Patent Publication Number: US-2009225290-A1

Title: Exposure apparatus and device fabrication method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exposure apparatus and a device fabrication method. 
     2. Description of the Related Art 
     An exposure apparatus has conventionally been employed to fabricate a micropatterned semiconductor device such as a semiconductor memory or logic circuit by using photolithography. The exposure apparatus projects and transfers a circuit pattern formed on a reticle (mask) onto a substrate such as a wafer by a projection optical system. 
     A minimum feature size (resolution) that the exposure apparatus can transfer is proportional to the wavelength of the exposure light, and is inversely proportional to the numerical aperture (NA) of the projection optical system. To keep up with demands for advances in micropatterning of semiconductor devices, the wavelength of the exposure light is shortening, and the NA of the projection optical system is increasing. In recent years, the so-called immersion technique of filling the space between the wafer and the final lens (final surface) of the projection optical system is attracting a great deal of attention as a technique for improving the resolution of the exposure apparatus (see Japanese Patent Laid-Open No. 2005-19864). The resolution of the exposure apparatus when, for example, the space between the wafer and the final lens of the projection optical system is filled with pure water (refractive index=1.33) is 1.33 times that when it is filled with a gas (air). As the liquid (to be referred to as an “immersion material” hereinafter) which fills the space between the wafer and the final lens of the projection optical system, a liquid (high-index liquid) having a refractive index higher than that of pure water is also under development (see Japanese Patent Laid-Open No. 2007-180450). Water added with a salt or an inorganic acid such as H 3 PO 4 , alcohol derivatives such as glycerol, and hydrocarbon-based organic liquids, for example, have been proposed as the immersion materials. 
     The exposure apparatus is generally accommodated in a chamber including a temperature adjusting circulation system which adjusts the temperature of the internal gas of the chamber and circulates it, and a chemical filter which removes chemical impurities in the chamber, in order to stabilize the apparatus environment (see Japanese Patent Laid-Open No. 9-280640). Japanese Patent Laid-Open No. 9-280640 discloses a technique of forming a chemical filter by stacking a plurality of thin filters. In this technique, only the filter on the upstream side, whose capacity to remove chemical impurities has degraded, is discarded, and the filter on the downstream side is used continuously. This makes it possible to efficiently exploit the removal capacity of the chemical filter. 
     Japanese Patent Laid-Open No. 2006-108581 proposes an exposure apparatus including a plurality of wafer stages in order to improve the throughput (productivity) and the alignment accuracy. 
     When a chemical filter is used in the exposure apparatus, it is important to suppress the running cost of the chemical filter. However, when a chemical filter is used in an immersion exposure apparatus which uses a high-index liquid as disclosed in Japanese Patent Laid-Open No. 2007-180450 as the immersion material, the following problems are posed. 
     Volatile components (a gas containing volatile components) which volatilize from the high-index liquid are removed by the chemical filter of the temperature adjusting circulation system. However, a high-index liquid is highly volatile, so its use shortens the lifetime (or increases the replacement frequency) of the chemical filter, resulting in an increase in the running cost. In replacing the chemical filter, the exposure apparatus including the temperature adjusting circulation system must be stopped. This increases the replacement frequency of the chemical filter, resulting in a decrease in the throughput of the exposure apparatus. 
     Furthermore, volatile components of the high-index liquid are often harmful (they are, for example, inflammable), so it is necessary to prevent their scattering over the entire exposure apparatus. It is also necessary to exhaust the internal gas (a gas containing volatile components) of the exposure apparatus to the outside after surely removing or reducing volatile components contained in the gas. 
     When the immersion exposure apparatus includes a plurality of wafer stages, the volume of the stage space increases. To stabilize the thermal environment of that space, it is necessary to, for example, supply a large amount of temperature-adjusted gas. This increases the flow rate of the gas which circulates through the apparatus. It is therefore necessary to increase the size of the chemical filter of the temperature adjusting circulation system, increase the number of chemical filters used, and frequently replace the chemical filter, resulting in an increase in the running cost. 
     A resin-based material used as a seal member in the exposure apparatus generally has no resistance to volatile components of the high-index liquid, resulting in a decrease in the seal function of the seal member due to its deterioration. 
     SUMMARY OF THE INVENTION 
     The present invention provides an exposure apparatus which can suppress an increase in the running cost and a decrease in the throughput even when a high-index liquid is used as the immersion material. 
