Abstract:
An exposure apparatus transfers a pattern from a mask onto a sensitive substrate. A film protects the mask, and a film frame, between the mask and the film, holds the film spaced away from a surface of the mask. The film has a first transmittance for radiation of a necessary wavelength and has a second transmittance for radiation of an unnecessary wavelength; the first transmittance is higher than the second transmittance. The film might reflect or absorb the unnecessary wavelength. The necessary wavelength may be an exposure wavelength and may also be in the range of extreme ultra violet radiation. An atmosphere around the mask transitions from an air atmosphere to a reduced-pressure atmosphere, or from a reduced-pressure atmosphere to an air atmosphere, at a speed that allows a difference between a pressure applied to one surface of the film and a pressure applied to the other surface of the film to be held at a predetermined value or smaller.

Description:
This patent application claims priority to provisional application No. 60/873,978 filed on Dec. 11, 2006, the contents of which are incorporated herein by reference. This patent application also claims priority to Japanese Patent Application No. 2006-039447, filed on Feb. 16, 2006, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates to an apparatus for protecting a lithography mask having a pattern for manufacturing a micro-device, such as a semiconductor device or a liquid crystal display device. Also, the present invention relates to an exposure apparatus that transfers the pattern through exposure. 
     B. Description of the Related Art 
     Projection lithography technology may use Extreme Ultraviolet (EUV) light or radiation having a short wavelength (5 to 50 nm) to enhance the resolving power for micro-fabrication of semiconductor device circuits. Because an optical element of transmission-refraction type, such as a conventional lens, may not be used in such a wavelength range, an optical element of reflection type, such as a mirror, and a mask of reflection type may be used. See U.S. Pat. No. 6,825,481. 
     In an exposure apparatus for fabricating semiconductor device circuits, a pattern surface of a mask is protected with a pellicle or the like made from a thin film, so as to prevent a foreign substance from adhering to the pattern provided on the mask. In an exposure apparatus using EUV, however, an amount of EUV light as exposure light is significantly decreased when passing through a foreign-substance protection film such as a pellicle, resulting in decrease in throughput. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an apparatus for protecting a mask capable of avoiding decrease in amount of light irradiating a pattern surface, and also to provide an exposure apparatus for transferring the pattern provided on the mask through exposure. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, an apparatus protects a projection lithography mask, the mask having a pattern for transfer to a substrate. The apparatus includes a film having a first transmittance for radiation of a necessary wavelength and having a second transmittance for radiation of an unnecessary wavelength, the first transmittance being higher than the second transmittance; and a film frame between the mask and the film, the film frame holding the film at a position spaced away from a surface of the mask. 
     According to another embodiment, an apparatus protects a projection lithography mask, the mask having a pattern for transfer to a substrate. The apparatus includes a film frame including a standing portion on a surface of the mask and a supporting portion protruding from the standing portion along the surface of the mask; and a film supported by the film frame at a position spaced away from the surface of the mask, wherein the standing portion and the supporting portion each have a filter. 
     According to another embodiment, an exposure apparatus transfers a pattern from a mask onto a sensitive substrate. A film transmitting light having a necessary wavelength and not transmitting light having an unnecessary wavelength protects the mask, and a film frame, between the mask and the film, holds the film at a position spaced away from a surface of the mask. 
     According to another embodiment, an atmosphere around the mask transitions from an air atmosphere to a reduced-pressure atmosphere, or from a reduced-pressure atmosphere to an air atmosphere, at a speed that allows a difference between a pressure applied to one surface of the film and a pressure applied to the other surface of the film to be held at a predetermined value or smaller. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. 
         FIG. 1  is an illustration showing a configuration of an exposure apparatus according to a first embodiment. 
         FIG. 2  is an illustration showing a configuration of an exposure area defining member according to the first embodiment. 
         FIG. 3  is a plan view showing a configuration of a mask according to the first embodiment. 
         FIG. 4  is a cross-sectional view showing the configuration of the mask according to the first embodiment. 
