JP3880006B2 - Method for manufacturing optical article - Google Patents

Description

  The present invention relates to a method for manufacturing an optical article such as a lens or a mirror. More specifically, the present invention relates to an optical thin film for an optical article suitably used for an exposure apparatus or an optical system using an excimer laser, and a manufacturing method thereof.

  Optical articles such as lenses, mirrors, and optical filters are used in optical devices such as cameras, telescopes, and microscopes, for example. These optical articles are provided with an antireflection film or an increased reflection film on the surface thereof in order to prevent reflection or enhance reflection.

  An exposure apparatus is one type of optical apparatus in which such an optical article is incorporated. This apparatus is used in a manufacturing process of a semiconductor integrated circuit and a photomask for manufacturing the semiconductor integrated circuit. A typical example of the exposure apparatus in this field is an exposure apparatus called a stepper.

  Conventionally, as an illumination light source of such an exposure apparatus, an ultrahigh pressure mercury lamp that emits g-line (435.8 nm), h-line (404.7 nm), and i-line (365 nm), a xenon / mercury arc lamp, or the like has been used. It was. However, recently, in order to realize exposure processing capability (throughput) per unit time and uniform illumination characteristics on an object to be exposed such as a wafer, deep ultraviolet rays (200 to 260 nm), high output, and a narrow spectrum width. Attempts have been made to use laser light that oscillates the luminous flux. In particular, an excimer laser is one of desirable light sources because it emits high-power light with a very narrow spectral width.

  As an optical article for excimer laser, an optical article obtained by vacuum-depositing an antireflection film described in JP-A Nos. 63-113501 and 63-113502 is known.

  However, for example, even if a lens has sufficient optical characteristics in the visible light optical system, it may be difficult to maintain optical characteristics sufficient to withstand use when used in an excimer laser optical system. there were. Specifically, the transmission characteristics of the optical thin film provided on the surface of the lens or mirror are not sufficient to take advantage of the excimer laser, and there is a problem in its durability.

  Furthermore, since an optical article for an exposure apparatus requires a very high precision surface property, the temperature conditions when forming an optical thin film are severe, and the film formation technique generally preferred is this. When such an optical article was produced, it could not be diverted as it was.

  As described above, in order to manufacture an optical article that can withstand the use of an excimer laser, the optical article must be designed with a new idea and a new approach.

  The present invention has been made in view of the above-described technical problems, and an object thereof is to provide a method for manufacturing an optical article having optical characteristics that can sufficiently withstand severe use conditions such as an excimer laser application.

  Another object of the present invention is to provide a method for producing an optical article having an optical thin film with little unnecessary light absorption and uniform physical characteristics over a large area.

  Still another object of the present invention is to provide a method for producing an optical article having an optical thin film that can be formed at a low temperature and is not adversely affected by stress such as film peeling.

  Of course, as long as it can withstand the excimer laser, it will show good characteristics even in an optical system using other light.

In the method for producing an optical article of the present invention, a first light-transmitting thin layer and a second light-transmitting thin layer having a refractive index higher than that of the first light-transmitting thin layer are laminated on the surface of the substrate. In the method of manufacturing an optical article,
A sputtering gas containing at least one atom selected from the group consisting of krypton or xenon was used for at least one of the first and second light-transmitting thin layers while the substrate was kept at 100 ° C. or lower. Depositing on the surface of the substrate by sputtering of the target .
In addition to the sputtering gas, an oxidizing gas is used as a reaction gas. Furthermore, it is preferable that at least the film-forming surface of the substrate is exposed to a nitrogen gas atmosphere and the back surface of the substrate is kept at 100 ° C. or lower before the sputtering.

  The present inventor found that a film containing at least one of these two atoms can maintain good transmittance for a long period of time, rather than a film containing no krypton or xenon obtained by vacuum deposition or sputtering using Ar gas. As a result, the present invention has been achieved.

According to the first aspect of the invention, there is provided an optical article manufacturing method in which plasma is uniformized and a large-area optical article having uniform characteristics can be easily manufactured at a low temperature of 100 ° C. or less.

According to the second aspect of the present invention, since an oxidizing gas is introduced as a reaction gas, an optical article that can produce an oxide film having a more stoichiometric composition and more excellent characteristics even with a non-single crystal film. The manufacturing method is obtained.
According to the invention which concerns on Claim 1, the manufacturing method of the optical article which can suppress the change of the surface shape of an optical article is obtained. In addition, degassing during film formation is reduced, and film peeling and generation of unnecessary products are suppressed.

  According to the third aspect of the invention, a method for producing an optical article in which degassing during film formation is suppressed can be obtained by exposing the substrate to a nitrogen gas atmosphere before sputtering.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, and can be used as a substitute for components as long as the object of the present invention is achieved. Various changes such as substitution with equivalents and changes in the materials used may be made.

(Optical article in which an optical thin film is laminated on the surface of a substrate)
FIG. 1 is a schematic cross-sectional view of an optical article having various optical thin films according to an embodiment of the present invention.

FIG. 1A shows a transmissive optical article in which an antireflection film 2 is provided on the surface of a translucent substrate 1, and is used as a lens, a light transmissive window, or the like.
Although the antireflection film 2 may be a single thin film, it may have a configuration in which translucent thin layers having different refractive indexes are laminated as shown in FIG. Here, the thin layer 2H is a thin layer having a high refractive index, and 2L is a thin layer having a low refractive index. By providing a thin layer having a low refractive index on the surface (air) side, an antireflection effect is provided.

FIG. 1C shows a configuration in which two light-transmitting thin layers having different refractive indexes are alternately stacked (four layers in total).
FIG. 1D shows a configuration having three types of light-transmitting thin layers having different refractive indexes and one low refractive index thin layer. Here, a thin layer 2H having a high refractive index, a thin layer 2L having a low refractive index, and a thin layer 2M having an intermediate refractive index are employed.

  FIG. 1E shows a configuration in which three light-transmitting thin layers having different refractive indexes are alternately stacked (six layers in total).

