Abstract:
A liquid immersion exposure apparatus includes an optical assembly having a final optical element, from which exposure light is projected through immersion liquid filling an optical path of the exposure light under the final optical element, a containment member surrounding a tip portion of the optical assembly, and a movable stage to hold a substrate and having an upper surface around the held substrate. An apparatus frame supports the optical assembly and the containment member, and an optical mount isolator, which has an actuator, isolates the optical assembly from vibrations of the apparatus frame. A first inlet of the containment member faces at least one of the substrate and the stage and collects fluid from a gap between the containment member and the at least one of the substrate and the stage. A gas supply outlet of the containment member supplies gas to the gap.

Description:
RELATED APPLICATION 
     This is a Divisional of U.S. patent application Ser. No. 12/926,029 filed Oct. 21, 2010 (now U.S. Pat. No. 8,810,768), which in turn is a Divisional of U.S. patent application Ser. No. 11/701,378 filed Feb. 2, 2007 (now U.S. Pat. No. 8,089,610), which is a Divisional of U.S. patent application Ser. No. 11/237,799 filed Sep. 29, 2005 (now U.S. Pat. No. 7,321,415), which is a Continuation of International Application No. PCT/IB2004/002704 filed Mar. 29, 2004, which claims the benefit of U.S. Provisional Patent Application No. 60/462,112 filed on Apr. 10, 2003 and U.S. Provisional Patent Application No. 60/484,476 filed on Jul. 1, 2003. The disclosures of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Lithography exposure apparatus are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that positions a reticle, an optical assembly, a wafer stage assembly that positions a semiconductor wafer, and a measurement system that precisely monitors the position of the reticle and the wafer. 
     Immersion lithography systems utilize a layer of immersion fluid that completely fills a gap between the optical assembly and the wafer. The wafer is moved rapidly in a typical lithography system and it would be expected to carry the immersion fluid away from the gap. This immersion fluid that escapes from the gap can interfere with the operation of other components of the lithography system. For example, the immersion fluid and its vapor can interfere with the measurement system that monitors the position of the wafer. 
     SUMMARY 
     The invention is directed to an environmental system for controlling an environment in a gap between an optical assembly and a device that is retained by a device stage. The environmental system includes a fluid barrier and an immersion fluid system. The fluid barrier is positioned near the device and encircles the gap. The immersion fluid system delivers an immersion fluid that fills the gap. 
     In one embodiment, the immersion fluid system collects the immersion fluid that is directly between the fluid barrier and at least one of the device and the device stage. In this embodiment, the fluid barrier includes a scavenge inlet that is positioned near the device, and the immersion fluid system includes a low pressure source that is in fluid communication with the scavenge inlet. Additionally, the fluid barrier can confine and contain the immersion fluid and any of the vapor from the immersion fluid in the area near the gap. 
     In another embodiment, the environmental system includes a bearing fluid source that directs a bearing fluid between the fluid barrier and the device to support the fluid barrier relative to the device. In this embodiment, the fluid barrier includes a bearing outlet that is positioned near the device. Further, the bearing outlet is in fluid communication with the bearing fluid source. 
     Additionally, the environmental system can include a pressure equalizer that allows the pressure in the gap to be approximately equal to the pressure outside the fluid barrier. In one embodiment, for example, the pressure equalizer is a channel that extends through the fluid barrier. 
     Moreover, the device stage can include a stage surface that is in approximately the same plane as an exposed surface of the device. As an example, the device stage can include a device holder that retains the device, a guard that defines the stage surface, and a mover assembly that moves one of the device holder and the guard so that the exposed surface of the device is approximately in the same plane as the stage surface. In one embodiment, the mover assembly moves the guard relative to the device and the device holder. In another embodiment, the mover assembly moves the device holder and the device relative to the guard. 
     The invention also is directed to an exposure apparatus, a wafer, a device, a method for controlling an environment in a gap, a method for making an exposure apparatus, a method for making a device, and a method for manufacturing a wafer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in conjunction with the following drawings of exemplary embodiments in which like reference numerals designate like elements, and in which: 
         FIG. 1  is a side illustration of an exposure apparatus having features of the invention; 
         FIG. 2A  is a cut-away view taken on line  2 A- 2 A of  FIG. 1 ; 
         FIG. 2B  is a cut-away view taken on line  2 B- 2 B of  FIG. 2A ; 
         FIG. 2C  is a perspective view of a containment frame having features of the invention; 
         FIG. 2D  is an enlarged detailed view taken on line  2 D- 2 D in  FIG. 2B ; 
         FIG. 2E  is an illustration of the portion of the exposure apparatus of  FIG. 2A  with a wafer stage moved relative to an optical assembly; 
         FIG. 3  is a side illustration of an injector/scavenge source having features of the invention; 
         FIG. 4A  is an enlarged detailed view of a portion of another embodiment of a fluid barrier; 
         FIG. 4B  is an enlarged detailed view of a portion of another embodiment of a fluid barrier; 
         FIG. 4C  is an enlarged detailed view of a portion of another embodiment of a fluid barrier; 
         FIG. 5A  is a cut-away view of a portion of another embodiment of an exposure apparatus; 
         FIG. 5B  is an enlarged detailed view taken on line  5 B- 5 B in  FIG. 5A ; 
         FIG. 6  is a perspective view of one embodiment of a device stage having features of the invention; 
         FIG. 7A  is a perspective view of another embodiment of a device stage having features of the invention; 
         FIG. 7B  is a cut-away view taken on line  7 B- 7 B in  FIG. 7A ; 
         FIG. 8A  is a flow chart that outlines a process for manufacturing a device in accordance with the invention; and 
         FIG. 8B  is a flow chart that outlines device processing in more detail. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a schematic illustration of a precision assembly, namely an exposure apparatus  10  having features of the invention. The exposure apparatus  10  includes an apparatus frame  12 , an illumination system  14  (irradiation apparatus), an optical assembly  16 , a reticle stage assembly  18 , a device stage assembly  20 , a measurement system  22 , a control system  24 , and a fluid environmental system  26 . The design of the components of the exposure apparatus  10  can be varied to suit the design requirements of the exposure apparatus  10 . 
