JP2005067937A - Method for manufacturing crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a crystal, by which a calcium fluoride crystal having excellent optical properties such as internal transmittance or laser durability can be manufactured. <P>SOLUTION: This method for manufacturing the crystal is characterized by including a purifying step for purifying a raw material to obtain a purified article by mixing the raw material of a crystalline substance and a scavenger, then melting the resulting mixture and solidifying, a growing step for melting the purified article purified in the purifying step and growing a single crystal of the raw material, a heat treating step for heat treating the single crystal grown in the growing step, a step for analyzing gas components generated in at least one step of the purifying step, the growing step and the heat treating step, and a step for controlling the temperature of the crystalline substance according to the gas components analyzed in the analyzing step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

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

  Calcium fluoride crystals are ideal as optical materials for optical elements such as lenses and diffraction gratings used in exposure optical systems because the transmittance of light in this wavelength range (ie, internal transmittance) is high among glass materials. is there.

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. A number of these calcium fluoride crystals having good optical characteristics and a method for producing the same have been proposed. For example, a calcium fluoride crystal having high transmittance is produced using a solid scavenger advantageous in safety. A crystal manufacturing method has been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 9-227293

However, calcium fluoride crystals manufactured by conventional crystal manufacturing methods show satisfactory optical characteristics for visible light, but laser durability is achieved for high-power light at short wavelengths such as excimer lasers. However, the optical properties have not been satisfactory yet, such as low homogeneity, high refractive index homogeneity and high birefringence, and difficulty in obtaining surface accuracy during polishing. In particular, the optical properties required for the calcium fluoride used in short F ₂ laser wavelength is very strict.

  Therefore, an object of the present invention is to provide a crystal manufacturing method capable of manufacturing a calcium fluoride crystal having excellent optical characteristics such as internal transmittance and laser durability.

  In order to achieve the above object, a crystal production method according to one aspect of the present invention includes a step of refining a refined raw material by mixing a raw material of a crystalline substance and a scavenger, melting and solidifying the raw material, A step of growing the single crystal of the raw material by melting and solidifying the purified product purified in the purification step, and a step of heat-treating the single crystal grown in the growth step, the purification step, Analyzing a gas component generated during at least one of the growth step and the heat treatment step, and controlling a temperature of the crystalline material based on the gas component analyzed in the analysis step; It is characterized by having.

  The crystal production method as one aspect of the present invention includes a step of refining a refined product of the raw material by mixing a raw material of a crystalline substance and a scavenger, melting and solidifying, and a refined product purified in the refining step And then solidifying the raw material single crystal, and heat-treating the single crystal grown in the growth step, the refining step, the growth step, and the annealing step. The method includes a step of monitoring a scavenging reaction in at least one of the steps, and a step of controlling the temperature of the crystalline substance based on the scavenging reaction monitored in the monitoring step.

  According to another aspect of the present invention, there is provided a crystal manufacturing apparatus, a processing chamber for storing a raw material of a crystalline substance, a gas analysis apparatus for analyzing a gas component in an atmosphere inside the processing chamber, and the gas analysis apparatus analyzed. And a temperature control unit that controls the temperature inside the processing chamber based on the gas component.

  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 or crystal manufacturing apparatus.

  An exposure apparatus according to 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 via 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 exposure apparatus described above; and performing a predetermined process on the exposed target object. And

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

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

  The present inventor has intensively studied the reason why the calcium fluoride crystal manufactured by the conventional crystal manufacturing method does not exhibit satisfactory optical characteristics for short-wavelength and high-power light, and as a result, the internal transmission of the crystal The decrease in the rate is due to the oxidation of the crystal and fluorine, and the reaction in the temperature rising process of the scavenger used for oxidation prevention and fluorination is greatly influenced by the analysis of the gas component of the gas generated in the furnace. I found that.

