Abstract:
A pellicle is mounted onto a mask that express a wafer, by pressing the pellicle to the mask using a mounting system. The pellicle includes a pellicle membrane, and a pellicle frame including a first portion on which the pellicle membrane is attched and a second portion by which the pellicle mounting system establishes contact therewith. A distance between a surface of the first portion and the surface of the mask may be equivalent to a distance between a surface of the second portion and the surface of the mask. The second portion may have a mechanism for prevention the pellicle mounting system from slipping thereon in a direction parallel to the surface of the mask. The pellicle frame may include a contact portion that has an inclined surface that guides the pellicle mounting system to be in contact with the pellicle frame.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pellicle that prevents a particle from directly lying on a mask used for exposing a wafer, to thereby defocus the particle. 
     2. Description of the Related Art 
     Pellicles have been widely used in semiconductor manufacturing in order to reduce the influence of foreign particles when exposing wafers using a mask. 
     FIG. 1 shows a structure of a conventional pellicle. The pellicle principally incorporates a pellicle frame  20  and a pellicle membrane  30 . A typical pellicle membrane  30  may include, for example, nitrocellulose and fluoropolymers. Because the pellicle membrane  30  has a thickness of approximate 1 micron it has very little strength to resist external forces. In addition to the pellicle frame  20  and the pellicle membrane  30 , the pellicle incorporates a first adhesive  40  and a second adhesive  50 . The pellicle frame  20  supports the pellicle membrane  30 , wherein they are adhered to each other by the second adhesive  50 . In the process of manufacturing semiconductors, a mask  10  is first prepared. The mask  10  is then cleaned and thereafter the surface of the mask  10  is inspected to detect any particles lying on the mask  10 . After it has been confirmed that the surface satisfies given criteria, the pellicle is mounted onto the mask  10 . Thereafter, the surface of the mask  10  is checked again. When the mask  10  is in good condition, a light source (not shown) placed at a side of the mask  10  irradiates a ray toward the mask  10 , whereby a wafer (not shown) placed at another side thereof is exposed to the ray through the mask  10 . 
     In mounting the pellicle onto the mask  10 , the pellicle is pressed to the mask  10  using the pellicle mounting system  60 . This pressing and the first adhesive  40  enables the pellicle to be fixed on the mask  10 . The first adhesive  40  may preferably be covered with a liner (not shown) for ease of handling. Such a liner is then removed before the pellicle is mounted. 
     As shown in FIG. 1, pressure is applied with the contact of the pellicle membrane  30  and the pellicle mounting system  60 . In other words, the pellicle mounting system  60  directly presses the pellicle membrane  30 . Because the pellicle membrane  30  is thin and therefore weak to external force, this pressing may damage the pellicle membrane  30 . Such damage, if severe, might cause foreign particles to invade the space surrounded by the mask  10  and the pellicle. Alternatively, the pellicle membrane  30  may peel away from the pellicle frame  20 . 
     To detect a particle on the mask  10 , a method is used wherein a light source obliquely irradiates a ray toward the mask  10  and a light detector detects a ray scattered by the particle. However, a conventional pellicle frame  20  might block a ray scattered by a particle lying near the pellicle frame  20  from reaching the detector, thereby blocking detection of such a particle. 
     Related to this, the size of such pellicle membranes  30  has increased and as a result, there are instances where the pellicle membrane  30  bends to its own weight. As a result, the exposure of the wafer fails, that is, the pattern on the mask  10  cannot be accurately copied to the wafer. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a pelicle which overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention. 
     According to an aspect of the present invention, there is provided a pellicle used for preventing a first particle from lying on a mask used for exposing a wafer and defocusing a second particle lying on the pellicle, the pellicle being mounted onto the mask by pressing the pellicle to the mask using a pellicle mounting system, the pellicle comprising: a pellicle membrane; and a pellicle frame including a first portion on which the pellicle membrane is attached and a second portion with which the pellicle mounting system establishes contact. 
     The distance between the surface of the first portion on which the pellicle membrane is attached and the surface of the mask on which the pellicle is mounted is preferably equivalent to the distance between a surface of the second portion with which the pellicle mounting system establishes contact and the surface of the mask. 
     A first distance between the surface of the first portion on which the pellicle membrane is attached and the surface of the mask on which the pellicle is mounted is preferably longer than a second distance between the surface of the second portion with which the pellicle mounting system establishes contact and the surface of the mask. 
     The second portion preferably has a mechanism for preventing the pellicle mounting system from slipping on the second portion in a direction in parallel with the surface of the mask. The mechanism preferably has a surface that resists the sliding of the pellicle mounting system. 