     According to one aspect of the present invention, there is provided an exposure apparatus which exposes a substrate via a liquid, the apparatus comprising a projection optical system configured to project a pattern of a reticle onto the substrate, a liquid supply unit configured to supply the liquid between the projection optical system and the substrate, a blowing nozzle which is arranged around the projection optical system on a side of the substrate and configured to blow a gas around the liquid supplied between the projection optical system and the substrate, and an exhaust unit configured to exhaust the gas in a space between the blowing nozzle and the liquid supplied between the projection optical system and the substrate, the exhaust unit including a removal member configured to remove a volatile component which volatilizes from the liquid and is contained in the gas in the space. 
     Further aspects and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing an exposure apparatus according to one aspect of the present invention. 
         FIG. 2  is a schematic view showing an exposure apparatus main unit of the exposure apparatus shown in  FIG. 1 . 
         FIG. 3  is an enlarged sectional view of the vicinity of the final surface (the surface closest to a wafer) of a projection optical system of the exposure apparatus shown in  FIG. 1 . 
         FIG. 4  is a schematic view showing an example of an exhaust unit shown in  FIG. 3 . 
         FIG. 5  is a schematic view showing another example of the exhaust unit shown in  FIG. 3 . 
         FIG. 6  is a schematic view showing still another example of the exhaust unit shown in  FIG. 3 . 
         FIG. 7  is a schematic view showing another arrangement of the exposure apparatus main unit of the exposure apparatus shown in  FIG. 1 . 
         FIG. 8  is a schematic view showing an exposure apparatus according to one aspect of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The same reference numerals denote the same members throughout the drawings, and a repetitive description thereof will not be given. 
       FIG. 1  is a schematic view showing an exposure apparatus  1  according to one aspect of the present invention. The exposure apparatus  1  is an immersion exposure apparatus which transfers the pattern of a reticle onto a substrate such as a wafer by the step &amp; scan scheme via a liquid supplied between a projection optical system and the substrate. However, the exposure apparatus  1  can adopt the step &amp; repeat scheme or another exposure scheme. 
     The exposure apparatus  1  includes an exposure apparatus main unit  10 , chamber  20 , and temperature adjusting circulation system  30 , as shown in  FIG. 1 . 
     The exposure apparatus main unit  10  includes a light source  102  and an illumination optical system including a shaping optical system  104 , fly-eye lens  106 , condenser lens  108 , field stop  110 , movable blind (variable field stop)  112 , and relay lens system  114 , as shown in  FIG. 2 . The exposure apparatus main unit  10  also includes a reticle stage  118  which mounts a reticle  116  and reference plate  120 , an interferometer  122 , a projection optical system  124 , and a wafer stage  128  which mounts a wafer  126 . The exposure apparatus main unit  10  also includes an interferometer  132 , liquid supply/exhaust mechanism  134 , liquid holding plate  136 , alignment detection system  138 , movable blind control unit  140 , reticle stage control unit  142 , wafer stage control unit  144 , and main control unit  146 . Note that  FIG. 2  is a schematic view showing the exposure apparatus main unit  10 . 
     The light source  102  is, for example, a KrF excimer laser having a wavelength of about 248 nm, an ArF excimer laser having a wavelength of about 193 nm, or an F 2  laser having a wavelength of about 157 nm. Alternatively, the light source  102  can be, for example, a pulse light source such as a metal vapor laser or YAG laser, or a continuous light source as a combination of a mercury lamp and an elliptic mirror. 
     If the light source  102  is a pulse light source, exposure is switched on/off by controlling power supplied to the pulse light source. If the light source  102  is a continuous light source, exposure is switched on/off by a shutter arranged in the shaping optical system  104 . However, since the exposure apparatus  1  includes the movable blind  112  in this embodiment, exposure may be switched on/off by opening/closing the movable blind  112 . 
     The shaping optical system  104  shapes light (illumination light) from the light source  102  (for example, shapes the light to have a predetermined beam diameter), and guides it to the fly-eye lens  106 . 
     The fly-eye lens  106  forms a large number of secondary light sources on its exit surface. 
     The condenser lens  108  converges the light from the large number of secondary light sources formed on the exit surface of the fly-eye lens  106 , and guides it to the movable blind  112  via the field stop  110 . 
     Although the field stop  110  is set closer to the condenser lens  108  than the movable blind  112  in this embodiment, it may be set closer to the relay lens system  114 . The field stop  110  forms a slit-shaped aperture. The light having passed through the field stop  110  turns into that having a slit-shaped section, and enters the relay lens system  114 . 