  The present inventor manufactured a number of calcium fluoride crystals by changing the conditions for adding the scavenger during the manufacture of the calcium fluoride crystals, and measured the optical characteristics (spectral transmittance, γ-ray durability).

  Regarding the spectral transmittance, a spectroscope capable of measuring a vacuum ultraviolet wavelength region of 120 nm to 300 nm and a spectroscope for ultraviolet-visible measurement for evaluating the generation of a color center after γ-ray irradiation were used.

The gamma ray durability can be examined more easily and cheaply than the laser durability, and it is possible to know whether or not a color center has occurred for a larger crystal as a whole. In addition, it is possible to determine the tendency of residual scavenger elements in the crystal and trace oxidation. As irradiation conditions, γ rays with an irradiation dose rate of 1 × 10 ⁶ R / h were irradiated for 1 hour to obtain a total dose of 1 × 10 ⁶ R. Based on these evaluations, the present inventor has found that crystals having good internal transmittance have less impurities, particularly residual scavenger constituent elements and oxidative deterioration of the crystals.

  The inventor also found in the furnace that it is important to optimize the scavenger reaction process to promote oxidation prevention and fluorination of the contained oxide in the purification, growth and annealing steps. It was found by performing mass spectrometry of the gas components.

  Hereinafter, a crystal manufacturing method as one aspect of the present invention will be described with reference to the accompanying drawings. In addition, the same reference number is attached | subjected about the same member in each figure, and the overlapping description is abbreviate | omitted. FIG. 1 is a flowchart for explaining a crystal manufacturing method 100 of the present invention. In the present embodiment, the crystal production method 100 will be described by taking the production of calcium fluoride crystals as an example, but the present invention is not limited to the production of calcium fluoride crystals.

  First, a high-purity calcium fluoride synthetic raw material is prepared as a raw material (step 102). It is important that the prepared raw material for high-purity calcium fluoride contains a very small amount of an element that degrades internal transmittance and laser durability, such as rare earth.

A synthetic raw material for high-purity calcium fluoride is produced, for example, by reacting calcium carbonate (CaCO ₃ ) and hydrofluoric acid (HF) as shown in the following chemical formula 1. Although the present invention does not exclude a method of removing impurities (for example, SiO ₂ ) by treating calcium fluoride with hydrogen fluoride, high-purity calcium fluoride is powdery and bulky unlike raw stone. This is preferable because the density is very small (particle diameter is about 10 μm to about 100 μm).

次いで、フッ化カルシウム原料とスカベンジャーとを混合する（ステップ１０４）。なお、フッ化カルシウム原料とスカベンジャーとを混合する時は、混合容器内にフッ化カルシウム原料とスカベンジャーを入れ、回転させて均一な混合を確保することが好ましい。

Next, the calcium fluoride raw material and the scavenger are mixed (step 104). In addition, when mixing a calcium fluoride raw material and a scavenger, it is preferable to put a calcium fluoride raw material and a 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. . A substance that reacts with the oxide mixed in the fluoride raw material to become an oxide that is easily vaporized is selected. In particular, zinc fluoride is desirable.

For example, a zinc fluoride (ZnF ₂ ) scavenger 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 ).

ここで、酸化防止及び酸化物のフッ化にはスカベンジャーの添加量を制御すること及び温度制御による還元反応、フッ化反応が重要である。

Here, in order to prevent oxidation and fluorination of the oxide, it is important to control the amount of scavenger added and to perform a reduction reaction and a fluorination reaction by temperature control.

  The amount of scavenger added in the present embodiment is 0.005 wt% or more and 0.5 wt% or less, more preferably 0.05 wt% or more and 0.2 wt% or less. When the addition amount is large, the refractive index homogeneity is lowered due to the residual amount of the scavenger, and the internal transmittance and the laser durability are lowered. In other words, controlling to an appropriate temperature for the oxidation reaction and oxide fluorination under such an added amount reduces the oxide in the crystal and reduces the scavenger residue. This reduces the impurities and crystal defects contained in the calcium fluoride crystal and provides a high-quality calcium fluoride crystal.

