Abstract:
A lithography apparatus includes a projection optical system that projects an image of a pattern, a first support member, a second support member that is flexibly coupled to the first support member by a first flexible coupling device such that the second support member is suspended from the first support member, and a second flexible coupling device that flexibly couples the projection optical system to the second support structure. This arrangement is capable of improving the vibration characteristics of the projection optical system.

Description:
BACKGROUND 
       [0001]    This invention relates to lithography apparatus and methods of performing lithographic exposure, commonly used to transfer a pattern onto a substrate in order to manufacture devices such as, for example, semiconductor devices, liquid crystal displays, etc. 
         [0002]    Many current lithography apparatus have a large body structure that holds the projection lens, the metrology system and that supports the reticle stage and components of the illumination unit. That body typically is made very rigid and heavy in order to inhibit external forces (such as vibrations), as well as internal forces (generated due to movement of the wafer and/or mask) from causing the apparatus to vibrate. In general, a lithography apparatus having support structures with high rigidity, while providing a high apparatus performance capability, tends to make the support structure, and thus the lithography apparatus, very heavy. The high weight also results in the body having undesirably low vibration frequencies. 
       SUMMARY 
       [0003]    According to aspects of the invention, a lithography apparatus that includes a projection optical system that projects an image of a pattern includes a first support member, a second support member that is flexibly coupled to the first support member by a first flexible coupling device such that the second support member is substantially isolated from vibrations in the first support member, and a second flexible coupling device that flexibly couples the projection optical system to the second support member. This arrangement is capable of reducing the overall size and weight of the lithography apparatus. 
         [0004]    According to preferred embodiments, the second support member is a metrology frame that also holds at least a measuring unit that measures a positional relationship between the projection optical system and a predetermined member, such as, for example, a substrate stage that holds a substrate onto which the image of the pattern is transferred by the projection optical system. 
         [0005]    According to some embodiments, the second flexible coupling device is disposed between an upward-facing surface of the second support member and a downward-facing surface of the projection optical system such that the weight of the projection optical system is transferred to the second support member. 
         [0006]    According to some embodiments, the second flexible coupling device inhibits vibrations from passing between the second support member and the projection optical system. The second flexible coupling device can be, for example, a passive vibration isolation system (such as, for example, rubber mounts) or an active vibration isolation system (having, for example, a voice-coil motor and damping structure). 
         [0007]    According to some embodiments, the first flexible coupling device suspends the second support member from the first support member. 
         [0008]    According to some embodiments, the first flexible coupling device includes a plurality of suspension members that extend between the first support member and the second support member. The suspension members are stiff in an axial direction and flexible in directions orthogonal to the axial direction. The suspension members can be, for example, wires, cables, rods or chains. 
         [0009]    According to some embodiments, the suspension members are rotatably attached to the second support member. 
         [0010]    According to some embodiments, the suspension members are directly attached to the first support member. According to other embodiments, the suspension members are attached to the first support member via a mounting device having a stiffness in the axial direction that is less than a stiffness of the suspension members in the axial direction. The mounting device can include, for example, a piston supported by gas so as to absorb vibrations in the axial direction. Other alternatives include springs and/or active vibration isolation devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    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: 
           [0012]      FIG. 1  is a schematic illustration of a lithography apparatus according to one embodiment of the invention; 
           [0013]      FIG. 2  is a schematic representation of a mounting device for mounting a suspension member to a main support frame according to one embodiment; and 
           [0014]      FIG. 3  is a schematic representation of a mounting device for mounting a suspension member to a main support frame according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0015]      FIG. 1  is a schematic illustration of a lithography apparatus according to one embodiment of the invention. While the  FIG. 1  embodiment is a scanning exposure apparatus in which a reticle R and a wafer W are moved synchronously relative to a projection optical system PL during exposure, the invention also is applicable to stationary lithography apparatus (sometimes called a “stepper”) in which the reticle R and the wafer W are maintained stationary during exposure, with the wafer being stepped from one shot area to the next between each exposure operation. 
