WO2009142284A1

WO2009142284A1 - Method for production of molded fluoride crystal article, optical member produced by the method, and optical device and ultraviolet ray washing device each comprising the optical member

Info

Publication number: WO2009142284A1
Application number: PCT/JP2009/059405
Authority: WO
Inventors: 美菜子安住
Original assignee: 株式会社ニコン
Priority date: 2008-05-23
Filing date: 2009-05-22
Publication date: 2009-11-26
Also published as: JP2013082620A; KR20110015621A; KR101394781B1; JPWO2009142284A1; KR20130041369A; JP5251976B2; JP5648675B2; KR101330974B1

Abstract

Disclosed is a method for producing a molded fluoride crystal article which has a different shape from that of a fluoride crystal base and has excellent optical properties readily. The method comprises heating the fluoride crystal base at a temperature lower than the melting point of the fluoride crystal base while compressing to mold the fluoride crystal base into a predetermined shape. In the method, the fluoride crystal base is compressed to initiate the deformation of the fluoride crystal base through recrystallization and the deformation is allowed to proceed until the fluoride crystal base has the predetermined shape.

Description

Method for producing a fluoride crystal molded body, and an optical member produced thereby, an optical device provided with the optical member, and an ultraviolet cleaning device

The present invention relates to a method for producing a fluoride crystal molded body for molding a fluoride crystal base material into a predetermined shape, an optical member provided with the fluoride crystal molded body produced by the method, and the optical member Optical device and ultraviolet cleaning device.

Conventionally, in optical systems of various devices using Xe excimer lamps, Kr excimer lamps, Ar excimer lamps, etc., particularly optical systems that transmit light with a wavelength of 200 nm or less, optical members made of fluorides such as calcium fluoride are used It is done. This optical member is often substantially formed of a single crystal. In order to grow a fluoride single crystal, single crystal growth techniques such as the Bridgman method and the Czochralski method are used.

In order to produce various optical members using a single crystal growth technique, it is necessary to grow a single crystal larger than a target optical member, and then process it into a target shape through processing steps such as cutting. Therefore, it is impossible to manufacture an optical member having a larger shape than the grown single crystal. Specifically, it has been difficult to obtain a large-sized optical member which normally transmits light with a wavelength of 200 nm or less at a diameter greater than 350 mm.

There is known a method of deforming a fluoride crystal base material at a temperature lower than the melting point. For example, in Non-Patent Document 1 below, changes in optical properties and mechanical properties due to forging of lithium fluoride and calcium fluoride are evaluated. A columnar calcium fluoride crystal base material is disposed between the upper ram and the lower ram in a pressure device, and heated at various temperatures in the range of 510 to 750 ° C. in a He gas atmosphere to obtain the upper ram and the lower ram It is disclosed that the fluoride crystals are deformed by pressing between them. It is also disclosed that lithium fluoride crystals are also forged by heating in the range of 300 to 600 ° C. using the apparatus.
OPTICAL ENGINEERING, Vol. 18 No. 6, Nov.-Dec. 1979, P602-609

However, according to the experiments of the present inventor, when the fluoride crystal base material is deformed and formed into a predetermined shape under the conditions such as the temperature disclosed in the above-mentioned document, the optical characteristics deteriorate remarkably, particularly, the vacuum ultraviolet region It was found that the decrease in the light transmittance of the light is remarkable.

Therefore, an object of the present invention is to provide a manufacturing method capable of easily producing a fluoride crystal molded body having a shape different from the fluoride crystal base material and having excellent optical properties from the fluoride crystal base material. It is to be. A further object of the present invention is to provide an optical member which is produced by such a production method and provided with a fluoride crystal molded article having excellent optical properties. Still another object of the present invention is to provide an optical device or an ultraviolet cleaning device using such an optical member.

According to a first aspect of the present invention, there is provided a method of producing a fluoride crystal molded body for forming a fluoride crystal base material into a predetermined shape, wherein the fluoride crystal base material is disposed between a pair of opposed pressure surfaces. When the fluoride crystal base material is heated at a constant temperature rising rate while applying a constant load between the pair of pressing surfaces, the deformation amount per unit time in the load direction of the fluoride crystal base material is maximum Where T is the temperature at which temperature is T and the pressure applied to the fluoride crystal base material at that temperature T is P, the fluoride crystal base material is at least the temperature T and the fluoride crystal base material is lower than the melting point There is provided a method for producing a fluoride crystal molded body, characterized in that the fluoride crystal base material is deformed by heating and pressurizing at a temperature above the pressure P.

According to a second aspect of the present invention, there is provided a method of producing a fluoride crystal molded body, which is characterized in that the fluoride crystal base material is deformed while being heated at a temperature lower than the melting point and pressurized to recrystallize. There is provided a method of producing a fluoride crystal molded body.

According to a third aspect of the present invention, there is provided an optical member comprising a fluoride crystal molded article produced by the production method of the present invention.

According to a fourth aspect of the present invention, there is provided an optical device in which the optical member is disposed in an optical path through which vacuum ultraviolet light having a wavelength of 125 nm to 200 nm is transmitted.

According to the fifth aspect of the present invention, there is provided an ultraviolet cleaning apparatus for irradiating vacuum cleaning light having a wavelength of 125 nm to 200 nm through the window material to the member to be cleaned, wherein the optical member is used as the window material. An ultraviolet cleaning device is provided.

According to the manufacturing method of the present invention, since the fluoride crystal base material is deformed while being pressurized and heated to be recrystallized, it is possible to maintain the optical properties of the fluoride crystal base material while maintaining the optical properties of the fluoride crystal base material It can be molded into different desired shapes. Further, in the manufacturing method of the present invention, recrystallization can be reliably generated because heating and pressing are performed under temperature conditions where the deformation amount (deformation speed) of the fluoride crystal base material is maximum.

