WO2004006309A1

WO2004006309A1 - Method of exposure and aligner

Info

Publication number: WO2004006309A1
Application number: PCT/JP2003/008415
Authority: WO
Inventors: Shunsuke Niisaka
Original assignee: Nikon Corporation
Priority date: 2002-07-03
Filing date: 2003-07-02
Publication date: 2004-01-15
Also published as: JPWO2004006309A1; AU2003246243A1

Abstract

A method of exposure and an aligner wherein yield and productivity in the production of microdevices such as semiconductor devices and liquid crystal display devices can be enhanced by the use of a method of cleaning optical devices, the method capable of satisfactorily cleaning optical devices with high efficiency. This exposure method comprises a step of cleaning optical devices as constituents of illumination optical system and/or projection optical system accommodated in a housing. In the cleaning step, the housing is charged with a gas of moisture content higher than that of a gas charged into the housing at the exposure of photosensitive substrate, and the illumination optical system and/or projection optical system is irradiated with exposure beams (e.g., ultraviolet radiation). In the housing charged with the gas of higher moisture content, water (moisture) present in the housing is exposed to ultraviolet radiation to thereby produce OH radicals exhibiting strong oxidative activity. Organic matter adhering to the surface of optical devices lying in the housing is oxidized and decomposed by the oxidative activity of OH radicals. Thus, cleaning of the optical devices can be accomplished.

Description

Description Exposure method and exposure apparatus

The present invention relates to an exposure method having a step of cleaning an optical element and an exposure apparatus for performing the method. More specifically, the present invention relates to an optical element using ultraviolet light having a wavelength of 200 nm or less such as an F ₂ excimer laser. TECHNICAL FIELD The present invention relates to an exposure method having a cleaning step of an optical element for cleaning a substrate and an exposure apparatus for executing the method. Background art

Conventionally, in a photolithography process for manufacturing a semiconductor device, a liquid crystal display device, and the like, an exposure apparatus that transfers a pattern on a mask (or reticle) to a substrate such as a wafer or a glass plate has been used. In recent years, as this type of exposure apparatus, a step-and-repeat type reduction projection exposure apparatus (so-called stepper) for transferring a pattern on a mask onto a substrate via a projection optical system, and a step-and-ski method have been proposed. Projection exposure apparatuses such as a scanning exposure type projection exposure apparatus of the Yang system (so-called scanning stepper) are mainly used. In this type of projection exposure apparatus, it is shortened wavelength of the exposure light in accordance with the required resolution increases, as recently illumination light for exposure _light, F ₂ excimer one laser light having a wavelength of about 1 5 7 nm is used, F ₂ excimer one the exposure apparatus has also been developed. However, in the case of vacuum ultraviolet (VUV) light having a wavelength of 200 nm or less, if air is present in the optical path, most of the energy is absorbed by water (moisture) present in the air, and the light is exposed to light. The energy required for exposure cannot be obtained on the surface of a certain substrate. For this reason, for example, in an F ₂ excimer laser exposure apparatus, most of the optical path in the optical system is replaced with a gas having a refractive index close to 1, such as N ₂ , and The pattern on the mask is efficiently transferred (exposed) onto the substrate using excimer laser light that has been narrowed to a wavelength that is less absorbed by water as illumination light for light. In general, a projection exposure apparatus uses a large number of optical elements such as lenses and mirrors in order to accurately transfer a pattern on a mask onto a substrate. However, the degassing generated from the housing or the lens barrel (housing of the projection optical system) in which these optical elements are housed, and impurities originally present in the atmosphere in the optical system cause impurities on the surface of the optical elements. Trace amounts of water and organic pollutants were attached. Contaminants such as water and organic systems, F ₂ excimer - and have a strong absorption to ultraviolet light of laser light or the like, particularly in the F ₂ excimer laser exposure apparatus, affixed to an optical surface The effects of trace amounts of water and contaminants reduced the transmittance of the optical system and the imaging performance of the optical system. As a result, the pattern transferred to the substrate also deteriorates, causing a reduction in the yield in the manufacture of micro devices such as semiconductor elements and liquid crystal display elements. By irradiating the surface of the optical element contaminated with the organic matter with ultraviolet light, the organic matter attached to the surface can be cut by the energy of the ultraviolet light. A method for cleaning an optical element using this method is known. However, this cleaning method has poor cleaning efficiency, and it has been necessary to irradiate the optical element with ultraviolet light for a long time in order to obtain a sufficient cleaning effect. For this reason, in addition to a decrease in work efficiency, there has been a problem that the optical element is damaged by a long time irradiation with ultraviolet light of high engineering energy on the glass material.

Disclosure of the invention

An object of the present invention is to provide a method for manufacturing a micro device such as a semiconductor device or a liquid crystal display device by using a method for cleaning an optical element capable of sufficiently and efficiently cleaning the optical element. An object of the present invention is to provide an exposure method and an exposure apparatus capable of improving yield and productivity. According to a first aspect of the present invention, the mask is formed by using an illumination optical system that irradiates an exposure beam onto a mask and a projection optical system that irradiates an exposure beam irradiated through the mask onto a photosensitive substrate. An exposure method for transferring the pattern formed thereon to the photosensitive substrate,

Supplying a gas having a higher moisture concentration than the gas in the housing during exposure of the photosensitive substrate into a housing surrounding at least one of the illumination optical system and the projection optical system;

By irradiating at least one of the illumination optical system and the projection optical system surrounded by the housing supplied with the gas having the high moisture concentration with the exposure beam, the illumination optical system and the projection optical system Cleaning the optical element constituting at least one of the above.

