WO2006077836A1

WO2006077836A1 - Method of working fluoride single crystal into one with cylindrical (100) crystal face

Info

Publication number: WO2006077836A1
Application number: PCT/JP2006/300546
Authority: WO
Inventors: Takafumi Yamazaki; Daisuke Totsuka; Masao Sekiguchi; Toshihiko Yamamoto
Original assignee: Mitsui Mining & Smelting Co., Ltd.; Nihon Kessho Kogaku Co., Ltd.
Priority date: 2005-01-19
Filing date: 2006-01-17
Publication date: 2006-07-27
Also published as: JP2006199528A; JP4756630B2

Abstract

A method of working a fluoride single crystal into one with cylindrical (100) crystal face wherein the strain/birefringence within (100) face orientation crystal has substantially been reduced. There is provided a method of working a fluoride single crystal into one with (100) crystal face, characterized in that a grown single crystal ingot is cut into a polyhedron and the polyhedron is annealed and further cut. Further, for example, there is provided a method of working a fluoride single crystal into one with cylindrical (100) crystal face, characterized in that a grown single crystal ingot is cut into a polyhedron and the polyhedron is annealed, further cut and subjected to cylindrical grinding so that the surface roughness (RMS) of single crystal face having undergone the cylindrical grinding is in the range of 0.1 to 5.0 μm.

Description

Specification

Processing method of cylindrical fluoride single crystal of (100) crystal plane

Technical field

The present invention relates to a method for processing a cylindrical fluoride single crystal having a (100) crystal plane, in which the strain birefringence inside the (100) plane crystal is greatly reduced. Here, the (100) crystal plane means that the bottom and top surfaces of the cylindrical and polyhedral fluoride single crystals are the (100) orientation crystal planes. An example of a cylindrical body is shown in (a) and a hexagonal columnar body is shown in Fig. 1 (b).

Background art

In recent years, semiconductor integration circuits used for microprocessors, memories, image sensors, and the like have been remarkably advanced in integration and functionality. For this reason, fine processing techniques have been required for wafer formation.

[0003] Photolithography is for exposing and transferring a fine pattern of the integrated circuit on a wafer, and an exposure apparatus called a stepper is used. Due to the demands of the above-mentioned fine processing technology, this stepper is also required to have high performance and high performance.

[0004] The projection lens of this stepper requires high resolution and deep depth of focus in order to obtain high imaging performance. Resolution and depth of focus are determined by exposure wavelength and numerical aperture (NA). In order to obtain a high resolution, the numerical aperture may be increased, but the depth of focus becomes shallow. Therefore, there is a limit to increasing the numerical aperture. The shorter the exposure wavelength, the smaller the angle of the diffracted light in the same pattern, so the numerical aperture of the lens is reduced. For this reason, it is required to shorten the exposure wavelength.

[0005] Because of these requirements, a stepper using an excimer laser beam such as KrF (wavelength 248 nm), ArF (wavelength 193 ηm), or F (wavelength 157 nm) as a light source has been proposed as a light source for an exposure apparatus.

2

ing. However, conventional glass materials can hardly cope with such shortening of wavelength.

[0006] As a glass material that can cope with such a short wavelength, a fluoride crystal can be cited. As fluoride crystals, single crystals that avoid the effects of grain boundaries and crystal orientations are used, and bridge crystals are used. It is nurtured by the Mann Law.

[0007] The characteristics required for a fluoride single crystal used as a lens material of an exposure apparatus are birefringence (strain birefringence), light transmittance, refractive index homogeneity, and the like.

[0008] In order to reduce strain birefringence and the like, annealing treatment is generally performed after growing a single crystal. In Patent Document 1 (Patent No. 3466948), annealing treatment is performed, and the birefringence (strain birefringence) of the fluoride crystal is reduced in a short time by controlling the cooling rate at that time. It describes what you can do.

[0009] Further, Patent Document 2 (Patent No. 3466950) discloses that dust and coloring are caused by annealing in a state in which a force that compensates the internal stress distribution of the fluoride crystal is stored during annealing. It is described that a fluoride crystal with reduced residual stress which is difficult to occur can be obtained.

[0010] In Patent Document 3 (Japanese Patent Laid-Open No. 2000-34193), the transmittance is improved by providing a surface cleaning step or an altered layer removal step after the annealing treatment step before the annealing treatment (heat treatment) step, respectively. It is described that a fluoride single crystal can be produced in which a deteriorated layer does not exist in the surface layer where the internal turbidity is high and the strain is low.