Moreover, since the optical member of the present invention is formed of the fluoride crystal molded body manufactured by the above-described manufacturing method, it has excellent optical characteristics. Moreover, since it shape | molds to a desired dimension irrespective of the dimension of the fluoride crystal base material used as a raw material, it becomes useful to various uses.

Furthermore, in the optical device of the present invention, since the optical member of the present invention is disposed in the optical path through which vacuum ultraviolet light with a wavelength of 125 nm to 200 nm is transmitted, the transmittance of vacuum ultraviolet light is high, and uses of vacuum ultraviolet light Preferred.

Moreover, since the ultraviolet cleaning device of the present invention uses the optical member of the present invention as a window material, it can be excellent in optical characteristics such as transmittance, and sufficiently secure the area of the transmission window. Therefore, it is suitable for efficient light cleaning of a large member.

It is a schematic sectional drawing which shows the shaping | molding apparatus used for the manufacturing method of embodiment of this invention. It is a schematic sectional drawing which shows the washing | cleaning part of the ultraviolet-ray washing | cleaning apparatus of embodiment of this invention. In the example and the comparative example, the result of having measured the transmittance | permeability of the wavelength range of 200 nm-120 nm with the vacuum ultraviolet region spectrophotometer is shown. In the example and the comparative example, after irradiating ArF excimer laser, the result of having measured the transmittance | permeability of a wavelength range of 800 nm-200 nm is shown. In an Example and a comparative example, it is a figure which shows the temperature change and deformation amount at the time of heating-pressing a fluoride crystal molded object. The fluoride crystal molded object obtained in the Example and the comparative example is shown, (a) is a top view, (b) is a side view. In an Example and a comparative example, it is a figure which shows the correlation with the maximum pressure and the maximum temperature at the time of heat-press molding, and the correlation with the pressure and temperature at the time of completion of deformation. FIG. 8 is a diagram connecting points between the maximum pressure and the maximum temperature during heat and pressure molding of FIG. 7 by a straight line. (A) (b) is a photograph of the upper surface and lower surface of the molded object obtained by Example 5, and crystal orientation is shown. It is a figure explaining the definition of the crystal orientation of FIG. FIG. 16 is a top view of a single crystal base material before forming in Example 5; The example which used the fluoride crystal molded object for the objective lens of the telescope is shown.

Hereinafter, embodiments of the present invention will be described.

The fluoride crystal molded body manufactured according to this embodiment is a molded body that can be used as various optical members for the purpose of transmitting light such as vacuum ultraviolet light, and has a flat plate shape, a spherical or aspherical convex shape or It has an appropriate shape such as a concave shape.

In order to manufacture the fluoride crystal molded body, it is manufactured by molding a preformed fluoride crystal base material by heating and pressing.

The fluoride crystal base material is, for example, a crystal of calcium fluoride, magnesium fluoride, barium fluoride, lanthanum fluoride, cerium fluoride, yttrium fluoride or the like. Calcium fluoride is preferred because it is excellent in optical characteristics such as transmittance to vacuum ultraviolet light.

It is preferable that the fluoride crystal base material is provided in advance with optical characteristics such as transmittance required for a molded article to be produced. It is because it is not easy to improve the optical characteristics in the molding process.

The fluoride crystal base material may be either a single crystal or a polycrystal, but is preferably a single crystal to obtain excellent optical properties. Here, it is sufficient that the fluoride crystal base material is a single crystal substantially as long as it is a single crystal, and it may slightly contain twin crystals and the like. The single crystal can be obtained, for example, using a single crystal growth technique such as the Bridgman method or the Czochralski method.

The forming of the fluoride crystal base material is performed at a temperature lower than the melting point. For example, the melting point of calcium fluoride is reported to be about 1350 ° C. When the liquid phase is generated by heating to a temperature higher than the melting point, new crystals are randomly formed when the liquid phase is solidified, and the optical properties of the obtained molded product are significantly deteriorated. In this forming, by heating and pressurizing the fluoride crystal base material, deformation due to recrystallization is started as it is in the solid phase, and then it is further deformed to a predetermined shape.

Here, the deformation by recrystallization is to deform while recrystallizing. In general, when crystal materials such as metals and ceramics are heated to a temperature below the melting point, they are rapidly softened and deformed crystals are separated and separated into polygonal fine grains. When mechanical processing such as rolling is performed, dislocations increased thereby are also extinguished by the heating, and the crystal grains become stable without internal strain (internal stress). This phenomenon is called recrystallization.

In the present invention, in order to deform the fluoride crystal base material, recrystallization is performed under pressure at a predetermined temperature. That is, in the present invention, the fluoride crystal base material is vacuumed by recrystallization while pressurizing the fluoride crystal base material at a predetermined temperature or higher, instead of recrystallizing the fluoride crystal base material only by heating. It can be deformed without deteriorating optical characteristics such as light transmittance in the ultraviolet region. As in the examples described later, the higher the pressure, the higher the deformation rate at a lower temperature, and so on, so it can be inferred that the temperature sufficient for initiating deformation due to recrystallization has a correlation with the pressure. Therefore, in the present invention, deformation due to recrystallization is started by combining temperature and pressure. In addition, since it is difficult to pinpoint the starting point of recrystallization precisely, it is sufficient to start deformation at a temperature and pressure at which deformation due to recrystallization surely occurs.

In the case where the fluoride crystal base material is deformed under the condition that at least one of temperature and pressure is too low, it is considered that deformation due to slippage of the crystal structure occurs, not deformation due to recrystallization. When deformation due to slippage occurs, lattice defects occur in the crystal as the deformation occurs, and optical characteristics such as transmittance decrease.