         [0016]    Although not shown in  FIG. 1 , the lithography apparatus includes a chamber in which the lithography apparatus is located, as well as a light source such as, for example, a laser light source. The light source can be a KrF excimer laser (wavelength 248 nm) or an ArF excimer laser (wavelength 193 nm), for example. The light source also could be a device that radiates an oscillating laser beam in an ultraviolet range such as an F 2  laser (wavelength 157 nm), a device that radiates a harmonic laser beam in a vacuum ultraviolet range that can be obtained by wavelength-converting a laser beam in a near infrared range supplied from a solid-state laser light source (YAG or a semiconductor laser, or the like). A mercury discharge lamp, or the like, also can be used, for example. 
         [0017]    In addition, the lithography apparatus can be a “dry” apparatus in which a gas is disposed between the projection optical system PL and the wafer W, or it can be an immersion lithography apparatus in which a liquid such as, for example, pure water, is disposed between the projection optical system PL and the wafer W. 
         [0018]    The lithography apparatus also includes various control systems for controlling the wafer stage WST, the reticle stage RST, the various measuring systems and the overall functioning of the apparatus. 
         [0019]    In the  FIG. 1  embodiment, the lithography apparatus includes a pedestal  100  on which the main support frame  20  and the wafer stage base  10  are mounted. It also is possible to mount the main support frame  20  and the wafer stage base  10  directly to the ground (the floor of the building in which the lithography apparatus is installed). The pedestal  100  is advantageous in that it is prefabricated with the appropriate mounting locations, piping and wiring, etc., which makes it easier to install the lithography apparatus in the factory. 
         [0020]    The wafer stage base  10  is mounted to the pedestal  100 , for example, by active or passive vibration isolation mounts  15 . The isolation mounts  15  are optional; the wafer stage base can be rigidly supported by the pedestal. If the isolation mounts  15  are passive, they can be, for example, rubber mounts, gas mounts, springs, or combinations of such structures. The passive vibration isolation mounts absorb high frequency vibrations from the ground or pedestal in  FIG. 1 . If the isolation mounts  15  are active vibration isolation mounts, they typically include an active element such as a voice-coil motor in addition to passive structure such as, for example, gas springs, mechanical springs, rubber mounts or any combination of these, with the voice-coil motor being driven by feedback and/or feedforward control so as to maintain the wafer stage base  10  motionless. Because it is well known to mount a wafer stage base  10  with passive or active vibration isolation mounts, no further description is provided herein. 
         [0021]    As shown in  FIG. 1 , the main support frame  20  also is mounted to the pedestal  100  by vibration isolation mounts  25 . The vibration isolation mounts  25  also could be active or passive vibration isolation mounts. It also is possible to directly mount the main support frame  20  to the pedestal  100  (or to the ground if there is no pedestal). The isolation mounts  25  can be omitted due to the use of such mounts for mounting the projection optical system PL and the reticle stage to the main support frame  20  as described below. 
         [0022]    In preferred embodiments, the main support frame  20  includes three upstanding pillars (only two are shown in  FIG. 1 ) having upper ends that are attached to a support base portion  22 . The pillars can be combined into one or two castings. It also is possible to have more than three pillars, such as, for example, four pillars. The pillars can be vertical, as shown in  FIG. 1 , or can be disposed at an angle such that the lower ends of the pillars are farther apart from each other than the upper ends of the pillars. See, for example,  FIG. 2  of WO 2006/038952. The disclosure of WO 2006/038952 is incorporated herein by reference in its entirety. 
