Abstract:
The present invention provides an exposure apparatus for transferring a pattern of an original to a substrate by use of light from a light source. The exposure apparatus includes an optical system to direct light from said light source to the substrate through the original, and to have a first element; a second element different from said first element; a first housing accommodating at least said first element and said second element; a second housing accommodated in said first housing and accommodating at least a part of said second element; and a first purge system to purge a first space between said first housing and said second housing.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to an exposure apparatus. In particular, the invention relates to an exposure apparatus used for exposing an object to be processed (substrate) such as a single crystal substrate for a semiconductor device or a glass substrate for a liquid crystal display (LCD). The present invention is suitable, for example, for an exposure apparatus using light beam having wavelength not longer than 200 nm.  
         [0003]     2. Related Background Art  
         [0004]     There is an increasing demand for miniaturization of a semiconductor element installed in an electronic device in order to respond to recent requests for reduction in size and thickness of the electronic device. Up to now, a projection exposure apparatus has been used in a lithography (printing) process for manufacturing a semiconductor element, the apparatus projecting and transferring a circuit pattern drawn on a reticle or mask (in this application, the two terms are interchangeably used) onto a wafer etc. by using a projection optical system.  
         [0005]     A resolution (minimum transferable size) R of a projection exposure apparatus is represented by the following expression using a wavelength λ of a light source and a numerical aperture (NA) of a projection optical system: 
 
 R=k   1   ×λ/NA  
 
 where k 1  represents a process constant defined by a development process etc. 
 
         [0006]     Accordingly, the shorter the wavelength, the higher the resolution. Based on this, in recent years, an exposure light source has shifted from a conventional extra-high pressure mercury lamp (g line (wavelength: about 436 nm) or i line (wavelength: about 365 nm)) to a KrF excimer laser (wavelength: about 248 nm) or an ArF excimer laser (wavelength: about 193 nm) having a shorter wavelength than conventional ones. Further, an F2 laser (wavelength: about 157 nm) is coming into practical use.  
         [0007]     Also, there arises a need to improve a throughput (the number of wafers to be processed per unit time) in a projection exposure apparatus. Since an exposure time for each object to be processed needs to be shortened in order to improve the throughput, an illuminance of exposure light, i.e., an exposure amount, in which each object to be processed is irradiated with light per unit time, needs to be increased.  
         [0008]     However, exposure light beam having a shorter wavelength (for example, light beam having a wavelength in a vacuum ultraviolet region) is absorbed in larger amount in oxygen or impurity (water vapor, carbon dioxide, organic material, or halide; also referred to as a contaminant) existing in an atmosphere in an optical path of the exposure light (reduction in transmissivity), resulting in reduction in throughput as well as in exposure light amount of the object to be processed. In general, as the wavelength of light beam shortens, photon energy gradually increases, causing a photochemical reaction between the contaminant and oxygen. If a product (ammonium sulfate or silicon dioxide) generated by the photochemical reaction adheres to an optical element, the surface of the optical element is fogged, leading to not only further reduction in exposure light amount but also deterioration in imaging performance.  
         [0009]     To that end, in a projection exposure apparatus employing an KrF excimer laser or ArF excimer laser as a light source, optical elements arranged in an optical path are accommodated in a space purged with inert gas in order to avoid reduction in transmissivity due to the absorption of light beam by oxygen etc. in an atmosphere in an optical path, or reduction in exposure light amount and deterioration in imaging performance due to adherence of the product generated by the photochemical reaction to the surface of the optical elements. Also, the purged space is made free of any substance having gas-producing property, which prevents a contaminant from being generated (see Japanese Patent Application Laid-Open No. H06-029179, for example).  
         [0010]      FIG. 9  is a schematic sectional view shoring a main structural part of a conventional exposure apparatus  1000 . Referring to  FIG. 9 , the exposure apparatus  1000  includes a lens unit  1200  provided inside a housing  1100  constituting an optical system. An exposure light EL from a light source  1400  is guided to the outside of the housing  1100  through a seal glasses  1300   a  and  1300   b.  A pipe  1500   a  for supplying an inset gas and a pipe  1500   b  for exhausting the air in the housing are provided inside the housing  1100 , for example. The inside of the housing  1100  is purged with the inert gas.  