[0011] In Patent Document 4 (Japanese Patent Laid-Open No. 2004-99409), in cooling associated with the production of a fluorite single crystal, the cooling rate is continuously increased while maintaining an internal stress level that does not cause plastic deformation. However, it is described that, even if a large fluorite single crystal whose strain birefringence tends to increase by cooling is used, the quality is high and the productivity is good.

[0012] In Patent Document 5 (Japanese Patent Laid-Open No. 10-251096), the homogeneity of the refractive index is obtained by annealing a fluorite single crystal that has been processed into a shape that approximates or resembles the planar contour shape of the final product. RMS value after correction of power component of wavefront aberration and RM of non-rotationally symmetric component

It is described that a fluorite single crystal having a small S value is obtained.

[0013] Patent Document 1: Japanese Patent No. 3466948

Patent Document 2: Japanese Patent No. 3466950

Patent Document 3: Japanese Patent Laid-Open No. 2000-34193

Patent Document 4: Japanese Unexamined Patent Application Publication No. 2004-99409

Patent Document 5: Japanese Patent Laid-Open No. 10-251096 Patent Documents:! To 5 specify lens conditions for exposure apparatus by specifying manufacturing conditions or manufacturing processes when manufacturing fluoride single crystals such as calcium fluoride (fluorite) single crystals. It improves the properties required for the fluoride single crystal used in the film, such as strain birefringence and transmittance.

[0015] The fluoride single crystal used in the optical system of the exposure apparatus combines (111) plane orientation and (100) plane single crystal to cancel the intrinsic birefringence, and (100) plane Significantly reducing the strain birefringence inside the orientation crystal is extremely important for applications such as lens materials for exposure equipment.

Disclosure of the invention

Problems to be solved by the invention

Accordingly, an object of the present invention is to provide a method for processing a cylindrical fluoride single crystal having a (100) crystal plane, in which the strain birefringence inside the (100) plane crystal is greatly reduced. is there. Means for solving the problem

As a result of the study, the present inventors have found that production of a low strain single crystal having a (100) plane orientation can be achieved by cutting an annealed fluoride single crystal polyhedron. . In addition, when machining after the above cutting, cylindrical grinding (rounding) is used as the machining, and the surface roughness (RMS) of the single crystal cylindrical grinding surface at that time is kept within a certain range, It has been found that further (100) orientation low strain single crystal production can be achieved.

[0018] That is, the present invention is characterized in that the grown single crystal ingot is cut to obtain a polyhedron, the polyhedron is annealed, and then cut further. The present invention provides a method for processing a product single crystal.

[0019] The present invention also provides a (100) crystal plane fluoride single crystal obtained by cutting a grown single crystal ingot to obtain a polyhedron, annealing the polygon, and further cutting and processing the polyhedron. The above processing is cylindrical grinding, and the surface roughness (RMS: root mean square roughness) of the single crystal cylindrical grinding surface (cylindrical side surface) after the cylindrical grinding is 0 .: The present invention provides a method for processing a cylindrical fluoride single crystal having a (100) crystal plane, which is characterized by! -5.0 xm.

[0020] Further, in the machining method according to the present invention, the cylindrical machining is performed in the direction of the cylindrical axis. Desirably, the cutting speed of the stone is 1 mm / min to 300 mm / min, and the rotation speed of the fluoride single crystal with respect to the grindstone is 5 rpm to 15 rpm. By using such conditions, the strain birefringence inside the (100) plane crystal can be further reduced.

[0021] Further, in the above processing method according to the present invention, it is desirable that the grindstone particle size of the cylindrical grinding is # 100 to # 240. By using a grindstone with such a grain size, the strain birefringence inside the (100) -oriented crystal can be further reduced.

The invention's effect

[0022] By the processing method according to the present invention, the strain birefringence of the (100) -oriented crystal inside of the cylindrical fluoride single crystal can be greatly reduced.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the present invention will be described.

[0024] Fluoride single crystal ingot growing step: In the processing method according to the present invention, a fluoride single crystal is first grown. As the fluoride single crystal, calcium fluoride, barium fluoride, strontium fluoride, magnesium fluoride, etc. are used as an optical component with high power transmission, and calcium fluoride called fluorite is representative. Is.