According to the findings of the present inventor, it has been found that the temperature and pressure at which deformation due to recrystallization reliably occurs can be determined as follows. That is, when the fluoride crystal base material is heated at a constant temperature rising rate while applying a constant load, the deformation amount per unit time in the load direction of the fluoride crystal base material (change in length per unit time in the load direction) The temperature T (hereinafter referred to as “maximum deformation temperature” as appropriate) at which the amount is a maximum value (hereinafter referred to as “maximum deformation speed” as appropriate) is measured. At this maximum deformation temperature, recrystallization of the fluoride crystal base material is considered to occur for the following reason. It is known that deformation due to pressurization of a fluoride crystal base material is caused by a sliding phenomenon, that is, dislocation of the crystal slips on the crystal plane. Since the activation energy for slippage is relatively small, the temperature dependency is also small. Therefore, even at relatively low temperatures, it occurs by stressing the crystals. On the other hand, as described above, recrystallization is a phenomenon in which the dislocations contained in the crystal are rearranged by heating to generate crystal nuclei, and the crystal nuclei grow as grains. The activation energy for recrystallization to occur is relatively high and therefore highly temperature dependent. For this reason, at high temperatures, the reaction rate of recrystallization is increased. Therefore, when the crystal is pressurized and deformed, if deformation amount per unit time does not change much with respect to the temperature rise of the crystal, it is considered that deformation due to slip has occurred. On the other hand, recrystallization occurs in a temperature range in which the deformation amount of the crystal per unit time is largely changed due to the temperature increase, for example, in the temperature range near the inflection point in volume change curve V in FIG. It is thought that In this way, the inventor infers that recrystallization of the fluoride crystal matrix reliably occurs at the maximum deformation temperature.

Whether or not the fluoride crystal base material is deformed through recrystallization can be verified by observing the crystal orientation after deformation. For example, the surface of the single crystal fluoride crystal base material before deformation as shown in FIG. 11 has a large number of grain boundaries recognized as shown in FIG. 9A due to the occurrence of deformation through recrystallization. Be Although the crystal orientation of the crystal grain specified by the Laue method is added in FIG. 9 (a), it can be seen that polycrystals are generated because those crystal orientations are random. Thus, it can be confirmed that recrystallization has occurred by observing the molded body in the fluoride crystal base material. On the other hand, when the fluoride crystal base material is deformed only by sliding without recrystallization, subgrain boundaries generated by sliding bands and crystal rotation are observed but no grain boundaries are observed. .

Furthermore, when the fluoride crystal base material is made of calcium fluoride, in order to reliably cause recrystallization under the heating and pressure as described above, the following formulas (1) to (5) are based on the results of the examples described later. It is good also as temperature T and pressure P which satisfy either of (4).

T ≧ 1125 ° C. and P ≧ 6.9 MN / m ² and −11.5 × P (MN / m ² ) +1285 <T (° C.) (1)
T ≧ 970 ° C. and P ≧ 13.9MN / m ² and ^{-22.3 × P (MN / m 2} ) +1435 <T (℃) ··· (2)
T ≧ 968 ° C. and P ≧ 20.8MN / m ² and ^{-0.289 × P (MN / m 2} ) +976 <T (℃) ··· (3)
T ≧ 883 ° C. and P ≧ 27.7MN / m ² and ^{-12.2 × P (MN / m 2} ) +1306 <T (℃) ··· (4)

In order to heat and pressurize the fluoride crystal base material to such temperature T and pressure P, the fluoride crystal base material is heated and heated, for example, because it is easy to prevent the failure of the fluoride crystal base material. It is preferable to start pressurization after that, and in particular, it is preferable to heat up to the temperature T and then start pressurization.

By starting pressurization, deformation of the fluoride crystal base material is started, but at this time, it is preferable to allow the temperature T and the pressure P to reach at the latest during the deformation of the fluoride crystal base material. Even if the crystal structure is disturbed by slip deformation before recrystallization starts, it can be improved by passing a deformation period by recrystallization thereafter. Preferably, the temperature T and the pressure P are reached at the start of the deformation. This is because deformation due to slippage of the crystal structure can be prevented, and excellent optical characteristics can be easily obtained.

After the deformation due to recrystallization is started, it is further deformed to a predetermined shape. At this time, after deformation due to recrystallization is started, it is preferable to continue applying pressure as it is to deform to a predetermined shape. After the deformation due to recrystallization is started, as long as the deformation due to pressure is continued, the optical characteristics of the obtained molded article can be easily secured sufficiently high. The reason for this is not clear, but the deformation due to recrystallization does not occur simultaneously with the deformation due to the slip of the crystal structure, and the deformation due to recrystallization continues or the slip occurs even if the slip and the recrystallization occur simultaneously. It is inferred that the resulting portion of is to replace the crystal grains by recrystallization.

In this embodiment, in order to form such a fluoride crystal base material, for example, a forming apparatus as shown in FIG. 1 can be used.

In the molding apparatus of FIG. 1, a molding die 13 capable of containing and pressurizing the fluoride crystal base material 11 is disposed in a chamber 10 made of a stainless steel container. The mold 13 is made of graphite, and the cylindrical mold 15, the lower mold 17 closing one end opening of the cylindrical mold 15, and the other mold opening from the other end opening of the cylindrical mold 15 are accommodated in the internal space And a pressure die 19 arranged as possible.

Here, the lower die 17 is supported by the support portion 23 via the support rod 21, and the pressure die 19 is connected to the pressure drive unit 27 via the pressure rod 25. The surface on the pressure mold 19 side of the lower mold 17 and the surface on the lower mold 17 side of the pressure mold 19 face each other to constitute a pressure surface.

The mold 13 is accommodated in a heat insulating frame 31 made of a heat insulating material having air permeability. The heating element 33 is disposed in the heat insulation frame 31 so that the inside of the chamber 10 can be heated, and the temperature detection unit 35 detects the temperature in the heat insulation frame 31 including the mold 13 and generates heat based on the detected temperature. The heating of the body 33 can be precisely controlled.

Further, the chamber 10 is airtight, and the support rod 21 and the pressure rod 25 are airtightly disposed by the

airtight seal portions

23a and 27a so as to be penetrated. An atmosphere gas introduction unit 37 and a vacuum evacuation unit 39 are connected to the chamber 10, and an inert gas can be introduced from the atmosphere gas introduction unit 37 and can be exhausted from the evacuation unit 39.