     The movable blind  112  includes two light-shielding plates  112   a  and  112   b  which define the dimension in the scanning direction (the X-axis direction), and two light-shielding plates (not shown) which define the dimension in a direction (the non-scanning direction, that is, the Y-axis direction) perpendicular to the scanning direction. The light-shielding plates  112   a  and  112   b  can be independently driven in the scanning direction. Likewise, the two light-shielding plates which define the dimension in the non-scanning direction can be independently driven in the non-scanning direction. In this embodiment, the light is applied to only an exposure region defined by the movable blind  112  in an illumination region on the reticle  116 , which is defined by the field stop  110 . 
     The relay lens system  114  sets the movable blind  112  and the reticle  116  (more specifically, the pattern surface of the reticle  116 ) to be conjugate to each other. The relay lens system  114  is a bilateral telecentric optical system whose telecentricity is maintained in the illumination region on the reticle  116 . 
     The reticle  116  has a circuit pattern and is held and driven by the reticle stage  118 . The reticle  116  is illuminated with a uniform illuminance by the slit-shaped illumination region formed by the light source  102  and illumination optical system. Note that a reticle  116  is accommodated in a reticle accommodation unit RC and picked up and transported to a reticle alignment unit RA by a reticle transport system RT, as shown in  FIG. 1 . The reticle  116  transported to the reticle alignment unit RA is aligned and held by the reticle stage  118 . 
     The reticle stage  118  holds the reference plate  120 , on which a calibration reference mark is formed, together with the reticle  116 . The reticle stage  118  scans the reticle  116  in the scanning direction (the X-axis direction). 
     The interferometer  122  detects the position (for example, the position in the X- and Y-axis directions and the rotation directions about the X- and Y-axes) of the reticle stage  118 . 
     The projection optical system  124  projects the circuit pattern (more specifically, a circuit pattern positioned in the exposure region defined by the movable blind  112  in the slit-shaped illumination region) of the reticle  116  onto the wafer  126 . 
     The wafer  126  is a substrate which is held by the wafer stage  128  and onto which the circuit pattern of the reticle  116  is projected (transferred). However, the wafer  126  can be substituted by a glass plate or another substrate. Note that a wafer  126  is accommodated in a wafer accommodation unit WC and picked up by a wafer transport system WT, as shown in  FIG. 1 . The wafer  126  picked up by the wafer transport system WT is transported through a wafer feed unit and held by the wafer stage  128 . 
     The wafer stage  128  holds the wafer  126  by chucking it by vacuum suction through a wafer chuck. The wafer stage  128  includes an X-Y stage which aligns the wafer  126  in a plane perpendicular to the optical axis of the projection optical system  124  and scans it in the scanning direction (the X-axis direction), and a Z stage which aligns the wafer  126  in the optical axis direction of the projection optical system  124 . A reference mark  130  for calibration or alignment of the wafer  126  is formed on the wafer stage  128 . Also, a measuring unit (not shown) which can measure, for example, the imaging performance of the projection optical system  124  and the illuminance on the wafer  126  is arranged on the wafer stage  128 . 
     The interferometer  132  detects the position (for example, the position in the X- and Y-axis directions and the rotation directions about the X- and Y-axes) of the wafer stage  128 . 
     The liquid supply/exhaust mechanism  134  includes a liquid supply unit which supplies a liquid L between the projection optical system  124  and the wafer  126 , and a liquid recovery unit which recovers the liquid L supplied between the projection optical system  124  and the wafer  126 . The liquid supply unit includes, for example, a liquid supply pipe, pump, liquid temperature adjusting unit, and filter. The liquid recovery unit includes, for example, a liquid recovery pipe, pump, and gas-liquid separation unit. 
     The liquid L preferably has a high transmittance with respect to the exposure light, and a refractive index higher than those of quartz and calcium fluoride. In this embodiment, the liquid L is a liquid (organic liquid) having a refractive index higher than 1.33. 
     The liquid holding plate  136  is arranged around the wafer  126  while being chucked by vacuum suction by the wafer stage  128 , and has a surface flush with that of the wafer  126 . The liquid holding plate  136  holds the liquid L, which is supplied between the projection optical system  124  and the wafer  126 , in the periphery of the wafer  126 . 
     In this embodiment, the alignment detection system  138  is an off-axis detection system and detects the alignment mark formed on the wafer  126 . 