         FIG. 5  is a graph showing distribution of illumination intensity in the Y direction. 
         FIG. 6  is a graph showing distribution of illumination intensity for correcting the distribution of illumination intensity in the Y direction. 
         FIG. 7  is an illustration showing another configuration of an exposure area defining member according to the first embodiment. 
         FIG. 8  is an illustration showing another configuration of a mask according to the first embodiment. 
         FIG. 9  is a plan view showing a configuration of a mask according to a second embodiment. 
         FIG. 10  is a cross-sectional view showing the configuration of the mask according to the second embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     An exposure apparatus and a mask according to a first embodiment will be described below with reference to the drawings.  FIG. 1  is an illustration showing a general configuration of an exposure apparatus according to the first embodiment. In the following description, XYZ orthogonal coordinate system is determined as shown in  FIG. 1 , and the positional relationship of components are described with reference to the XYZ orthogonal coordinate system. The XYZ orthogonal coordinate system is determined such that the X-axis and the Y-axis are parallel to a wafer W as a sensitive substrate, and the Z-axis is orthogonal to the wafer W. In practice, the XYZ orthogonal coordinate system in the drawing is determined such that the X-Y plane is parallel to a horizontal plane, and Z-axis is along a vertical direction. In this embodiment, the wafer W is moved (scanning direction) in the X direction. 
     The exposure apparatus includes an EUV light source  31  that emits EUV light  32 . A power source  30  is connected to the EUV light source  31 . Operating the power source  30  causes the EUV light source  31  to emit the EUV light  32 . A control device  51  controls the operation of the power source  30 . By controlling the operation of the power source  30 , the light intensity of the EUV light  32  emitted from the EUV light source  31  may be varied, and consequently, an amount of exposure light may be varied. 
     The EUV light  32  emitted from the EUV light source  31  becomes parallel light beams through a concave reflection mirror  34 , which is provided in an illumination optical system  33  and serves as a collimator mirror, and the light beams enter an optical integrator  35 . The optical integrator  35  includes an entrance fly-eye mirror  35   a  and an exit fly-eye mirror  35   b . The entrance fly-eye mirror  35   a  has a plurality of arcuate elemental mirrors aligned in parallel. The incident surface of the entrance fly-eye mirror  35   a  is located at a position optically conjugated with respect to surfaces of a mask M and the wafer W (described later), or it is located in the vicinity of that position. The EUV light incident on the entrance fly-eye mirror  35   a  is wave front-divided by each of the elemental mirrors of the entrance fly-eye mirror  35   a.    
     The EUV light incident on the entrance fly-eye mirror  35   a  is reflected by the entrance fly-eye mirror  35   a  and enters the exit fly-eye mirror  35   b . The exit fly-eye mirror  35   b  has a plurality of rectangular elemental mirrors aligned in parallel. The irradiation surface of the exit fly-eye mirror  35   b  is located at a position optically conjugated with respect to a pupil position of a projection optical system PL (described later), or it is located in the vicinity of that position. The EUV light reflected by each of the elemental mirrors of the entrance fly-eye mirror  35   a  enters each of the elemental mirrors of the exit fly-eye mirror  35   b . Accordingly, a plurality of light-condensing points are produced at the irradiation side of the exit fly-eye mirror  35   b  or at the vicinity thereof in accordance with the number of the elemental mirrors of the exit fly-eye mirror  35   b . The light-condensing points serve as a secondary light source. 
     The EUV light reflected by the exit fly-eye mirror  35   b  is deflected by a flat reflection mirror  36 , passes through a long, arcuate field stop slit S of an exposure area defining member defining member  1 , and forms an arcuate illumination area on the mask M (reflection-type mask). 