[0025] Fluoride raw materials such as fluoride powder and dissolved pulverized products are put into a crucible for growth and melted, and then slowly cooled to grow crystals to produce a fluoride single crystal ingot having a diameter of about 250 mm to 350 mm. As the crystal growth method, the Bridgman method (stock burger method, crucible descending method) or Chiyoklarsky method is adopted. The crucible to be used is preferably a graphite norebo.

[0026] In the growth of this fluoride single crystal, the furnace temperature is raised to a temperature above which the fluoride raw material of the crucible melts, and after the crucible is lowered, a temperature gradient of 5 ° C / hr to 25 ° C / hr. Reduce the single crystal grown to a room temperature. All during the training carried out in a vacuum atmosphere ^{(1 X 10 "3 Pa ~l} X 10 _5 Pa). Growth rate (reduction rate) of the single crystal is Gyotsu at 0 · lmm / hr~5 • OmmZhr.

[0027] Simple annealing treatment and cutting process of fluoride single crystal ingot: The fluoride single crystal ingot grown in this way has a residual strain that is too large to cause cracks in the ingot. Occurs. Therefore, at a low temperature to prevent cracks in the ingot It is desirable that annealing be performed in a simple atmosphere, specifically 200 to 500 ° C, 7 to 21 days in an inert atmosphere to reduce residual strain.

[0028] An ingot having a reduced residual strain is obtained by using a diamond saw or the like, for example, from lmm / min to

It is cut at a speed of 15mmZmin to make a polygon. Polygonal bodies such as hexagonal cylinders and octagonal cylinders are generally used as the polygons. The cutting size and side orientation are arbitrary.

[0029] Annealing process of fluoride single crystal polyhedron: Next, the fluoride single crystal polyhedron is annealed in an annealing furnace. The annealing conditions are generally in an inert atmosphere with a maximum temperature of 1100 ° C to 1300 ° C, a temperature gradient in the annealing furnace of 0.4 ° C / cm or less, and a temperature of 0.4 ° C Zhr or more. The temperature falls at the rate of temperature drop. The annealing period is 1 to 2 months. Thus, annealing the fluoride single crystal polyhedron can reduce the strain birefringence.

[0030] Cutting and processing of fluoride single crystal polyhedrons: Examples of bottom (top) shapes in cutting and processing steps of fluoride single crystal polyhedrons (hexagonal prisms) are shown in Figs. 2 (a) to (c), respectively. ). Figure 2 (a) shows the bottom shape of the fluoride single crystal polyhedron before and after annealing, and the bottom shape is an unequal hexagon. Fig. 2 (b) shows the bottom shape after cutting the fluoride single crystal polyhedron after annealing, and the bottom shape is a substantially regular hexagon. The circle inside the substantially regular hexagon is a region where a predetermined cylindrical crystal is to be obtained. Fig. 2 (c) shows the bottom shape after cylindrical grinding of a fluoride single crystal polyhedron, and the bottom shape is a perfect circle conforming to product standards.

In this step, first, the fluoride single crystal polyhedron subjected to the annealing treatment is cut.

The cutting is performed at the same speed as described above using a diamond saw or the like as described above. The shape of the fluoride to be cut and the cut size are arbitrarily determined depending on the shape and size of the final product, but in the present invention, the shape is finally cylindrical, so that the shape is a polygonal column that is close to this. It is preferable to use a hexagonal columnar body or an octagonal columnar body.

In the processing method of the present invention, a low strain single crystal having a (100) orientation is achieved by cutting the annealed fluoride single crystal polyhedron. Further, in the processing method of the present invention, as will be described later, by processing under specific conditions after cutting, further production of a low strain single crystal having a (100) plane orientation can be achieved. Next, a fluoride single crystal of a polygonal columnar body whose bottom surface shape is cut as shown in FIG. 2 (b) is processed. Cylindrical grinding, that is, rounding is adopted as the processing. In the present invention, in this cylindrical grinding process, the cutting speed of the grindstone in the direction of the cylindrical axis is preferably lm m / min to 300 mmz min, more preferably 5 mm / min to 15 mm min. (Work), that is, the rotation speed of the fluoride single crystal is preferably 5 rpm to 15 rpm, more preferably 5 rpm to 10 rpm. If the cutting speed or rotational speed is outside the above range, the strain birefringence inside the crystal with the (100) orientation cannot be significantly reduced. Further, the grindstone particle size used in this cylindrical grinding process is preferably # 100 to ヰ 240, and more preferably # 120 to # 180. By using a grindstone with such a grain size, the strain birefringence inside the (100) -oriented crystal is further reduced. By cylindrical grinding, a cylindrical body with a perfect bottom as shown in Fig. 2 (c) is obtained. The diameter of the bottom is determined by product standards.