         [0011]     The exposure apparatus  1000  includes a rotating member  1700  having a plurality of filters  1600   a  and  1600   b  for adjusting a light amount of the exposure light EL, and a motor  1800  for driving the rotating member  1700 , inside the housing  1100 . The motor  1800  is disposed onto a motor holder  1820  fixed to the housing  1100  through a flange  1810 . Note that a motor wiring  1830  is connected to a control unit or a power supply unit through an air-tight connector (not shown).  
         [0012]     If the motor  1800  has a gas-producing property, an exhaust gas EG adheres to the lens unit  1200  due to a photochemical reaction, leading to deterioration in imaging performance as well as reduction in exposure light amount. To that end, members such as a motor etc. used in an optical system of the exposure apparatus are composed of members discharging as little exhaust gas EG as possible in order to prevent dust generation or gas-production.  
         [0013]     However, with a structure of the aforementioned conventional exposure apparatus, it becomes more difficult to sufficiently suppress reduction in throughput and deterioration in imaging performance due to contamination of an optical element, as the wavelength of the exposure light becomes shortened. Although the motor is configured so as to minimize the exhaust gas production as mentioned above, it is impossible to use undesirable materials to maintain performance of the motor. For example, a solder or resin is used for a stator or a coil wire wound inside the stator, or other such internal members. Even if materials having low gas-producing property are basically selected, however an adhesive, grease, or the like is used therefor as well. As a result, as photon energy of the exposure light increases, a photochemical reaction is activated, so that an exhaust gas in a trace amount, which otherwise might cause no photochemical reaction, turns into a contaminant.  
         [0014]     The exhaust gas discharged from the motor is known to contain moisture. In particular, light beam of an F2 laser is largely absorbed by moisture or oxygen. Hence, it is necessary to keep a water and oxygen content in an optical path at an extremely low level. However, the structure of the conventional exposure apparatus requires long time to reach such a water or oxygen content as to satisfy a required optical performance. This is supposedly because it takes much time to purge with an inert gas the air having intruded and accumulated in the inside of the motor or in minute gaps of a lens holding mechanism or other such mechanisms. Alternatively, this is supposedly trigged by moisture in an exhaust gas discharged from the motor. In addition, for example, if the optical element is fogged, an exposure apparatus needs to be open (canceling the purge with the inert gas) for replacing the optical element; at this time, moisture in the air may be mixed thereinto, so the apparatus should be stopped until the water or moisture content reaches such a level as to satisfy the required exposure performance again, leading to reduction in throughput.  
       SUMMARY OF THE INVENTION  
       [0015]     It is therefore an exemplified object of the present invention to provide an exposure apparatus capable of suppressing adherence of a contaminant to an optical element surface, and realizing a high throughput and a satisfactory imaging performance.  
         [0016]     According to one aspect of the invention, an exposure apparatus for transferring a pattern of an original onto a substrate by use of a light beam from a light source includes an optical system for guiding the light beam from the light source to the substrate through the original, a first housing accommodating at least a first element and a second element different from the first element of the optical system, a second housing accommodated in the first housing and accommodating at least a part of the second element, and a first purge system for purging a first space between the first housing and the second housing.  
         [0017]     According to the present invention, it is possible to provide an exposure apparatus capable of suppressing adherence of a contaminant to an optical element surface, and realizing a high throughput and a satisfactory imaging performance.  