In this molding apparatus, the mold 13 is made of graphite. It is preferable to use graphite having a high purity of 10 wtppm or less, particularly an ultrahigh purity of 2 wtppm or less, not graphite having a general purity of more than 10 wtppm as ash. This is because the penetration of the alkali metal and the alkaline earth metal element from the mold 13 into the obtained fluoride crystal molded body can be made shallow.

The alkali metal and alkaline earth metal elements that have permeated into the fluoride crystal molded body can be removed from the fluoride crystal molded body by removing the surface of the fluoride crystal molded body, but the mold 13 has an ash content of 10 wtppm or less By using high purity graphite, the thickness to be cut can be reduced to about 5 mm.

In order to form the fluoride crystal base material 11 using such a forming apparatus, first, the fluoride crystal base material 11 is accommodated in the forming die 13. In a state in which the fluoride crystal base material 11 is accommodated in the mold 13, the center of the lower mold 17 is locally abutted on the surface on the pressure mold 19 side and / or each central surface of the pressure mold 19 on the lower mold 17 side. Arranged in the state. In this state, the mold 13 is placed in the heat insulation frame 31, the lower mold 17 is supported by the support rod 21, and the pressure rod 25 is connected to the pressure mold 19 to seal the chamber 10.

Thereafter, evacuation may be performed from the evacuation unit 39, evacuation may be performed, and molding may be started with the inside of the chamber 10 in a low pressure state, but preferably, inert gas is introduced from the atmosphere gas introducing unit 37 after evacuation. Make the inside an inert gas atmosphere. When the inside of the chamber 10 is made into an inert gas atmosphere, the amount of impurities mixed in the obtained fluoride crystal molded body can be easily suppressed as compared with the case where the inside of the chamber 10 is simply brought into a low pressure state for molding. Examples of the inert gas include nitrogen gas and helium gas.

Next, heating and pressure are applied while maintaining the atmosphere in the chamber 10 to deform the fluoride crystal base material 11. Before the forming step, a predetermined temperature and a predetermined pressure at which deformation due to recrystallization can be reliably generated are measured in advance, and such temperature and pressure are set. Based on the knowledge of the present inventor, the temperature (maximum deformation temperature) T and the pressure P at that time may be used to indicate the maximum deformation speed as described above.

In this embodiment, first, the fluoride crystal base material 11 is heated to a predetermined temperature by heating the heating element 33 in the heat insulating frame 31 while detecting the temperature by the temperature detection unit 35. After the temperature rise, the temperature is maintained and pressurization is started. In pressing, with the lower mold 17 and the cylindrical mold 15 supported by the support portion 23 through the support rod 21, the pressure drive unit 27 moves the pressure mold 19 to the lower mold 17 side through the pressure rod 25. The compression is performed by maintaining a state in which a constant load is applied to the pressure mold 19.

Here, if the predetermined pressure is applied to the fluoride crystal base material 11 at the start of pressurization and the temperature and pressure that produce the maximum deformation rate as described above are reached, then from the deformation start point of the fluoride crystal base material 11 It is thought that deformation by recrystallization occurs.

Thereafter, while controlling the calorific value of the heating element 33 and maintaining the temperature of the fluoride crystal base material 11, the deformation is advanced by maintaining a state in which a constant load is applied to the pressing die 19. During the deformation period, the contact area between the pressure die 19 and the fluoride crystal base material 11 increases, so the pressure applied to the fluoride crystal base material 11 gradually decreases, but the deformation due to recrystallization is started After that, the pressure is continuously continued as it is to deform it into a predetermined shape. Once deformation by recrystallization is started, at the end of deformation, the pressure may not satisfy the conditions of deformation by recrystallization.

After being deformed to a predetermined shape, it is gradually cooled to room temperature, taken out from the forming apparatus, and subjected to various processing as necessary, thereby completing the production of a fluoride crystal molded body.

In this embodiment, after completion of molding, processing is performed to remove the surface of the fluoride crystal molded body in contact with the mold 13. As a result, the alkali metal and alkaline earth metal elements permeating the fluoride crystal compact from the graphite of the mold 13 are removed, and the concentration of each of the alkali metal and alkaline earth metal elements in the fluoride crystal compact is 10 wt ppb or less Can be

Furthermore, when the material used as the fluoride crystal base material 11 has a low content of impurities, such as a single crystal, Cr, Mn, Fe, Co, and the like contained in the obtained fluoride crystal molded body The concentrations of Ni, Ba, Zn, La, Ce, and Pb can be 50 wtppb or less.

When the fluoride crystal molded body is a uniform plate-like member having a uniform thickness, the variation width of the thickness is 1 mm or less, the warpage is 0.5% or less, and the surface roughness Ra is 50 nm or less. Thus, for example, an optical member can be manufactured by lapping both surfaces with # 1200 abrasive grains in a large-sized Oscar-type polishing machine, followed by polishing with cerium oxide, and thereafter performing washing and drying. it can.

In the optical member manufactured in this manner, the grain size of the crystal grains excluding the mother crystal which is the crystal structure of the fluoride crystal base material 11 before deformation is uniform with a diameter of 20 mm or less.

In addition, the initial transmission per 10 mm thickness at a wavelength of 126 nm is 65% or more, the initial transmission per 10 mm thickness at a wavelength of 146 nm is 85% or more, and / or the initial transmission per 10 mm thickness at a wavelength of 172 nm It has excellent optical properties with a transmittance of 90% or more.

Therefore, it can be used for an excimer lamp device that emits vacuum ultraviolet light with a wavelength of 125 nm to 200 nm.

Moreover, the shape of such an optical member has a shape different from the fluoride crystal base material 11 used. By appropriately selecting the shape of the mold 13, for example, the cross-sectional area of at least one direction can be made to be 350 × 350 mm or more, and the total length of the outer periphery of the cross-section is 1600 mm or more In addition, the thickness in the direction orthogonal to the cross section can be 3 to 20 mm.