  FIG. 1 (f) shows an optical article having a light-reflective film 4 on a light-transmitting or non-light-transmitting substrate 3, and the light-reflective film 4 has light-transmitting thin layers having different refractive indexes. It is a laminated structure. Here, reflection is enhanced by disposing a thin layer 4H having a high refractive index on the surface side. 4L is a thin layer having a low refractive index. Although not shown in the drawings, the increased reflection film 4 may be formed by repeatedly laminating the thin layer 4L and the thin layer 4H in multiple layers (for example, 10 to 100 layers).

  The materials of the substrates 1 and 3 and the material of each thin layer are appropriately selected according to the wavelength of light used and the configuration of the optical thin film. The same applies to the thicknesses of the substrates 1 and 3 and the thickness of each thin layer. The thickness of each thin layer is selected from the range of about 0.1 nm to 1 μm.

(Substrate)
Examples of the material of the substrate 1 in the present invention include translucent substrates such as fused quartz and fluorite. However, some adjustment material may be included to adapt to the light to be used. Specifically, it contains SiO ₂ as a main component and contains B ₂ O ₃ , Na ₂ O, K ₂ O, PbO, Al ₂ O _{3 and the} like. Examples of the substrate 3 for an increased reflection film such as a mirror include those in which a highly reflective metal film is provided on the light-transmitting surface described above and metals.

(Translucent thin layer)
The material of the light-transmitting thin layer for constituting the optical thin film in the present invention is appropriately selected from the same group of materials as shown below for both the antireflection film 2 and the enhanced reflection film 4. Examples of materials included in the group include silicon oxide (1.44), tantalum oxide (2.17), aluminum oxide (1.72), zirconium oxide (2.25), and hafnium oxide (2.25). , Non-single crystalline oxides such as yttrium oxide (2.10) and scandium oxide (2.11), or magnesium fluoride (1.43), neodymium fluoride (1.66), calcium fluoride (1 .46), non-single crystalline fluorides such as lithium fluoride (1.37), sodium aluminum fluoride (1.35), thorium fluoride (1.59) and lanthanum fluoride (1.59). Can be mentioned. The inside of () is an example of the refractive index in the light of wavelength 248nm corresponding to a KrF excimer laser.

(Elements contained in optical thin film)
The elements contained in the optical thin film according to the present invention have been found as a result of repeating many experiments by the present inventors.

  An optical article used in an excimer laser optical system generates heat due to its high power if it absorbs some laser light, and the heat is stored during use. As a result, it was found that the surface property of the optical article deteriorates and the translucency of the optical thin film deteriorates.

  As a countermeasure, the present inventors have found that when the element in the present invention is contained in an optical thin film, the optical absorption of the optical thin film is nearly zero. Furthermore, even if it is adopted in an optical system in which a large number of lenses are combined, even total light absorption can be reduced to almost zero. Since such an optical article was used, the reliability of the exposure apparatus could be remarkably improved.

The optical thin film used in the present invention is a non-single crystal thin film containing at least one atom selected from the group of xenon (Xe) and krypton (Kr ) . When the optical thin film is composed of a large number of thin layers, at least one thin layer among them may contain the atoms. In particular, when the thin layer is formed of an oxide, the effect is remarkable. When the content of the atoms does not exceed 5 atomic% and is contained in the thin layer, the filling rate of the amorphous film is improved and the durability is excellent. More preferably, it is 3 atomic% or less, and optimally 1 atomic% or less. The appropriate lower limit of the content is 0.5 atomic ppm. In the case where the optical thin film is composed of a large number of thin layers, it is preferable that the adhesiveness of each film is improved by making the content of the atoms in each film different from each other. Further, it is assumed that the excellent total durability improves when should not exceed 10 atomic percent amorphous film packing fraction content when it contains one or more of the above two elements. The content of these elements can be measured by Rutherford backscattering analysis (RBS), secondary ion mass spectrometry (SIMS), or total reflection X-ray fluorescence diffraction.

  Furthermore, when the above three elements are contained in a thin layer, it is possible to obtain a high quality film by suppressing the contents of argon (Ar), helium (He), and neon (Ne) to 0.1 atomic% or less. More preferred above.

(Light used in optical systems in which optical articles are used)
Examples of light used in an optical system in which the optical article of the present invention is used include ultraviolet light such as i-line, far ultraviolet light, and laser light. Examples of lasers that output such light include He—Cd laser (442 nm), Ar + laser (488, 515 nm), He—Ne laser (544, 633 nm), and semiconductor laser (780 nm).

In particular, the optical article of the present invention is suitable for an i-line or excimer laser optical system, and is particularly suitable for an excimer laser optical system. Examples of the excimer laser include F ₂ (157 nm), ArF (193 nm), KrCl (222 nm), KrF (248 nm), ClF (284 nm), XeCl (308 nm), I ₂ (342 nm), XeF (351 nm, 353 nm). and so on. Among these, a KrF excimer laser, a XeCl laser, or an ArF excimer laser is preferably used for the exposure apparatus.

  More desirably, in addition to these excimer lasers for exposure, if an optical article with good transmission characteristics can be formed even for light of a relatively long wavelength, such as an alignment He-Ne laser, alignment with the projection optical system is possible. Since it can be applied to an exposure apparatus that employs a TTL (Through The Lens) alignment system that performs high-precision alignment by passing light, its use is more preferable because it further expands.

(Manufacturing method and manufacturing apparatus)
Hereinafter, a manufacturing method and a manufacturing apparatus for manufacturing an optical thin film containing at least one atom selected from the group of xenon (Xe) and krypton (Kr ) will be described.

Examples of the method for producing the optical thin film used in the present invention include chemical vapor deposition (CVD) and physical vapor deposition (PVD) using the above rare gas. if at least one of the thin layer constituting the optical thin film, krypton, deposited by sputtering using a sputtering gas containing at least one atom selected from xenon emission or Ranaru group.