         [0018]     Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form apart thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0020]      FIG. 1  is a schematic sectional view showing a structure of an exposure apparatus according to an embodiment of the present invention;  
         [0021]      FIG. 2  is a schematic sectional view showing an example of a structure of an illumination system unit shown in  FIG. 1 ;  
         [0022]      FIG. 3  is a schematic sectional view showing a structure of an illumination system unit as a modified example of the illumination system unit shown in  FIG. 2 ;  
         [0023]      FIG. 4  is a schematic sectional view showing a structure of an illumination system unit as a modified example of the illumination system unit shown in  FIG. 2 ;  
         [0024]      FIG. 5  is a schematic sectional view showing a structure of an illumination system unit as a modified example of the illumination system unit shown in  FIG. 2 ;  
         [0025]      FIG. 6  is a schematic sectional view showing a structure of an illumination system unit as a modified example of the illumination system unit shown in  FIG. 2 ;  
         [0026]      FIG. 7  is a flowchart illustrative of how to manufacture a device (semiconductor chip such as an IC or LSI, LCD, CCD, or the like);  
         [0027]      FIG. 8  is a flowchart of a detailed process flow of wafer processing in step S 4  shown in  FIG. 7 ; and  
         [0028]      FIG. 9  is a schematic sectional view showing a main structural part of a conventional exposure apparatus. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     Hereinafter, an exposure apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the same reference symbols are assigned to the same members throughout the drawings, and repetitive explanation is omitted. Here,  FIG. 1  is a schematic sectional view showing a structure of an exposure apparatus  1  according to the embodiment of the present invention.  
         [0030]     As shown in  FIG. 1 , the exposure apparatus  1  includes an illuminator  10  for illuminating a reticle  20  having a circuit pattern formed thereon; a projection optical system  30  for projecting diffraction ray diffracted by the reticle pattern onto an object to be processed (plate)  40 ; and a stage  50  for supporting the object to be processed  40 .  
         [0031]     The exposure apparatus  1  serves as a projection exposure apparatus for projecting the circuit pattern formed on the reticle  20  to the plate  40  through exposure, by using a step-and-scan process or step-and-repeat process, for example. Such an exposure apparatus is suitable for a lithography process requiring sub-micron processing or processing on or below the quarter-micron order. Hereinbelow, in this embodiment, description will be given taking as an example of an exposure apparatus employing the step-and-scan process (also called “scanner”). Here, the “step-and-scan process” refers to an exposure method including sequentially scanning a wafer relative to the reticle to project the reticle pattern to the wafer thorough exposure, and moving the wafer, which has undergone exposure corresponding to one shot, stepwise up to the next exposure region. The “step-and-repeat process” means an exposure method including moving a wafer stepwise for each collective exposure, up to an exposure region for the next shot.  
         [0032]     The illuminator  10  includes an illumination optical system  14  and a light source portion  12  for illuminating the reticle  20  having a transfer circuit pattern formed thereon.  
         [0033]     The light source portion  12  can employ an ArF excimer laser having a wavelength of about 193 nm, an KrF excimer laser having a wavelength of 248 nm, or the like as a light source. However, the kind of light source is not limited to the excimer laser but an F2 laser having a wavelength of about 153 nm or YAG laser may be used, for instance. Besides, the number of light sources is not limited. For example, if two solid lasers operating independently of each other are used, the solid lasers cause no coherence therebetween and considerably reduce speckles caused by the coherence. An optical system may be oscillated linearly or pivotally for further reduction in speckle. When the laser is used for the light-source portion  12 , it is preferable to use a beam shaping optical system for shaping parallel bema emitted from the laser light source into a desired beam shape and incoherence optical system for making coherent laser beam incoherent. A light source applicable to the light source portion  12  is not limited to the laser but one or more lamps such as mercury lamps or xenon lamps can be used.  
         [0034]     The illumination optical system  14  is an optical system for illuminating the reticle  20 , which includes a lens, a mirror, an optical integrator, and an aperture stop. This is, for example, an optical system where a condenser lens, a flyeye lens, an aperture stop, another condenser lens, a slit, and an imaging optical system are arrayed in the stated order.  
         [0035]     The illumination optical system  14  is composed of a plurality of illumination system units  100  having lenses etc. arranged therein.  FIG. 2  is a schematic sectional view showing an example of a structure of the illumination system unit  100  shown in  FIG. 1 . The illumination system unit  100  includes: a first housing  110  that defines a first space AS 1  kept in a first atmosphere; and a second housing  140  that is isolated from the first atmosphere and also accommodated in the first housing  110  to define a second space AS 2  kept in a second atmosphere, and has a double structure. The illumination system unit  100  guides an exposure light EL from the light source portion  12  through a seal glasses  150   a  and  150   b  provided in the first housing  110 .  