  The thus obtained mixture of calcium fluoride powder and scavenger is subjected to purification treatment (step 106). In such a purification process, a gas component generated during the purification process is analyzed, and temperature control is performed based on the analysis result. In particular, in the purification process for the purpose of reducing impurities, it is possible to reduce oxides and scavenger constituent elements with good controllability by performing temperature control using gas analysis in the furnace. Effective in improving internal transmittance and laser durability.

  FIG. 2 is a schematic block diagram showing an exemplary form of a refining furnace 200 as an example of the crystal production apparatus of the present invention. Referring to FIG. 2, reference numeral 210 denotes a chamber of the refining furnace 200, which is connected to a vacuum exhaust system 240 including a dry pump 242, a mechanical booster pump 244, a turbo molecular pump 246, and an abatement system 248. Note that the exhaust pumps 242 to 248 are not limited to these types. For the abatement system (trap) 248, both a cooling trap that cools the exhaust gas and deposits and removes harmful components in the exhaust gas, and a high-temperature trap that thermally decomposes the exhaust gas can be applied. it can.

  The chamber 210 is insulated by a heat insulating material 212 and houses the crucible 220 and the heater 230. The crucible 220 is made of, for example, carbon, has a substantially cylindrical shape, and is rotatably supported by the crucible support mechanism 250. If necessary, the crucible support mechanism 250 is configured to allow the crucible 220 to be lowered. The rotation by the crucible support mechanism 250 is performed in order to make the temperature of the crucible 220 uniform.

  The chamber 210 is also connected to a cooling pipe 214 for temperature adjustment. The temperature in the chamber 210 can be controlled by the heater 230 and the cooling pipe 214. The thermocouple 216 is made of, for example, platinum, and measures the temperature of the crucible 220 from the vicinity of the outer wall of the crucible 220.

Thereafter, the heater 230 is energized to heat the mixture AL in the crucible 220 to perform dehydration and other adsorbate removal. The refinement furnace 200 is evacuated to a vacuum level of 1 × 10 ⁻³ Pa or more by the vacuum evacuation system 240. Next, the calcium fluoride raw material is completely melted through 350 ° C. to 1100 ° C. which is a temperature range of the scavenging reaction.

  In this temperature rising process, the reaction gas generated in the crucible 220 is detected by the gas analyzer 500 through the gas introduction nozzle 218, and the scavenging reaction (antioxidation, fluorination) in the crucible 220 is monitored to control the temperature. .

  FIG. 3 is a schematic block diagram showing an exemplary embodiment of the gas analyzer 500 shown in FIG. The gas analyzer 500 analyzes gas components in the atmosphere inside the chamber 210. More specifically, the gas analyzer 500 analyzes the gas components generated in the crucible 220 by the scavenging reaction and released into the chamber 210. As shown in FIG. 3, the gas analyzer 500 includes a detection unit 510, an analysis unit 520, and a control unit 530.

  The detection unit 510 detects a gas component inside the chamber 220 introduced through the gas introduction nozzle 218. The detection result of the gas component detected by the detection unit 510 is sent to the analysis unit 520, and the type and amount (gas partial pressure) of the generated gas are analyzed. Based on the analysis result, the control unit 530 controls the temperature of the chamber 210 via the heater 230 and the cooling pipe 214. As a result, the temperature of the chamber 210 is controlled so that the scavenging reaction in the crucible 220 acts sufficiently and no scavenger remains.

  After melting, the molten state is maintained for several hours to several tens of hours in order to remove residual harmful elements. During this time, if necessary, the gas generated in the crucible 220 is analyzed by the gas analyzer 500 through the gas introduction nozzle 218, and the discharge state of the residual scavenger constituent elements is monitored from the gas analysis result to determine the melting time. Further, the solid scavenger added to the calcium fluoride raw material is harmful depending on the optical characteristics if it remains in the crystal, so it is completely evaporated and removed in the melt.