  FIG. 2 is a schematic diagram showing a basic configuration of an optical thin film manufacturing apparatus used in the present invention. The production apparatus 11 includes a film forming chamber 12 for performing sputtering, and a load lock as a preliminary chamber that is provided as necessary, and that carries the film forming substrate 1 into and out of the chamber 12 and can accommodate the substrate 1 therein. The chamber 13, the exhaust means 14, and the gas supply means 15 are provided. In the film forming chamber 12, a target 12a, a substrate holder 12b, a magnet 12c, and an electrode 12d are arranged, and the electrode 12d is connected to a high frequency power source. A gate valve 13a is disposed between the load lock chamber 13 and the film forming chamber 12, and the atmospheres of these two chambers are separated and independent from each other.

  The exhaust means 14 is arranged together with valves and pipes by selecting at least one suitable pump from various pumps such as a turbo molecular pump, a cryopump, a mechanical booster pump, and an oil diffusion pump.

Gas supply means, krypton, gas cylinder and housing a single xenon emission, valves, gas flow controllers, and piping and the like. Of course, you may enable it to supply oxidizing gas, such as oxygen, as needed.

  The production procedure is as follows. The base housed in the load lock chamber 13 is placed on the holder 12b in the chamber 12 with the gate valve 13a opened. In the load lock chamber 13, if necessary, the substrate may be exposed to a nitrogen atmosphere and heated so that the substrate does not exceed 100 ° C.

  After the gate valve 13a is closed and the chamber 12 is evacuated, krypton, xenon, or the like is supplied as a sputtering gas. Of course, when reactive sputtering is performed, a reactive gas such as oxygen is further supplied. Radio frequency power is supplied to the electrode 12d to cause glow discharge plasma of the rare gas. Thus, the constituent atoms of the target 12a are knocked out by the rare gas and deposited on the surface of the substrate. At this time, in order to suppress the change in the surface shape, it is desirable to control the temperature by providing a heating / cooling means and a temperature sensor in the holder 12b so that the substrate temperature does not exceed 100 ° C. by the plasma. Of course, if the temperature does not exceed 100 ° C. without cooling, there is no need for such a controller.

  When the optical thin film is composed of two or more kinds of thin layers, the above steps may be repeated by changing the target material. In order to improve the throughput, a plurality of targets may be arranged in one chamber and a target exposed to plasma may be selected. Alternatively, a plurality of film formation chambers may be prepared and provided independently to form a single thin layer.

Krypton contained in the thin layer, in order to control the amount of xenon emission is or supply amount of the gas, the temperature of the substrate, so that the content by controlling the pressure during film formation does not exceed 5 atomic% Be careful. In addition, when forming a thin layer of oxide, reactive sputtering using pure metal such as aluminum or tantalum and oxygen as a reactive gas, or simple sputtering using an oxide target can be cited. It is preferable to perform reactive sputtering by supplying an oxidizing gas together with the rare gas as a target.

  When sputtering is performed using the rare gas, a large plasma region having a uniform energy distribution can be generated, and the energy dependency of the film quality is improved. FIG. 3 is an example of a graph showing the variation of the reflectance with respect to the ion irradiation energy, and shows that the transmittance (low reflectance) is excellent over a wide range of energy. It can be seen that when this is 100% argon, good transmittance is shown only in a very limited range. This indicates that the reproducibility of film formation is good, the adjustment range of each parameter during film formation is widened, and film formation is facilitated.

The conditions employed in the sputtering of the present invention are as follows.
The pressure during sputtering is not particularly limited as long as the discharge can be stably maintained, and is specifically 1 to 5 mTorr.

  As the RF power, a value that can remove the adsorbed impurities without damaging the thin layer may be selected. Specifically, the power is 5 W to 50 W. For the same reason, the time is suitably 1 minute to 20 minutes.

Noble gas for sputtering Kr, besides X e atom alone, can be used or a mixed gas thereof, Ar, the He, also mixed gas of Ne. In the case of a mixed gas of Kr and Xe, their volume ratio is not limited, but for example, the volume ratio of Xe and Kr is preferably 1: 1. In the case of mixing with Ar, He, and Ne, it is better to make the amount smaller than the gas of Kr and Xe so that these atoms are not excessively taken into the thin layer.

  As the frequency of the applied power decreases, the self-bias of the target increases negatively and the sputtering rate increases, but on the other hand, variations in irradiation energy occur, so 10 MHz to 500 MHz is suitable.

  According to another experiment of the present inventor, when a non-light-transmitting film of silicon (Si) or aluminum (Al) is formed by sputtering, the sputtering using Xe is performed on the deposited Si film or Al film. Xe content was not observed. This is in contrast to the fact that Ar is easily incorporated into the film by sputtering using Ar.

Thus, by using a sputtering method of the present invention, Xe, to be contained in the optical thin film is in a range not exceeding 5 atomic percent K r atom, a relatively low temperature of the base, for plasma generation power The deposition may be performed at a relatively low frequency and in a mixed atmosphere with oxygen gas at a relatively low deposition rate. Specific setting values will be described later. By doing so, a very small amount of Xe and Kr can be taken into the translucent optical thin film.

  Even in the formation of metal oxides, it is preferable to mix oxygen with these gases. This has the effect of repairing the damaged metal oxide by oxidizing the bond that has broken the bond to the metal oxide from the evening get. The ratio is preferably 20% by volume or less of oxygen with respect to the rare gas. This is because if the amount of oxygen is too large, the film formation rate becomes extremely slow, the effect of surface activity by rare gas ions is reduced, and a dense film cannot be formed. Further, when the evening get is a metal and a metal oxide is formed as a film, the amount of oxygen relative to the rare gas is larger than that in the case of a metal oxide target. However, rather than oxidizing the metal on the lens to form a metal oxide, it is more preferable to target a high-purity metal oxide and oxidize and reinforce a weak part of the lens. A simple film can be formed.

  Hereinafter, another example of an optical thin film manufacturing apparatus used in the present invention will be described. This apparatus is a sputtering apparatus capable of controlling the energy of ions irradiating the lens surface and supplying deposited atoms.