The exposure method of the present invention includes a cleaning step of cleaning an optical element constituting an illumination optical system and / or a projection optical system housed in a housing. In the cleaning process, the housing is filled with a gas having a higher moisture concentration than the gas filled in the housing during exposure of the photosensitive substrate, and an exposure beam (for example, ultraviolet light) is irradiated with an illumination optical system and / or a projection optical system. Irradiation. In a housing filled with the gas having a high moisture concentration, water (moisture) present in the housing is irradiated with ultraviolet light, thereby generating a strong oxidizing OH radical, and oxidation of the OH radical. By the action, the organic substances adhered to the surface of the optical element existing in the housing are oxidized and decomposed. The optical element can be cleaned by removing the oxidatively decomposed organic matter, for example, together with the exhaust of the gas in the housing. In the present invention, the high water concentration is preferably 0.5 ppm to 10 ppm. If the water concentration is lower than 0.5 ppm, the amount of OH radicals generated is small, The cleaning effect of the optical element due to the oxidizing action is not sufficient. On the other hand, if the moisture concentration is higher than 1 O ppm, the ultraviolet light is absorbed by the moisture in the housing, and the light amount of the ultraviolet light decreases as the position of the optical element moves away from the light source. Insufficient. In the present invention, the gas preferably contains an inert gas, for example, nitrogen or helium. Further, it is preferable that the gas having a high water concentration further contains ozone. Oxidation of ozone contained in the gas allows for more efficient <optical element cleaning. In the present invention, it is preferable that a transmittance of at least one of the illumination optical system and the projection optical system with respect to an exposure beam is measured, and the cleaning step is performed when the measured transmittance falls below a predetermined value. Is preferred. Thereby, the optical system in the exposure apparatus can be always maintained in a good state. Further, it is preferable that the exposure beam is F ₂ excimer laser light. According to a second aspect of the present invention, there is provided an exposure apparatus for exposing a photosensitive substrate with an exposure beam through a mask having a predetermined pattern,

A light source for generating the exposure beam;

An illumination optical system including an optical element for irradiating the mask with an exposure beam generated from the light source;

A projection optical system including an optical element for projecting the pattern of the mask onto the photosensitive substrate;

A housing surrounding at least one of the illumination optical system and the projection optical system;

A water concentration adjusting device for adjusting the water concentration in the housing in accordance with the exposure step and the optical element cleaning step. Since the exposure apparatus of the present invention has the moisture concentration adjusting device, it is possible to adjust the moisture concentration in the housing in the optical element cleaning step to be higher than the moisture concentration in the housing in the exposure step. In this way, by irradiating the optical element with the exposure beam after adjusting the moisture concentration, 〇H radicals are generated in the housing, and the oxidizing action of the OH radicals causes the optical element existing in the housing to be strongly oxidized. Organic substances adhering to the child surface can be decomposed and removed. In the present invention, it is preferable that the moisture concentration adjusting device adjusts the moisture concentration in the housing such that the cleaning step of the optical element is higher in the cleaning step of the optical element than in the exposing step. The apparatus further includes a transmittance detection device that detects a transmittance of at least one of the illumination optical system and the projection optical system. It is desirable to adjust the water concentration. In the exposure apparatus of the present invention, the water concentration adjusting device is connected to the housing and the first tank in which the first gas is stored, and the gas is connected to the housing and the gas is filled in the first tank. A second tank filled with a second gas having a high moisture concentration; a first gas and a second tank from the first tank to a housing surrounding at least one of the illumination optical system and the projection optical system; And a switching valve for switching the supply of the second gas from the fuel cell. In this case, by controlling the opening / closing operation of the switching valve, the first gas in the first tank and the second gas in the second tank can be supplied to the housing in a switchable manner. In the exposure process, the switching valve is controlled to supply the first gas in the first tank into the housing, and in that state, the exposure beam generated from the light source is sensitized through the illumination optical system, the mask, and the projection optical system. Irradiate on the substrate. Thereby, the photosensitive substrate is exposed in a pattern corresponding to the pattern formed on the mask. On the other hand, in the cleaning process, the switching valve is controlled to supply the second gas having a higher moisture concentration than the first gas from the second tank into the housing surrounding at least one of the illumination optical system and the projection optical system. I do. In this state, at least one of the illumination optical system and the projection optical system may be irradiated with the exposure beam generated from the light source. Further, the present invention The exposure apparatus further comprises: a transmittance detection device that detects at least one transmittance of the illumination optical system and the projection optical system; and a control device that controls the switching valve. It is desirable to control the switching valve according to the transmittance detected by the transmittance detector. In the present invention, the second gas preferably has a water concentration of 0.5 ppm to 1 O ppm. If the water concentration is lower than 0.5 ppm, the amount of generated 0 H radicals is small, and the cleaning effect of the optical element by the oxidizing action is not sufficient. On the other hand, if the moisture concentration is higher than 1 O ppm, the ultraviolet light is absorbed by the moisture in the housing, and the light amount of the ultraviolet light decreases as the position of the optical element moves away from the light source. Will be enough. Further, it is preferable that the first and second gases include nitrogen or helium. Further, it is preferable that the second gas contains ozone. The optical element can be more efficiently cleaned by the oxidizing action of ozone contained in the second gas. Further, in the present invention, the light source is preferably an F ₂ excimer laser. The exposure apparatus of the present invention further includes a beam matching unit provided between the light source and the illumination optical system and including an optical element, and a housing surrounding the beam matching unit. It is preferable that the water concentration adjusting device adjusts the water concentration in the housing surrounding the beam matching unit so that the optical element cleaning step is higher than the exposure step. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an exposure apparatus according to the present invention.