         [0023]    A reticle stage base  30  is mounted on and supported by the main support frame  20 , for example, by passive or active vibration isolation mounts  35 . Mounts  35  are optional and need not always be provided. A movable reticle stage RST holding a reticle R is controlled to move in at least the Y direction on the reticle stage base  30 . The reticle stage RST can have 1, 3 or 6 degrees of freedom, for example. The reticle stage RST can be the type of stage that includes a countermass CM that moves synchronously in a direction opposite to the direction in which the reticle stage RST moves so as to counteract the reaction forces generated when the reticle stage RST moves. See, for example, U.S. Pat. No. 6,246,204, the disclosure of which is incorporated herein by reference in its entirety. Of course, if the lithography apparatus is a stepper, the reticle does not need to move. An illumination optical system (not shown) also is provided and can be entirely mounted on, or have components mounted on, the main support frame  20 . 
         [0024]    A reticle stage interferometer unit  50  also is mounted on the main support frame  20 . Reticle stage interferometer unit  50  also could be supported on projection lens frame member  60 , to be described below. In preferred embodiments, the reticle stage interferometer  50  is mounted to the main support frame  20  via an active or a passive vibration isolation mount  55 . The vibration isolation mount  55  is optional. The reticle stage interferometer  50  emits a measurement beam  52  to the projection optical system PL and emits a measurement beam  54  to the reticle stage RST so that the position of the reticle stage RST relative to the projection optical system PL can be determined. This information then is used to control the movement of the reticle stage RST. For simplicity of explanation, each measurement beam  52  and  54  is referred to in the singular; however, as is known, each beam  52 ,  54  can be one or more beams depending on the number of axes measured. For example, each beam can include four or more beams, and measurements can be obtained in the X, Y, Z, ⊖X, ⊖Y and ⊖Z axes. Thus,  FIG. 1  is merely a simplified diagram in that the beams  52 ,  54  typically would be a plurality of beams emitted in different directions. 
         [0025]    As shown in  FIG. 1 , a projection lens frame member  60  is suspended from the main support frame  20  by suspension members  80 . While only two suspension members  80  are shown in  FIG. 1 , according to preferred embodiments, three suspension members  80  are provided. More than three suspension members  80  also could be provided, although three is preferred. The projection lens frame member  60  of the  FIG. 1  embodiment is typically a large casting with a hole sized for the projection lens PL. The member  60  should be rigid and stable. Member  60  could be annular, circular, square, triangular or C-shaped, for example. 
         [0026]    The suspension members  80  are stiff in the Z-direction but flexible in the X- and Y-directions, and thus function as a flexible coupling device between main support frame  20  and projection lens frame member  60 . Members  80  can be a wire, rod, beam, cable or chain, for example. A lower end of each member  80  is attached to an upper surface of the projection lens frame member  60 . The support members  80  should be attached to the frame member  60  in a manner that allows them to rotate freely relative to the frame member  60 . For example, if the members  80  are flexible wires, cables or chains, the ends can be rigidly attached to the frame member  60  because the wire, cable or chain itself can bend or twist to act like a flexible joint. If the member  80  is a beam or a rod that is relatively stiff in bending, then flexible joints should be provided at the connection of the members  80  to the frame member  60 . Each flexible joint can be, for example, a universal joint, a ball joint, a ball-in-socket, etc. A flexure also can be included with the support member  80 . 
         [0027]    The upper ends of the suspension members  80  can be attached to the main support frame  20  in a manner similar to the manner in which the lower ends of the members  80  are attached to the projection lens frame member  60 . Such an attachment would make the attachment of the projection lens frame member  60  to the main support frame  20  relatively rigid in the Z-direction, but flexible in the X- and Y-directions. It is, however, preferable to attach the upper end of each suspension member  80  to the main support frame  20  with a mounting device  90  that has a stiffness in the Z-direction that is less than a stiffness of the suspension members  80  in the Z-direction. The mounting members  90  absorb vibrations of the main support frame  20  in the Z-direction so that such vibrations do not reach the projection lens frame member  60 . The mounting devices  90  should be passive or active vibration isolators, although only one degree of freedom is needed. The mounting devices  90  alternatively can be provided at the lower end of the suspension members  80  (that is, between the members  80  and the projection lens frame member  60 ). In that alternative, the upper ends of the members  80  should be flexibly attached to the support base portion  22  of the main support frame  20  as described above (that is, using a flexible joint, although that would not be needed if the suspension members are wires, cables or chains). 