     The movable blind control unit  140  controls driving of the movable blind  112  (the two light-shielding plates  112   a  and  112   b  which define the dimension in the scanning direction, and the two light-shielding plates which define the dimension in the non-scanning direction). 
     The reticle stage control unit  142  controls driving of the reticle stage  118  (e.g., the alignment operation and scanning operation of the reticle stage  118 ) based on the position of the reticle stage  118  detected by the interferometer  122 . 
     The wafer stage control unit  144  controls driving of the wafer stage  128  (e.g., the alignment operation and scanning operation of the wafer stage  128 ) based on the position of the wafer stage  128  detected by the interferometer  132 , and the detection result obtained by the alignment detection system  138 . 
     The main control unit  146  includes a CPU and memory (neither are shown), and controls, for example, the movable blind control unit  140 , reticle stage control unit  142 , and wafer stage control unit  144  to control the operation of the exposure apparatus  1  including the exposure apparatus main unit  10 . The main control unit  146  also controls supply and recovery of the liquid L through the liquid supply/exhaust mechanism  134 . 
     In transferring the circuit pattern of the reticle  116  to each shot region on the wafer  126 , the reticle  116  is scanned at a velocity VR in the X-axis direction (for example, the negative direction) with respect to the slit-shaped illumination region defined by the field stop  110 . Also, the wafer  126  is scanned at a velocity β·VR (where β is the projection magnification of the projection optical system  124 ) in the X-axis direction (for example, the positive direction) in synchronism with the scanning of the reticle  116 . With this operation, the circuit pattern of the reticle  116  is transferred to each shot region on the wafer  126  step by step. 
     Referring back to  FIG. 1 , the chamber  20  accommodates the entire exposure apparatus  1  including the exposure apparatus main unit  10 . More specifically, the chamber  20  accommodates the entire exposure apparatus  1  by partitioning it into a plurality of spaces having an almost airtight structure. In this embodiment, the chamber  20  accommodates the entire exposure apparatus  1  by partitioning it into five spaces, that is, an exposure apparatus main unit space, reticle accommodation unit space, wafer accommodation unit space, reticle stage space, and wafer stage space. Note that the exposure apparatus main unit space accommodates the exposure apparatus main unit  10  except for the light source  102 , reticle stage  118 , and wafer stage  128 . The reticle accommodation unit space accommodates, for example, the reticle accommodation unit RC and reticle transport system RT. The wafer accommodation unit space accommodates, for example, the wafer accommodation unit WC and wafer transport system WT. The reticle stage space accommodates the reticle stage  118 . The wafer stage space accommodates the wafer stage  128 . 
     The temperature adjusting circulation system  30  adjusts the temperature of the internal gas of the chamber  20  and circulates it in a circulation channel including the interior of the chamber  20 . In this embodiment, the temperature adjusting circulation system  30  adjusts the temperature of the gas for each of the five spaces, that is, the exposure apparatus main unit space, reticle accommodation unit space, wafer accommodation unit space, reticle stage space, and wafer stage space. The temperature adjusting circulation system  30  includes, for example, a thermometer which measures the temperature of the gas in each space, a temperature adjusting device which adjusts the temperature of the gas, and a temperature adjusting circulation system control unit which controls devices such as the temperature adjusting device (that is, it controls the temperature of the gas) based on the measurement result obtained by the thermometer. The temperature adjusting device includes, for example, a refrigerant circulation unit, heat exchanger, and temperature adjusting unit. 
     A gas temperature-adjusted by a refrigerant circulation unit  304 , heat exchanger  306 , temperature adjusting unit  308 , and thermometer  310  under the control of a temperature adjusting circulation system control unit  302  is supplied to the exposure apparatus main unit space through a fan  312 . At this time, the gas supplied to the exposure apparatus main unit space is clean as it passes through a chemical filter  314  and dust removal filter  316  arranged in the gas flow channel in the chamber  20 . The chemical filter means a filter which removes chemical impurities contained in the internal gas of the chamber  20 . The gas supplied to the exposure apparatus main unit space returns to the temperature adjusting device through a return unit  318 , and is temperature-adjusted again by the refrigerant circulation unit  304 , heat exchanger  306 , temperature adjusting unit  308 , and thermometer  310 . Note that the exposure apparatus main unit space has an almost airtight structure, as mentioned above, and has a positive pressure with respect to the exterior of the chamber  20 . Note also that, in this embodiment, an outside air intake  320  for taking in the air outside the chamber  20  (outside air) is provided in order to suppress leakage of the gas from the exposure apparatus main unit space. 