[0034] The surface roughness (RMS) of the single crystal cylindrical grinding surface (cylindrical side surface) after cylindrical grinding obtained in this way is from 0 · l / im to 5.0 / im, and even 1 · 0 / im to 2.0 / im. A single crystal having such a surface roughness can reduce strain birefringence inside the (100) -oriented crystal.

[0035] Finally, surface grinding is performed to make the two opposing faces of the single crystal parallel to obtain a product thickness. The cutting speed at this time is normally 0 · 05 mm / min to 0.2 mm / min.

[0036] A product of the fluoride single crystal produced in this manner and having a significantly reduced strain birefringence inside the (100) -oriented crystal.

Hereinafter, the present invention will be specifically described based on examples and the like.

Example 1

[0038] A calcium fluoride single crystal ingot grown by the Bridgeman Stock Burger method was subjected to a simple annealing treatment in an argon atmosphere at 250 ° C for 14 days, and then cut to obtain a calcium hexagonal columnar body. The calcium fluoride hexagonal column was annealed. The annealing treatment was performed at a maximum temperature of 1 100 ° C to 1300 ° C in an inert atmosphere, with a temperature gradient in the annealing furnace of 0.4 ° C / cm or less, and a temperature decrease rate of 0.4 ° C / h or more. The annealing period is one month. The annealed calcium fluoride hexagonal columnar body was further cut to obtain a calcium fluoride hexagonal columnar body that was slightly smaller.

[0040] Calcium fluoride hexagonal column before and after annealing and calcium fluoride after cutting Hexagonal columnar (100) orientation birefringence (average, deviation, mean square root, maximum, minimum) ) Was measured using an automatic strain birefringence meter. The results are shown in Table 1. Note that the unit of strain birefringence is nmZcm.

[0041] [Table 1]

Example 2

[0042] In the same manner as in Example 1, a calcium fluoride single crystal ingot grown by the Bridgeman Stock Burger method was subjected to a simple annealing treatment, and then cut to obtain a calcium fluoride hexagonal columnar body, followed by an annealing treatment. Was given.

The annealed calcium fluoride hexagonal column was further cut to obtain a calcium fluoride hexagonal column that was slightly smaller.

[0044] Calcium fluoride hexagonal column before and after annealing and calcium fluoride after cutting Hexagonal columnar (100) orientation birefringence (average, deviation, mean square root, maximum, minimum) ) Was measured using an automatic strain birefringence meter. The results are shown in Table 2.

[0045] [Table 2] Example 2 Before annealing treatment After annealing treatment After annealing treatment, only cutting process Diameter (mm) 1 1 0 1 10 1 10

Average (m) 1 .53 1 .68 0.85

Deviation (σ) 0.95 0.84 0.54

Root mean square (rms) 1.80 1.87 1.01

Maximum (max) 4.52 4.77 2.82

Minimum (min) 0.35 0.37 0.04

Example 3

[0046] Calcium fluoride single crystal grown by Bridgeman Stock Burger method

The ingot was subjected to a simple annealing treatment and then cut to obtain a calcium fluoride hexagonal columnar body. The calcium fluoride hexagonal column was annealed. The annealing treatment was performed in an inert atmosphere with a maximum temperature of 1100 ° C to 1300 ° C, a temperature gradient in the annealing furnace of 0.4 ° C / cm or less, and a temperature decrease rate of 0.4 ° CZh or more. The annealing period is one month.

[0047] The annealed calcium fluoride hexagonal columnar body was further cut and then subjected to cylindrical grinding to produce a calcium fluoride cylinder having a diameter of 100 mm. Machining conditions were a grinding wheel cutting speed of 5mm / min in the direction of the cylinder axis, a workpiece rotation speed of 15i "pm against the grinding wheel, and a grinding wheel grain size of # 150.

[0048] Strain birefringence (mean, deviation, root mean square) within the 50 to 110 mm diameter in the calcium fluoride hexagonal column after annealing and the calcium fluoride cylinder after cylindrical grinding Maximum and minimum) were measured using an automatic strain birefringence meter. The results are shown in Table 3. The surface roughness (RMS) of the single crystal cylindrical grinding surface (cylindrical side surface) after cylindrical grinding was 1 · 1 / im.