       FIG. 2  is an illustration showing a configuration of the exposure area defining member  1 . The exposure area defining member  1  is disposed between the mask M and the projection optical system PL, and has the arcuate field stop slit S for defining the exposure area of the wafer W. Because the EUV light passes through the arcuate field stop slit S, the illumination area on the mask M becomes arcuate. It is important that the exposure area of the EUV light led onto the wafer W has a predetermined shape. Thus, the EUV light may be blocked by the field stop slit S before the EUV light is reflected by the mask M. Alternatively, the EUV light may be blocked by the field stop slit S after the EUV light is reflected by the mask M. While the exposure area in this embodiment is determined to be arcuate, the exposure area may be some other shape. 
     The mask M includes a pattern and is mounted on a mask stage  55 . The mask stage  55  may be moved in the X, Y, and Z-axis directions, and in rotation directions about the X, Y, and Z-axes. 
       FIG. 3  is a plan view showing a configuration of the mask M according to the first embodiment.  FIG. 4  is a cross-sectional view showing the configuration of the mask M taken along line A-A in  FIG. 3 . 
     As shown in  FIGS. 3 and 4 , the mask M includes a protection apparatus, such as a protection film  10 . The foreign-substance protection film  10  may be separated from the surface of the mask M by a predetermined distance, such as for example, 10 mm. For example, the position may be determined such that the distance is in a range of from 1 to 50 mm (preferably, a range of from 6 to 20 mm). If the distance between the mask M and the foreign-substance protection film  10  is too small, any foreign substance adhered onto the foreign-substance protection film  10  and the shape of the structure such as supports  14   a  and  14   b  (described later) might be undesirably transferred to the wafer W. If the distance between the mask M and the foreign-substance protection film  10  is too large, the foreign-substance protection film  10  might mechanically interfere with other structure (e.g., the exposure area defining member  1 ) disposed in the immediate vicinity of the mask M. The foreign-substance protection film  10  thus prevents a foreign substance from adhering onto the surface of the mask M. 
     The foreign-substance protection film  10  preferably transmits light in a wavelength range necessary for exposure, for example, light with a wavelength of 13.5 nm, from among the EUV light  32 . In addition, the foreign-substance protection film  10  preferably absorbs light in a wavelength range unnecessary for exposure. For example, the protection film  10  may include a zirconium thin film. The thin film may be a single layer film, but may also be a multilayer film. While the foreign-substance protection film  10  preferably absorbs light in the unnecessary wavelength range in this embodiment, the light in the unnecessary wavelength range may be reflected. If a multilayer film is employed, only the unnecessary light may be reflected. 
     A zirconium film with a 1500 Å mesh, available from Luxel Corporation, is a further, more specific example of a foreign-substance protection film  10 . This film typically has about a 70% transmittance of 13.5 nm wavelength radiation and about a 10% transmittance of 200 nm wavelength radiation. The zirconium film thus transmits radiation having a necessary wavelength and does not transmit radiation having an unnecessary wavelength. 
     According to an exemplary multilayer film, a first film, such as silicon, that may be relatively easily prepared as a self-supported film is selected. A single film or a multilayer film that decreases the unnecessary light is then formed on the upper or lower side of the first film. For example, a silicon film of 200 nm in thickness may be prepared, and then a zirconium film of 100 nm in thickness may be formed thereon. 
     The selected thickness of the foreign-substance protection film  10  preferably minimizes attenuation of the exposure light, while still allowing the foreign-substance protection film  10  to be self-supported. The appropriate thickness of the foreign-substance protection film  10  may be determined case by case according to the material and area of the protection film  10 , and the presence of other structure, such as a support. For example, the thickness of the foreign-substance protection film  10  may be in a range of from 50 to 1000 nm. In a case where the light with the unnecessary wavelength is not actively eliminated, the protection film may use other material such as silicon, a silicon compound, carbon, diamond, or polyimide. The foreign-substance protection film  10  may also serve as a wavelength selective filter. Therefore, the illumination optical system  33  does not need to have a separate wavelength selective filter, and the amount of exposure light in the whole system may be improved. 