     A number of Figures include an orientation system that illustrates an X axis, a Y axis that is orthogonal to the X axis, and a Z axis that is orthogonal to the X and Y axes. It should be noted that these axes can also be referred to as the first, second and third axes. 
     The exposure apparatus  10  is particularly useful as a lithographic device that transfers a pattern (not shown) of an integrated circuit from a reticle  28  onto a semiconductor wafer  30  (illustrated in phantom). The wafer  30  is also referred to generally as a device or work piece. The exposure apparatus  10  mounts to a mounting base  32 , e.g., the ground, a base, or floor or some other supporting structure. 
     There are a number of different types of lithographic devices. For example, the exposure apparatus  10  can be used as a scanning type photolithography system that exposes the pattern from the reticle  28  onto the wafer  30  with the reticle  28  and the wafer  30  moving synchronously. In a scanning type lithographic device, the reticle  28  is moved perpendicularly to an optical axis of the optical assembly  16  by the reticle stage assembly  18  and the wafer  30  is moved perpendicularly to the optical axis of the optical assembly  16  by the wafer stage assembly  20 . Irradiation of the reticle  28  and exposure of the wafer  30  occur while the reticle  28  and the wafer  30  are moving synchronously. 
     Alternatively, the exposure apparatus  10  can be a step-and-repeat type photolithography system that exposes the reticle  28  while the reticle  28  and the wafer  30  are stationary. In the step and repeat process, the wafer  30  is in a constant position relative to the reticle  28  and the optical assembly  16  during the exposure of an individual field. Subsequently, between consecutive exposure steps, the wafer  30  is consecutively moved with the wafer stage assembly  20  perpendicularly to the optical axis of the optical assembly  16  so that the next field of the wafer  30  is brought into position relative to the optical assembly  16  and the reticle  28  for exposure. Following this process, the images on the reticle  28  are sequentially exposed onto the fields of the wafer  30 , and then the next field of the wafer  30  is brought into position relative to the optical assembly  16  and the reticle  28 . 
     However, the use of the exposure apparatus  10  provided herein is not limited to a photolithography system for semiconductor manufacturing. The exposure apparatus  10 , for example, can be used as an LCD photolithography system that exposes a liquid crystal display device pattern onto a rectangular glass plate or a photolithography system for manufacturing a thin film magnetic head. 
     The apparatus frame  12  supports the components of the exposure apparatus  10 . The apparatus frame  12  illustrated in  FIG. 1  supports the reticle stage assembly  18 , the wafer stage assembly  20 , the optical assembly  16  and the illumination system  14  above the mounting base  32 . 
     The illumination system  14  includes an illumination source  34  and an illumination optical assembly  36 . The illumination source  34  emits a beam (irradiation) of light energy. The illumination optical assembly  36  guides the beam of light energy from the illumination source  34  to the optical assembly  16 . The beam illuminates selectively different portions of the reticle  28  and exposes the wafer  30 . In  FIG. 1 , the illumination source  34  is illustrated as being supported above the reticle stage assembly  18 . Typically, however, the illumination source  34  is secured to one of the sides of the apparatus frame  12  and the energy beam from the illumination source  34  is directed to above the reticle stage assembly  18  with the illumination optical assembly  36 . 
     The illumination source  34  can be a light source such as a mercury g-line source (436 nm) or i-line source (365 nm), a KrF excimer laser (248 nm), an ArF excimer laser (193 nm) or a F 2  laser (157 nm). The optical assembly  16  projects and/or focuses the light passing through the reticle  28  onto the wafer  30 . Depending upon the design of the exposure apparatus  10 , the optical assembly  16  can magnify or reduce the image illuminated on the reticle  28 . It also could be a 1× magnification system. 
     When far ultra-violet radiation such as from the excimer laser is used, glass materials such as quartz and fluorite that transmit far ultra-violet rays can be used in the optical assembly  16 . The optical assembly  16  can be either catadioptric or refractive. 
     Also, with an exposure device that employs radiation of wavelength 200 nm or lower, use of the catadioptric type optical system can be considered. Examples of the catadioptric type of optical system are shown in Japanese Laid-Open Patent Application Publication No. 8-171054 and its counterpart U.S. Pat. No. 5,668,672, as well as Japanese Laid-Open Patent Application Publication No. 10-20195 and its counterpart U.S. Pat. No. 5,835,275. In these cases, the reflecting optical device can be a catadioptric optical system incorporating a beam splitter and concave mirror. Japanese Laid-Open Patent Application Publication No. 8-334695 and its counterpart U.S. Pat. No. 5,689,377 as well as Japanese Laid-Open Patent Application Publication No. 10-3039 and its counterpart U.S. Pat. No. 873,605 (Application Date: Jun. 12, 1997) also use a reflecting-refracting type of optical system incorporating a concave mirror, etc., but without a beam splitter, and can also be employed with this invention. The disclosures of the above-mentioned U.S. patents and application, as well as the Japanese Laid-Open patent applications publications are incorporated herein by reference in their entireties. 
     In one embodiment, the optical assembly  16  is secured to the apparatus frame  12  with one or more optical mount isolators  37 . The optical mount isolators  37  inhibit vibration of the apparatus frame  12  from causing vibration to the optical assembly  16 . Each optical mount isolator  37  can include a pneumatic cylinder (not shown) that isolates vibration and an actuator (not shown) that isolates vibration and controls the position with at least two degrees of motion. Suitable optical mount isolators  37  are sold by Integrated Dynamics Engineering, located in Woburn, Mass. For ease of illustration, two spaced apart optical mount isolators  37  are shown as being used to secure the optical assembly  16  to the apparatus frame  12 . However, for example, three spaced apart optical mount isolators  37  can be used to kinematically secure the optical assembly  16  to the apparatus frame  12 . 
     The reticle stage assembly  18  holds and positions the reticle  28  relative to the optical assembly  16  and the wafer  30 . In one embodiment, the reticle stage assembly  18  includes a reticle stage  38  that retains the reticle  28  and a reticle stage mover assembly  40  that moves and positions the reticle stage  38  and reticle  28 . 