  The apparatus shown in FIG. 6 is an rf-dc coupled bias sputtering apparatus. In FIG. 6, reference numerals 91 and 911 denote vacuum chambers, and reference numeral 911 denotes a load lock chamber. Reference numeral 920 denotes a lens stocker connected to the load lock chamber and having a clean N2 flowing constantly. Reference numeral 912 denotes a halogen lamp, which can be preheated in the load lock chamber 911. Reference numeral 92 is a target, 93 is a magnet for efficiently generating plasma, 94 is a convex lens attached to the lens support member 1002 by lens restraint, and this lens support member is attached to the lens holder. Has a rotating system. Reference numeral 96 denotes a high frequency power source capable of changing the frequency, 97 denotes a matching circuit, 98 denotes a direct current power source for determining the direct current potential of the target, and 100 denotes a low pass filter of the target. Although not shown, it is preferable to provide a second high-frequency power source on the lens side and control the energy of ions irradiated onto the lens with higher accuracy. In this example, the lens holder is made of SUS316, but the potential is a floating potential.

  The vacuum chambers 91, 911, and 920 are made of a material with little degassing, and are made of, for example, SUS316. The inner surface of the chamber was subjected to electric field polishing and electric field composite polishing as surface treatment, and a passive oxide film made of high-purity oxygen was formed on a mirror-finished surface having a surface smoothness of Rmax <0.1 μm (T. Ohmi). et al Extended Abstracts, 174th Electrochemical Society, Fall Meeting, 396, 579-580, Oct. 1988). Therefore, the structure is such that gas is hardly adsorbed and impurity contamination is suppressed as much as possible.

  The gas supply system, including the mass flow controller and the filter, is all made of SUS316 by subjecting it to electropolishing and passive oxidation, so as to suppress the amount of impurities when introducing the process gas into the chamber as much as possible. The exhaust system is configured as follows. The main pump is a magnetically levitated tandem turbomolecular pump, which uses a dry pump as an auxiliary pump. The exhaust system is an oil-free system, and the system is configured so that there is little impurity contamination. Note that the second stage turbo molecular pump is a large flow type pump, and the pumping speed is maintained even for a vacuum degree of mTorr order during plasma generation. The lens 94 is introduced into the vacuum chamber 91 through a load lock chamber provided in contact with the chamber to prevent impurities from entering the vacuum chamber 91.

As a result, the amount of impurities introduced into the chamber is several ppb or less even with the largest amount of moisture. The background vacuum degree of the vacuum chamber is achieved at 10 ⁻⁸ or less. In addition, since a variable high-frequency power supply capable of up to several hundred MHz is installed on the target, high-density plasma can be generated, and self-bias and plasma potential can be changed. A DC power supply for applying a DC potential is connected to the target via a low-pass filter. When the target is conductive, the target potential can be controlled by the DC power supply. With this configuration,
a) Deposition rate b) Energy of ions irradiated on the substrate c) Deposition conditions such as plasma density can be controlled.

  FIG. 7 is a view showing a chamber of another sputtering apparatus used in the present invention.

  In the chamber 91, two triangular columnar target holders are arranged. The configuration of this target holder is different from the apparatus shown in FIG. 6, and other configurations are the same as those of the apparatus of FIG.

  In this target method, one of three types of targets can be selected and sputtered by rotating the holders 92a and 92b.

  In the example of FIG. 7, the case where tantalum oxide, aluminum oxide, or silicon oxide is used as a target is illustrated.

  During sputtering, the rotation angle of the holder is adjusted so that the surface of the target is inclined with respect to the surface of the substrate. By doing so, it is easy to form a uniform film on a substrate having any surface shape and size such as a concave lens, a convex lens, and a concave mirror.

  FIG. 8 is a graph showing the energy distribution of ions irradiating the surface of the substrate grounded to the ground with respect to the frequency of the high frequency power applied to the target. This figure is for a pressure of 7 mTorr, Ar ions, and Xe ions. The higher the frequency, the sharper the energy distribution, and the two peaks that appear at low frequencies disappear, resulting in a distribution with one energy peak. . This is because the higher the frequency, the more difficult the ions are shaken to the high frequency, that is, to obtain a stable plasma potential. For this reason, when controllability is considered, the higher the frequency, the better. However, when the frequency is too high, the wavelength becomes the same as that of the substrate, which causes in-plane distribution.

  As the ion species, heavier atoms have smaller fluctuations due to high frequency and are more preferable for obtaining a stable plasma potential. The heavier in the order of Kr, Xe, and Rn, the smaller the energy distribution, and the in-plane distribution of film characteristics A good one is obtained. Although the optimum value of the frequency use range varies depending on the atom used, when using Kr, Xe, Rn, about 10 to 500 MHz is preferred. On the other hand, with respect to the energy supply to the surface of the deposited film by ion irradiation, if the ions have the same energy, heavier atoms can efficiently give energy only to the vicinity of the surface. Moreover, it is less likely to penetrate deeply into the film and cause damage. Therefore, a dense film is formed and the surface flatness is improved.

  FIG. 9 shows the incident energy dependence as a normalized value of the sputtering rate of Ar and Xe gas with respect to the Si target. It can be seen that even when the energy value is the same, Ar enters the Si target deeply and performs the sputtering phenomenon, and as a result, the sputtering rate is larger than Xe (the slope of the graph is large).

Hereinafter, a lens stocker using the optical article of the present invention will be described.
In general, several tens of layers of water molecules are adsorbed on the surface of a substrate left in the atmosphere (Nakagawa, Izumi, Ohmi “Measurement of solid surface adsorbed moisture using anhydrous HF”, 19th Ultra Ultra Clean Technology Symposium, pp 41, 1993). Therefore, when this water molecule is deposited on the lens surface, such as an antireflection film, it is likely to be a major factor that degrades the film quality by being taken into the film as a contaminant. On the other hand, the activation energy indicated by the surface temperature of the water molecules adsorbed on the lens surface, that is, the surface containing SiO ₂ as a main component and the surface density of the number of adsorbed molecules is 0.09 eV, and the water molecules between the second layer and thereafter are water molecules. It has been reported that the activation energy is 0.12 eV because of the bond (M. Nakamura et al Extended Abstracts, 180th Electrochemical Society Meeting, Phoenix, Abstract No. 534, pp. 798-799, October 1991). . In order to remove the water molecules, clean nitrogen with few water molecules is constantly flowing in the lens stocker.