FIG. 2 is a flowchart showing an exposure step and an optical element cleaning step in the exposure apparatus of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[How to clean optical elements]

First, a method for cleaning an optical element used in the exposure apparatus of the present invention will be described. thickness

On a substrate made of fluorite 3 mm, Mg F _2, each layer of the tooth 3 _'3 and [\ / 19 F _2, formed from the substrate side. In this case, Mg F _2, teeth and _"3 and 1 ^ 9 " ₂ was formed to have a thickness of 10.2 nm, 23.5 nm and 26.7 nm, respectively. Thus, an optical element was obtained. The transmittance of the optical element thus obtained was obtained. and where a measurement at the vacuum ultraviolet spectrometer wavelength 1 57 nm, was 98.3%. in this optical element, the output per Roh \ Riresu is 6 m J / cm ^2, wavelength 1 57 A vacuum ultraviolet laser beam (F ₂ excimer laser beam) of 65 nm was irradiated with a 65-million pulse, and the transmittance of this optical element was measured again with the above-mentioned vacuum ultraviolet spectrometer and found to be 97.2%. This decrease in transmittance is caused by the fact that organic substances existing around the optical element adhere to the surface of the optical element when the optical element is irradiated with laser light. Next, an optical element having the same configuration as that described above was placed in a nitrogen atmosphere having a water concentration of 0.3 ppm, and a vacuum ultraviolet laser having a wavelength of 157 nm was applied to this optical element in the same manner as described above. The light was irradiated with a 65-million pulse, and the transmittance of the optical element after laser irradiation was measured using a vacuum ultraviolet spectrometer to be 97.2%. On the other hand, an optical element of the same configuration was placed in a nitrogen atmosphere with a water concentration of 1 ppm, and a vacuum ultraviolet laser with a wavelength of 157 nm was applied to the optical element in the same manner as above. The light was irradiated with a pulse of 25 mm.The transmittance of the optical element after the irradiation of the laser light was measured. 3%, the original transmittance before laser beam irradiation is maintained. This indicates that the optical element is being cleaned. The mechanism for cleaning the optical element is as follows. When water (H ₂ 0) is irradiated with F ₂ excimer laser light, O H radicals are generated by the photolysis reaction. The generated OH radical has a strong oxidizing action, and the oxidizing action oxidizes and decomposes organic matter. That is, by disposing an optical element in an atmosphere covered with a gas having a predetermined moisture concentration and irradiating the optical element with F ₂ excimer laser light, organic substances attached to the optical element surface are oxidized, is decomposed in the gas such as C 0 ₂ and H ₂ 0 is removed. Next, an example in which the above-described method for cleaning an optical element is applied to an exposure apparatus will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of an exposure apparatus according to the present invention. In the present embodiment, a scanning type exposure apparatus for semiconductor manufacturing that transfers a pattern on a reticle as a mask to a plurality of shot areas on a wafer as a substrate by a step-and-scan method will be described. The exposure apparatus 10 mainly includes a light source unit 12 as a light source, an illumination optical system 14, a reticle stage RST for holding a reticle R, a projection optical system PL, a wafer stage WST for holding a wafer W, and There is one control device 20 for driving and controlling these. As the light source unit 1 2, F ₂ excimer monodentate apparatus is used. The light source unit 12 is actually installed on the floor above the installation floor or in another room (for example, a service room that is less clean than the ultra-clean room where the exposure unit is installed). It is shown above the illumination optical system 14 for convenience. The light source unit 12 is a light transmitting system beam including a housing HS 1 and optical elements (including a cylindrical lens and a beam expander) arranged in the housing HS 1. It is connected via a matching unit BMU to a housing HS 2 in which an illumination optical system 14 is arranged. In this embodiment, the beam matching unit BMU and the illumination optical system 14 constitute an illumination optical system that irradiates the light from the light source unit 12 to the reticle R. The light source unit 12 includes a laser resonator 12a, a beam splitter 12b having a transmittance of about 97%, and a beam splitter 12b arranged on an optical path of laser light emitted from the laser resonator 12a. It consists of a beam monitor mechanism 12c arranged on the reflected light path of the splitter 12b and a high voltage power supply (not shown). The laser resonator 12a includes a narrow-band module and a laser chamber including a discharge electrode (both not shown). The band narrowing module is configured by combining a prism and a diffraction grating (grating), and reduces the spectrum width of the laser light emitted from the laser resonator 12a to about the natural oscillation spectrum width. The output is narrowed to about 1/100 to 1/300. The narrow-band module may be configured by an optical element such as an interference type band filter in which two plane mirrors called an etalon (Fabry—Perotetalon) are arranged in parallel. The beam monitor mechanism 12 includes a diffuser, an etalon element, a line sensor, and an energy monitor (all not shown). The light that has passed through the diffuser constituting the beam monitor mechanism 12c is diffracted by the etalon element to form a fringe panel. The fringe pattern corresponds to the center wavelength and the half-width of the spectrum of the incident light, and an image signal corresponding to the fringe pattern is output from the line sensor to the control device 20. The control device 20 obtains information on the optical characteristics of the light incident on the beam monitor mechanism 12c by performing predetermined signal processing on the imaging signal of the fringe pattern. At the same time, the control device 20 detects the energy power of the laser beam based on the output of the energy monitor. The light source unit 12 is provided with a drive mechanism 18 for a spectroscopic element such as a grating, a prism, or an etalon that constitutes the laser resonator 12a. The drive mechanism 18 is controlled by the controller 20 based on information on the optical characteristics of the incident light with respect to the beam monitor mechanism 12c (detection results of the beam monitor mechanism 12c), and the center wavelength and the spectral half width Is adjusted to fall within a desired range. In this case, the center wavelength can be adjusted substantially continuously within a predetermined range, for example, 156.9 nm to 157.6 nm. That is, in the present embodiment, the wavelength of the laser light (F ₂ excimer laser light) emitted from the laser resonator 12 a can be adjusted by the drive mechanism 18. In the light source unit 12, a shirt (not shown) for blocking laser light according to control information from the control device 20 is provided on the side of the illumination optical system 14 of the beam splitter 12b. Are located. The illumination optical system 14 is composed of a secondary light source forming optical system including an energy rough adjuster, a fly-eye lens, a condensing lens system, a reticle blind, and an imaging lens system (all not shown). Are arranged in a predetermined positional relationship in the housing HS2. The laser light emitted from the light source unit 12 becomes the illumination light for exposure having a substantially uniform illuminance distribution through the illumination optical system 14 and forms a rectangular (or arc-shaped) illumination area on the reticle R. Light up. A beam splitter 14a having a transmittance of about 97% is disposed between the secondary light source forming optical system of the illumination optical system 14 and the imaging lens system. On the optical path of the light reflected by the beam splitter 14a, an incident light amount measuring device 22 called an integrator sensor composed of photoelectric conversion elements is arranged. The photoelectric conversion signal of the light amount measured by the incident light amount measuring device 22 is sent to the control device 20. The output of the photoelectric conversion signal in the incident light amount measuring device 22 is calibrated