     Somewhat similarly, the device stage assembly  20  holds and positions the wafer  30  with respect to the projected image of the illuminated portions of the reticle  28 . In one embodiment, the device stage assembly  20  includes a device stage  42  that retains the wafer  30 , a device stage base  43  that supports and guides the device stage  42 , and a device stage mover assembly  44  that moves and positions the device stage  42  and the wafer  30  relative to the optical assembly  16  and the device stage base  43 . The device stage  42  is described in more detail below. 
     Each stage mover assembly  40 ,  44  can move the respective stage  38 ,  42  with three degrees of freedom, less than three degrees of freedom, or more than three degrees of freedom. For example, in alternative embodiments, each stage mover assembly  40 ,  44  can move the respective stage  38 ,  42  with one, two, three, four, five or six degrees of freedom. The reticle stage mover assembly  40  and the device stage mover assembly  44  can each include one or more movers, such as rotary motors, voice coil motors, linear motors utilizing a Lorentz force to generate drive force, electromagnetic movers, planar motors, or other force movers. 
     Alternatively, one of the stages could be driven by a planar motor that drives the stage by an electromagnetic force generated by a magnet unit having two-dimensionally arranged magnets and an armature coil unit having two-dimensionally arranged coils in facing positions. With this type of driving system, either the magnet unit or the armature coil unit is connected to the stage base and the other unit is mounted on the moving plane side of the stage. 
     Movement of the stages as described above generates reaction forces that can affect performance of the photolithography system. Reaction forces generated by the wafer (substrate) stage motion can be mechanically transferred to the floor (ground) by use of a frame member as described in U.S. Pat. No. 5,528,100 and Japanese Laid-Open Patent Application Publication No. 8-136475. Additionally, reaction forces generated by the reticle (mask) stage motion can be mechanically transferred to the floor (ground) by use of a frame member as described in U.S. Pat. No. 5,874,820 and Japanese Laid-Open Patent Application Publication No. 8-330224. The disclosures of U.S. Pat. Nos. 5,528,100 and 5,874,820 and Japanese Laid-Open Patent Application Publication Nos. 8-136475 and 8-330224 are incorporated herein by reference in their entireties. 
     The measurement system  22  monitors movement of the reticle  28  and the wafer  30  relative to the optical assembly  16  or some other reference. With this information, the control system  24  can control the reticle stage assembly  18  to precisely position the reticle  28  and the device stage assembly  20  to precisely position the wafer  30 . The design of the measurement system  22  can vary. For example, the measurement system  22  can utilize multiple laser interferometers, encoders, mirrors, and/or other measuring devices. The stability of the measurement system  22  is essential for accurate transfer of an image from the reticle  28  to the wafer  30 . 
     The control system  24  receives information from the measurement system  22  and controls the stage mover assemblies  40 ,  44  to precisely position the reticle  28  and the wafer  30 . Additionally, the control system  24  can control the operation of the environmental system  26 . The control system  24  can include one or more processors and circuits. 
     The environmental system  26  controls the environment in a gap  246  (illustrated in  FIG. 2B ) between the optical assembly  16  and the wafer  30 . The gap  246  includes an imaging field  250  (illustrated in  FIG. 2A ). The imaging field  250  includes the area adjacent to the region of the wafer  30  that is being exposed and the area in which the beam of light energy travels between the optical assembly  16  and the wafer  30 . With this design, the environmental system  26  can control the environment in the imaging field  250 . 
     The desired environment created and/or controlled in the gap  246  by the environmental system  26  can vary according to the wafer  30  and the design of the rest of the components of the exposure apparatus  10 , including the illumination system  14 . For example, the desired controlled environment can be a fluid such as water. The environmental system  26  is described in more detail below. 
     A photolithography system (an exposure apparatus) according to the embodiments described herein can be built by assembling various subsystems in such a manner that prescribed mechanical accuracy, electrical accuracy, and optical accuracy are maintained. In order to maintain the various accuracies, prior to and following assembly, every optical system is adjusted to achieve its optical accuracy. Similarly, every mechanical system and every electrical system are adjusted to achieve their respective mechanical and electrical accuracies. The process of assembling each subsystem into a photolithography system includes mechanical interfaces, electrical circuit wiring connections and air pressure plumbing connections between each subsystem. Needless to say, there also is a process where each subsystem is assembled prior to assembling a photolithography system from the various subsystems. Once a photolithography system is assembled using the various subsystems, a total adjustment is performed to make sure that accuracy is maintained in the complete photolithography system. Additionally, it is desirable to manufacture an exposure system in a clean room where the temperature and cleanliness are controlled. 
       FIG. 2A  is a cut-away view taken on line  2 A- 2 A in  FIG. 1  that illustrates a portion of the exposure apparatus  10  including the optical assembly  16 , the device stage  42 , the environmental system  26 , and the wafer  30 . The imaging field  250  (illustrated in phantom) also is illustrated in  FIG. 2A . 
     In one embodiment, the environmental system  26  fills the imaging field  250  and the rest of the gap  246  (illustrated in  FIG. 2B ) with an immersion fluid  248  (illustrated in  FIG. 2B ). As used herein, the term “fluid” shall mean and include a liquid and/or a gas, including any fluid vapor. 
     The design of the environmental system  26  and the components of the environmental system  26  can be varied. In the embodiment illustrated in  FIG. 2A , the environmental system  26  includes an immersion fluid system  252  and a fluid barrier  254 . In this embodiment, (i) the immersion fluid system  252  delivers and/or injects the immersion fluid  248  into the gap  246  and captures the immersion fluid  248  flowing from the gap  246 , and (ii) the fluid barrier  254  inhibits the flow of the immersion fluid  248  away from near the gap  246 . 
     The design of the immersion fluid system  252  can vary. For example, the immersion fluid system  252  can inject the immersion fluid  248  at one or more locations at or near the gap  246  and/or the edge of the optical assembly  16 . Alternatively, the immersion fluid  248  may be injected directly between the optical assembly  16  and the wafer  30 . Further, the immersion fluid system  252  can scavenge the immersion fluid  248  at one or more locations at or near the gap  246  and/or the edge of the optical assembly  16 . In the embodiment illustrated in  FIG. 2A , the immersion fluid system  252  includes four spaced apart injector/scavenge pads  258  (illustrated in phantom) positioned near the perimeter of the optical assembly  16  and an injector/scavenge source  260 . These components are described in more detail below. 