  Water molecules on the surface are removed over time. If the lens temperature is kept at about 90 ° C., the removal speed increases, which is efficient. At room temperature, for example, the lens is placed in a lens stocker for about one week, and clean nitrogen is allowed to flow, and then the lens is introduced into the load lock chamber and evacuated. Through the above process, water molecules on the lens surface are almost removed.

For clean nitrogen supply system for supplying clean nitrogen to the lens stocker it will be described with reference to FIG. 1 0. 301 is a liquefied nitrogen gas tank, 302 is an evaporator, 303 is a purifier, 304 is a SUS pipe, 305, 306 and 310 are SUS pipes subjected to passive oxidation treatment, 307 is a pressure regulator, 308 is a mass flow controller, and 309 is nitrogen gas Two-way three-way valve for introduction, 311 is a lens stocker, 313 is a valve, 314 is an exhaust pump, and 315 and 312 are SUS pipes.

  The liquefied nitrogen gas is supplied from 301, and the amount of water passing through the purifier is 0.1 ppb or less, and the number of particles of 0.1 μm or more is below the detection limit. As a purifier, PEGASUS200E manufactured by Nippon Oxygen, which has both an adsorption type and a getter type, was used. Clean nitrogen gas is introduced into the lens stocker through a pressure regulator and a mass flow controller, but the input section is divided into six so that the gas circulates inside the lens stocker. For removing moisture from the lens surface, the lens surface may be installed near the introduction portion and sprayed, but is not particularly limited. Nitrogen introduced into the lens stocker is exhausted from the exhaust pump through the valve 313. The exhaust pump has a great effect when substituting nitrogen with air from the normal atmosphere. However, after that, the exhaust pump need not be used, and extruded exhaust or the like may be used.

(Exposure equipment)
Hereinafter, an exposure apparatus using the optical article of the present invention will be described.
Examples of the exposure apparatus include a reduction projection exposure apparatus using a lens optical system and a lens-type equal magnification projection exposure apparatus.
In particular, in order to expose the entire wafer surface, a stepper employing a step-and-repeat method in which one small section (field) of the wafer is exposed, the wafer is moved one step, and the next one field is exposed is desirable. . Of course, it is also suitably used in a microscan exposure apparatus.

  FIG. 4 shows a schematic configuration of the exposure apparatus of the present invention. In the figure, 21 is an illumination light source unit, 22 is an exposure mechanism unit, and 21 and 22 are configured separately and independently. That is, both are physically separated. Reference numeral 23 denotes an illumination light source, which is a high-output large-sized light source such as an excimer laser. Reference numeral 24 denotes a mirror, reference numeral 25 denotes a concave lens, reference numeral 26 denotes a convex lens, and reference numerals 25 and 26 serve as beam expanders, which expand the laser beam diameter to the size of an optical integrator. Reference numeral 27 denotes a mirror, and 28 denotes an optical integrator for uniformly illuminating the reticle. The illumination light source unit 21 includes a laser 23 to an optical integrator 28. Reference numeral 29 denotes a mirror, and reference numeral 30 denotes a condenser lens that collimates the light beam emitted from the optical integrator 28. Reference numeral 31 denotes a reticle on which a circuit pattern is drawn, reference numeral 31a denotes a reticle holder that sucks and holds the reticle, reference numeral 32 denotes a projection optical system that projects the reticle pattern, and reference numeral 33 denotes a wafer on which the pattern of the reticle 31 is printed on the projection lens 32. Reference numeral 34 denotes an XY stage which holds the wafer 33 by suction and moves in the XY direction when printing is performed by step-and-repeat. Reference numeral 35 denotes a surface plate of the exposure apparatus.

  The exposure mechanism unit 22 includes a mirror 29 to a surface plate 35 that are part of the illumination optical system. Reference numeral 36 denotes an alignment means used for TTL alignment. The normal exposure apparatus includes an autofocus mechanism, a wafer transfer mechanism, and the like, which are also included in the exposure mechanism section 22.

  FIG. 5 is an example of an optical article used in the exposure apparatus of the present invention, and is a lens used in the projection optical system of the exposure apparatus shown in FIG. This lens assembly is constituted by combining 11 lenses L1 to L11 without bonding them to each other. The optical thin film of the present invention can be provided as an antireflection film or an increased reflection film on the surface of the lens or mirror shown in FIGS. 4 and 5 or the mirror or lens of the mirror type exposure apparatus (not shown).

Example 1
In the following, a method for forming a thin film made of Ta ₂ O ₅ on a 120 mm quartz substrate, for example, using the sputtering apparatus shown in FIG. 6 will be specifically described. A target having a thickness of 5 inches × 15 inches and a thickness of 6 mm was used. The purity is a high-purity product of 0.9999 or higher. First, contaminants slightly adsorbed on the substrate surface were removed by ion irradiation with a weak energy value (referred to as a surface cleaning step). As an example, 5 mTorr of Xe was used as the introduced gas.

First, clean nitrogen was introduced into the load lock chamber to atmospheric pressure, and then the substrate together with the support member was transferred from the lens stocker to the load lock chamber. After closing the gate valve between the load lock chamber and the stocker, the load lock chamber was evacuated. The ultimate vacuum was 3 × 10 ⁻⁸ Torr. Here, it is also possible to perform degassing by providing a heating mechanism such as a halogen lamp and heating at about 80 ° C. to 99 ° C. Next, the gate valve between the load lock chamber and the sputter chamber was opened, the lens was transferred to the sputter chamber together with the support member, and mounted on the holder. When Xe gas is introduced into the sputtering chamber while rotating the substrate by a rotating mechanism connected to the holder, the pressure becomes 5 mTorr, and after stabilization, a high frequency of 100 MHz and a high frequency of 20 W is introduced as RF power to generate plasma. The minutely adsorbed contaminants on the lens surface were removed by performing Xe ion irradiation with a weak energy value for a minute.