  Subsequently, it is not necessary to adjust the lattice arrangement of the calcium fluoride crystal in which the crucible 220 is lowered and the molten calcium fluoride raw material is gradually cooled to grow crystals, so there is no need to slow down the descending speed of the crucible 220. . Although the present embodiment includes a case where the crucible 220 is not lowered, the effect of removing impurities is improved by lowering the crucible 220.

  Since this process does not require the temperature control as the single crystal growth process (step 108) described later, the obtained crystal may be polycrystalline or have grain boundaries. The upper part of the crystal thus obtained, that is, the last crystallized part with time is removed. Such a portion is a portion where impurities are likely to collect (that is, segregation). Therefore, by removing this portion, impurities that adversely affect the characteristics are removed.

  If the purity of the obtained crystal is insufficient, the crystal is again put in the crucible 220, and a series of steps of melting, crystallization, and top removal is repeated a plurality of times. Note that an inert gas may be introduced into the chamber 210 if necessary.

  After the purification process is performed, a single crystal growth process is performed on the refined product RF (step 108). In such a crystal growth process, gas components generated during the crystal growth process are analyzed, and temperature control is performed based on the analysis result.

  The single crystal growth step is a step of growing a single crystal of calcium fluoride to improve the quality of the crystal (ie, adjusting the lattice arrangement). As the growth method, an appropriate method is selected according to the size of the crystal and the purpose of use. The purified refined product RF is put into a crucible 320 housed in a chamber 310 of a crystal growth furnace 300 shown in FIG. FIG. 4 is a schematic block diagram showing an exemplary embodiment of a crystal growth furnace 300 as an example of the crystal manufacturing apparatus of the present invention.

  Referring to FIG. 4, reference numeral 310 denotes a chamber of the crystal growth furnace 300, which is connected to a vacuum exhaust system 340 including a dry pump 342, a mechanical booster pump 344, a turbo molecular pump 346, and an abatement system 348.

  The chamber 310 is insulated by a heat insulating material 312 and houses the crucible 320 and the heater 330. The crucible 320 is made of, for example, carbon, has a substantially cylindrical shape, has a high hermeticity, and is supported by the crucible support / pull-down mechanism 350 so as to be rotatable and vertically movable. The rotation by the crucible support / pull-down mechanism 350 is performed in order to make the temperature of the crucible 320 uniform.

  The chamber 310 is also connected to a cooling pipe 314 for temperature adjustment. A desired temperature gradient can be formed in the vertical direction shown in FIG. 4 by the heater 330 and the cooling pipe 314. The thermocouple 316 is made of, for example, platinum, and measures the temperature of the crucible 320 from the vicinity of the outer wall of the crucible 320.

  Thereafter, the heater 330 is energized to heat the calcium fluoride refined product (secondary raw material) RF in the crucible 320 to about 1420 ° C., thereby completely melting the refined product RF. During this time, as described above, the scavenging reaction (antioxidation, fluorination) in the crucible 320 is monitored by the gas analyzer 500 through the gas introduction nozzle 318, and if necessary, the temperature rising process is controlled to control impurities (oxygen mixing). , Lattice defects, etc.).

  Thereafter, the crucible 320 is gradually lowered at a speed of 1 mm / h (passing through a predetermined temperature gradient), and the molten refined product RF is removed to grow a single crystal of calcium fluoride.

  Subsequently, heat treatment (annealing) is performed on the crystal-grown calcium fluoride single crystal MC (step 110). In such heat treatment, gas components generated during the heat treatment are analyzed, and temperature control is performed based on the analysis result.

  The annealing process is a process of reducing the birefringence by heat treating the grown single crystal MC of calcium fluoride to remove the stress remaining in the crystal. The grown single crystal MC is put into a crucible 420 housed in a chamber 410 of an annealing furnace 400 shown in FIG. FIG. 5 is a schematic block diagram showing an exemplary form of an annealing furnace 400 as an example of the crystal manufacturing apparatus of the present invention.