         [0036]     Referring to  FIG. 2 , the illumination system unit  100  has a lens unit  112  and optical member  120  inside the first space AS 1  defined by the first housing  110 . The first space AS 1  is purged with an inert gas by means of a pipe  114  for supplying the inert gas and pipe  116  for exhausting, which are provided to the first housing  110 , and is kept at the first atmosphere.  
         [0037]     The optical member  120  is arranged inside the first space AS 1  purged with the inert gas and driven by a motor  130  accommodated inside the second housing  140  as described later. The optical member  120  is composed of, in this embodiment, a turret  122  and filters  124 . Mounted on the turret  122  serving as a rotating member are the filters  124  of plural kinds different in degree of controlling the exposure light EL. The motor  130  is used to drive the turret  122  so as to switch between the plural filters  124 .  
         [0038]     The motor  130  is accommodated in the second housing  140  and isolated from the first space AS 1 . The motor  130  is held to a flange  132  and attached to a motor holder  118  in the first housing  110  through the flange  132 . Also, the flange  132  has a partition  132   a  that defines the second space AS 2  together with the second housing  140 .  
         [0039]     The flange  132  has a sealing member  136  formed of a material having low gas-producing property, such as Teflon or fluororubber for the purpose of avoiding discharge of an exhaust gas from an internal member of the motor  130  having gas-producing property, through a drive shaft  134  of the motor  130 . In other words, the sealing member  136  is disposed between the flange  132  and the drive shaft  134  of the motor  130  to bring the flange  132  and the drive shaft  134  into close contact with each other. The member having gas-producing property includes, for example, a plating member for a stator etc., an insulating member for a coil etc., grease used in a bearing etc., and an adhesive or solder etc. used for connecting wirings.  
         [0040]     In the second housing  140 , provided between the flange  132  (its partition  132 a) and the second housing  140  is a sealing member  142  composed of an O-ring formed of a material having low gas-producing property, such as fluororubber with a view to avoiding diffusion into the first space AS 1  of the exhaust gas from the stator of the motor  130  or exhaust gas from the motor  130 , which leaks from a gap thereof. This provision enables isolation of the second space AS 2  defined by the flange  132  and the second housing  140 .  
         [0041]     A motor wiring  137  and motor connector  138  are connected to a device (e.g., power supply) outside the exposure apparatus  1  by means of wiring (not shown) thorough an air-tight connector  148  provided to the second housing  140 . Also, the second housing  140  has a pipe  144  for supplying the inert gas and a pipe  146  for exhausting; the second space AS 2  can be purged with the inset gas and kept at the second atmosphere, aside from the first space AS 1 .  
         [0042]     The second space AS 2  is thereby supplied with a clean inert gas and the air is exhausted therefrom all the time, preventing the exhaust gas from the motor  130  from leaking to the first space AS 1 . Therefore, the illumination system unit  100  can prevent a photochemical reaction between the exposure light EL and the exhaust gas from the motor  130 , prevent any contaminant from adhering to an optical element (i.e., the lens unit  112  or filter  124 ) surface, realize a high throughput, and exert a satisfactory imaging performance.  
         [0043]     Besides, a cooling effect can be also obtained, making it possible to keep heat generated by the motor  130  from being transferred to its surrounding optical element (i.e., lens unit  112 ). Note that a pressure of the second space AS 2  is set lower than that of the first space AS 1  (set to a negative pressure relative to that of the first space), whereby the exhaust gas from the motor  130  is prevented from leaking from the second space AS 2  to the first space AS 1  even if the sealing member  142  deteriorates.  
         [0044]     In this way, the illumination system unit  100  can block out a current of the exhaust gas from the motor  130  and is applicable to the exposure apparatus  1  irrespective of the gas-producing property of a member constituting the motor  130 . Further, even if the exposure apparatus is open for maintenance etc., it is possible to prevent the air from intruding in a minute space of the motor  130 , which can shorten a time from halt to restart-up of the apparatus.  