         [0028]    As shown in  FIG. 1 , the projection lens PL is mounted to and supported by the suspended projection lens frame member  60  via flexible coupling devices  62 . As shown in  FIG. 1 , the flexible coupling devices  62  are disposed between an upper surface of the frame member  60  and a lower surface of a flange FL of the projection optical system PL. Although only two flexible mounting devices  62  are shown in  FIG. 1 , according to preferred embodiments, there are preferably three of the coupling devices  62 . The coupling devices can be passive vibration isolation members or active vibration isolation members. If passive, the isolation members  62  can include rubber or elastomer members, mechanical springs (coil, leaf, etc.), gas (or vacuum) filled chambers, or combinations thereof. If the coupling devices are active vibration isolation members, they can include voice-coil motors, attractive or repulsive magnets (permanent magnets, electromagnets or a combination) or an actively-controlled pressure chamber. The devices  62  can be a combination of passive and active isolation devices. 
         [0029]    The coupling devices  62  are compliant (that is, not completely stiff) in at least the Z-direction (vertical direction). The coupling devices also can be compliant in the X- and Y-directions. The mounting devices thus absorb (or at least reduce the transmission of) vibrations in the direction(s) in which they are compliant. 
         [0030]    In addition, according to some embodiments, a wafer stage interferometer  40  is rigidly mounted to the frame member  60  mounting member  45 . The wafer stage interferometer  40  measures the position of the wafer stage WST relative to the projection optical system PL using beams  44  and  42 , similar to beams  54  and  52  of the reticle stage interferometer  50 . Beam  42  is emitted to the projection optical system PL and beam  44  is emitted to the wafer stage WST. As with the reticle stage interferometer  50 , beams  42  and  44  are shown in simplified form, and actually are constituted by a plurality of beams extending in different directions depending on the axes of measurement. Other measurement devices can be rigidly mounted to the frame member  60  in addition to, or instead of, the wafer stage interferometer  40 . Such other measurement devices includes, for example, devices for measuring the position of the wafer surface (this can be done, for example, with an oblique measurement beam that is reflected from the substrate surface and detected with a detector), and devices for measuring alignment of the substrate relative to the reticle, etc. The reticle stage interferometer  50  also can be mounted to the frame member  60 . 
         [0031]      FIG. 2  shows one example of a possible structure for the mounting device  90  in  FIG. 1 . In this embodiment, each mounting device  90 A is an isolation member having a piston  92  to which the upper end of each suspension member  80  is attached by a ball joint  94 .  FIG. 2  also shows a ball-in-socket joint  84  that attaches the lower end of the suspension member  80  to the frame member  60 . The isolation member  90 A is filled with gas at pressure below atmospheric pressure such that it exerts an upward force on suspension member  80  which supports gravity weight of frame  60  and such that it has low stiffness in the Z-direction. Therefore, the isolation member reduces or prevents Z-direction vibrations from being transmitted to the suspension members  80  (and thus to the projection lens frame member  60 ) from the main support frame  20 . The isolation members  90 A also provide the lifting force to support the weight of the projection lens frame member  60  and all components (include the projection lens PL) mounted to the frame  60 . Other examples of structures that can be used as isolation members of the mounting devices  90  include: rubber or elastomer members, attractive or repulsive magnets (permanent magnet, electro-magnets or a combination), mechanical springs  90 B (coil, leaf, etc.) as shown in  FIG. 3 , gas springs, a piston supported by pressurized gas, or any combination of passive and active isolation devices. 