According to the manufacturing method of the fluoride crystal molded body as described above, since the fluoride crystal base material 11 is deformed by heating and pressing, it can be formed into a shape different from that of the fluoride crystal base material 11, and single crystal growth Even large-sized members that can not be manufactured directly can be easily manufactured.

Then, during molding, the fluoride crystal base material 11 is pressed to start deformation due to recrystallization, and then it is deformed to a predetermined shape, so that the crystal structure is deformed like slip deformation or deformation in the molten state. Can be prevented from being violently disturbed. In particular, since deformation due to slippage of crystal structure and deformation due to recrystallization can not occur simultaneously, as in the deformation due to slippage of crystal structure, a large number of defects occur in the crystal structure, and optical properties, especially vacuum ultraviolet range It is possible to easily manufacture a fluoride crystal molded body having excellent optical properties without deteriorating the light transmittance.

Next, an example in which the molded fluoride crystal thus obtained is used in an ultraviolet cleaning device will be described. FIG. 2 shows an ultraviolet cleaning device.

The ultraviolet cleaning device 60 is airtightly configured by combining the light source unit 63 that is airtightly configured and the plurality of light sources 61 is disposed, and the light source unit 63, and the cleaning object that can accommodate the cleaning object 73 inside It comprises an accommodating portion 71.

The light source portion 63 and the cleaning object storage portion 71 are adjacent to each other through the opening 65, and the window member 50 made of the fluoride crystal molded body manufactured as described above is attached to the opening 65. There is. By mounting the window member 50 in a hermetically sealed state around the entire circumference of the opening 65, airtightness is secured independently of the inside of the light source unit 63 and the inside of the cleaning object storage unit 71.

Here, as the light source 61, for example, a vacuum ultraviolet light source such as a Xe excimer lamp, a Kr excimer lamp, or an Ar excimer lamp that emits vacuum ultraviolet light with a wavelength of 125 nm to 200 nm is used. Since these light sources 61 are usually tube-shaped discharge tubes, it is preferable to arrange a plurality of light sources in parallel as needed in order to irradiate a large area with uniform illuminance. The distance between the light source 61 and the window member 50 is approximately several tens of mm.

A support member 75 is provided inside the object-to-be-cleaned storage portion 71, and the object to be cleaned 73 is placed on the support member 75 so as to face the light source 61 via the window material 50. It is configured. The object to be cleaned 73 is, for example, a large diameter semiconductor wafer, a glass substrate for a liquid crystal display, or the like. The distance between the object to be cleaned 73 and the window member 50 is approximately several tens of mm.

In the ultraviolet ray cleaning apparatus 60, the object to be cleaned 73 is accommodated in the to-be-cleaned object containing portion 71, and the light source portion 63 and the to-be-cleaned object containing portion 71 are airtightly closed. The light cleaning is performed by applying light to the object to be cleaned 73 from the light source 61.

At the time of cleaning, in order to suppress attenuation of light rays by residual gas such as oxygen and to prevent consumption of the light source 61 due to active species such as ozone generated by light irradiation, a light source unit using gas supply means and exhaust means not shown The inside of the 63 is replaced by an inert gas such as nitrogen.

According to such an ultraviolet ray cleaning device 60, since a fluoride crystal molded body is used as the window member 50 disposed between the light source unit 63 and the object to be cleaned 73, vacuum ultraviolet light is transmitted with high transmittance. It is possible to effectively wash the object to be cleaned 73.

And since this window material 50 is shape | molded from the fluoride crystal base material 11 in plate shape, and the area of the permeation | transmission surface is formed wide enough by one window material 50, a large-sized to-be-cleaned thing Even in the case of cleaning 73, it is possible to arrange and configure one window member 50 in one opening 65. Therefore, as compared to the case where a plurality of small window members are combined to form a window having a large area as in the prior art, a joining member or a cross-shaped support member for combination is not necessary. It is possible to avoid the problem that light is not emitted. Further, since the seal length between the window member 50 and the opening 65 can be shortened, it is easy to ensure the airtightness of the light source unit 63 and the cleaning object storage unit 71.

Therefore, according to such an ultraviolet ray cleaning device 60, it is easy to efficiently clean a large object to be cleaned 73 such as a semiconductor wafer having a diameter of 300 mm or a substrate for a liquid crystal display having a large area. It is easy to improve the durability.

In addition, the obtained fluoride crystal molded body can be used, for example, in an optical device system such as an astronomical telescope for ground use or artificial satellite. For example, as shown in the conceptual view of FIG. 12, a fluoride crystal molded body can be used as the objective lens 102 of the telescope 100 provided with the objective lens 102 and the eyepiece 104 supported by the lens barrel 106.

Hereinafter, examples of the present invention will be described.

Example 1
<Preparation of calcium fluoride crystal base material>
A substantially single-crystal calcium fluoride ingot grown by the Bridgman method was prepared, and a cylindrical sample having a diameter of 30 mm and a thickness of 10 mm was cut out from a part thereof. The two opposite faces in the thickness direction of this sample are precisely polished so that the degree of parallelism is within 10 seconds, the flatness per face is within 6 Newton rings, and the surface roughness (rms) for each face is 10 Å or less. And finish polishing with a high purity SiO ₂ powder so as not to leave an abrasive that causes surface absorption.

The transmittance of the sample in the wavelength range of 200 nm to 120 nm was measured with a vacuum ultraviolet spectrophotometer. The results are shown in FIG. Here, it was confirmed that the transmittance including reflection at a wavelength of 126 nm is 65% or more, the light transmittance at a wavelength of 146 nm is 85% or more, and the light transmittance at a wavelength of 172 nm is 90% or more.