         [0045]     Referring next to  FIG. 3 , an illumination system unit  100 A as a modified example of the illumination system unit  100  shown in  FIG. 2  will be explained.  FIG. 3  is a schematic sectional view showing a structure of the illumination system unit  100 A as the modified example of the illumination system unit  100  shown in  FIG. 2 . The illumination system unit  100 A is similar to the illumination system unit  100  but is different therefrom in terms of the first atmosphere of the first space AS 1  defined by the first housing  110 .  
         [0046]     Referring to  FIG. 3 , the illumination system unit  100 A has a lens unit  112  and an optical member  120  inside the first space AS 1  defined by the first housing  110 . The first space AS 1  is maintained at a predetermined degree of vacuum by means of an evacuating pipe  160 , which is provided to the first housing  110 .  
         [0047]     In the illumination system unit  100 A, like the illumination system unit  100 , the motor  130  is arranged inside the second space AS 2  isolated from the first space AS 1 , and defined by the flange  132  and the second housing  140 , thereby preventing the exhaust gas from the motor  130  from leaking to the first space AS 1 .  
         [0048]     Even if the exhaust gas from the motor  130  leaks from the second space AS 2  where the motor  130  is disposed, the inert gas is supplied to the second space AS 2  through the pipe  144  and gas including the exhaust gas from the motor  130  is exhausted from the second space through the pipe  146 . An adverse influence of the exhaust gas can be suppressed.  
         [0049]     The illumination system unit  100 A can block out the current of the exhaust gas from the motor  130  even if the first space AS 1  is evacuated to a predetermined degree of vacuum, and is also applicable to the exposure apparatus  1  irrespective of its gas-producing property of a member constituting the motor  130 . Accordingly, the illumination system unit  100 A can prevent a photochemical reaction between the exposure light EL and the exhaust gas from the motor  130 , prevent any contaminant from adhering to optical elements (i.e., the lens unit  112  or filter  124 ) surface, realize a high throughput, and exert a satisfactory imaging performance.  
         [0050]     Referring next to  FIG. 4 , an illumination system unit  100 B as another modified example of the illumination system unit  100  shown in  FIG. 2  will be explained.  FIG. 4  is a schematic sectional view showing a structure of the illumination system unit  100 B as the modified example of the illumination system unit  100  shown in  FIG. 2 . The illumination system unit  100 B is similar to the illumination system unit  100  but is different therefrom in terms of the second atmosphere of the second space AS 2  defined by the second housing  140 .  
         [0051]     Referring to  FIG. 4 , the illumination system unit  100 B has a lens unit  112  and an optical member  200  inside the first space AS 1  defined by the first housing  110 . The first space AS 1  is purged with an inert gas by means of the pipe  114  for supplying the inert gas and pipe  116  for exhausting, which are provided to the first housing  110 , and is kept at the first atmosphere.  
         [0052]     In the illumination system unit  100 B, like the illumination system unit  100 , the motor  130  is disposed inside the second space AS 2  isolated from the first space AS 1 , and defined by the flange  132  and the second housing  140 . The second housing  140  has an evacuating pipe  170  and the second space AS 2  can be evacuated and kept at a predetermined degree of vacuum, aside from the first space AS 1 . Thus, the exhaust gas from the motor  130  neither fills the second space AS 2  nor leaks to the first space AS 1  from the second space AS 2 .  
         [0053]     The illumination system unit  100 B evacuates the second space AS 2  to a predetermined degree of vacuum, making it possible to block out a current of the exhaust gas from the motor  130 . In addition, the pressure of the second space AS 2  becomes lower than that of the first space AS 1 , whereby the exhaust gas from the motor  130  is kept from leaking from the second space AS 2  to the first space AS 1  even if the sealing member  142  deteriorates.  
         [0054]     Therefore, the illumination system unit  100 B can prevent a photochemical reaction between the exposure light EL and the exhaust gas from the motor  130 , prevent any contaminant from adhering to an optical element (i.e., the lens unit  112  or filter  124 ) surface, realize a high throughput, and exert a satisfactory imaging performance.  