       FIG. 2A  also illustrates that the optical assembly  16  includes an optical housing  262 A, a last optical element  262 B, and an element retainer  262 C that secures the last optical element  262 B to the optical housing  262 A. 
       FIG. 2B  is a cut-away view of the portion of the exposure apparatus  10  of  FIG. 2A , including (i) the optical assembly  16  with the optical housing  262 A, the last optical element  262 B, and the element retainer  262 C, (ii) the device stage  42 , and (iii) the environmental system  26 .  FIG. 2B  also illustrates the gap  246  between the last optical element  262 B and the wafer  30 , and that the immersion fluid  248  (illustrated as circles) fills the gap  246 . In one embodiment, the gap  246  is approximately 1 mm. 
     In one embodiment, the fluid barrier  254  contains the immersion fluid  248 , including any fluid vapor  249  (illustrated as triangles) in the area near the gap  246  and forms and defines an interior chamber  263  around the gap  246 . In the embodiment illustrated in  FIG. 2B , the fluid barrier  254  includes a containment frame  264  (also referred to herein as a surrounding member), a seal  266 , and a frame support  268 . The interior chamber  263  represents the enclosed volume defined by the containment frame  264 , the seal  266 , the optical housing  262 A and the wafer  30 . The fluid barrier  254  restricts the flow of the immersion fluid  248  from the gap  246 , assists in maintaining the gap  246  full of the immersion fluid  248 , allows for the recovery of the immersion fluid  248  that escapes from the gap  246 , and contains any vapor  249  produced from the fluid. In one embodiment, the fluid barrier  254  encircles and runs entirely around the gap  246 . Further, in one embodiment, the fluid barrier  254  confines the immersion fluid  248  and its vapor  249  to a region on the wafer  30  and the device stage  42  centered on the optical assembly  16 . 
     Containment of both the immersion fluid  248  and its vapor  249  can be important for the stability of the lithography tool. For example, stage measurement interferometers are sensitive to the index of refraction of the ambient atmosphere. For the case of air with some water vapor present at room temperature and 633 nm laser light for the interferometer beam, a change of 1% in relative humidity causes a change in refractive index of approximately 10 −8 . For a 1 m total beam path, this can represent an error of 10 nm in stage position. If the immersion fluid  248  is water, a droplet of water 7 mm in diameter evaporating into a 1 m 3  volume changes the relative humidity by 1%. Relative humidity is typically monitored and corrected for by the control system  24 , but this is based on the assumption that the relative humidity is uniform, so that its value is the same in the interferometer beams as at the monitoring point. However, if droplets of water and its attendant vapor are scattered around on the wafer and stage surfaces, the assumption of uniform relative humidity may not be valid. 
     In addition to the risk to the interferometer beams, water evaporation may also create temperature control problems. The heat of vaporization of water is about 44 kJ/mole. Evaporation of the 7 mm drop mentioned above will absorb about 430 J which must be supplied by the adjacent surfaces. 
       FIG. 2C  illustrates a perspective view of one embodiment of the containment frame  264 . In this embodiment, the containment frame  264  is annular ring shaped and encircles the gap  246  (illustrated in  FIG. 2B ). Additionally, in this embodiment, the containment frame  264  includes a top side  270 A, an opposite bottom side  270 B (also referred to as a first surface) that faces the wafer  30 , an inner side  270 C that faces the gap  246 , and an outer side  270 D. The terms top and bottom are used merely for convenience, and the orientation of the containment frame  264  can be rotated. The containment frame  264  can have another shape. Alternatively, for example, the containment frame  264  can be rectangular frame shaped or octagonal frame shaped. 
     Additionally, as provided herein, the containment frame  264  may be temperature controlled to stabilize the temperature of the immersion fluid  248 . 
     Referring back to  FIG. 2B , the seal  266  seals the containment frame  264  to the optical assembly  16  and allows for some motion of the containment frame  264  relative to the optical assembly  16 . In one embodiment, the seal  266  is made of a flexible, resilient material that is not influenced by the immersion fluid  248 . Suitable materials for the seal  266  include rubber, Buna-N, neoprene, Viton or plastic. Alternatively the seal  266  may be a bellows made of a metal such as stainless steel or rubber or a plastic. 
       FIG. 2D  illustrates an enlarged view of a portion of  FIG. 2B , in partial cut-away. The frame support  268  connects and supports the containment frame  264  to the apparatus frame  12  and the optical assembly  16  above the wafer  30  and the device stage  42 . In one embodiment, the frame support  268  supports all of the weight of the containment frame  264 . Alternatively, for example, the frame support  268  can support only a portion of the weight of the containment frame  264 . In one embodiment, the frame support  268  can include one or more support assemblies  274 . For example, the frame support  268  can include three spaced apart support assemblies  274  (only two are illustrated). In this embodiment, each support assembly  274  extends between the apparatus frame  12  and the top side  270 A of the containment frame  264 . 
     In one embodiment, each support assembly  274  is a flexure. As used herein, the term “flexure” shall mean a part that has relatively high stiffness in some directions and relatively low stiffness in other directions. In one embodiment, the flexures cooperate (i) to be relatively stiff along the X axis and along the Y axis, and (ii) to be relatively flexible along the Z axis. The ratio of relatively stiff to relatively flexible is at least approximately 100/1, and can be at least approximately 1000/1. Stated another way, the flexures can allow for motion of the containment frame  264  along the Z axis and inhibit motion of the containment frame  264  along the X axis and the Y axis. In this embodiment, each support assembly  274  passively supports the containment frame  264 . 
     Alternatively, for example, each support assembly  274  can be an actuator that can be used to adjust the position of the containment frame  264  relative to the wafer  30  and the device stage  42 . Additionally, the frame support  268  can include a frame measurement system  275  that monitors the position of the containment frame  264 . For example, the frame measurement system  275  can monitor the position of the containment frame  264  along the Z axis, about the X axis, and/or about the Y axis. With this information, the support assemblies  274  can be used to adjust the position of the containment frame  264 . In this embodiment, each support assembly  274  can actively adjust the position of the containment frame  264 . 