At this time, the substrate surface was in a floating potential, and the lens surface was irradiated with approximately 3 eV of Xe ions, which is a potential difference from the plasma potential. This potential difference is made uniform by using a gas that is heavier than Ar gas, and the uniformity of ion energy to be irradiated is increased. If the irradiation energy is too high, damage will remain on the surface, and it seems that a dense Ta ₂ O ₅ film cannot be formed in the subsequent film formation process. The temperature of the substrate is room temperature, and there is a slight increase due to ion irradiation, but it is necessary to suppress the lens surface microstructure to the extent that it does not exceed 100 ° C.

Thereafter, a Ta ₂ O ₅ film is formed by sputtering. Once the plasma is stopped by interrupting the high-frequency introduction, Xe gas and O ₂ gas are introduced into the sputtering chamber so that the gas flow volume ratio Xe / O ₂ = 10/1 and the total pressure becomes 5 mTorr. Then, after stabilization, plasma was generated by introducing a high frequency of 1 kW as a frequency of 15 MHz and RF power to form a film. The film formation rate was 0.5 nm / sec, and the film was formed with a crystal vibration type film thickness meter until the film thickness reached 250 nm. The ratio of Xe irradiation to one Ta ₂ O ₅ was 9.2. At this time, the energy of Xe ions irradiated on the substrate surface was 8 eV. At this time, it was confirmed by RBS analysis that Xe incorporated into the Ta ₂ O ₅ film was 0.1%.

For the Ta ₂ O ₅ film formed under the above conditions and a film that does not contain Xe formed in the same manner except that the Xe gas is changed to a granular gas, the film is irradiated with i-line with doubled power for 500 hours. The transmittance and reflectance were measured by a spectroscopic method, and the optical absorption of the film was calculated and expressed as an extinction coefficient.
The extinction coefficient was 4.5 for Ar and 0.1 for Xe.

  In this example, since the purpose was to produce an antireflection film for i-line, the measurement wavelength was 365 nm. It can be seen that when Xe is used as the sputtering gas compared to when Ar is used, a high-quality film having a small extinction coefficient and difficult to optically absorb is formed.

  In this way, the obtained article was placed in an i-line optical system, irradiated with i-rays twice the dose used in a normal exposure apparatus, and the change with time in the transmittance of the lens was measured. The result is shown in FIG. In the case of a film having a film formed by sputtering using Ar without using Xe, the transmittance is extremely deteriorated when the irradiation time exceeds a predetermined time T1, whereas in this embodiment, the transmittance is hardly deteriorated. I couldn't see it.

  Further, the in-plane distribution of the refractive index was about 10% better than that of the comparative sample obtained using Ar gas without using Kr, Xe, and Rn.

(Example 2)
This example differs from Example 1 in that an optical thin film made of several types of tantalum oxide was produced by changing the amount of ion irradiation energy. The other points were the same as in Example 1.
Similar to FIG. 11 of Example 1, the change with time of the transmittance was measured for the optical thin film of this example. FIG. 12 is a graph summarizing the amount of deterioration of the transmittance after the elapse of the same time T2 as in FIG. 11 compared to the initial value.

  Compared to Ar comparison data obtained by the same method as that prepared using Ar gas for comparison in Example 1, the range of ion irradiation energy that can produce a high-quality film with little change over time is wide. I understand. This means that when Xe is used as the sputtering gas, a high-quality film can be easily produced with good reproducibility.

(Example 3)
This example differs from Example 1 in that instead of the Xe / O ₂ gas of Example 1, the following gas was used and an optical thin film made of several types of tantalum oxide was produced.

  The gas used in this example is 100 volume% Kr gas, a mixed gas in which the volume ratio of Kr and Xe is 2: 8, 1: 1, 8: 2, and the volume ratio of Xe and Ar is 2: 8, 1: There are 10 types of gas mixtures, which are 1,8: 2 mixed gas and Kr: Ar volume ratios are 2: 8, 1: 1, 8: 2. Moreover, many samples were produced by changing the ion irradiation energy amount. The other points were the same as in Example 1.

  For evaluation of the sample, the change in transmittance over time was measured in the same manner as in Example 2. FIG. 13 is a graph showing the results. Compared with the comparative data of Ar, it can be seen that the range of the amount of ion irradiation energy that can produce a high-quality film with little change with time is wide. This means how easy it is to produce a good quality film with good reproducibility by using Kr or Xe.

Example 4
In this example, a mixed gas having a different volume ratio of Xe and O ₂ is used, and a temperature controller is attached to the substrate holder to control the temperature during film formation in the range of 150 ° C. to 20 ° C. The difference from Example 1 is that an optical thin film made of several types of tantalum oxide was produced by controlling the deposition rate in the range of 200 MHz to 10 MHz and setting the deposition rate to 0.1 nm / sec to 1 nm / sec. Moreover, many samples were produced by changing the ion irradiation energy amount. The other points were the same as in Example 1.

  For the evaluation of the sample, RBS analysis was performed to measure the amount of Xe contained in the sample. FIG. 14 is a graph summarizing the degree of change over time in the transmittance with the amount of Xe as a parameter. The vertical axis in FIG. 14 is shown normalized as 1.0 when only Ar gas is used.

  From FIG. 14, a sample in which the amount of Xe is in the range of 0.5 atomic ppm to 5 atomic percent is preferable, a sample in which the amount of Xe is in the range of 0.5 atomic ppm to 3 atomic percent is more preferable, and the amount of Xe is 0. It can be seen that a sample in the range of 5 atomic ppm to 1 atomic% is optimal.

(Example 5)
The present example is different in that instead of the mixed gas in which the volume ratio of Xe and O ₂ used in Example 4 is changed, a mixed gas in which the volume ratio of Kr and O ₂ is changed is used. The other points were the same as in Example 4.