         [0055]     Referring next to  FIG. 5 , an illumination system unit  100 C as still another modified example of the illumination system unit  100  shown in  FIG. 2  will be explained.  FIG. 5  is a schematic sectional view showing a structure of the illumination system unit  100 C as the modified example of the illumination system unit  100  shown in  FIG. 2 . The illumination system unit  100 C is similar to the illumination system unit  100  but is different therefrom in terms of the first atmosphere of the first space AS 1  and second atmosphere of the second space AS 2  defined by the first housing  110  and the second housing  140 , respectively.  
         [0056]     Referring to  FIG. 5 , the illumination system unit  100 C has the lens unit  112  and optical member  120  inside the first space AS 1  defined by the first housing  110 . The first space AS 1  is maintained at a predetermined degree of vacuum by means of the evacuating pipe  160 , which are provided to the first housing  110 .  
         [0057]     In the illumination system unit  100 C, like the illumination system unit  100 , the motor  130  is disposed inside the second space AS 2  isolated from the first space AS 1 , and defined by the flange  132  and the second housing  140 . The second housing  140  has the evacuating pipe  170  and the second space AS 2  can be evacuated and kept at a predetermined degree of vacuum, aside from the first space AS 1 .  
         [0058]     Thus, the exhaust gas from the motor  130  neither fills the second space AS 2  nor leaks to the first space AS 1  from the second space AS 2 . Note that the pressure of the second space AS 2  is set equal to or lower than that of the first space AS 1 , making it possible to prevent the exhaust gas from leaking without applying a large load to the sealing members  136  and  142 . Further, the negative pressure aids in preventing the exhaust gas from the motor  130  from leaking from the second space AS 2  to the first space AS 1  even if the sealing member  142  deteriorates.  
         [0059]     Accordingly, the illumination system unit  100 C can prevent a photochemical reaction between the exposure light EL and the exhaust gas from the motor  130 , prevent any contaminant from adhering to an optical element (i.e., the lens unit  112  or filter  124 ) surface, realize a high throughput, and exert a satisfactory imaging performance.  
         [0060]     Referring next to  FIG. 6 , an illumination system unit  100 D as still another modified example of the illumination system unit  100  shown in  FIG. 2  will be described.  FIG. 6  is a schematic sectional view showing a structure of the illumination system unit  100 D as the modified example of the illumination system unit  100  shown in  FIG. 2 . The illumination system unit  100 D is similar to the illumination system unit  100  but is different therefrom in terms of the structure of the flange  190 .  
         [0061]     Referring to  FIG. 6 , the motor  130  has an ordinary shape and is fixed to the flange  190  through a fixing member  180 . Bolts  182  are used to connect the motor  130  and the fixing member  180 , and the fixing member  180  and the flange  190 . Note that a sealing member  192  is provided to the flange  190  for keeping air-tightness between the flange  190  and the drive shaft  134  of the motor  130 . Hence, a structure sealing the drive shaft  134  can be obtained only by using the bolts  182  for connection among the motor  130 , the fixing member  180 , and the flange  190 .  
         [0062]     The second housing  140  is attached to the flange  190  so as to accommodate the motor  130  and the fixing member  180 , through the sealing member  142  such as an O-ring. The motor wiring  137  and a motor connector  138  are connected to a device (e.g., power supply) outside the exposure apparatus  1  by means of wiring (not shown) through the air-tight connector  148  provided to the second housing  140 .  
         [0063]     Similar to the illumination system unit  100 , the second housing  140  has the pipe  144  for supplying the inert gas, and the pipe  146  for exhausting. Thus, the second space AS 2  can be purged with the inert gas aside from the first space AS 1 . The second space AS 2  is thereby supplied with a clean inert gas and the air is exhausted therefrom all the time, preventing the exhaust gas from the motor  130  from leaking to the first space AS 1 .  