  Referring to FIG. 5, reference numeral 410 denotes a chamber of the annealing furnace 400, which is connected to a vacuum exhaust system 440 including a dry pump 442, a mechanical booster pump 444, a turbo molecular pump 446, and an abatement system 448.

  The chamber 410 is insulated by a heat insulating material 412 and houses the crucible 420 and the heater 430. The crucible 420 is made of, for example, carbon, has a substantially cylindrical shape, is configured in a multistage manner, and is supported by a crucible support member 450. The chamber 410 is also connected to a cooling pipe 414 for temperature adjustment. The temperature of the chamber 410 can be controlled by the heater 430 and the cooling pipe 414. The thermocouple 416 is made of platinum, for example, and measures the temperature of the crucible 420 from the vicinity of the outer wall of the crucible 420.

  In the annealing step, the crucible 420 is heated uniformly to about 900 ° C. to about 1000 ° C. to remove the distortion of the calcium fluoride single crystal MC while remaining solid. During this time, as described above, the scavenging reaction during the temperature rise is monitored by the gas analyzer 500 through the gas introduction nozzle 418 provided in the vicinity of the crucible 420, and the temperature in the annealing furnace 400 is controlled as necessary. It is possible to prevent oxidation of the single crystal MC during annealing.

  In the annealing step, stress in the crystal and dislocations in the crystal can be reduced through annealing. Thereafter, the temperature of the calcium fluoride single crystal MC is gradually cooled to room temperature so as not to generate stress while maintaining the state in which distortion is eliminated.

  The calcium fluoride crystal thus obtained was measured for spectral transmittance (based on a measured crystal thickness of 10 mm), and the transmittance at a wavelength of 157 nm was high (about 90%), and the transmittance at a wavelength of 130 nm was 80% or more. Extract things. Refractive index homogeneity is determined from the transmitted wavefront and surface accuracy measurement with an interferometer, and the birefringence is measured with a high-accuracy strain meter.

  Thereafter, a single crystal of calcium fluoride is formed on the required optical element. Optical elements include lenses, diffraction gratings, optical film bodies and their composites, such as lenses, multi-lenses, lens arrays, lenticular lenses, fly-eye lenses, aspheric 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 fluoride crystal optical article. 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 has few crystal defects, the adhesion of the antireflection film is also excellent.

  In polishing processing to form the required optical article shape (convex lens, concave lens, disk shape, plate shape, etc.), partial surface accuracy is reduced due to the low dislocation density in the calcium fluoride crystal. Is extremely small and can be machined with high accuracy below the allowable value.

By combining various lenses thus obtained, a projection optical system and illumination optical system suitable for excimer lasers, particularly ArF excimer lasers and F ₂ lasers, can be constructed. An exposure apparatus for photolithography can be configured by combining an excimer laser light source, an optical system having a lens made of calcium fluoride crystals obtained by the crystal manufacturing method of the present invention, and a stage capable of moving the substrate. .

  After adding 0.2% by weight of zinc fluoride as a scavenger to the required amount of commercially available high-purity calcium fluoride powder raw material, and mixing and dispersing both, the carbon crucible is placed in a carbon crucible. Filled.

Next, the crucible filled with the raw material was transferred to a refining furnace, the inside of the furnace was evacuated to a vacuum degree of 6 × 10 ⁻³ Pa, and the crucible was heated to 250 ° C. and dehydrated for 48 hours. Melted by heating. During the temperature increase, the gas generated in the furnace was analyzed, and hydrofluoric acid having a mass number of 20 or fluorine having a mass number of 19 was monitored to control the rate of temperature increase. The gas to be monitored is not limited to hydrofluoric acid having a mass number of 20 and fluorine having a mass number of 19, but may be carbon monoxide having a mass number of 28 and carbon dioxide having a mass number of 44.