     In each of the reticle accommodation unit space and wafer accommodation unit space, a circulation system is configured by a refrigerant circulation unit, heat exchanger, temperature adjusting unit, thermometer, and fan under the control of the temperature adjusting circulation system control unit  302 , as in the exposure apparatus main unit space. Gases supplied to the reticle accommodation unit space and wafer accommodation unit space are clean as they pass through dust removal filters  322  and  324 . The gases supplied to the reticle accommodation unit space and wafer accommodation unit space return to the temperature adjusting device through the return unit  318 . 
     A gas temperature-adjusted by the refrigerant circulation unit  304 , the heat exchanger  306 , a temperature adjusting unit  326 , and a thermometer  328  under the control of the temperature adjusting circulation system control unit  302  is supplied to the reticle stage space through a fan  330  and duct  332 . At this time, the gas supplied to the reticle stage space is clean as it passes through a dust removal filter  334 . The gas supplied to the reticle stage space returns to the temperature adjusting device through the return unit  318 . 
     A gas temperature-adjusted by the refrigerant circulation unit  304 , the heat exchanger  306 , a temperature adjusting unit  336 , and a thermometer  338  under the control of the temperature adjusting circulation system control unit  302  is supplied to the wafer stage space through a fan  340  and duct. At this time, the gas supplied to the reticle stage space is clean as it passes through a dust removal filter  344 . 
     Note that the wafer stage space contains volatile components which volatilize from the liquid L because it stores the liquid L. Accordingly, the gas which returns to the temperature adjusting device from the wafer stage space contains volatile components which volatilize from the liquid L. To cope with this situation, in this embodiment, a removal member  342  which removes volatile components which volatilize from the liquid L is arranged in the circulation channel of the temperature adjusting circulation system  30  upstream of the chemical filter  314  in the direction in which the internal gas of the chamber  20  flows. The removal member  342  can be, for example, activated carbon which has chemical properties different from those of the chemical filter  314 , absorbs volatile components which volatilize from the liquid L, and is less expensive than the chemical filter  314 . With this arrangement, the gas which has returned to the temperature adjusting device from the wafer stage space and contains volatile components which volatilize from the liquid L passes through the chemical filter  314  after volatile components which volatilize from the liquid L are removed by the removal member  342 . This makes it possible to prevent shortening of the lifetime (i.e., an increase in the replacement frequency) of the chemical filter  314  due to volatile components which volatilize from the liquid L because the chemical filter  314  need not remove the volatilized components which volatilize from the liquid L. It is therefore possible to suppress an increase in the running cost and a decrease in the throughput even when a liquid (organic liquid) having a refractive index higher than 1.33 is used as the liquid L. Note that removing (absorbing) volatile components which volatilize from the liquid L by the removal member  342  makes it possible to prevent an increase in the density of volatile components contained in the internal gas of the chamber  20 . 
     The gas around the liquid L supplied between the projection optical system  124  and the wafer  126 , that is, a gas containing a large amount of volatile components which volatilize from the liquid L may be exhausted outside the chamber  20 , as shown in  FIG. 3 . There exists an interface with the gas around the liquid L, in which volatile components volatilize from the liquid L. In addition, the liquid L moves on the wafer  126  or on the liquid holding plate  136  upon driving the wafer stage  128 , so volatile components volatilize from the liquid L as it stays behind the wafer  126  or the liquid holding plate  136 . Therefore, a gas containing a large amount of volatile components which volatilize from the liquid L is present around the liquid L.  FIG. 3  is an enlarged sectional view of the vicinity of the final surface (the surface closest to the wafer  126 ) of the projection optical system  124 . 
     Referring to  FIG. 3 , a liquid supply pipe  1342  and liquid recovery pipe  1344  of the liquid supply/exhaust mechanism  134  are arranged near the final surface of the projection optical system  124 . A blowing nozzle  1346  which blows a gas to the periphery of the liquid L is arranged outside the liquid recovery pipe  1344  (i.e., in the periphery of the projection optical system  124  on its substrate side) in order to stably maintain the liquid L supplied between the projection optical system  124  and the wafer  126 . The blowing nozzle  1346  blows a gas to the periphery of the liquid L to form an air curtain, thereby limiting the space, in which a gas containing a large amount of volatile components which volatilize from the liquid L is present, to a partial space. It is therefore possible to efficiently exhaust a gas containing a large amount of volatile components which volatilize from the liquid L by inserting an exhaust unit  40  between the liquid recovery pipe  1344  and the blowing nozzle  1346  and exhausting the gas in the space formed by the air curtain, as shown in  FIG. 3 . A removal member  402  which removes volatile components which volatilize from the liquid L is arranged in the exhaust channel of the exhaust unit  40 . This makes it possible to exhaust the gas by removing or reducing volatile components in the gas. The removal member  402  is activated carbon, as in the removal member  342 . 