         [0064]     In this way, the illumination system unit  100 D can block out a current of the exhaust gas from the motor  130  and is also applicable to the exposure apparatus  1  irrespective of the shape of the motor  130  and the gas-producing property of a member constituting the motor  130 . In other words, the illumination system unit  100 D can prevent a photochemical reaction between the exposure light EL and the exhaust gas from the motor  130 , prevent any contaminant from adhering to an optical element (i.e., the lens unit  112  or filter  124 ) surface, realize a high throughput, and exert a satisfactory imaging performance. Note that in the illumination system unit  100 D, although both the first space AS 1  and the second space AS 2  are purged with the inert gas, the same effect can be obtained even if the first space AS 1  (or second space AS 2 ) is purged with the inert gas and the second space AS 2  (or first space AS 1 ) is evacuated to a predetermined degree of vacuum, or both the first space AS 1  and the second space AS 2  are evacuated to a predetermined degree of vacuum.  
         [0065]     As described above, with the illumination system units  100 ,  100 A,  100 B,  100 C, and  100 D, it is possible to prevent reduction in throughput and deterioration in imaging performance caused by the adherence of the exhaust gas from a member having gas-producing property, which constitutes the motor, to a lens, a mirror, or the like. In particular, in the case of using a laser having a short wavelength such as an F2 laser, which is absorbed by the moisture or oxygen, the reduction in the transmissivity of the exposure beam due to the absorption of the exposure beam by the air or moisture existent coming out from the motor can be suppressed by a simple configuration. Also, even if the exposure apparatus  1  is open for maintenance etc., the air can be kept from intruding in a minute space in the motor.  
         [0066]     Referring back to  FIG. 1 , the reticle  20  is made of, for example, quartz, a circuit pattern (or image) to be transferred is formed thereon, and the reticle is supported and driven by a reticle stage (not shown). The diffraction ray from the reticle  20  is projected onto the object to be processed  40  through the projection optical system  30 . The reticle  20  and object to be processed  40  are optically conjugated with each other. The exposure apparatus  1  of this embodiment is a scanner and thus scans the object to be processed  40  and the reticle  20  at a scanning rate ratio corresponding to a reduction ratio, whereby the pattern on the reticle  20  is transferred onto the object to be processed  40 . Note that with an exposure apparatus employing a step-and-repeat process (also called “stepper”), exposure is carried out in a state where the reticle  20  and the object to be processed  40  stand still.  
         [0067]     The projection optical system  30  projects a circuit pattern formed on the reticle  20 , in a reduced form, to the object to be processed  40 . As the projection optical system  30 , an optical system composed exclusively of plural lens elements, an optical system composed of a plurality of lens elements and at least one concave mirror (catadioptric optical system), an optical system composed of a plurality of lens elements and at least one diffractive optical element such as kinoform, and an optical system composed entirely of mirrors can be used. If chromatic aberration needs to be corrected, a plurality of lens elements made of glass materials different from each other in dispersion value (Abbe number) may be used; alternatively, the diffractive optical element is configured so as to involve dispersion opposite to that of the lens element. A projection system unit is applicable to the projection optical system  30  as well, similarly to the illumination system unit  100 , the projection system unit including the first housing that defines the first space kept at the first atmosphere and the second housing  140  that is isolated from the first atmosphere and accommodated inside the first housing to define the second space kept at the second atmosphere, and having a double structure. This makes it possible to prevent a photochemical reaction between the exposure light and the contaminant existent in the projection optical system  30 , keep the contaminant from adhering to the optical element surface, realize a high throughput, and exert a satisfactory imaging performance.  
         [0068]     The object to be processed  40  is a wafer in this embodiment but includes a wide variety of objects to be processed, for example, a liquid crystal substrate. The object to be processed  40  is applied with a photoresist. A photoresist application step includes a preprocess (upstream step), an adhesion improver applying process, a photoresist applying process, and a prebaking process. The preprocess includes cleaning, drying, and the like. The adhesion improver applying process is a surface modifying process for enhancing adhesion of a photoresist to a base (hydrophobilizing process through surfactant application), where the surface is coated with an organic film of hexamethyl-disilazane (HMDS) or the like or subjected to steaming. The prebaking process is a baking process but is softer than a baking process following the development and directed to remove a solvent.  
