by subtracting 1st to 36th term components is 20 ppb or less. A manufacturing method for manufacturing a single crystal from a raw material of a crystalline substance stored in a crucible,
A plurality of heaters are disposed in the space in which the crucible moves, and a temperature gradient of 10 ° C./cm or less is formed across the crystal melting point;
Growing a crystal of the raw material melted by moving the crucible at a speed of 0.5 mm / h or less;
And a step of slowly cooling the crystal grown in the growth step at a cooling rate of 5 ° C./h or less to return to room temperature. The crucible has a conical conical portion at the bottom of the crucible where the growth of the crystal starts,
The crystal manufacturing method according to claim 3, wherein the conical part has a cone angle of 60 degrees or more and 90 degrees or less.   The crystal manufacturing method according to claim 3, wherein the fluoride single crystal is calcium fluoride.   The set temperature of the plurality of heaters in the step of gradually cooling is set to a temperature of 1000 ° C or higher over 100 hours and then returned to room temperature at the cooling rate. A method for producing a fluoride single crystal.   4. The fluoride according to claim 3, further comprising the step of maintaining a constant temperature for 20 hours or more after all the set temperatures of the plurality of heaters are matched at a temperature of 1000 ° C. or higher in the slow cooling step. A method for producing a single crystal.   An optical element manufactured using the fluoride single crystal according to claim 1.   An optical element manufactured from a single crystal manufactured using the method for manufacturing a fluoride single crystal according to any one of claims 3 to 7.   10. The optical element according to claim 8, 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, the object to be processed is exposed by irradiating the object to be processed with an optical system including the optical element according to claim 8 or 9. An exposure apparatus characterized by: Exposing the object to be processed using the exposure apparatus according to claim 11;
And developing the exposed object to be processed.