     In addition, the foreign-substance protection film  10  is supported by a foreign-substance protection film frame  12 , and the entire surface of the foreign-substance protection film  10  is supported by the supports  14   a  and  14   b . By the provision of the supports  14   a  and  14   b , the foreign-substance protection film  10  is hardly broken, and it is likely to be self-supported. Accordingly, the foreign-substance protection film  10  may be thinner, and the attenuation of the light with the exposure wavelength may be reduced. The supports  14   a  may comprise an extra-fine line member, such as a wire. The supports  14   a  may extend straight along the same direction that the mask M and the wafer W are scanned in the X direction (scanning direction). The supports  14   b  may comprise an extra-fine line member, such as a wire. The supports  14   b  may extend to follow the profile of a fixed exposure area, the fixed exposure being formed on the wafer W. The fixed exposure area preferably extends in the Y direction (the direction orthogonal to the scanning direction) as shown in  FIG. 4 , i.e., a profile along the Y direction of the field stop slit S, or a profile approximate to that profile. 
     The EUV light reflected by the mask M forms an image of a pattern of the mask M on the wafer W through the projection optical system PL including a plurality of reflection mirrors (for instance, six reflection mirrors M 1  to M 6  are shown in  FIG. 1 ). A wafer stage  56  holds the wafer W. The wafer stage  56  preferably moves in the X, Y, and Z-axis directions and preferably rotates about the X, Y, and Z-axes. 
     Interferometers measure the positions of the mask stage  55  and wafer stage  56 . The interferometers output the measurement results to the control device  51 . The control device  51  outputs driving signals  57  and  58  to the mask stage  55  and the wafer stage  56 . Actuators, such as linear motors or air actuators, move the mask stage  55  and the wafer stage  56 , based on the driving signals  57  and  58  output from the control device  51 . 
     In this embodiment, the supports  14   a  and  14   b  may correct illumination unevenness (unevenness of light intensity) generated in the exposure area. Because the supports  14   a  are formed straight along the scanning direction, the illumination intensity is varied one-dimensionally by the supports  14   a , for instance, as shown in the graph of  FIG. 5 , thereby generating illumination unevenness. If the illumination unevenness becomes a bottleneck in an exposure procedure, correction is necessary so that illumination uniformity meets the specifications. For example, distribution of illumination intensity (distribution of exposure light) as shown in the graph of  FIG. 6 , i.e., distribution of illumination intensity inverse to that shown in  FIG. 5 , is applied, and accordingly, the illumination unevenness (distribution of exposure light) due to the supports  14   a  can be corrected. In particular, the profile of the field stop slit S employs the profile shown in  FIG. 7 , in order to apply the illumination intensity as shown in the graph of  FIG. 6 . While the profile of the field stop slit S has the wave form only at the upper portion shown in  FIG. 7 , the lower portion or both the upper and lower portions may be varied in profile. Alternatively, a light-shielding member may be disposed at the aperture of the field stop slit S for the above-mentioned correction. 
     Because the supports  14   b  are formed along the Y direction, the supports  14   b  may cause an error in the amount of exposure light while scanning and exposing. In such a case, by controlling the scanning speeds of the mask stage  55  and wafer stage  56 , the amount of exposure light may be controlled to correct the error of the amount of exposure light caused by the supports  14   b . In particular, at the scanning over the supports  14   b , the scanning speeds of the mask stage  55  and wafer stage  56  are reduced, and the amount of exposure light is increased, thereby correcting the decrease in the amount of exposure light caused by the supports  14   b . While scanning over an area not occupied by the supports  14   b , the scanning speeds of the mask stage  55  and wafer stage  56  are increased, and the amount of exposure light is decreased, thereby correcting the decrease in the amount of exposure light caused by the supports  14   b.    