     In one embodiment, the environmental system  26  includes one or more pressure equalizers  276  that can be used to control the pressure in the chamber  263 . Stated another way, the pressure equalizers  276  inhibit atmospheric pressure changes or pressure changes associated with the fluid control from creating forces between the containment frame  264  and the wafer  30  or the last optical element  262 B. For example, the pressure equalizers  276  can cause the pressure on the inside of the chamber  263  and/or in the gap  246  to be approximately equal to the pressure on the outside of the chamber  263 . For example, each pressure equalizer  276  can be a channel that extends through the containment frame  264 . In one embodiment, a tube  277  (only one is illustrated) is attached to the channel of each pressure equalizer  276  to convey any fluid vapor away from the measurement system  22  (illustrated in  FIG. 1 ). In alternative embodiments, the pressure equalizer  276  allows for a pressure difference of less than approximately 0.01, 0.05, 0.1, 0.5, or 1.0 PSI. 
       FIG. 2B  also illustrates several injector/scavenge pads  258 .  FIG. 2D  illustrates one injector/scavenge pad  258  in more detail. In this embodiment, each of the injector/scavenge pads  258  includes a pad outlet  278 A and a pad inlet  278 B that are in fluid communication with the injector/scavenge source  260 . At the appropriate time, the injector/scavenge source  260  provides immersion fluid  248  to the pad outlet  278 A that is released into the chamber  263  and draws immersion fluid  248  through the pad inlet  278 B from the chamber  263 . 
       FIGS. 2B and 2D  also illustrate that the immersion fluid  248  in the chamber  263  sits on top of the wafer  30 . As the wafer  30  moves under the optical assembly  16 , it will drag the immersion fluid  248  in the vicinity of a top, device surface  279  of the wafer  30  with the wafer  30  into the gap  246 . 
     In one embodiment, referring to  FIGS. 2B and 2D , the device stage  42  includes a stage surface  280  that has approximately the same height along the Z axis as the top, exposed surface  279  of the wafer  30 . Stated another way, in one embodiment, the stage surface  280  is in approximately the same plane as the exposed surface  279  of the wafer  30 . In alternative embodiments, for example, approximately the same plane shall mean that the planes are within approximately 1, 10, 100 or 500 microns. As a result thereof, the distance between the bottom side  270 B of the containment frame  264  and the wafer  30  is approximately equal to the distance between the bottom side  270 B of the containment frame  264  and the device stage  42 . In one embodiment, for example, the device stage  42  can include a disk shaped recess  282  for receiving the wafer  30 . Some alternative designs of the device stage  42  are discussed below. 
       FIG. 2D  illustrates that a frame gap  284  exists between the bottom side  270 B of the containment frame  264  and the wafer  30  and/or the device stage  42  to allow for ease of movement of the device stage  42  and the wafer  30  relative to the containment frame  264 . The size of the frame gap  284  can vary. For example, the frame gap  284  can be between approximately 5 μm and 3 mm. In alternative examples, the frame gap  284  can be approximately 5, 10, 50, 100, 150, 200, 250, 300, 400, or 500 microns. 
     In certain embodiments, the distance between the bottom side  270 B and at least one of the wafer  30  and/or the device stage  42  is shorter than a distance between the end surface (e.g., the last optical element  262 B or the bottom of the optical housing  262 A) of the optical assembly  16  and at least one of the wafer  30  and/or the device stage  42 . 
     Additionally, a wafer gap  285  can exist between the edge of the wafer  30  and the wafer stage  42 . In one embodiment, the wafer gap  285  is as narrow as possible to minimize leakage when the wafer  30  is off-center from the optical assembly  16  and lying partly within and partly outside the fluid containment frame  264  region. For example, in alternative embodiments, the wafer gap  285  can be approximately 1, 10, 50, 100, 500, or 1000 microns. 
       FIG. 2D  also illustrates that some of the immersion fluid  248  flows between the containment frame  264  and the wafer  30  and/or the device stage  42 . In one embodiment, the containment frame  264  includes one or more scavenge inlets  286  that are positioned at or near the bottom side  270 B of the containment frame  264 . The one or more scavenge inlets  286  are in fluid communication with the injector/scavenge source  260  (illustrated in  FIG. 2B ). With this design, the immersion fluid  248  that escapes in the frame gap  284  can be scavenged by the injector/scavenge source  260 . In the embodiment illustrated in  FIG. 2D , the bottom side  270 B of the containment frame  264  includes one scavenge inlet  286  that is substantially annular groove shaped and is substantially concentric with the optical assembly  16 . Alternatively, for example, the bottom side  270 B of the containment frame  264  can include a plurality of spaced apart annular groove shaped, scavenge inlets  286  that are substantially concentric with the optical assembly  16  to inhibit the immersion fluid  248  from completely exiting the frame gap  284 . Still alternatively, a plurality of spaced apart apertures oriented in a circle can be used instead of an annular shaped groove. 
     In one embodiment, the injector/scavenge source  260  applies a vacuum and/or partial vacuum on the scavenge inlet  286 . The partial vacuum draws the immersion fluid  248  between (i) a small land area  288  on the bottom side  270 B, and (ii) the wafer  30  and/or the device stage  42 . The immersion fluid  248  in the frame gap  284  acts as a fluid bearing  289 A (illustrated as an arrow) that supports the containment frame  264  above the wafer  30  and/or the device stage  42 , allows for the containment frame  264  to float with minimal friction on the wafer  30  and/or the device stage  42 , and allows for a relatively small frame gap  284 . With this embodiment, most of the immersion fluid  248  is confined within the fluid barrier  254  and most of the leakage around the periphery is scavenged within the narrow frame gap  284 . 
     Additionally, the environmental system  26  can include a device for creating an additional fluid bearing  289 B (illustrated as an arrow) between the containment frame  264  and the wafer  30  and/or the device stage  42 . For example, the containment frame  264  can include one or more bearing outlets  290 A that are in fluid communication with a bearing fluid source  290 B of a bearing fluid  290 C (illustrated as triangles). In one embodiment, the bearing fluid  290 C is air. In this embodiment, the bearing fluid source  290 B provides pressurized air  290 C to the bearing outlet  290 A to create the aerostatic bearing  289 B. The fluid bearings  289 A,  289 B can support all or a portion of the weight of the containment frame  264 . In alternative embodiments, one or both of the fluid bearings  289 A,  289 B support approximately 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 percent of the weight of the containment frame  264 . In one embodiment, the concentric fluid bearings  289 A,  289 B are used to maintain the frame gap  284 . 