in advance with respect to the output of a reference illuminometer (not shown). Also, the output of the above-described energy monitor is calibrated with respect to the output of the photoelectric conversion signal in the incident light meter 22. The conversion factor (or conversion function) of these output values Is determined in advance, and the value is stored in the memory in the control device 20. The reticle chamber RR houses the reticle R and the reticle stage RST in a sealed state. Reticle R is fixed on reticle stage RST by electrostatic attraction. The reticle stage RST can be driven on a reticle base (not shown) at a predetermined scanning speed in a predetermined scanning direction (Y-axis direction in FIG. 1) by a reticle driving unit 24 such as a linear motor. . Further, reticle stage RST is configured to be able to be finely driven by reticle driving section 24 in the rotation direction (0 direction) with reference to the X axis direction orthogonal to the Y axis and the Z axis orthogonal to the XY plane. I have. The position of the reticle stage RST is always detected by a reticle laser interferometer (hereinafter referred to as “reticle interferometer”) 25 with a resolution of about 0.5 to 1 nm. The position information (or speed information) of reticle stage RST obtained by reticle interferometer 25 is sent to control device 20. Control device 20 controls the position of reticle stage RST by driving reticle driving section 24 based on the transmitted position information (or speed information) of reticle stage RST. The projection optical system PL is arranged below the reticle stage RST such that the optical axis AX is in the Z-axis direction. The projection optical system PL is a refraction optical system that has a telecentric optical arrangement on both sides within the lens barrel CL and includes a plurality of lens elements arranged at predetermined intervals in the optical axis AX direction. The projection optical system PL is a reduction optical system having a predetermined projection magnification (for example, 1Z5 or 1/4). By the projection optical system PL, a reduced image (partially inverted image) of the circuit pattern in the illumination area of the reticle R is formed in an exposure area conjugate to the illumination area on the wafer W coated with a photo resist on the surface. . Wafer stage WST is arranged below projection optical system PL. The wafer stage WST is placed on a wafer base (not shown), It is driven movably in the XY plane by a driving device 26 composed of a motor or the like. On the upper surface of wafer stage WST, wafer W is fixed by electrostatic attraction via a wafer holder (not shown). A moving mirror 28 is provided on the upper surface of wafer stage WST. The position of the wafer stage WST in the XY plane can be adjusted from 0.5 to 0.5 by irradiating the moving mirror 28 with a measuring beam from a wafer laser interferometer (hereinafter referred to as “wafer interferometer”) 30. It is always detected with a resolution of about 1 nm. The position information (or speed information) of the wafer stage WST obtained by the wafer interferometer 30 is sent to the controller 20. The controller 20 is driven based on the position information (or speed information) of the wafer stage WST. By driving the device 26, the position of the wafer stage WST is controlled. Further, on the upper surface of wafer stage WST, an emitted light amount measuring device 32 composed of a photoelectric conversion element is fixed. The light-receiving surface of the emitted light quantity measuring device 32 is set to be substantially the same height as the surface of the wafer W, and the photoelectric conversion signal corresponding to the light amount obtained by the emitted light quantity measuring device 32 is transmitted to the control device 20. Supplied to The output of the photoelectric conversion signal in the emitted light quantity measuring device 32 is previously calibrated with the output of the incident light quantity measuring device 22 described above. The conversion coefficients (or conversion functions) of these outputs are obtained in advance, and the values are stored in the memory of the control device 20. The wafer stage WST, the wafer W, the movable mirror 28, the wafer interferometer 30, the emitted light quantity measuring device 32, and the driving device 26 are housed in a sealed state in the wafer chamber WR. In the exposure apparatus 10 of the present embodiment, the housing HS 1 housing the beam matching unit BMU, the housing HS 2 housing the illumination optical system 14 and the mirror housing the projection optical system PL The supply pipe system and the exhaust pipe system are connected to the cylinder C respectively. Although not shown, the reticle chamber RR and the wafer chamber WR are also connected to an air supply piping system and an exhaust piping system, respectively. The reticle chamber RR and the wafer chamber WR may be filled with nitrogen gas or Pum gas is supplied. The supply of these gases is controlled by a solenoid valve (not shown) installed in the supply piping system. As shown in Fig. 1, the housing HS1, housing HS2, and lens barrel CL are connected to one end of air supply piping 34A, 34B, and 34C, respectively, as an air supply piping system. . The other end sides of the air supply pipes 34A, 34B, and 34C are each branched in a forked shape. One of the bifurcated branches of the air supply pipes 34A and 34B is connected to a tank T1 containing a nitrogen gas having a water concentration of 0.3 ppm. The other of the two branches of the air supply pipes 34A and 34B is connected to a tank T2 containing a nitrogen gas having a water concentration of 1 Ppm. One of the bifurcated branch of the supply pipe 34 C is connected to a tank T 3 containing helium gas having a water concentration of 0.3 ppm. The other branch of the bifurcated supply pipe 34 C is connected to a tank T 4 containing helium gas with a water concentration of 1 ppm. Solenoid valves that open and close each pipe (gas passage) are provided between the supply pipe 34 A branch and tank T 1 and between the supply pipe 34 A branch and tank T 2. 38 A and 38 B are provided respectively. Similarly, each pipe (gas passage) is opened and closed between the branch of the air supply pipe 34B and the tank T1 and between the branch of the air supply pipe 34B and the tank T2. Solenoid valves 38 C and 38 D are provided, respectively. In addition, between the branch of the air supply piping 34 C and the tank T 3 and between the branch of the air supply piping 34 C and the tank T 4, electromagnetic valves for opening and closing each pipe (gas passage) are provided. Valves 38E and 38F are provided, respectively. These solenoid valves 38 A to 38 F are controlled to be opened and closed by a control device 20. The control method of the solenoid valve will be described later. In addition, housing HS 1, housing HS 2 and lens barrel CL One end of each of the exhaust pipes 40A, 40B and 40C is connected. The other ends of the exhaust pipes 40 A, 40 B, and 40 C are connected to a common exhaust pipe 42. The gas exhausted from the housing of each optical system is exhausted from the exhaust pipe 42 via the exhaust pipes 40A, 40B, and 40C. In the middle of the exhaust pipes 40 A, 40 B, and 40 C, moisture sensors 44 A, 44 B that detect the concentration of moisture in the gas flowing in the exhaust pipes (gas passages). And 44 C are provided respectively. The values of the moisture concentrations detected by these moisture sensors 44A to 44C are sent to the control device 20. The control device 20 mainly includes a microcomputer (or workstation) and a memory. As described above, the control device 20 controls the driving device of each component of the exposure device 10 and also controls the opening and closing operations of the solenoid valves 38A to 38F. Further, the control device 20 sends a signal from the light source unit 12 to the illumination optical system 14 based on the output of the incident light amount measuring device 22 and the output of the energy monitor 12a constituting the beam monitoring mechanism 12c. A calculation function for calculating the transmittance of the optical system up to the position of the beam splitter 14a (hereinafter referred to as "first transmittance" as appropriate), and the output of the incident light quantity measuring device 22 and the measurement of the output light quantity Has a calculation function of calculating the transmittance of the optical system from the position of the beam splitter 14a to the wafer surface (hereinafter, appropriately referred to as "second transmittance") based on the output of the beam splitter 32 .