  Similar to Example 4, SIMS analysis was performed on the sample. Taking the amount of Kr as a parameter and looking at the degree of change in refractive index with time, a sample with a Kr amount in the range of 5 atomic% is preferable, as in Example 4, and Kr is 0.5 atomic ppm. A 13 atomic percent sample was more preferred and one atomic percent was found to be optimal.

(Example 6)
In this example, a mixed gas in which the volume ratio of Xe, Kr, and O ₂ is changed instead of the mixed gas in which the volume ratio of Xe and O ₂ used in Example 4 is changed is different. The other points were the same as in Example 4.

  As in Example 4, RBS analysis was performed on the sample. Using the total content of Kr and Xe as a parameter, looking at the degree of change in transmittance over time, a sample in which the total amount does not exceed 10 atomic% is preferable, and a sample with a total of 5 atomic% or less is optimal. It was.

(Example 7)
In this example, the antireflection film formed on the lens is composed of a low refractive index layer composed mainly of SiO ₂ , a second refractive index layer, a fourth refractive index layer and a sixth refractive index layer in order from the air side to the lens side. Is different from Example 1 in that Al ₂ O ₃ is a high refractive index layer mainly composed of Al ₂ O ₃ . As the substrate, quartz glass was used, and a lens for a KrF excimer laser was produced. FIG. 15 is a schematic cross-sectional view showing the layer structure of the optical thin film according to this example.

  Deposition conditions for bias sputtering are shown below, but the same conditions as in Example 1 are used until the surface cleaning step.

Thereafter, cause discharge against Al ₂ O ₃ target was deposited Al ₂ O ₃ containing Xe on the lens. The film forming conditions at this time are shown below.

RF frequency: 20 MHz
High frequency power: 1.5kW
Xe / O ₂ gas = 10: 1, pressure: 5 mTorr
Growth rate: 0.2 nm / sec
Then depositing SiO ₂ was changed to SiO ₂ target by rotating the target holder. The film forming conditions at this time are shown below.

RF frequency: 13.56 MHz
High frequency power: 1.5kW
Xe / O ₂ gas = 5: 1, pressure: 5 mTorr
Growth rate: 0.7 nm / sec
Under such conditions, an antireflection film for the ultraviolet light of a 248 nm excimer laser having a refractive index and an optical film thickness as shown in Table 1 was formed. The refractive index in the table is a refractive index with respect to 248 nm ultraviolet light.

  FIG. 16 is a graph showing the reflection characteristics of this film. FIG. 17 is a graph showing the change over time in the transmittance of the film normalized to 1.0 when the Xe gas portion is similarly formed instead of Ar. FIG. 17 clearly shows that a long life is obtained when Xe gas is used.

  The evaluation described above is an accelerated durability test in which the optical system shown in FIG. 5 is assembled using the lens produced in this example, and light having a light amount twice as large as the light amount used for a normal excimer laser stepper is irradiated for 1000 hours. Obtained by.

(Example 8)
In this example, the antireflection film formed on the lens is composed of a low refractive index layer mainly composed of SiO ₂ as the first and third layers in order from the air side to the lens side, and the second, fourth and sixth layers are Ta _2. This is different from Example 1 in that O ₅ is a layer containing a high-refractive-index layer whose main component is a fifth layer Al ₂ O ₃ . As the substrate, a lens made of quartz glass was used. FIG. 18 is a schematic cross-sectional view showing the layer structure of the optical thin film according to this example.

  Deposition conditions for bias sputtering are shown below, but the same conditions as in Example 1 are used until the surface cleaning step.

Thereafter, the Ta ₂ O ₅ target is discharged to deposit Ta ₂ O ₅ containing Xe and Kr on the lens. The film forming conditions at this time are shown below.
RF frequency: 100 MHz
High frequency power: 2kW
Xe / Kr / O ₂ gas = 5: 5: 1, pressure: 5 mTorr
Growth rate: 0.2 nm / sec
Then depositing SiO ₂ was changed to SiO ₂ target by rotating the target holder. The film forming conditions at this time are shown below.

RF frequency: 100 MHz
High frequency power: 2kW
Xe / Kr / O ₂ gas = 5: 5: 1, pressure: 5 mTorr
Growth rate: 0.4 nm / sec
When forming an Al ₂ O ₃ film, similarly, the target holder is rotated to change to an Al ₂ O ₃ target, and an Al ₂ O ₃ film containing Xe and Kr is deposited. The film forming conditions at this time are shown below.

RF frequency: 100 MHz
High frequency power: 2kW
Xe / Kr / O ₂ gas = 5: 5: 1, pressure: 5 mTorr
Growth rate: 0.1 nm / sec
Under such conditions, an antireflection film was formed for both ultraviolet light having a center wavelength of 365 nm and visible light having a center wavelength of 550 to 650 nm so as to have a refractive index and an optical film thickness as shown in Table 2. The refractive index in the table is the refractive index for 365 nm light.

  FIG. 19 is a diagram showing the reflection characteristics of this film. FIG. 20 is a graph showing the change over time in the transmittance of the film normalized by assuming that the Xe gas and Kr gas portions are changed to Ar as 1.0. FIG. 20 clearly shows that a long life is obtained when a mixed gas of Xe and Kr is used.

  The above evaluation was obtained by the same test as in Example 7 using the lens of this example and the optical system shown in FIG. 5 instead of the excimer laser and using i-line that generates ultraviolet light of 365 nm as a light source.

Example 9
In this example, the antireflection film formed on the lens is formed from the air side to the lens side in order from the first, third,..., (49) layers, a high refractive index layer composed mainly of Ta ₂ O ₅ , second, second. 4. Sixth layer... The difference from Example 1 is that the 50th layer is a low refractive index layer mainly composed of SiO ₂ . As the substrate, a lens made of quartz glass was used.

  Deposition conditions for bias sputtering are shown below, but the same conditions as in Example 1 are used until the surface cleaning step.