[0049] [Table 3]

Example 4 [0050] A calcium fluoride single crystal ingot grown by the Bridgeman Stock Burger method was subjected to a simple annealing treatment, and then cut to obtain a calcium fluoride hexagonal columnar body.

[0051] The calcium fluoride hexagonal columnar body was annealed, cut and cylindrically ground according to Example 3 to produce a calcium fluoride cylindrical body having a diameter of 150 mm.

[0052] Strain birefringence (mean, deviation, root mean square) of (100) orientation within 50 to 150 mm diameter in hexagonal columnar calcium fluoride after annealing and calcium fluoride cylinder after cylindrical grinding Maximum and minimum) were measured using an automatic strain birefringence meter. The results are shown in Table 4. The surface roughness (RMS) of the single crystal cylindrical grinding surface (cylindrical side surface) after cylindrical grinding was 1.

[0053] [Table 4]

Comparative example

[0054] [Comparative Example 1]

As in Example 3, a calcium fluoride single crystal ingot grown by the Bridgeman Stock Burger method was subjected to a simple annealing treatment, and then cut to obtain a calcium fluoride (111) -oriented hexagonal columnar body. The calcium fluoride hexagonal columnar body was annealed, cut and cylindrically ground according to Example 3. Calcium fluoride hexagonal column after annealing, and (111) orientation birefringence (average, deviation, root mean square, maximum, minimum) within a diameter of 87mm to 240mm in cylindrical calcium fluoride after cylindrical grinding Was measured using an automatic strain birefringence measuring instrument. The results are shown in Table 5.

[0055] [Table 5]

Comparison example "! After processing a After processing and after cylindrical grinding Diameter (mm) 87 101 145 179 240 87 101 145 179 240 Average (m) 0.13 0.14 0.16 0.19 0.25 0.14 0.15 0.18 0.21 0.26 Deviation (σ) 0.07 0.07 0.1 1 0.12 0.18 0.08 0.09 0.12 0.14 0.1 9 root mean square (rms) 0.15 0.16 0.20 0.22 0.31 0.16 0.18 0.22 0.25 0.32 bold (max) 0.34 0.65 1.71 1.71 1.71 0.42 0.65 0.65 1.02 1.38 minimum (min) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 [0056] [Comparative Example 2]

A calcium fluoride single crystal ingot grown by the Bridgeman Stock Burger method was subjected to a simple annealing treatment and then cut to obtain a calcium fluoride hexagonal columnar body.

The calcium fluoride hexagonal columnar body was subjected to cylindrical grinding under the same conditions as in Example 3 to produce a calcium fluoride cylindrical body. Next, this calcium fluoride cylinder was annealed under the same conditions as in Example 3, and finally a calcium fluoride cylinder having a diameter of 130 mm was produced.

[0058] Automatic strain birefringence measurement (average, deviation, root mean square, maximum, minimum) of (100) plane orientation within 50mm to 120mm diameter in the finally obtained calcium fluoride cylinder Measured using a vessel. The results are shown in Table 6. The surface roughness (RMS) of the single crystal cylindrical grinding surface (cylindrical side surface) after cylindrical grinding was 1.7 μm.

[0059] [Table 6]

[0060] [Comparative Example 3]

The calcium fluoride cylinder produced in Comparative Example 2 was again subjected to cylindrical grinding under the same conditions as in Example 3, and finally a calcium fluoride cylinder having a diameter of 129 mm was produced.

[0061] Automatic strain birefringence measurement (average, deviation, root mean square, maximum, minimum) of (100) plane orientation within 50mm to 120mm diameter in the finally obtained calcium fluoride cylinder Measured using a vessel. The results are shown in Table 7. The surface roughness (RMS) of the single crystal cylindrical grinding surface (cylindrical side surface) after cylindrical grinding was 1.8 μm.

[0062] [Table 7] Comparative Example 3 After cylindrical grinding, annealing, and circular grinding Diameter (mm) 50 75 100 120 Average (m) 2.01 2.24 2.52 2.41 Deviation (σ) 0.77 1.02 1.16 1.1 Average square root (rms) 2.1 5 2.46 2.77 2.65 Maximum (max) 3.68 4.97 6.34 6.34 Minimum, min) 0.09 0.09 0.09 0.09

[0063] [Comparative Example 4]

The calcium fluoride cylinder produced in Comparative Example 3 was again subjected to cylindrical grinding under the same conditions as in Example 3, and finally a calcium fluoride cylinder having a diameter of 120 mm was produced.