     The exhaust unit  40  preferably has an arrangement as shown in  FIG. 4  in order to exhaust the gas by surely removing or reducing volatile components which volatilize from the liquid L. In addition to the removal member  402 , the exhaust unit  40  shown in  FIG. 4  includes a density detection unit  404  which detects the density of volatile components which volatilize from the liquid L, a shutoff unit  406  which shuts off the exhaust channel, and a detection unit  408  which detects whether the removal member  402  is arranged in the exhaust channel.  FIG. 4  is a schematic view showing an example of the exhaust unit  40 . In  FIG. 4 , the arrows indicate the flow (flow direction) of a gas which contains volatile components that volatilize from the liquid L and is exhausted by the exhaust unit  40 . 
     Referring to  FIG. 4 , a gas containing volatile components which volatilize from the liquid L undergoes removal of the volatile components and is exhausted outside the chamber  20 . Note that as the removal member  402  removes volatile components which volatilize from the liquid L, its capacity to remove volatile components degrades. For this reason, it often becomes impossible for the removal member  402  to sufficiently remove or reduce volatile components which volatilize from the liquid L. In this case, the exhaust unit  40  exhausts the gas still containing volatile components which volatilize from the liquid L. 
     To solve this problem, the density detection unit  404  is arranged in the exhaust channel of the exhaust unit  40  downstream of the removal member  402 , and detects the density of volatile components contained in the gas having passed through the removal member  402 . If the density of volatile components detected by the density detection unit  404  is equal to or higher than a threshold, the exhaust is stopped by shutting off the exhaust channel by the shutoff unit  406 . With this operation, a gas containing volatile components which volatilize from the liquid L and have a density equal to or higher than a threshold can be prevented from being exhausted outside the chamber  20 . In other words, only a gas having surely undergone removal or reduction of volatile components which volatilize from the liquid L can be exhausted outside the chamber  20 . It is also possible to detect the density of oxygen contained in the gas having passed through the removal member  402  by the density detection unit  404 , and determine that the density of volatile components contained in the gas is equal to or higher than a threshold if the density of oxygen is equal to or lower than a predetermined density. 
     When the removal member  402  has reached the end of its lifetime (that is, it has lost the capacity to remove volatile components), it can no longer remove volatile components which volatilize from the liquid L contained in the gas. To cope with this situation, the removal member  402  is detachably arranged in the exhaust channel of the exhaust unit  40  for replacement. When the removal member  402  having reached the end of its lifetime is replaced, it is not arranged in the exhaust channel of the exhaust unit  40 , so a gas containing volatile components which volatilize from the liquid L is exhausted directly. 
     To avoid this situation, the detection unit  408  is arranged in the exhaust channel of the exhaust unit  40 , and detects whether the removal member  402  is arranged in the exhaust channel. If the detection unit  408  determines that the removal member  402  is not arranged in the exhaust channel of the exhaust unit  40 , the exhaust is stopped by shutting off the exhaust channel by the shutoff unit  406 . With this operation, a gas containing volatile components which volatilize from the liquid L can be prevented from being exhausted directly. In other words, only a gas having surely undergone removal or reduction of volatile components which volatilize from the liquid L can be exhausted outside the chamber  20 . Note that the shutoff unit  406  keeps the exhaust channel of the exhaust unit  40  shut off until the detection unit  408  detects that the removal member  402  is arranged in the exhaust channel. 
     Such an arrangement (the density detection unit  404 , shutoff unit  406 , and detection unit  408 ) which exhausts only a gas having surely undergone removal or reduction of volatile components which volatilize from the liquid L to the outside of the chamber  20  is also applicable to the removal member  342  shown in  FIG. 1 . This makes it possible to prevent a gas containing volatile components which volatilize from the liquid L and have a density equal to or higher than a threshold from circulating through the chamber  20 . 