[Method for cleaning optical element in exposure apparatus]

Next, a method for cleaning the optical elements constituting the optical system (beam matching unit BMU, illumination optical system 14 and projection optical system PL) of the exposure apparatus 10 configured as described above will be described with reference to FIGS. This will be described using 2. At the time of normal exposure, the solenoid valves 38A to 38F are in the closed state, and the gas contained in each ink does not flow into the housing or the lens barrel via the air supply pipe. Although it is in a state, a high-concentration nitrogen gas (first nitrogen gas) having a water concentration of 0.3 ppm is contained in the inside of the housing of the beam matching unit BMU and the illumination optical system 14 and in the exhaust pipe system. , Helium gas (first helium gas) with a moisture concentration of 0.3 ppm remains inside the lens barrel of the projection optical system PL and the exhaust pipe system. As shown in FIG. 2, according to the exposure method of the present invention, an exposure step is first started (step S 1). When the predetermined time has elapsed (for example, each time the exposure of a predetermined number of wafers is completed), the exposure process is interrupted (step S 2), and the controller 20 controls the first transmittance and the second transmittance. The value is measured (step S3). It is determined whether at least one of the first transmittance and the second transmittance is lower than a preset value (Step S4), and the first transmittance and the second transmittance are determined. If at least one of the values is lower than a preset value, the process proceeds to an optical element cleaning step described below. While the exposure process is interrupted, the solenoid valves 38 B, 38 D and 38 F are opened under the control of the controller 20. When the solenoid valve is opened, nitrogen gas (second nitrogen gas) with a water concentration of 1 ppm from tank 2 is supplied to the beam matching unit BMU housing via the air supply pipes 34A and 34B. HS 1 and the illumination optical system 14 are supplied into the housing HS 2 respectively. At the same time, a helium gas (second helium gas) containing a water concentration of 1 ppm is supplied from the tank 4 to the lens barrel CL containing the projection optical system PL via the air supply pipe 34C (step S). Five ) . In particular, helium gas having high thermal conductivity was used in the lens barrel CL of the projection optical system transmission PL in order to prevent the deterioration of the imaging characteristics due to heat. As a result, the first nitrogen gas filled in the housings HS 1 and HS 2 and the first nitrogen gas filled in the lens barrel CL are transferred to the housing HS 1 through the respective exhaust pipe systems. , HS 2 and the lens barrel C are exhausted, and the inside of the housings HS 1 and HS 2 is almost completely replaced by the second nitrogen gas, and the inside of the lens barrel CL is replaced by the second helium gas. The control device 20 outputs water from the water sensors 44 A, 44 B, and 44 C connected to the exhaust piping system connected to the housings HS 1 and HS 2 and the lens barrel CL, respectively. When the concentration becomes 1 ppm or more, it is determined that the gas in the housing (including the lens barrel) of each optical system has been replaced with the second nitrogen gas or helium gas. Next, the housing of each optical system (barrel The supply of gas into the housing is stopped by closing all solenoid valves in the air supply piping system connected to the Next, the controller 20 starts outputting a trigger pulse to the high-voltage power supply in the light source unit 12, and starts emitting laser light (F ₂ excimer laser light) from the laser resonator 12 a. . At this time, the shirt (not shown) in the light source unit 12 is in a closed state. With the start of laser light emission, laser light (pulsed ultraviolet light) is incident on the beam monitor mechanism 12c via the beam splitter 12b, and the above-described fringe pattern is imaged from the beam monitor mechanism 12c. Information on the signal and the pulse energy value is sent to the controller 20. Next, when the laser beam enters a predetermined state based on the information obtained by the beam monitor mechanism 12c, a shutter (not shown) in the light source unit 12 is opened by an instruction from the control device 20. It is. As a result, laser light is emitted from the light source unit 12, and the emitted laser light is applied to the gas inside each space (housing) in which the beam matching unit BMU, the illumination optical system 14, and the projection optical system PL are installed. And the optical element. Within each housing (including the barrel), since the moisture concentration 1 ppm of nitrogen gas or helium gas is filled, as described above, the optical element by irradiating a laser beam (F ₂ excimer laser light) Cleaning is performed (Step S 6) Immediately after the cleaning of the optical element is started, the wafer stage WST is moved so that the emitted light amount measuring device 32 arranged on the wafer stage is located immediately below the projection optical system PL. Let me do it. Next, the output of the incident light amount measuring device 22, the output of the energy monitor constituting the beam monitoring mechanism 12 c, and the output of the emission light amount measuring device 32 are simultaneously captured, and the above-described first transmittance and second transmission The rate is determined (step S7). Next, wafer stage WST is moved so that emission light meter 32 retracts from immediately below projection optical system PL. Thereafter, at predetermined time intervals, the projection optical system PL The movement of the wafer stage WST for lowering and retreating and the measurement of the first and second transmittances are repeated.