Then, a Ta ₂ O ₅ target is discharged to deposit Ta ₂ O ₅ on the quartz glass. The film forming conditions at this time are shown below.
RF frequency: 100 MHz
High frequency power: 2kW
Xe / Kr / Ar / O ₂ gas = 5: 5: 1: 1, pressure: 5 mTorr
Growth rate: 0.3 nm / sec
Then depositing a SiO ₂ film was changed to SiO ₂ target by rotating the target holder. The film forming conditions at this time are shown below.

RF frequency: 100 MHz
High frequency power: 2kW
Xe / Kr / Ar / O ₂ gas = 5: 5: 1: 1, pressure: 5 mTorr
Growth rate: 0.5nm / Sec
Under such conditions, a reflection enhancing film for near ultraviolet light having a center wavelength of 365 nm was formed.

FIG. 21 shows the time change of the reflectance with respect to the film formed in the same manner except that the Xe gas and Kr gas are replaced with Ar and the other portions are formed in the same manner. Obviously, when Xe and Kr gases are used, the lifetime becomes long.
The above experiment was performed using the lens manufactured in this example and assembling the optical system shown in FIG.

(Example 10)
In this example, a mixed gas in which the volume ratio of Xe and O ₂ is changed is used, and a temperature controller is attached to the substrate holder to control the temperature during film formation in the range of 150 ° C. to 20 ° C. and the frequency of power energy. Was controlled in the range of 200 MHz to 10 MHz, and the deposition rate was 0.1 nm / sec to 1 nm / sec to produce optical thin films made of several types of aluminum oxide. The other points were the same as in Example 4.
FIG. 22 is a graph showing transmittance stability with respect to the amount of Xe.

It is a typical sectional view of an optical article which has an optical thin film of the present invention. It is a schematic diagram which shows the basic composition of the preparation apparatus used in order to form the optical thin film of this invention. It is an example of the graph which shows the fluctuation | variation of the reflectance with respect to the ion irradiation energy in this invention. It is the schematic which shows the structure of the exposure apparatus of this invention. It is typical sectional drawing which shows an example of the optical component used for the exposure apparatus of this invention. 1 is a schematic view of a sputtering apparatus according to Example 1. FIG. It is a schematic diagram which shows the chamber of another preparation apparatus used in order to form the optical thin film of this invention. It is the graph which showed the energy distribution which the ion irradiated to the board | substrate surface grounded to earth has with respect to the frequency of the high frequency electric power thrown into a target. It is a graph which shows the relationship between the energy which Ar ion and Xe ion which concern on this invention inject into a Si target, and a sputtering rate. It is the schematic which shows the clean nitrogen supply system which concerns on this invention. 4 is a graph showing a change with time in transmittance according to Example 1. 6 is a graph showing transmittance stability according to Example 2. 6 is a graph showing transmittance stability according to Example 3. 10 is a graph showing transmittance stability according to Example 4. 10 is a schematic cross-sectional view showing a layer configuration of an optical thin film according to Example 7. FIG. 10 is a graph showing the reflection characteristics of an optical thin film according to Example 7. 10 is a graph showing a change with time of transmittance of an optical thin film according to Example 7. 10 is a schematic cross-sectional view showing a layer configuration of an optical thin film according to Example 8. FIG. 10 is a graph showing reflection characteristics of an optical thin film according to Example 8. 12 is a graph showing a change with time of transmittance of an optical thin film according to Example 8. 10 is a graph showing a change in reflectance of an optical thin film according to Example 9 with time. 10 is a graph showing transmittance stability according to Example 10.

Explanation of symbols

1, 3 substrate,
2 antireflection film,
2H thin layer with high refractive index,
2L low refractive index thin layer,
2M A thin layer having an intermediate refractive index between the high refractive index thin layer 2H and the low refractive index thin layer 2L.
4H high refractive index thin layer,
4L low refractive index thin layer,
11 Production device,
12 Deposition chamber
12a target,
12b substrate holder,
12c magnet,
12d electrode,
13 Load lock room,
13a gate valve,
14 exhaust means,
15 gas supply means,
21 Illumination light source part,
22 exposure mechanism,
23 Illumination light source,
24 mirror,
25 concave lens,
26 Convex lens,
27 Mirror
28 Optical integrator,
29 Mirror,
30 condenser lens,
31 A reticle on which a circuit pattern is drawn,
31a A reticle holder that holds and holds a reticle;
32 projection optical system for projecting a reticle pattern,
33 wafers,
34 XY stage,
35 Surface plate,
36 alignment means used for TTL alignment,
L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11 lenses,
91 Vacuum chamber
92 targets,
92a, 92b holder,
93 Magnet for generating plasma efficiently,
94 Convex lens,
96 High-frequency power supply that can change the frequency,
97 matching circuit,
98 DC power supply for determining the DC potential of the target,
100 target low-pass filter,
1002 a lens support member,
911 load lock chamber,
912 halogen lamp,
920 Lens Stocker,
301 liquefied nitrogen gas tank,
302 evaporator,
303 purification device,
304 SUS piping,
305, 306, 310 Passive oxidation treated SUS piping,
307 pressure regulator,
308 Mass flow controller,
309 Double 3-way valve for introducing nitrogen gas,
311 Lens stocker,
312, 315 SUS piping,
313 valve,
314 Exhaust pump.

Claims (3)

In the method of manufacturing an optical article in which a first light-transmitting thin layer and a second light-transmitting thin layer having a refractive index higher than that of the first light-transmitting thin layer are laminated on the surface of the substrate,
A sputtering gas containing at least one atom selected from the group consisting of krypton or xenon was used for at least one of the first and second light-transmitting thin layers while the substrate was kept at 100 ° C. or lower. A method for producing an optical article , comprising depositing on the surface of the substrate by sputtering a target . The method for manufacturing an optical article according to claim 1, wherein an oxidizing gas is used as a reaction gas in addition to the sputtering gas. 2. The method of manufacturing an optical article according to claim 1, wherein at least a film formation surface of the substrate is held at 100 [deg.] C. or lower in a nitrogen gas atmosphere before the sputtering.