Next, to this sample, after the ArF excimer laser energy density 50 mJ / cm ² / pulse to ¹⁰⁵ pulse irradiation, the transmittance was measured in the wavelength range of 200nm from 800 nm. The results are shown by line A in FIG.

Next, separately from this sample, a block having a diameter of 150 mm and a thickness of 250 mm was cut out from a single crystal ingot, and the surface was cleaned with an alcohol such as methanol to obtain a crystal base material 11.

<Heating and pressure forming>
The crystal base material 11 was molded using a molding apparatus as shown in FIG.

The crystal base material 11 was accommodated in a carbon-made mold 13 with a diameter of 500 mm and a height of 300 mm, and was placed at the center of the lower mold 17 and the pressure mold 19 was in contact with the top. The stainless steel chamber 10 was sealed and evacuated from the vacuum evacuation unit 39 to 10-1 Pa or less, N ₂ gas was introduced from the atmosphere gas introduction unit 37 to maintain the inside in a nitrogen atmosphere of 0.92 MPa.

Next, while heating with the heating element 33, a load was applied by the pressure rod 25, and molding was performed by heating and pressing, and the amount of deformation was measured. The temperature change at the time of molding is shown by line T in FIG. 5, and the amount of deformation is shown by line V in FIG. The pressurization period is noted at the top of FIG.

In this heat and pressure forming, first, heat is generated by a heating element (heater) 33, and the temperature in the heat insulating frame 31 containing the forming die 13 is raised at a constant temperature rising rate, and reached 20 ° C. Pressurization was started (in FIG. 5, the process to reach 20 ° C. was omitted). The load applied to the pressure rod 25 during the pressure application period was 38 ton and constant.

In this state, the crystal base material 11 was deformed by continuing the temperature raising at a constant temperature rising rate while applying a constant load to the pressure rod 25. During the deformation period, the amount of deformation per unit time in the load direction gradually increases, and the increase in the amount of deformation per unit time ends 190 minutes after the start of heating, and the temperature at the maximum amount of deformation per unit time is 1000 Degree.

Thereafter, after the temperature of the crystal base material 11 reached 1000 ° C., the temperature was maintained at 1000 ° C. until the deformation was completed, and the pressurization was continuously continued, and the deformation was finished about 270 minutes after the start of heating. Thereafter, the crystal compact was gradually cooled to room temperature and taken out. The obtained crystal compact had a diameter of 500 mm and a height of 22 mm.

<Evaluation of optical characteristics>
As shown in FIG. 6, a molded sample 53 having a diameter of 30 mm and a thickness of 10 mm was collected from the peripheral portion of the obtained crystal molded body 51. The two faces of the molded sample 53 facing in the thickness direction have a parallelism of 10 seconds or less, a flatness of 6 Newton rings or less on each side, and a surface roughness (rms) of 10 angstroms or less on each side. Precision polishing was carried out, and further, finish polishing with high purity SiO ₂ powder was carried out so that no abrasive agent causing surface absorption remains.

The transmittance of the molded sample in the wavelength range of 200 nm to 120 nm was measured with a vacuum ultraviolet spectrophotometer. The results are shown in line B of FIG. This molded sample was found to have a reflectance and transmission of at least 65% at a wavelength of 126 nm, a light transmittance of at least 85% at a wavelength of 146 nm, and a light transmittance of at least 90% at a wavelength of 172 nm. The

Then, an ArF excimer laser energy density 50 mJ / cm ² / pulse was 10 ⁵ pulses irradiated to the molded samples was measured for transmittance in a wavelength range of 200nm from 800 nm. The result is shown by line B in FIG. From the measurement results of the transmittance, it was found that the molded sample had a transmittance substantially equal to that of the crystal base material 11 before molding, and the increase in the induced absorption accompanying the molding was suppressed.

Next, when each concentration of the alkali metal element and the alkaline earth metal element contained in the molded sample was measured, it was 100 wtppb or less. The concentration of each of Cr, Mn, Fe, Co, Ni, Ba, Zn, La, Ce and Pb contained in this molded sample was measured and found to be 50 wtppb or less.

<Collection of plate material>
From the obtained molded product, a window 50 of 350 mm square was cut out and attached as the window 50 to the opening 50 of the ultraviolet cleaning device as shown in FIG. It was possible to clean the object to be cleaned by irradiating the ultraviolet light through the window member 50 using this ultraviolet cleaning device.

Example 2
The five calcium fluoride crystal base materials (No. 1 to No. 5) were prepared in the same manner as in Example 1 except that the load applied to the calcium fluoride crystal base material 11 was changed. It formed below. With respect to forming conditions under these loads, the pressure receiving area of the crystal base 11 is calculated from the shape and deformation of the original crystal base 11, and the pressure receiving area and the load applied to the pressure rod 25 are used to calculate each. The pressure at the time was calculated. The temperature (maximum deformation temperature) and the pressure at which the amount of deformation per unit time is maximized are set to five crystal base materials No. 5 The following table shows 1-5.

The relationship between the maximum deformation temperature obtained for these crystal base materials and the pressure thereof is shown in FIG. 7 by points. From these points, an approximate straight line F by the least square method was created. As the deformation of the crystal base material progresses, the area of the portion of the crystal base material receiving a constant load increases, so the pressure gradually decreases. Therefore, the pressure and temperature at the completion of deformation (forming) are indicated by points 1 in FIG. 7, and from these points, the approximate straight line L by the least square method is created.

From this result, it was revealed that the correlation between the pressure P and the temperature T when the amount of deformation per unit time is maximized is such that the higher the pressure, the lower the temperature.

Further, the straight lines connecting the respective ◆ points shown in FIG. 7 are expressed by the following equations (5) to (8) as shown in FIG.