The control device 20 monitors changes in the first and second transmittances measured at predetermined time intervals, and determines whether both of the change rates of the transmittances are equal to or less than a predetermined value (for example, substantially zero). Judgment is made (step S8). If the rate of change is equal to or less than the predetermined value, it can be considered that the cleaning of the optical element has been completed. When it is considered that the cleaning of the optical element is completed, the shutter in the light source unit 12 is closed, the output of the trigger pulse to the high-voltage power supply in the light source unit 12 is stopped, and the air supply piping system is stopped. The electromagnetic valves 38Α, 38C and 38Ε are opened, and the first nitrogen gas and helium gas are supplied into the housing of each optical system for a predetermined time (step S9). As a result, the second nitrogen gas and the helium gas remaining in the housing (including the lens barrel) of each optical system are exhausted through the exhaust piping system, and are almost completely converted into the first nitrogen gas and the helium gas, respectively. Is replaced by When the outputs of the water sensors 44Α, 44Β, and 44C all reach a moisture concentration of less than 0.3 ppm, the control device 20 removes the gas in the housing of each optical system from the first. Is determined to have been replaced by nitrogen gas or helium gas. In this state, the normal exposure process can be restarted (step S10). When the rate of change of the transmittance is larger than the predetermined value, the cleaning of the optical element is continued until the rate of change of the transmittance of the optical element becomes equal to or less than the predetermined value. The cleaning of the optical element in the optical system housing in such an exposure apparatus is particularly required when the optical element is easily stained and the necessity of cleaning is high. It is effective when the operation is stopped or when the exposure condition or illumination condition of the exposure apparatus is changed (when replacing the aperture stop in the illumination optical system, replacing the reticle, changing the pupil aperture in the projection optical system, etc.). is there. This minimizes downtime during the operation of the system, enables efficient cleaning of optical elements, and enables the exposure system to always exhibit its original performance. [Operation of exposure apparatus]

Next, the exposure process of the exposure apparatus shown in FIG. 2 will be briefly described. First, a reticle loader and a wafer loader (both not shown) controlled by the controller 20 load the reticle R into the reticle stage RST (installation) and load the wafer W into the wafer stage WST (installation). Done. Next, supply air piping systems 38A, 38C, 38E connected to each optical system, and unillustrated air supply piping systems connected to the reticle chamber RR and wafer chamber WR, respectively. After opening the solenoid valves and supplying the first nitrogen gas or helium gas for a predetermined time, each solenoid valve is closed. Next, using a reticle microscope, a fiducial mark plate on the wafer stage WST, and an alignment detection system (all not shown), preparatory operations such as reticle alignment and baseline measurement are performed according to a predetermined procedure. Then, using an alignment detection system (not shown), for example, an EGA (enhanced ■ global alignment) as disclosed in Japanese Patent Application Laid-Open No. 61-44429 is used. Execute the alignment measurement. After the alignment measurement, the exposure operation of the step-and-scan method is performed as follows. First, the wafer stage WST is moved so that the first shot (first shot) area on the wafer W becomes the starting position of the scanning exposure. At the same time, the reticle stage RST is moved so that the reticle R becomes the scanning exposure start position. Next, based on the position information of reticle R in the XY plane measured by reticle interferometer 25 and the position information of wafer W in the XY plane measured by wafer interferometer 30, reticle drive unit 24 Scanning exposure of wafer W on wafer stage WST is performed while controlling reticle stage RST and wafer stage WST synchronously by controlling driving device 26 respectively. At this time, the reticle R on the reticle stage RST and the wafer W on the wafer stage WST are synchronized along the Y-axis so that they face each other at a speed ratio according to the projection magnification of the projection optical system PL. Moving. In addition, The light quantity control during scanning exposure is performed based on the output of the incident light quantity measuring device 22 and the output of the energy monitor, for example, the pulse energy of the laser light output from the laser resonator 12a or the laser resonator 12a. This is performed by adjusting the oscillation frequency.