         [0032]    Placing the flexible coupling device  62  between the projection lens PL and the frame  60  is beneficial in that it can eliminate problematic vibrations that occur between the projection lens PL and the frame  60 . Both the projection lens PL and the frame  60  typically are large, massive structures. To prevent distortion of either component, they must be connected by a substantially kinematic attachment. In conventional systems, this is achieved by a bolted connection at three points. Because the bolted connections are not infinitely stiff, the apparatus has a vibration mode where the projection lens PL and the frame  60  act as two masses connected by a spring (the mechanical-bolt-connection). Typically the natural frequency of this vibration is in the 50-150 Hz range. Modem lithography apparatus are particularly sensitive to vibrations in this frequency range. 
         [0033]    Using an intentionally compliant connection between the projection lens PL and the frame  60  (that is, using the flexible coupling devices  62  between the projection lens PL and the frame  60 ) removes the “spring” between the two masses, and eliminates the vibration mode. In this way, stability and imaging performance of the lithography apparatus are improved. 
         [0034]    The  FIG. 1  embodiment includes many other vibration isolating elements. In the general, the more that the various modules can be isolated from each other, the more improvement can be obtained in the machine performance. There is, however, a tradeoff in that each vibration isolating device, particularly active isolating devices, adds complexity to the system. Accordingly, one or more of the vibration isolating devices of the  FIG. 1  embodiment can be eliminated. 
         [0035]    Although the  FIG. 1  embodiment uses suspension members  80  to suspend frame  60 , the frame  60  could be supported in other ways that do not involve suspension. For example, the frames  60  could be supported by pillars that are mounted to the ground (or a base) via vibration isolating devices (passive or active). However, combining the suspension members  80  with the flexible coupling devices  62  between the projection lens PL and the frame  60  has advantages. The pendulum effect of the members  80  provides a low lateral stiffness and therefore good isolation of the lateral vibrations. This avoids the challenges of making the flexible coupling devices  62  low-stiffness six degree-of-freedom support and vibration isolators. 
         [0036]    The lithography apparatus of the above-mentioned embodiments can be manufactured by incorporating and optically adjusting an illumination optical system composed of a plurality of lenses and a projection system into the main body of the lithography apparatus, and installing the reticle stage and the wafer stage composed of a plurality of mechanical parts to the main body of the lithography apparatus, connecting wires and pipes, and performing overall adjustment (electrical adjustment, operation check, etc.). Furthermore, it is preferable that manufacturing of the lithography apparatus is performed in a clean room with controlled temperature and cleanliness. 
         [0037]    Furthermore, when a semiconductor device is manufactured by using the lithography apparatus of the above-described embodiments, the semiconductor device is manufactured by a step of designing a performance capability and function of the device, a step of manufacturing a reticle based on the designing step, a step of forming a wafer from a silicon material, a step of performing alignment by the lithography apparatus of the above-mentioned embodiment and exposing a pattern of the reticle onto a wafer, a step of forming a circuit pattern such as etching or the like, a step of assembling a device (including a dicing process, a bonding process, a packaging process), a step of testing, and the like. 
         [0038]    This invention can be applied to a liquid immersion type exposure apparatus disclosed in, for example, International Publication No. WO 99/49504. Furthermore, this invention can be applied to a lithography apparatus using extreme ultraviolet light (EUV light) having a wavelength of several nm-100 nm as an exposure beam. 
         [0039]    Furthermore, this invention is not limited to the application for the lithography apparatus for manufacturing a semiconductor device. For example, this invention can be applied to a lithography apparatus for manufacturing various devices such as a liquid crystal display element formed on a square-shaped glass plate, or a display device such as a plasma display or the like, or an imaging element (CCD), a micro-machine, a thin-film magnetic head, a DNA chip, or the like. Furthermore, this invention can be applied to a lithography process (lithography apparatus) in which a mask (photomask, reticle, or the like) having a mask pattern of various devices is formed by using a photolithographic process. 
         [0040]    While the invention has been described with reference to preferred embodiments thereof, which are exemplary, it is to be understood that the invention is not limited to the preferred embodiments or constructions. The invention is intended to cover various modifications and arrangements. In addition, while the various elements of the preferred embodiments are shown in various combinations and configurations, that are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.