     Depending upon the design, the bearing fluid  290 C can have the same composition or a different composition than the immersion fluid  248 . However, some of the bearing fluid  290 C may escape from the fluid barrier  254 . In one embodiment, the type of bearing fluid  290 C is chosen so that the bearing fluid  290 C and its vapor do not interfere with the measurement system  22  or temperature stability of the exposure apparatus  10 . 
     In another embodiment, the partial vacuum in the scavenge inlets  286  pulls and urges the containment frame  264  toward the wafer  30 . In this embodiment, the fluid bearing  289 B supports part of the weight of the containment frame  264  as well as opposes the pre-load imposed by the partial vacuum in the scavenge inlets  286 . 
     In addition, the pressurized air  290 C helps to contain the immersion fluid  248  within the containment frame  264 . As provided above, the immersion fluid  248  in the frame gap  284  is mostly drawn out through the scavenge inlets  286 . In this embodiment, any immersion fluid  248  that leaks beyond the scavenge inlets  286  is pushed back to the scavenge inlets  286  by the bearing fluid  290 C. 
     The frame gap  284  may vary radially, from the inner side  270 C to the outer side  270 D, to optimize bearing and scavenging functions. 
     In  FIG. 2D , the bearing outlet  290 A is substantially annular groove shaped, is substantially concentric with the optical assembly  16  and the scavenge inlet  286 , and has a diameter that is greater than the diameter of the scavenge inlet  286 . Alternatively, for example, the bottom side  270 B of the containment frame  264  can include a plurality of spaced apart annular groove shaped, bearing outlets  290 A that are substantially concentric with the optical assembly  16 . Still alternatively, a plurality of spaced apart apertures oriented in a circle can be used instead of an annular shaped groove. Alternatively, for example, a magnetic type bearing could be used to support the containment frame  264 . 
     As illustrated in  FIGS. 2B and 2D , the wafer  30  is centered under the optical assembly  16 . In this position, the fluid bearings  289 A,  289 B support the containment frame  264  above the wafer  30 .  FIG. 2E  is an illustration of the portion of the exposure apparatus  10  of  FIG. 2A  with the device stage  42  and the wafer  30  moved relative to the optical assembly  16 . In this position, the wafer  30  and the device stage  42  are no longer centered under the optical assembly  16 , and the fluid bearings  289 A,  289 B (illustrated in  FIG. 2D ) support the containment frame  264  above the wafer  30  and the device stage  42 . 
       FIG. 3  is a first embodiment of the injector/scavenge source  260 . In this embodiment, the injector/scavenge source  260  includes (i) a low pressure source  392 A, e.g. a pump, having an inlet that is at a vacuum or partial vacuum that is in fluid communication with the scavenge inlet  286  (illustrated in  FIG. 2D ) and the pad inlets  278 B (illustrated in  FIGS. 2B and 2D ) and a pump outlet that provides pressurized immersion fluid  248 , (ii) a filter  392 B in fluid communication with the pump outlet and that filters the immersion fluid  248 , (iii) a de-aerator  392 C in fluid communication with the filter  392 B and that removes any air, contaminants, or gas from the immersion fluid  248 , (iv) a temperature control  392 D in fluid communication with the de-aerator  392 C and that controls the temperature of the immersion fluid  248 , (v) a reservoir  392 E in fluid communication with the temperature control  392 D and that retains the immersion fluid  248 , and (vi) a flow controller  392 F that has an inlet in fluid communication with the reservoir  392 E and an outlet in fluid communication with the pad outlets  278 A (illustrated in  FIGS. 2B and 2D ), the flow controller  392 F controlling the pressure and flow to the pad outlets  278 A. The operation of these components can be controlled by the control system  24  (illustrated in  FIG. 1 ) to control the flow rate of the immersion fluid  248  to the pad outlets  278 A, the temperature of the immersion fluid  248  at the pad outlets  278 A, the pressure of the immersion fluid  248  at the pad outlets  278 A, and/or the pressure at the scavenge inlets  286  and the pad inlets  278 B. 
     Additionally, the injector/scavenge source  260  can include (i) a pair of pressure sensors  392 G that measure the pressure near the pad outlets  278 A, the scavenge inlets  286  and the pad inlets  278 B, (ii) a flow sensor  392 H that measures the flow to the pad outlets  278 A, and/or (iii) a temperature sensor  392 I that measures the temperature of the immersion fluid  248  delivered to the pad outlets  278 A. The information from these sensors  392 G- 392 I can be transferred to the control system  24  so that that control system  24  can appropriately adjust the other components of the injector/scavenge source  260  to achieve the desired temperature, flow and/or pressure of the immersion fluid  248 . 
     The orientation of the components of the injector/scavenge source  260  can be varied. Further, one or more of the components may not be necessary and/or some of the components can be duplicated. For example, the injector/scavenge source  260  can include multiple pumps, multiple reservoirs, temperature controllers or other components. Moreover, the environmental system  26  can include multiple injector/scavenge sources  260 . 
     The rate at which the immersion fluid  248  is pumped into and out of the chamber  263  (illustrated in  FIG. 2B ) can be adjusted to suit the design requirements of the system. Further, the rate at which the immersion fluid  248  is scavenged from the pad inlets  278 B and the scavenge inlets  286  can vary. In one embodiment, the immersion fluid  248  is scavenged from the pad inlets  278 B at a first rate and is scavenged from the scavenge inlets  286  at a second rate. As an example, the first rate can be between approximately 0.1-5 liters/minute and the second rate can be between approximately 0.01-0.5 liters/minute. However, other first and second rates can be utilized. 
     The rates at which the immersion fluid  248  is pumped into and out of the chamber  263  can be adjusted to (i) control the leakage of the immersion fluid  248  below the fluid barrier, (ii) control the leakage of the immersion fluid  248  from the wafer gap  285  when the wafer  30  is off-center from the optical assembly  16 , and/or (iii) control the temperature and purity of the immersion fluid  248  in the gap  246 . For example, the rates can be increased in the event the wafer  30  is off-center, the temperature of the immersion fluid  248  becomes too high and/or there is an unacceptable percentage of contaminants in the immersion fluid  248  in the gap  246 . 