When the transfer of the reticle pattern to one shot area is completed, the wafer stage WST is step-moved by one shot area in the X-axis direction, and the scanning exposure for the next shot area is similarly performed. By repeating the step movement and the scanning exposure in this manner, a predetermined number of shots of the exposure pattern are transferred onto the wafer W. In this embodiment, the method of cleaning the beam matching unit, the illumination optical system, and the projection optical system of the exposure apparatus has been described. However, the air supply pipe connected to the housing of the optical system desired to be cleaned. By controlling only the solenoid valve of the system as described above, it is also possible to selectively clean only some of the optical systems (for example, only the illumination optical system, or the beam matching unit and the projection optical system). it can. Since the water concentration is low in the housing of the optical system where cleaning is not performed, it is possible to suppress the energy absorption of laser light due to the influence of the water in the housing. Thus, effective cleaning of the optical element can be performed even in a projection optical system which is considered to be far from the light source. Further, in the present embodiment, the beam matching unit of the exposure apparatus, and the method of cleaning the optical elements of the illumination optical system and the projection optical system have been described. By controlling and irradiating the exposure beam, it is also possible to clean the optical element in the reticle chamber, that is, the reticle. In the present embodiment, the optical element is cleaned while the first nitrogen gas and the first helium gas in the optical system are replaced with the second nitrogen gas and the second helium gas, respectively. The present invention is not limited to this. For example, instead of the second nitrogen gas, the moisture concentration may be supplied mixed gas of nitrogen gas and Saizo emissions 0 ₃ is 1 ppm. Further, instead of the second helium gas, water content concentration but it may also be supplied mixed gas of Heriumugasu ozone 0 ₃ is 1 ppm. A mixed gas of nitrogen gas or helium gas and ozone 0 ₃ was filled in the housing or lens barrel, further irradiating F ₂ excimer laser light (vacuum ultraviolet light). In analogy to the present implementation embodiment, organic contaminants Substance in adhering to the optical element surface in the housing or barrel is cut by the energy of the F ₂ excimer one laser light, in addition to the oxidizing action of 0 H the radical Le The optical element can be more efficiently cleaned by the oxidizing action of ozone contained in the mixed gas. Further, in this embodiment, after the supply of the second nitrogen gas or the helium gas into the housing of the beam matching unit and the illumination optical system and the lens barrel of the projection optical system is completed, the optical element is cleaned by irradiating a laser beam. However, the optical element may be cleaned by irradiating the optical element with laser light in a state where the second nitrogen gas or the room gas is continuously supplied into each housing. Thus, the atmosphere in the housing can be maintained at a predetermined moisture concentration, so that the optical element can be efficiently cleaned in a stable state. Therefore, the optical element can be sufficiently cleaned in a shorter time, that is, the irradiation time of the F ₂ excimer laser beam (vacuum ultraviolet light) can be shortened, so that the glass material constituting the optical element is damaged. Can be reduced. Further, in the present embodiment, the supply of the gas into the housing is stopped while the optical element is being cleaned by irradiating the laser beam, but the second nitrogen gas or the helium gas is supplied at a predetermined rate. After the supply for a time, the first nitrogen gas or the helium gas may be supplied during the cleaning of the optical element. In the present embodiment, nitrogen gas and helium gas having a water concentration of 1 ppm were used. The concentration of water contained in the gas is not limited to this, but may be any as long as the concentration of water is in the range of 0.5 ppm to 10 ppm. If the water concentration is lower than 0.5 ppm, a predetermined amount of 0 H radical cannot be obtained, so that the oxidizing action is not sufficient and the cleaning effect of the optical element is reduced. On the other hand, if the water concentration is higher than 1 O ppm, light is absorbed by the water in the housing during the cleaning process, and the cleaning effect of the optical element decreases as the distance from the light source increases. In the present embodiment, the nitrogen gas is supplied to the beam matching unit and the illumination optical system, but a helium gas may be supplied instead of the nitrogen gas. Similarly, in this embodiment, helium gas is supplied to the projection optical system, but nitrogen gas may be supplied instead of helium gas. In any case, it goes without saying that a gas whose moisture concentration is within a predetermined range is used. In this embodiment, the nitrogen gas is supplied to the reticle chamber RR and the wafer chamber WR, but a helium gas may be supplied instead of the nitrogen gas. The projection optical system of the exposure apparatus of the present invention is not limited to a projection optical system in which all optical elements are composed of refractive lenses. It may be a catadioptric projection optical system composed of elements. Further, the projection optical system is not limited to a reduction system projection optical system, and may be a unit magnification system or an enlargement system projection optical system. In this embodiment, the gas is supplied by directly connecting the pipe to the lens barrel of the projection optical system. However, the projection optical system may be housed in a gas-sealed chamber, and the gas may be supplied into such a chamber. . In the exposure apparatus of the present embodiment, an F ₂ excimer laser is used as a light source, but the light source is not limited to this, and an excimer laser such as ArF or KrF, EUV light, or the like may be used. Also, for example, the oscillation wavelength is set to any of the wavelengths of 248 nm, 193 nm, and 157 nm. A harmonic of a fixed laser such as a YAG laser having a vector may be used. In addition, a single-wavelength laser beam in the infrared or visible range oscillated by a DFB semiconductor laser or fiber laser is amplified by, for example, a fiber amplifier doped with erbium (or both erbium and ytterbium). Alternatively, a harmonic converted into a wavelength of ultraviolet light using a nonlinear optical crystal may be used. For example, if the oscillation wavelength of a single-wavelength laser is in the range of 1.51 to 1.59 Atm, a 10th harmonic with a generated wavelength in the range of 151 to 159 nm will be output. . In particular, when the oscillation wavelength is in the range of 1.57-1.58171, the 10th harmonic whose generated wavelength is in the range of 157-158 nm, that is, the wavelength substantially equal to that of the F ₂ excimer laser Ultraviolet light can be obtained. If the oscillation wavelength is in the range of 1.03 to 1.12 m, a 7th harmonic whose output wavelength is in the range of 147 to 160 nm is output. When the wavelength is within the range of 0 99 to 1.106 yum, it is possible to obtain a 7th harmonic having a generation wavelength within the range of 157 to 158 Aim, that is, ultraviolet light having substantially the same wavelength as the F ₂ excimer laser. Can be. At this time, a ytterbium-doped-fiber laser is used as the single-wavelength oscillation laser. In the present embodiment, a scanning exposure apparatus for manufacturing a semiconductor in which a pattern on a reticle as a mask is transferred to a plurality of shot areas on a wafer as a substrate by a step-and-scan method has been described. However, the present invention is not limited to this, and is not limited to a step-and-repeat type projection exposure apparatus (stepper), but also a step-and-scan type and a step-and-repeat type for a liquid crystal. The present invention can also be applied to a projection exposure apparatus. The structure and exposure operation of a scanning exposure apparatus is described in detail, for example, in U.S. Patent No. 6,341,007 B1, and to the extent permitted by the laws of the country designated or selected in this international application, This US patent is incorporated herein by reference. In the exposure apparatus of the present invention, optical adjustment is performed after an illumination optical system and a projection optical system composed of a plurality of lenses are incorporated into the exposure apparatus main body, and a reticle stage and a wafer stage including a large number of mechanical parts are used. Wiring and piping are carried out after the laser is attached to the exposure apparatus body, and overall adjustments (electrical adjustment, operation confirmation, etc.) are performed. It is desirable that the manufacture of the exposure apparatus be performed in a clean room where the temperature, cleanliness, etc. are controlled. Further, a semiconductor device can be manufactured by using the exposure apparatus of the present invention. A semiconductor device is designed using a design process for designing according to the function and performance of the device, a reticle manufacturing process for manufacturing a reticle based on the design, a wafer manufacturing process for obtaining a wafer from silicon material, and an exposure apparatus. A wafer exposure step of transferring the pattern formed on the reticle onto the wafer, a wafer processing step of performing physical and chemical treatment on the wafer on which the reticle pattern has been transferred, and a processing of the processed wafer into a device. It is manufactured through a device assembly process (including a dicing process, a bonding process, and a packaging process), an inspection process for inspecting device functions and performance, and the like. INDUSTRIAL APPLICABILITY In the present invention, by using the above-described method for cleaning an optical element, an optical element constituting an illumination optical system, a projection optical system, or the like of an exposure apparatus can be easily and efficiently cleaned. Therefore, the optical system of the exposure apparatus can always be maintained in a good state. As a result, the yield and productivity in manufacturing micro devices such as semiconductor devices and liquid crystal display devices can be improved.