     Alternatively, by controlling the light intensity of the EUV light  32  emitted from the EUV light source  31 , using the power source  30 , the amount of exposure light may be controlled to correct the error of the amount of exposure light caused by the supports  14   b . In such a case, while scanning over the supports  14   b , the light intensity of the EUV light  32  emitted from the EUV light source  31  is increased, and accordingly, the amount of exposure light is increased, thereby correcting the decrease in the amount of exposure light due to the supports  14   b . While scanning over an area not occupied by the supports  14   b , the light intensity of the EUV light  32  emitted from the EUV light source  31  is decreased, and the amount of exposure light is decreased, thereby correcting the decrease in the amount of exposure light due to the supports  14   b . Still alternatively, a light-decreasing filter may be disposed in the middle of the optical path, or gas may be applied thereto, for controlling the exposure amount. Still alternatively, the thickness of the foreign-substance protection film  10  at the area not occupied by the supports  14   b  may be relatively increased, so that an amount of light is decreased at the area not occupied by the supports  14   b , by the same amount as that reduced at an area occupied by the supports  14   b.    
     The mask according to the first embodiment includes the foreign-substance protection film  10  that prevents a foreign substance from adhering onto the pattern surface. The foreign-substance protection film  10  may also serve as a wavelength selective filter that transmits the light in the wavelength range necessary for the exposure and absorbs the light with the unnecessary wavelength. Therefore, even if a wavelength selective filter is not additionally provided, a pattern can be illuminated with the light in the wavelength range necessary for exposure. A decrease in the amount of exposure light due to the additional foreign-substance protection film may also be prevented. In addition, because the supports  14   a  and  14   b  for supporting the foreign-substance protection film  10  are provided, the thickness of the foreign-substance protection film  10  may be decreased, thereby preventing the decrease in amount of exposure light. 
     With the exposure apparatus according to the first embodiment, the illumination unevenness due to the supports  14   a  and  14   b  may be corrected appropriately, thereby providing effective exposure. 
     Although the mask according to the first embodiment has the foreign-substance protection film  10  supported by the supports  14   a  and  14   b  as shown in  FIG. 3 , supports  14   c  as shown in  FIG. 8 , provided straight along the X direction (scanning direction), alone may be provided. The mask shown in  FIG. 8  has a smaller supporting strength of the foreign-substance protection film  10  than the mask M shown in  FIG. 3 . In such a case, however, the degree of illumination unevenness due to the supports may decrease because supports having a profile of the field stop slit S along Y direction are not provided to extend in Y direction. Accordingly, only the one dimensional, illumination unevenness due to the supports  14   c  has to be corrected, thereby more easily correcting the illumination unevenness. 
     Next, an exposure apparatus and a mask according to a second embodiment will be described below with reference to the drawings. The configuration of the exposure apparatus according to the second embodiment is similar to that of the first embodiment, and hence, the detailed description of the exposure apparatus according to the second embodiment will be omitted. In the description of the exposure apparatus according to the second embodiment, the same numerals as that of the first embodiment are applied to the same components. 
       FIG. 9  is a plan view showing a configuration of a mask M 2  according to the second embodiment.  FIG. 10  is a cross-sectional view showing the configuration of the mask M 2  taken along line B-B in  FIG. 9 . As shown in  FIGS. 9 and 10 , the mask M 2  includes a foreign-substance protection film  20  spaced away from the surface of the mask M 2 . The protection film  20  may be, for example, 10 mm away from the mask M. The foreign-substance protection film  20  prevents a foreign substance from adhering to the surface of the mask M 2 . 
     Foreign-substance protection film frames  22  support the foreign-substance protection film  20 . Each of the foreign-substance protection film frames  22  includes a standing portion  22   a  standing on the peripheral edge of the surface of the mask M 2 , and a supporting portion  22   b  protruding from the standing portion  22   a  along the surface having the pattern of the mask M 2 . The standing portion  22   a  and supporting portion  22   b  each have a plurality of filters  24 . The filters  24  prevent foreign substances from entering into the pattern surface and allow air to circulate sufficiently. 
     The amount of air circulating through the filters is determined depending on the thickness and area of the filters. Also, the amount of foreign substance to be removed is determined depending on the thickness of the filters. To increase the amount of air circulating through the filters while holding the capability of the filters for removing the foreign substance, it is necessary to increase the area of the filter. Therefore, in this embodiment, as many filters  24  as possible are provided at the standing portion  22   a  and supporting portion  22   b . Because the foreign-substance protection film  20  is transported between an air space and a vacuum space (described later), the filters  24  may reduce the difference between an air-pressure applied to an inner surface and the pressure applied to an outer surface of the foreign substance protection film  20 , to avoid action of a stress due to the difference between the pressure applied to the inner surface and the pressure applied to the outer surface. 