     Instead of being absorbed by activated carbon serving as the removal member  342 , volatile components which volatilize from the liquid L can be removed by cooling a gas containing volatile components which volatilize from the liquid L, as shown in  FIG. 5 .  FIG. 5  is a schematic view showing another example of the exhaust unit  40 . The exhaust unit  40  shown in  FIG. 5  includes a heat exchanger  412 , refrigerant circulation system  414 , and recovery unit  416 . In  FIG. 5 , the arrows indicate the flow (flow direction) of a gas which contains volatile components which volatilize from the liquid L and is exhausted by the exhaust unit  40 . 
     Referring to  FIG. 5 , the heat exchanger  412  cools a gas containing volatile components which volatilize from the liquid L. The heat exchanger  412  is set to a temperature equal to or lower than that, at which volatile components which volatilize from the liquid L condense, by the refrigerant circulation system  414 . Accordingly, volatile components which volatilize from the liquid L and are contained in the gas are condensed by the heat exchanger  412  and removed from the gas. The volatile components (i.e., the liquid L) which are condensed by the heat exchanger  412  are recovered by a recovery unit  416  including, for example, a drain pan and drain. In this manner, the exhaust unit  40  shown in  FIG. 5  can exhaust a gas containing volatile components which volatilize from the liquid L after removing or reducing the volatile components by cooling the gas to a predetermined temperature (the temperature at which volatile components condense) or less. A gas containing volatile components which volatilize from the liquid L and have a density equal to or higher than a threshold may be prevented from being exhausted outside the chamber  20  by arranging the density detection unit  404  and shutoff unit  406 , as shown in  FIG. 4 , downstream of the heat exchanger  412 . 
     Since volatile components which volatilize from the liquid L and are contained in the gas are generally organic components, they can be removed upon being chemically decomposed using a photochemical reaction, as shown in  FIG. 6 .  FIG. 6  is a schematic view showing still another example of the exhaust unit  40 . The exhaust unit  40  shown in  FIG. 6  includes a decomposing unit  420 . The decomposing unit  420  includes ultraviolet lamps  422  serving as the irradiation units, and a photocatalyst member  424 . The ultraviolet lamps  422  are arranged in the exhaust channel of the exhaust unit  40  to face the photocatalyst member  424  having a thin film of a photocatalyst (for example, titanium oxide) on its surface. In  FIG. 6 , the arrows indicate the flow (flow direction) of a gas which contains volatile components which volatilize from the liquid L and is exhausted by the exhaust unit  40 . 
     Referring to  FIG. 6 , a gas containing volatile components which volatilize from the liquid L contacts the photocatalyst member  424  which is excited upon being irradiated with ultraviolet rays from the ultraviolet lamps  422 . With this operation, because volatile components which volatilize from the liquid L and are contained in the gas undergo oxidative decomposition and are removed from the gas, the exhaust unit  40  shown in  FIG. 6  can exhaust the gas after removing or reducing the volatile components. Although the volatile components are decomposed using the ultraviolet lamps  422  and the photocatalyst member  424  as the decomposing unit  420  in this embodiment, they may undergo oxidative decomposition by ozone generated by irradiating the gas with ultraviolet rays. Alternatively, a gas containing volatile components which volatilize from the liquid L and have a density equal to or higher than a threshold may be prevented from being exhausted outside the chamber  20  by arranging the density detection unit  404  and shutoff unit  406 , as shown in  FIG. 4 , downstream of the decomposing unit  420 . 
     Although the exhaust unit  40  exhausts the gas around the liquid L supplied between the projection optical system  124  and the wafer  126  in this embodiment, it is also applicable to a case in which the internal gas of the chamber  20  is exhausted outside without being circulated through it. 
     The exposure apparatus main unit  10  often includes a plurality of wafer stages (for example, two wafer stages  128  and  128 ′), as shown in  FIG. 7 .  FIG. 7  is a schematic view showing another arrangement of the exposure apparatus main unit  10 . The two wafer stages  128  and  128 ′ can move between an exposure area in which the wafer  126  is exposed and a measurement area in which the wafer  126  is measured. An alignment detection system  138  which detects an alignment mark formed on the wafer  126  is set in the measurement area. A surface detection system  152  which detects the surface state, such as the level and tilt, of the wafer  126 , and the like are also set in the measurement area. 
     A partition plate  154  for partitioning the exposure area and the measurement area is interposed between the exposure area and the measurement area, as shown in  FIG. 7 . The partition plate  154  can be driven vertically and is controlled by a partition plate control unit  156 . For example, under the control of the partition plate control unit  156 , the partition plate  154  is driven vertically when the wafer stages  128  and  128 ′ move between the exposure area and the measurement area. 