1125 ≦ T ≦ 1205 (° C.):
-11.5 × P (MN / m ² ) + 1285 = T (° C.) (5)
970 ≦ T ≦ 1125 (° C.):
−22.3 × P (MN / m ² ) + 1435 = T (° C.) (6)
968 ≦ T ≦ 970 (° C.):
−0.289 × P (MN / m ² ) + 976 = T (° C.) (7)
883 ≦ T ≦ 968 (° C.):
−12.2 × P (MN / m ² ) + 1306 = T (° C.) (8)

Therefore, when using calcium fluoride crystals as the crystal base material 11, the deformation conditions are set such that the pressure P and the temperature T applied to the crystal base material 11 satisfy at least one of the equations (5) to (8). In this case, since the crystal base material 11 starts deformation due to recrystallization, it can be formed into a desired shape while suppressing deterioration of optical characteristics such as a decrease in transmittance and an increase in induced absorption.

Crystal matrix No. 1 to No. With respect to No. 5, the upper surface and the lower surface of the formed crystals were observed, respectively. In both cases, a large number of grain boundaries were observed on the upper and lower surfaces of the compact (see FIGS. 9A and 9B). Further, the crystal orientation was measured by a single crystal orientation rapid measurement apparatus RASCO (manufactured by Rigaku Corporation). As a result, since the crystal orientation of the crystal grain of the compact was random, it turned out that it is a polycrystal. This indicates that recrystallization has occurred.

Further, it is clear that the higher the pressure and the higher the temperature, the easier the recrystallization will occur. Therefore, the pressure P and the temperature T applied to the crystal base material 11 are more than boundary values represented by the equations (5) to (8) In the high pressure / high temperature region as well, since it is considered that recrystallization similarly occurs, deformation by recrystallization can be initiated according to the present invention. That is, even when the pressure P and the temperature T applied to the crystal base material 11 are set to satisfy at least one of the conditions of formulas (1) to (4), deformation due to recrystallization can be similarly started. . Here, the temperature T in the equations (1) to (4) is in a range lower than the melting point of the crystal base material 11, and the pressure P is a range in which the crystal base material 11 does not cause mechanical fracture such as buckling at the temperature T. It is desirable to

[Example 3]
In Example 3, after heating the calcium fluoride crystal base material 11 to 1050 ° C., a load of 38 tons was loaded, and the crystal base material 11 was continuously deformed to the target shape while keeping the temperature and the load constant. At this time, the pressure at the start of deformation was 21.1 MN / m ² . The pressure and temperature values are shown in FIG. 8 (Ex. 3). The other conditions were the same as in Example 1, and a crystal molded body 51 was produced, and a sample for measurement of a molded body was produced from the obtained crystal molded body 51.

After the energy density of 50mJ / cm ² 10 ⁵ pulses irradiated per pulse an ArF excimer laser with a wavelength of 193nm in the molded body measurement sample 53, the transmittance was measured in the wavelength range of 200nm from 800 nm. The result is shown by line E in FIG.

The heating temperature and the pressure at the start of deformation in Example 3 satisfy the equations (2) and (3), and by starting the deformation due to recrystallization under this condition, the increase of the induced absorption is suppressed while suppressing the increase. It has been found that the crystal base material can be formed into a desired shape.

Example 4
In Example 4, after heating the crystal base material 11 to 1100 ° C., a load of 27 tons was loaded, and the crystal base material 11 was continuously deformed to the target shape while keeping the temperature and the load constant. At this time, the pressure at the start of deformation was 15.0 MN / m ² . The pressure and temperature values are shown in FIG. 8 (Ex. 4). The other conditions were the same as in Example 1, and a crystal molded body 51 was produced, and a sample for measurement of a molded body was produced from the obtained crystal molded body 51.

After the molded body sample for measuring 53 to 10 ⁵ pulse irradiation at an energy density 50 mJ / cm ² per pulse to ArF excimer laser with a wavelength of 193 nm, in Figure 4 the result of measuring the transmittance in the wavelength range of 200nm from 800nm It is indicated by line F.

The heating temperature and the pressure at the start of deformation in Example 4 satisfy the equation (2), and by starting the deformation due to recrystallization under this condition, it is possible to suppress the increase in the induced absorption, while suppressing the crystal base material It has been found that can be molded into the desired shape.

Comparative Examples 1 and 2
In the same manner as in Example 3, except that the pressure and temperature applied to the crystal base material 11 during heat and pressure forming were 600 ° C. and 38 tons in Comparative Example 1 and 600 ° C. and 76 tons in Comparative Example 2, respectively. A body 51 was produced, and a sample for measurement of a molded body 53 was produced from the obtained crystal molded body 51. The pressure during the start of deformation is 21.1MN / ^{m 2} in Comparative Example 1 was 42.2MN / ^{m 2} in Comparative Example 2. The pressure and temperature values are shown in FIG. 8 (Com. 1, Com. 2).

The transmittance of a sample 53 for measurement of each molded body in a wavelength range of 300 nm to 120 nm was measured with a vacuum ultraviolet spectrophotometer. The results are shown in FIG. 3. The energy density per pulse of an ArF excimer laser of 193 nm wavelength is 50 mJ / after 10 ⁵ pulse irradiation in cm ^2, and shows the results of measuring the transmittance in the wavelength range of 200nm from 800nm to FIG. In FIG. 4, line C indicates the result of Comparative Example 1, and line D indicates the result of Comparative Example 2.

As shown in FIG. 3, the molded product molded at a low temperature as in Comparative Examples 1 and 2 has a low transmittance of light of a short wavelength, and as shown in FIG. It is suggested that there are many defects in the crystal structure.

[Example 5]
Next, a compact having a diameter of 50 mm and a height of 20 mm was formed from a calcium fluoride single crystal base material having a diameter of 30 mm and a height of 50 mm, and whether deformation due to recrystallization occurred was confirmed.

The molding was performed in the same manner as in Example 1 except that the load applied by the pressure rod 25 was 1.5 ton. The temperature at which the amount of deformation per unit time was maximum was 970 ° C., the pressure at that time was 20.8 MN / m ² , and the molding was completed in a molding time of 30 minutes. This result was similar to the case of the pressure of 20.8 MN / m ² in Example 2.