  FIG. 6 is a graph showing a change accompanying a temperature rise of the gas generated in the furnace. In this figure, the horizontal axis represents time, the left vertical axis represents the partial pressure of the generated gas, and the right vertical axis represents the furnace temperature. Referring to FIG. 6, since hydrofluoric acid having a mass number of 20 began to be generated from around 700 ° C., the scavenging reaction was sufficiently performed by slowing the heating rate.

  If the rate of temperature rise after the generation of hydrofluoric acid is not slowed, the scavenging reaction, oxidation prevention and fluorination, will not be sufficiently achieved, and the spectral transmittance in the vacuum ultraviolet region will decrease. That is, the gas analysis in the furnace is performed to monitor the generation of fluorine or hydrofluoric acid during the temperature increase, and the temperature increase rate is slowed to such an extent that oxidation prevention and fluorination are sufficiently accelerated. Thereby, lattice defects due to oxidation and lack of fluorine can be prevented, and a high-purity secondary material for crystal growth sufficient to improve the internal transmittance of the crystal can be obtained.

  The melting time was set to 100 hours suitable for removing harmful elements among the constituent elements of the solid scavenger. After removing harmful unnecessary elements, it was gradually cooled to solidify the raw material. A harmful unnecessary portion on the surface of the calcium fluoride block was removed to obtain a secondary material before crystal growth.

Next, the block was placed in a crucible for single crystal growth. As a scavenger, zinc fluoride was put in a 0.02% by weight crucible. The inside of the furnace was evacuated and the crucible was heated to go through a dehydration process. In order to melt and degas the calcium fluoride in the crucible, the degree of vacuum was about 6 × 10 ⁻³ Pa and the temperature was kept at 1420 ° C. for 50 hours.

  Next, the crucible was lowered at a rate of 1 mm / h to grow a good quality calcium fluoride single crystal. Since it is desirable that the pulling rate at this time corresponds to the crystal growth rate, it goes without saying that it is necessary to take into account the size and shape of the crystal to be manufactured. In general, the pulling speed needs to be slowed as the crystal size increases.

Next, a calcium fluoride single crystal grown in a crucible of an annealing furnace and zinc fluoride added in an amount of 0.001% by weight based on the weight of the calcium fluoride single crystal were added. The inside of the furnace was evacuated and kept at a temperature of 300 ° C. for about 24 hours to remove moisture in the furnace. When the degree of vacuum in the furnace became 5 × 10 ⁻⁴ Pa or less, the temperature of the crucible was increased from room temperature to 1140 ° C. at a rate of 50 ° C./h, and then held at about 1140 ° C. for about 50 hours.

  Then, it was cooled to room temperature at a rate of 5 ° C./h and cooled. The cooling rate at this time needs to be reduced according to the crystal size. In other words, it is difficult to make the birefringence very small unless slow.

  Table 1 shows the optical properties of the calcium fluoride crystal obtained in this example in comparison with the conventional example.

本発明の特徴は、フッ化物の結晶製造の精製工程、成長工程及びアニール工程のうち、特に、精製工程で昇温中のスカベンジング反応（酸化防止、フッ化）をガス分析によって監視し、坩堝内に発生するガスの状態から類推して結晶の酸化防止及びフッ化を促進するように坩堝の温度を制御する。これにより、真空紫外波長領域の内部透過率及びレーザー耐久性を向上させることができる。なお、坩堝内に発生するガスのガス分析は、必要により、結晶成長及びアニール工程においても有効である。

The feature of the present invention is that the scavenging reaction (antioxidation, fluorination) during the temperature increase in the purification process is monitored by gas analysis among the purification process, growth process and annealing process of fluoride crystal production. The temperature of the crucible is controlled so as to promote the oxidation prevention and fluorination of the crystal by analogy with the state of the gas generated inside. Thereby, the internal transmittance and laser durability in the vacuum ultraviolet wavelength region can be improved. Note that the gas analysis of the gas generated in the crucible is also effective in the crystal growth and annealing steps if necessary.