         [0069]     The stage  50  supports the object to be processed  40 . Any structure known in the art is applicable to the stage  50 , so an explanation of its detailed structure and operation is omitted here. For example, the stage  50  can move the object to be processed  40  in XY directions by use of a linear motor. The reticle  20  and the object to be processed  40  are scanned in synchronism with each other, for example. A laser interferometer is used, for example, to monitor the positions of the stage  50  and reticle stage (not shown), both of which are driven at a constant speed ratio. The stage  50  is placed on a stage surface table supported onto a floor etc. through a damper, for instance. The reticle stage and the projection optical system  30  are placed on a lens barrel surface table (not shown) supported to a base flame set on the floor etc., for example, through the damper.  
         [0070]     A light beam emitted from the light source portion  12  serves to subject the reticle  20  to Koehler illumination upon exposure by means of the illumination optical system  14 , for example. The light beam that is reflective of the reticle pattern after passing through the reticle  20  is reduced at a predetermined magnification (e.g., ¼ or ⅕) by the projection optical system  30  and focused on the object to be processed  40 .  
         [0071]     The exposure apparatus  1  can prevent a contaminant due to the exhaust gas from the motor, from adhering to the optical element surface by use of the illumination system units  100 ,  100 A,  100 B,  100 C, and  100 D or projection system unit (not shown), whereby a device (semiconductor device, LCD device, image pickup device (CCD etc.), thin-film magnetic head, etc.) can be offered with high resolution and throughput, and low cost.  
         [0072]     Hereinbelow, referring to  FIGS. 7 and 8 , an embodiment of a device manufacturing method using the aforementioned exposure apparatus  1  will be described.  FIG. 7  is a flowchart illustrative of how to manufacture a device (semiconductor chip such as an IC or LSI, LCD, CCD, etc.). Here, description is given taking manufacture of the semiconductor chip as an example. In step  1  (circuit design), a circuit design of the device is carried out. In step  2  (mask making), a mask having a designed circuit pattern formed thereon is made. In step  3  (wafer fabrication), a wafer is fabricated using silicon or other such materials. Step  4  (wafer processing) is referred to as an upstream process, in which a mask and wafer are used to form an actual circuit on the-wafer by means of a lithography technique of the present invention. Step  5  (packaging) is referred to as a downstream process, in which the wafer fabricated in step  4  is turned into a semiconductor chip and which includes an assembly step (dicing and bonding), a packaging step (chip encapsulation), or other such steps. In step  6  (testing), the semiconductor device manufactured in step  5  is subjected to tests for operation and durability, for example. The semiconductor device is manufactured through those steps, followed by shipment (step  7 ).  
         [0073]      FIG. 8  is a flowchart of a detailed process flow of the wafer processing in step  4 . In step  11  (oxidation), the wafer surface is oxidized. In step  12  (CVD), an insulating film is formed on the wafer surface. In step  13  (electrode formation), an electrode is formed on the wafer through evaporation etc. In step  14  (ion implantation), ions are implanted into the wafer. In step  15  (resist processing), a photoresist is applied onto the wafer. In step  16  (exposure), the circuit pattern of the mask is projected to the wafer through exposure by use of the exposure apparatus  1 . In step  17  (developing), the exposed wafer is developed. In step  18  (etching), a portion other than the developed resist image is etched off. In step  19  (resist stripping), an unnecessary resist after the etching is stripped off. Repeating those steps forms multiple circuit patterns on the wafer. The device manufacturing method according to the present invention makes it possible to manufacture the device with a quality higher than conventional ones. As set forth above, the device manufacturing method using the lithography technique of the present invention, and its resulting device are regarded as an embodiment of the present invention.  
         [0074]     The preferred embodiment of the present invention has been described so far. However, the present invention is not limited thereto but allows various modifications and changes without departing from the gist of the invention. For example, the present invention is applicable to an EUV exposure apparatus using EUV light beam as a light source. Also, the member accommodated in the second housing is not limited to the motor but may be members discharging contaminants.  
         [0075]     The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention the following claims are made.  
         [0076]     This application claims priority from Japanese Patent Application No. 2003-402900 filed on Dec. 2, 2003, which is hereby incorporated by reference herein.