     The type of immersion fluid  248  can be varied to suit the design requirements of the apparatus  10 . In one embodiment, the immersion fluid  248  is water. Alternatively, for example, the immersion fluid  248  can be a fluorocarbon fluid, Fomblin oil, a hydrocarbon oil, or another type of oil. More generally, the fluid should satisfy certain conditions: 1) it must be relatively transparent to the exposure radiation; 2) its refractive index must be comparable to that of the last optical element  262 B; 3) it should not react chemically with components of the exposure system  10  with which it comes into contact; 4) it must be homogeneous; and 5) its viscosity should be low enough to avoid transmitting vibrations of a significant magnitude from the stage system to the last optical element  262 B. 
       FIG. 4A  is an enlarged view of a portion of another embodiment of the fluid barrier  454 A, a portion of the wafer  30 , and a portion of the device stage  42 . In this embodiment, the fluid barrier  454 A is somewhat similar to the corresponding component described above and illustrated in  FIG. 2D . However, in this embodiment, the containment frame  464 A includes two concentric, scavenge inlets  486 A that are positioned at the bottom side  470 B of the containment frame  464 A. The two scavenge inlets  486 A are in fluid communication with the injector/scavenge source  260  (illustrated in  FIG. 2B ). With this design, the immersion fluid  248  that escapes in the frame gap  284  can be scavenged by the injector/scavenge source  260 . In this embodiment, the bottom side  470 B of the containment frame  464  includes two scavenge inlets  486 A that are each substantially annular groove shaped and are substantially concentric with the optical assembly  16 . 
     With this design, the injector/scavenge source  260  applies a vacuum or partial vacuum on the scavenge inlets  486 A. The partial vacuum draws the immersion fluid  248  between a small land area  488  on the bottom side  470 B and the wafer  30  and/or the device stage  42 . In this embodiment, the majority of the immersion fluid  248  flows under the land  488  and into the inner scavenge inlet  486 A. Additionally, the immersion fluid  248  not removed at the inner scavenge inlet  486 A is drawn into the outer scavenge inlet  486 A. 
       FIG. 4B  is an enlarged view of a portion of another embodiment of the fluid barrier  454 B, a portion of the wafer  30 , and a portion of the device stage  42 . In this embodiment, the fluid barrier  454 B is somewhat similar to the corresponding component described above and illustrated in  FIG. 2D . However, in this embodiment, the containment frame  464 B includes one bearing outlet  490 B and two scavenge inlets  486 B that are positioned at the bottom side  470 B. The scavenge inlets  486 B are in fluid communication with the injector/scavenge source  260  (illustrated in  FIG. 2B ) and the bearing outlet  490 B is in fluid communication with the bearing fluid source  290 B (illustrated in  FIG. 2D ). However, in this embodiment, the bearing outlet  490 B is positioned within and concentric with the scavenge inlets  486 B. Stated another way, the bearing outlet  490 B has a smaller diameter than the scavenge inlets  486 B, and the bearing outlet  490 B is closer to the optical assembly  16  than the scavenge inlets  486 B. Further, with this design, the bearing fluid  290 C (illustrated in  FIG. 2D ) can be a liquid that is the same in composition as the immersion fluid  248 . With this design, the bearing fluid  290 C in the frame gap  284  can be scavenged by the injector/scavenge source  260  via the scavenge inlets  486 B. 
       FIG. 4C  is an enlarged view of a portion of another embodiment of the fluid barrier  454 C, a portion of the wafer  30 , and a portion of the device stage  42 . In this embodiment, the fluid barrier  454 C is somewhat similar to the corresponding component described above and illustrated in  FIG. 2D . However, in this embodiment, the containment frame  464 C includes one bearing outlet  490 C and two scavenge inlets  486 C that are positioned at the bottom side  470 B. The scavenge inlets  486 C are in fluid communication with the injector/scavenge source  260  (illustrated in  FIG. 2B ) and the bearing outlet  490 C is in fluid communication with the bearing fluid source  290 B (illustrated in  FIG. 2D ). However, in this embodiment, the bearing outlet  490 C is positioned between the two scavenge inlets  486 C. Stated another way, the inner scavenge inlet  486 C has a smaller diameter than the bearing outlet  490 C, and the bearing outlet  490 C has a smaller diameter than the outer scavenge inlet  486 C. With this design, the inner scavenge inlet  486 C is closer to the optical assembly  16  than the bearing outlet  490 C. 
     It should be noted that in each embodiment, additional scavenge inlets and addition bearing outlets can be added as necessary. 
       FIG. 5A  is a cut-away view of a portion of another embodiment of the exposure apparatus  510 , including the optical assembly  516 , the device stage  542 , and the environmental system  526  that are similar to the corresponding components described above.  FIG. 5A  also illustrates the wafer  30 , the gap  546 , and that the immersion fluid  548  fills the gap  546 .  FIG. 5B  illustrates an enlarged portion of  FIG. 5A  taken on line  5 B- 5 B. 
     However, in the embodiment illustrated in  FIGS. 5A and 5B , the fluid barrier  554  includes an inner barrier  555  in addition to the containment frame  564 , the seal  566 , and the frame support  568 . In this embodiment, the inner barrier  555  is annular ring shaped, encircles the bottom of the optical assembly  516 , is concentric with the optical assembly  516 , and is positioned within the containment frame  564  adjacent to the seal  566 . 
     The inner barrier  555  can serve several purposes. For example, the inner barrier  555  can limit the amount of immersion fluid  548  escaping to the containment frame  564 , reducing the scavenging requirements at the scavenge inlets  586 , and also reducing the leakage of immersion fluid  548  into the wafer gap  285  when the wafer  30  is off-center from the optical assembly  516  and lying partly within and partly outside the fluid containment frame  564  region. With this design, the fluid injection/scavenge pads  558  can be used to recover the majority of the immersion fluid  548  from the chamber  563 . Additionally, if the immersion fluid  548  is maintained at or near the level of the top of the inner barrier  555 , pressure surges associated with injection of the immersion fluid  548  can be reduced, because excess immersion fluid  548  overflows the top of the inner barrier  555 , creating a static pressure head. Some pressure surge may remain even in this situation due to surface tension effects. These effects can be reduced by increasing the height of the inner barrier  555  shown in  FIG. 5B . For example, if the immersion fluid is water, the height should preferably be several mm or more. Additionally, the remaining pressure surge can be reduced or eliminated by adjusting the “wettability” of the surfaces of inner barrier  555  and optical assembly  516  in contact with the immersion fluid  548  to reduce surface tension forces. In one embodiment, the inner barrier  555  can maintain a significant fluid height difference with a gap of approximately 50 μm between the bottom of the inner barrier  55  and the top of the wafer  30  or the device stage  42 . 