  Hereinafter, an exemplary exposure apparatus 700 of the present invention will be described with reference to FIG. Here, FIG. 7 is a schematic block diagram showing an exemplary embodiment of an exposure apparatus 700 as one aspect of the present invention. As shown in FIG. 7, the exposure apparatus 700 includes an illumination device 710 that illuminates a reticle 720 on which a circuit pattern is formed, a projection optical system 730 that projects diffracted light generated from the illuminated reticle pattern onto a plate 740, and a plate And a stage 745 for supporting 740.

  The exposure apparatus 700 is a projection exposure apparatus that exposes a plate 740 with a circuit pattern formed on the reticle 720 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 next exposure region for every batch exposure of the wafer.

  The illumination device 710 illuminates a reticle 720 on which a transfer circuit pattern is formed, and includes a light source unit 712 and an illumination optical system 714.

As the light source unit 712, 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 YAG laser may be used, and the number of light sources is 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 712, 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 712 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 714 is an optical system that illuminates the reticle 720, 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 714 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 714.

  The reticle 720 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 720 passes through the projection optical system 730 and is projected onto the plate 740. The reticle 720 and the plate 740 are optically conjugate. Since the exposure apparatus 700 of this embodiment is a scanner, the pattern of the reticle 720 is transferred onto the plate 740 by scanning the reticle 720 and the plate 740 at a speed ratio of the reduction magnification ratio. In the case of a step-and-repeat type exposure apparatus (referred to as “stepper”), exposure is performed with the reticle 720 and the plate 740 being stationary.

  The projection optical system 730 is an optical system that projects light reflecting a pattern on the reticle 720 disposed on the object plane onto the plate 740 disposed on the image plane. The projection optical system 730 includes an optical system including only 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 730.

  In this embodiment, the plate 740 is a wafer, but widely includes a liquid crystal substrate and other objects to be processed. The plate 740 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 745 supports the plate 740. Since any structure known in the art can be applied to the stage 745, a detailed description of the structure and operation is omitted here. For example, the stage 745 can move the plate 740 in the XY directions using a linear motor. For example, the reticle 720 and the plate 740 are synchronously scanned, and the positions of the stage 745 and the reticle stage (not shown) are monitored by, for example, a laser interferometer or the like, and both are driven at a constant speed ratio. The stage 745 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 730 have a damper on a base frame mounted 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 712 illuminates the reticle 720 with, for example, Koehler illumination by the illumination optical system 714. Light that passes through the reticle 720 and reflects the reticle pattern is imaged on the plate 740 by the projection optical system 730. The illumination optical system 714 and the projection optical system 730 used by the exposure apparatus 700 include an optical element manufactured from calcium fluoride according to the present invention and transmit ultraviolet light, far ultraviolet light, and vacuum ultraviolet light with high transmittance. 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 example of a device manufacturing method using the above-described exposure apparatus 700 will be described with reference to FIGS. FIG. 8 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by the lithography technique of the present invention using the mask and the wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4. The assembly process (dicing, bonding), packaging process (chip encapsulation), and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 9 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 700 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 700 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 known method other than the crucible lowering method, a method of fixing the crucible and pulling up the heater, a method of gradually decreasing the heater output, and the like.

It is a flowchart for demonstrating the crystal manufacturing method of this invention. It is a schematic block diagram which shows one exemplary form of the refinement | purification furnace as an example of the crystal manufacturing apparatus of this invention. FIG. 3 is a schematic block diagram showing an exemplary form of the gas analyzer shown in FIG. 2. It is a schematic block diagram which shows one example form of the crystal growth furnace as an example of the crystal manufacturing apparatus of this invention. It is a schematic block diagram which shows one example form of the annealing furnace as an example of the crystal manufacturing apparatus of this invention. It is a graph which shows the change accompanying the temperature rise of the gas generated in the furnace. 1 is a schematic block diagram showing an exemplary embodiment of an exposure apparatus as one aspect of the present invention. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 9 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 8.