[0064] Automatic strain birefringence measurement (average, deviation, root mean square, maximum, minimum) of (100) plane orientation within 50mm to 120mm diameter in the finally obtained calcium fluoride cylinder Measured using a vessel. The results are shown in Table 8. The surface roughness (RMS) of the single crystal cylindrical grinding surface (cylindrical side surface) after cylindrical grinding was 1.8 μm.

[0065] [Table 8]

[0066] [Comparative Example 5]

The calcium fluoride hexagonal columnar body was annealed according to Example 3, and then immersed in an etching solution (O + HCl: concentration 10%) to dissolve the surface between 0.05 mm and 0.1 mm.

2

[0068] Automatic birefringence (average, deviation, root mean square, maximum, minimum) within 50 to 120 mm diameter of (100) plane orientation of calcium fluoride hexagonal column before and after etching treatment Measured using a refractometer. The results are shown in Table 9.

[0069] [Table 9]

[0070] From the results in Tables 1 to 9, the following can be seen. That is, in Example 1 and Example 2, the force S obtained by cutting the calcium fluoride hexagonal column and the strain birefringence in the (100) plane orientation are reduced, so that the strain birefringence can be reduced. Yes (see Table 1 and Table 2). In Examples 3 and 4, the calcium fluoride hexagonal columnar body was cut and then subjected to cylindrical grinding under certain conditions. However, since the strain birefringence in the (100) plane orientation was further reduced, Refraction can be further reduced (see Table 3 and Table 4). However, as in Comparative Example 1, even if the calcium hexagonal columnar body is subjected to cylindrical grinding under certain conditions, the strain birefringence in the (111) plane orientation does not change significantly before and after cylindrical processing (Table 5). reference).

Comparative Example 2 to Comparative Example 4 are obtained by subjecting the calcium fluoride hexagonal columnar body to cylindrical grinding before annealing, and after annealing to 0 to 2 times cylindrical grinding. Since the strain birefringence of the direction does not become small, the strain birefringence is not reduced (see Table 6 to Table 8). In Comparative Example 5, the stress birefringence of the (100) plane orientation is not reduced by force chemical grinding, which is an etching treatment of a calcium fluoride hexagonal columnar body, so the strain birefringence is not reduced (see Table 9). .

Industrial applicability

The cylindrical fluoride single crystal obtained by the processing method according to the present invention is suitable as a lens for an exposure apparatus because the strain birefringence inside the (100) plane crystal is greatly reduced. It can also be used as a glass material for other optical components.

Brief Description of Drawings

[FIG. 1] FIG. 1 shows a (100) crystal plane, FIG. 1 (a) is a cylindrical body, and FIG. 1 (b) is a hexagonal cylindrical body.

[FIG. 2] FIG. 2 is a view of cutting a fluoride single crystal polyhedron (hexagonal column) of the processing method according to the present invention, It is a figure which shows an example of the bottom face (top surface) shape in a process, FIG. 2 (a) is front and back, FIG. 2 (b) is after cutting | disconnection, FIG.2 (c) is after cylindrical grinding.

Claims

The scope of the claims

[1] A method for processing a fluoride single crystal on a (100) crystal plane, comprising cutting a grown single crystal ingot to obtain a polygon, annealing the polygon, and further cutting the polygon.

[2] In the method for processing a fluoride single crystal on a (100) crystal plane, the grown single crystal ingot is cut to obtain a polygon, and the polygon is annealed and then cut and processed. (100) crystal face, wherein the surface roughness (RMS) of the single crystal cylindrical grinding surface after cylindrical grinding is 0 · l / im to 5.0 / im Method of processing cylindrical fluoride single crystal.

[3] The grinding speed of the grinding wheel in the cylindrical axis direction is lmm / min to 300mm.

The processing method of the cylindrical fluoride single crystal according to claim 2, wherein the rotational speed of the fluoride single crystal with respect to the grindstone is 5 rpm to 15 rpm.

[4] The method for processing a cylindrical fluoride single crystal according to claim 2 or 3, wherein the grindstone particle size of the cylindrical grinding is # 100 to # 240.