     Before exposure, the mask M 2  is carried-in to the mask stage  55  through a load-lock chamber by a mask-transporting device while being protected by the foreign-substance protection film  20 . After exposure, the mask M 2  is carried-out from the mask stage  55  through the load-lock chamber by the mask-transporting device. The load-lock chamber may be evacuated or released to air. 
     In particular, the mask M 2  protected with the foreign-substance protection film  20  is carried-in to the load-lock chamber in an air atmosphere by the mask-transporting device, and the load-lock chamber is evacuated so as to carrying in the mask M 2  to the exposure apparatus in a vacuum atmosphere. The mask M 2  is shifted from an air atmosphere to a vacuum atmosphere (reduced-pressure atmosphere), at a rate of change, for example 100 Pa/sec, that allows the difference between the pressure applied to the inner surface and the pressure applied to the outer surface of the foreign-substance protection film  20  to be held at a predetermined value or smaller. The difference between the pressure applied to the inner surface and the pressure applied to the outer surface of the foreign-substance protection film  20  is varied depending on the break strength determined in accordance with the thickness, material, and the like of the foreign-substance protection film  20 , or depending on the allowed applied stress determined in accordance with the area of the foreign-substance protection film  20 . The rate of change may be determined by calculations or experiments in accordance with these parameters. In shifting to a vacuum environment from an air environment, when the load-lock chamber is evacuated at a predetermined rate, the difference between the pressure applied to the inner surface and the pressure applied to the outer surface is increased at the beginning, and the difference of the pressures is reduced halfway. This is because the variation in degree of vacuum in the chamber with respect to time is logarithmic. Therefore, it is preferable that the rate of evacuation is slow at the beginning and gradually increased. 
     The mask M 2  provided with the foreign-substance protection film  20  is carried-in from the load-lock chamber, now at a vacuum atmosphere, to the mask stage  55  for exposure. After exposure, the mask M 2  provided with the foreign-substance protection film  20  is carried-out from the exposure apparatus in a vacuum atmosphere and is transported to the load-lock chamber in a vacuum atmosphere. The load-lock chamber transitions to an air atmosphere, so that the mask M 2  is handed over to the mask-transporting device in the air atmosphere. At this time, the mask M 2  is shifted to the air atmosphere from the vacuum atmosphere (reduced-pressure atmosphere), at a rate of change, for example, 100 Pa/sec, that allows the difference between the pressure applied to the inner surface and the pressure applied to the outer surface of the foreign-substance protection film  20  to be held at a predetermined value or smaller. 
     The mask according to the second embodiment includes the foreign-substance protection film  20  that prevents a foreign substance from adhering to the pattern surface. In addition, the plurality of filters  24  are provided at the standing portions and supporting portions of the foreign-substance protection film  20 . Accordingly, the difference between the pressure applied to the inner surface and the pressure applied to the outer surface of the foreign-substance protection film  20  may be controlled appropriately. Therefore, the foreign-substance protection film  20  is less likely to break because of stress due to the difference between the pressure applied to the inner surface and the pressure applied to the outer surface. 
     In addition, with the exposure apparatus according to the second embodiment, the mask M 2  may be shifted to a vacuum atmosphere from an air atmosphere, or it may be shifted to the an air atmosphere from a vacuum atmosphere, at a rate of change that allows the difference between the pressure applied to the inner surface and the pressure applied to the outer surface of the foreign-substance protection film  20  to be held at the predetermined value or smaller. Accordingly, the foreign-substance protection film  20  is less likely to break because of the stress due to the difference between the pressure applied to the inner surface and the pressure applied to the outer surface of the foreign-substance protection film  20 . 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.