Explanation of symbols

200 Refining furnace 210 Chamber 212 Heat insulating material 214 Cooling pipe 216 Thermocouple 218 Gas introduction nozzle 220 Crucible 230 Heater 240 Vacuum exhaust system 242 Dry pump 244 Mechanical booster pump 246 Turbo molecular pump 248 Detoxification system 250 Crucible support mechanism 300 Crystal growth furnace 400 Annealing furnace 500 Gas analyzer 510 Detector 520 Analyzer 530 Controller 700 Exposure apparatus

Claims (21)

A step of refining the raw material by mixing the raw material of the crystalline substance and the scavenger, melting and then solidifying the raw material;
Growing the single crystal of the raw material by melting and then solidifying the purified product purified in the purification step;
Heat-treating the single crystal grown in the growth step,
Analyzing a gas component generated during at least one of the purification step, the growth step, and the heat treatment step;
And a step of controlling the temperature of the crystalline substance based on the gas component analyzed in the analyzing step. A step of refining the raw material by mixing the raw material of the crystalline substance and the scavenger, melting and then solidifying the raw material;
Growing the single crystal of the raw material by melting and then solidifying the purified product purified in the purification step;
Heat-treating the single crystal grown in the growth step,
Monitoring a scavenging reaction during at least one of the purification step, the growth step and the annealing step;
And a step of controlling the temperature of the crystalline substance based on the scavenging reaction monitored in the monitoring step. The crystal manufacturing method according to claim 1, wherein the temperature control step controls a melting time of the raw material in the purification step. 3. The crystal manufacturing method according to claim 1, wherein the temperature control step controls a melting time of the raw material in the growth step. 3. The crystal manufacturing method according to claim 1, wherein the temperature control step controls a time of the heat treatment of the heat treatment step. The crystal manufacturing method according to claim 1, wherein the gas component has a mass number of 19, 20, 28, and 44. The crystal production method according to claim 1, wherein the gas component is F, HF, CO, or CO ₂ . The crystal production method according to claim 1, wherein the raw material is calcium fluoride. A processing chamber for storing a crystalline material,
A gas analyzer for analyzing gas components in the atmosphere inside the processing chamber;
A crystal manufacturing apparatus comprising: a temperature control unit configured to control a temperature inside the processing chamber based on the gas component analyzed by the gas analyzer. The gas analyzer includes a detection unit that detects the gas component;
The crystal manufacturing apparatus according to claim 9, further comprising an analysis unit that analyzes the gas component detected by the detection unit. The crystal manufacturing apparatus according to claim 9, wherein the gas component analyzed by the gas analyzer has a mass number of 19, 20, 28, and 44. The crystal manufacturing apparatus according to claim 9, wherein the gas component analyzed by the gas analyzer is F, HF, CO, CO ₂ . The crystal manufacturing apparatus according to claim 9, wherein the processing chamber is a refining furnace for refining the raw material of the crystalline substance. The crystal manufacturing apparatus according to claim 9, wherein the processing chamber is a growth furnace for growing a single crystal from a raw material of the crystalline substance. The crystal manufacturing apparatus according to claim 9, wherein the processing chamber is an annealing furnace for annealing a single crystal grown from a raw material of the crystalline substance. The crystal manufacturing apparatus according to claim 9, wherein the raw material is calcium fluoride. An optical element manufactured from a single crystal manufactured using the crystal manufacturing method according to claim 1. An optical element manufactured from a single crystal manufactured using the crystal manufacturing apparatus according to any one of claims 9 to 16. 19. The optical element according to claim 17, 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 with the exposure light via an optical system including the optical element according to claim 19. An exposure apparatus characterized by that. Exposing an object to be processed using the exposure apparatus according to claim 20;
And performing a predetermined process on the exposed object to be processed.

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