     When the wafer  126  is exposed in the exposure area, a liquid L is supplied between the projection optical system  124  and the wafer  126 , and the liquid L supplied between the projection optical system  124  and the wafer  126  is recovered. Therefore, a gas containing a large amount of volatile components which volatilize from the liquid L is present in the space around the liquid L in the exposure area. 
     To cope with this situation, when the wafer  126  is exposed in the exposure area, the partition plate  154  inserted between the exposure area and the measurement area is driven downwards to partition the space into an exposure area and a measurement area. This makes it possible to limit the space, in which a gas containing volatile components which volatilize from the liquid L is present, to the exposure area. Therefore, an exhaust unit  40  including a removal member  402  which removes volatile components which volatilize from the liquid L need only be set in the exposure area. In this manner, even when the wafer stage space widens by providing a plurality of wafer stages, limiting the space in which a gas containing volatile components which volatilize from the liquid L makes it possible to prevent an increase in the size of the exhaust unit  40  (removal member  402 ), thus preventing an increase in the running cost. Although the partition plate  154  preferably perfectly partitions the exposure area and the measurement area, it is only necessary that the partition plate  154  serve to decrease the density of volatile components which volatilize from the liquid L and are contained in the gas in the measurement area. Although the partition plate  154  can be driven vertically in this embodiment, it may be fixed as long as the two wafer stages  128  and  128 ′ can move between the exposure area and the measurement area. In place of the partition plate  154 , a forming unit which forms an air curtain for partitioning the exposure area and the measurement area may be provided. 
     A gas containing a large amount of volatile components which volatilize from the liquid L is present in the wafer stage space, as mentioned above, so the wafer stage space is preferably maintained airtight using seal members  62 ,  64 , and  66 , as shown in  FIG. 8 .  FIG. 8  is a schematic view showing an exposure apparatus  1  according to one aspect of the present invention. 
     Referring to  FIG. 8 , the wafer stage space is set to have an airtight structure by the seal members  62 ,  64 , and  66 , and supplied with a temperature-adjusted gas from the temperature adjusting circulation system  30 . The gas supplied to the wafer stage space flows through the wafer accommodation unit space and returns to the temperature adjusting device through a return unit  362  having a channel different from the channel of the return unit  318 . In the temperature adjusting device, the gas having returned from the wafer stage space is cooled by a refrigerant circulation unit  364  and heat exchanger  366  so that volatile components which volatilize from the liquid L and are contained in the gas are removed by a removal member  368  including, for example, activated carbon. The gas from which volatile components which volatilize from the liquid L are removed undergoes removal of chemical impurities by a chemical filter  370 , is temperature-adjusted by a thermometer  338  and temperature adjusting unit  336 , and is supplied to the wafer stage space through a fan  340  and duct. 
     Although a material, which has elasticity and flexibility, such as rubber or a resin is preferably used as the seal members  62 ,  64 , and  66 , it generally has no resistance to volatile components which volatilize from the liquid L. In view of this, the seal members  62 ,  64 , and  66  are made of a bellows metal having a resistance to volatile components which volatilize from the liquid L so that the seal functions of the seal members  62 ,  64 , and  66  are suppressed from degrading due to the presence of the volatile components, thus maintaining the airtightness of the wafer stage space. Alternatively, the seal members  62 ,  64 , and  66  may be made of a flexible member (for example, rubber or a resin) having, on its surface, a metal having a resistance to volatile components which volatilize from the liquid L. Although three seal members  62 ,  64 , and  66  are used in this embodiment, the present invention is not particularly limited to this, and four seal members, for example, may be used. The seal members  62 ,  64 , and  66  can be used not only to set the wafer stage space to have an airtight structure but also set other spaces to have an airtight structure. 
     In this manner, the exposure apparatus  1  can suppress an increase in the running cost and a decrease in the throughput even when a high-index liquid is used as the liquid L supplied between the projection optical system  124  and the wafer  126 . Hence, the exposure apparatus  1  can provide high-quality devices (e.g., a semiconductor device and a liquid crystal display device with a high throughput and a good economical efficiency. The devices are fabricated by a step of exposing a substrate (e.g., a wafer or a glass plate) coated with a photoresist (photosensitive agent) using the exposure apparatus  1 , a step of developing the exposed substrate, and other known steps. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2008-056624 filed on Mar. 6, 2008, which is hereby incorporated by reference herein in its entirety.