Claims

The scope of the claims

1. Using an illumination optical system that irradiates the exposure beam onto the mask and a projection optical system that irradiates the photosensitive substrate with the exposure beam irradiated via the mask, the pattern formed on the mask is An exposure method for transferring to a photosensitive substrate,

By irradiating at least one of the illumination optical system and the projection optical system surrounded by the housing supplied with the gas having the high moisture concentration with the exposure beam, the illumination optical system and the projection optical system A step of cleaning at least one of the optical elements.

2. The exposure method according to claim 1, wherein the high water concentration is from 0.5 Ppm to 10 Ppm.

3. The exposure method according to claim 1, wherein the gas having a high water concentration contains nitrogen or helium.

4. The exposure method according to claim 3, wherein the gas further contains ozone.

5. Further, the transmittance of at least one of the illumination optical system and the projection optical system to the exposure beam is measured, and when the measured transmittance falls below a predetermined value, the cleaning step is performed. 2. The exposure method according to claim 1, wherein:

6. The exposure beam exposure method according to claim 1, characterized in that the F ₂ excimer one laser light.

7. An exposure apparatus for exposing a photosensitive substrate with an exposure beam through a mask having a predetermined pattern,

A light source for generating the exposure beam;

An illumination optical system for irradiating the mask with an exposure beam generated from the light source;

A water concentration adjusting device for adjusting the water concentration in the housing in accordance with the exposure step and the optical element cleaning step.

8. The exposure apparatus according to claim 7, wherein the moisture concentration adjusting device adjusts the moisture concentration in the housing such that the cleaning step of the optical element is higher than the exposure step.

9. The apparatus further includes a transmittance detector that detects transmittance of at least one of the illumination optical system and the projection optical system, and the moisture concentration adjustment device is configured to detect the transmittance detected by the transmittance detector. 8. The exposure apparatus according to claim 7, wherein the moisture concentration in the housing is adjusted according to the condition.

10. The water concentration adjusting device is connected to the housing and stores a first gas in the first tank and a first tank connected to the housing and having a higher water concentration than the gas filled in the first tank. 10. A second tank filled with the second gas, a first gas from the first tank and a second gas from the second tank into a housing surrounding at least one of the illumination optical system and the projection optical system. The exposure apparatus according to claim 7, further comprising: a switching valve that switches supply of the gas.

11. A transmittance detection device for detecting transmittance of at least one of the illumination optical system and the projection optical system, and a control device for controlling the switching valve, wherein the control device includes the transmittance detection device. 10. The exposure apparatus according to claim 10, wherein the switching valve is controlled according to the transmittance detected in the step (a).

12. The exposure apparatus according to claim 7, wherein the moisture concentration of the second gas is 0.5 to 10 ppm.

13. The exposure apparatus according to claim 7, wherein the first and second gases include nitrogen or helium.

14. The method of claim 13, wherein the second gas further comprises ozone.

15. The light source according to claim 7, wherein the light source is an F ₂ excimer laser.

16. A beam matching unit provided between the light source and the illumination optical system, the beam matching unit including an optical element, and a housing surrounding the beam matching unit. 8. The exposure apparatus according to claim 7, wherein the water concentration in the housing surrounding the matching unit is adjusted so that the cleaning step of the optical element is higher than the exposure step.