The photograph of the upper surface of the obtained molded object is shown to Fig.9 (a), and the photograph of a lower surface is shown to (b). In this picture, the grain boundaries were traced with a pencil to make the crystal grains more visible. The crystal orientation specified by the Laue method was measured using a single crystal orientation rapid measurement apparatus RASCO (manufactured by Rigaku Corporation). The crystal orientation is indicated by arrows and numerical values in the figure. In the single crystal base material before forming shown in the reference, no grain boundary is observed at all as shown in FIG.

As apparent from FIGS. 9A and 9B, in the compact obtained from the single crystal base material, a large number of crystal grain boundaries are recognized, and the crystal orientations of the respective crystal grains are random. Thus, it was clearly confirmed that recrystallization had occurred because it was in a polycrystalline form. The crystal base material No. 1 of Example 2 1 to No. The appearance as shown in FIGS. 9 (a) and 9 (b) was observed even with the molded body obtained from No. 5.

The numerical value of the crystal orientation in the figure is the deviation angle α of the surface from the (111) plane as shown in FIG. 10, and the direction of the arrow is the x axis when the <111> axis is projected onto the xy plane. The azimuth angle β from is shown.

In the above embodiments, the method of the present invention has been illustrated by way of an example of forming a calcium fluoride crystal base material, but other fluoride crystal base materials can be deformed and manufactured according to the present invention.

According to the present invention, it is possible to easily form a calcium fluoride crystal base material having a desired shape without deteriorating the optical properties of the calcium fluoride crystal base material. The obtained molded product is very useful as an optical device using vacuum ultraviolet light or an optical component of a light cleaning device.

DESCRIPTION OF SYMBOLS 10 chamber 11 fluoride crystal base material 13 shaping | molding die 17 lower mold | type 19 pressurization type | mold 23 support part 27 pressurization drive part 33 heating element 50 window material 60 ultraviolet-ray cleaning apparatus

Claims

A method for producing a fluoride crystal molded body, which shapes a fluoride crystal base material into a predetermined shape,
Disposing the fluoride crystal base material between a pair of opposed pressure surfaces;
When the fluoride crystal base material is heated at a constant temperature rising rate while applying a constant load between the pair of pressing surfaces, the deformation amount per unit time in the load direction of the fluoride crystal base material is maximized Assuming that the temperature is T, and the pressure applied to the fluoride crystal base material at the temperature T is P, the fluoride crystal base material is higher than the temperature T and the fluoride crystal base material is lower than the melting point. A method of producing a fluoride crystal molded body, characterized in that the fluoride crystal base material is deformed by heating and pressurizing to the pressure P or more.
The method for manufacturing a fluoride crystal molded body according to claim 1, further comprising: obtaining the temperature T and the pressure P in advance before deforming the fluoride crystal base material.
The method for producing a fluoride crystal molded body according to claim 1 or 2, wherein the pressure P is applied to the fluoride crystal base material after the fluoride crystal base material is heated to the temperature T.
The fluoride crystal base material is a calcium fluoride crystal base material, and the calcium fluoride crystal base material is heated and pressurized to a pressure P at a temperature T satisfying any of the following formulas (1) to (4). The method according to any one of claims 1 to 3, wherein the fluoride crystal base material is deformed by
T ≧ 1125 ° C. and P ≧ 6.9 MN / m 2 and −11.5 × P (MN / m 2 ) +1285 <T (° C.) (1)
T ≧ 970 ° C. and P ≧ 13.9MN / m 2 and -22.3 × P (MN / m 2 ) +1435 <T (℃) ··· (2)
T ≧ 968 ° C. and P ≧ 20.8MN / m 2 and -0.289 × P (MN / m 2 ) +976 <T (℃) ··· (3)
T ≧ 883 ° C. and P ≧ 27.7MN / m 2 and -12.2 × P (MN / m 2 ) +1306 <T (℃) ··· (4)
A method for producing a fluoride crystal compact,
A method for producing a fluoride crystal molded body comprising heating the fluoride crystal base material at a temperature lower than the melting point and deforming while being pressurized to recrystallize.
The method for producing a fluoride crystal molded body according to claim 5, wherein the fluoride crystal base material is a fluoride single crystal.
The method for producing a fluoride crystal compact according to claim 5, wherein the fluoride crystal base material is made of calcium fluoride.
The fluoride crystal base material is placed by placing the fluoride crystal base material between a pair of opposing pressing surfaces, and applying a constant load between the pair of pressing surfaces. The manufacturing method of the fluoride-crystal molded object as described in any one of 5 thru | or 7.
An optical member comprising a fluoride crystal molded product produced by the production method according to any one of claims 1 to 8.
The optical member according to claim 9, wherein the fluoride crystal base material is a single crystal, and the fluoride crystal molded body contains a polycrystal.
The light transmittance at a wavelength of 126 nm is 65% or more, the light transmittance at a wavelength of 146 nm is 85% or more, the light transmittance at a wavelength of 172 nm is 90% or more, and the area of at least one cross section in one direction is 350 × An optical member comprising a fluoride crystal molded body having a length of 350 mm or more.
The optical member according to claim 11, wherein a total length of an outer periphery of the cross section is 1600 mm or more.
Each concentration of the contained alkali metal element and alkaline earth metal element is 100 wtppb or less, and each concentration of Cr, Mn, Fe, Co, Ni, Ba, Zn, La, Ce, Pb contained The optical member according to any one of claims 9 to 12, having a weight of 50 wtppb or less.
An optical device comprising the optical member according to any one of claims 10 to 13 in an optical path through which vacuum ultraviolet light with a wavelength of 125 nm to 200 nm is transmitted.
In an ultraviolet cleaning device for irradiating a member to be cleaned with vacuum ultraviolet light having a wavelength of 125 nm to 200 nm through the window material,
An ultraviolet cleaning device using the optical member according to any one of claims 10 to 13 as the window member.