       FIG. 6  is a perspective view of one embodiment of a device stage  642  with a wafer  630  positioned above the device stage  642 . In this embodiment, the device stage  642  includes a device table  650 , a device holder  652 , a guard  654 , and a guard mover assembly  656 . In this embodiment, the device table  650  is generally rectangular plate shaped. The device holder  652  retains the wafer  630 . In this embodiment, the device holder  652  is a chuck or another type of clamp that is secured to the device table  650 . The guard  654  surrounds and/or encircles the wafer  630 . In one embodiment, the guard  654  is generally rectangular plate shaped and includes a circular shaped aperture  658  for receiving the wafer  630 . 
     In one embodiment, the guard  654  can include a first section  660  and a second section  662 . One or more of the sections  660 ,  662  can be moved, removed or recessed to provide easy access for loading and removing the wafer  630 . 
     The guard mover assembly  656  secures the guard  654  to the device table  650 , and moves and positions the guard  654  relative to the device table  650 , the device holder  652 , and the wafer  630 . With this design, the guard mover assembly  656  can move the guard  654  so that the top, stage surface  680  of the guard  654  is approximately at the same Z height as the top exposed surface  679  of the wafer  630 . Stated another way, the guard mover assembly  656  moves the guard  654  so that the stage surface  680  is approximately in the same plane as the exposed surface  679  of the wafer  630 . As a result thereof, the guard  654  can be moved to adjust for wafers  630  of alternative heights. 
     The design of the guard mover assembly  656  can be varied. For example, the guard mover assembly  656  can include one or more rotary motors, voice coil motors, linear motors, electromagnetic actuators, and/or other type of force actuators. In one embodiment, the guard mover assembly  656  moves and positions the guard  654  along the Z axis, about the X axis and about the Y axis under the control of the control system  24  (illustrated in  FIG. 1 ). A sensor  681  (illustrated as a box) can be used to measure the relative heights of the guard surface  680  and the wafer top surface  679 . Information from the sensor  681  can be transferred to the control system  24  (illustrated in  FIG. 1 ) which uses information from the height sensor  681  to control the guard mover assembly  656 . 
       FIG. 7A  is a perspective view of another embodiment of a device stage  742  with a wafer  730  positioned above the device stage  742 .  FIG. 7B  is a cut-away view taken from  FIG. 7A . In this embodiment, the device stage  742  includes a device table  750 , a device holder  752 , a guard  754 , and a holder mover assembly  756 . In this embodiment, the device table  750  is generally rectangular plate shaped. The device holder  752  retains the wafer  730 . The guard  754  is generally rectangular plate shaped and includes a circular shaped aperture  758  for the wafer  730 . In this embodiment, the guard  754  is fixedly secured to the device table  750 . The holder mover assembly  756  secures the device holder  752  to the device table  750  and moves and positions the device holder  752  relative to the device table  750  and the guard  754 . With this design, the holder mover assembly  756  can move the device holder  752  and the wafer  730  so that the top stage surface  780  of the guard  754  is approximately at the same Z height as the top exposed surface  779  of the wafer  730 . A sensor  781  can be used to measure the relative heights of the top stage surface  780  and the top exposed surface  779  of the wafer  730 . The information from the sensor  781  can be transferred to the control system  24  (illustrated in  FIG. 1 ) which uses information from the height sensor to control the holder mover assembly  756 . 
     For example, the holder mover assembly  756  can include one or more rotary motors, voice coil motors, linear motors, electromagnetic actuators, and/or other types of force actuators. In one embodiment, the holder mover assembly  756  moves and positions the device holder  752  and the wafer  730  along the Z axis, about the X axis and about the Y axis under the control of the control system  24  (illustrated in  FIG. 1 ). 
     Semiconductor devices can be fabricated using the above described systems, by the process shown generally in  FIG. 8A . In step  801  the device&#39;s function and performance characteristics are designed. Next, in step  802 , a mask (reticle) having a pattern is designed according to the previous designing step, and in a parallel step  803  a wafer is made from a silicon material. The mask pattern designed in step  802  is exposed onto the wafer from step  803  in step  804  by a photolithography system described hereinabove in accordance with the invention. In step  805  the semiconductor device is assembled (including the dicing process, bonding process and packaging process). Finally, the device is then inspected in step  806 . 
       FIG. 8B  illustrates a detailed flowchart example of the above-mentioned step  804  in the case of fabricating semiconductor devices. In  FIG. 8B , in step  811  (oxidation step), the wafer surface is oxidized. In step  812  (CVD step), an insulation film is formed on the wafer surface. In step  813  (electrode formation step), electrodes are formed on the wafer by vapor deposition. In step  814  (ion implantation step), ions are implanted in the wafer. The above mentioned steps  811 - 814  form the preprocessing steps for wafers during wafer processing, and selection is made at each step according to processing requirements. 
     At each stage of wafer processing, when the above-mentioned preprocessing steps have been completed, the following post-processing steps are implemented. During post-processing, first, in step  815  (photoresist formation step), photoresist is applied to a wafer. Next, in step  816  (exposure step), the above-mentioned exposure device is used to transfer the circuit pattern of a mask (reticle) to a wafer. Then in step  817  (developing step), the exposed wafer is developed, and in step  818  (etching step), parts other than residual photoresist (exposed material surface) are removed by etching. In step  819  (photoresist removal step), unnecessary photoresist remaining after etching is removed. Multiple circuit patterns are formed by repetition of these preprocessing and post-processing steps. 
     While the exposure apparatus  10  as shown and described herein is fully capable of providing the advantages described herein, it is merely illustrative of embodiments of the invention. No limitations are intended to the details of construction or design herein shown.