     A first distance between the surface of the first portion on which the pellicle membrane is attached and the surface of the mask on which the pellicle is mounted is preferably shorter than a second distance between the surface of the second portion with which the pellicle mounting system establishes contact and the surface of the mask. 
     The second distance is preferably longer than a third distance necessary for defocusing the second particle. The pellicle frame includes a contact portion that has an inclined surface and that guides the pellicle mounting system to the establishment of contact with the pellicle frame. The inclined surface is preferably directed outward. The inclined surface is directed inward. 
     According to another aspect of the present invention, there is provided a pellicle that prevents a particle from lying on a mask used for exposing a wafer, comprising: a pellicle membrane; a pellicle frame on which the pellicle membrane is attached; and a supporting member that prevents the pellicle membrane from bending. 
     The pellicle frame preferably includes a fixing mechanism that fixes the supporting member on the pellicle frame. The supporting member preferably lies under the pellicle membrane. The supporting member preferably lies over the pellicle membrane. The supporting member and the pellicle membrane are preferably adhered to each other. 
     The supporting member is preferably a string. The fixing mechanism preferably has a hook for fixing the string. The mechanism preferably has a defined recess for fixing the string. The fixing mechanism preferably has solder for fixing the string. 
     The supporting member is preferably a net. The fixing mechanism preferably uses solder to fix the net. 
     The pellicle frame preferably includes a thick portion thicker than other portions, wherein the supporting member is the thick portion. 
     According to further another aspect of the present invention, there is provided a method of detecting a particle on a mask used for exposing a semiconductor wafer, comprising: applying a ray to the mask on which a pellicle is mounted using a pellicle mounting system, the pellicle including a pellicle membrane and a pellicle frame having a first portion on which the pellicle membrane is attached and a second portion establishing contact with the pellicle mounting system, a surface of the first portion on which the pellicle membrane is attached being lower than a surface of the second portion with which the pellicle mounting system establishes contact, and being higher than the height of the pellicle membrane necessary for defocusing the particle, and receiving a scattering ray produced by the particle from the applied ray. 
     According to still another aspect of the present invention, there is provided a method of mounting a pellicle on a mask comprising: mounting the pellicle on the mask using a pellicle mounting system, the pellicle including a pellicle frame comprising a first contact portion having a first inclined surface, the pellicle mounting system including a second contact portion having a second inclined surface, and the first surface guiding the second surface to establishment of contact between the first contact portion and the second contact portion. 
     According to still another aspect of the present invention, there is provided a method of removing a pellicle from a mask comprising: removing the pellicle from the mask using a pellicle demounting system, the pellicle including a pellicle frame comprising a first contact portion having a first inclined surface, the pellicle demounting system including a second contact portion having a second inclined surface, and the first surface guiding the second surface to removal of the second contact portion from the first contact portion. 
     The method preferably comprises heating the mask to weaken adhesion of an adhesive between the pellicle frame and the pellicle demounting system. 
     According to still another aspect of the present invention, there is provided a method of exposing a wafer, comprising: applying a ray to the wafer through a mask, the mask on which a pellicle is mounted, the pellicle including a pellicle membrane; a pellicle frame on which the pellicle membrane is attached; and a supporting member that prevents the pellicle membrane from bending. 
     According to still another aspect of the present invention, there is provided a method of manufacturing a semiconductor device using a mask, comprising: applying a ray to the mask on which a pellicle is mounted using a pellicle mounting system, the pellicle including a pellicle membrane and a pellicle frame having a first portion on which the pellicle membrane is attached and a second portion establishing contact with the pellicle mounting system, a surface of the first portion on which the pellicle membrane is attached being lower than a surface of the second portion with which the pellicle mounting system establishes contact, and being higher than the height of the pellicle membrane necessary for defocusing the particle, and receiving a scattering ray produced by a particle lying on the mask from the applied ray. 
     According to still another aspect of the present invention, there is provided a method of manufacturing a semiconductor device using a wafer, comprising: applying a ray to the wafer through a mask, the mask on which a pellicle is mounted, the pellicle including a pellicle membrane; a pellicle frame on which the pellicle membrane is attached; and a supporting member that prevents the pellicle membrane from bending. 
     This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the structure of a conventional pellicle; 
     FIG. 2 shows the structure of a pellicle according to a first preferred embodiment of the present invention; 
     FIGS. 3A and 3B are top views of the pellicle frame of FIG.2; 
     FIG. 4 shows a structure of a pellicle according to a second embodiment of the present invention; 
     FIGS. 5A and 5B show structures of pellicles according to a third embodiment of the present invention; 
     FIGS. 6A and 6B show structures of pellicles according to a fourth embodiment of the present invention; 
     FIGS. 7A and 7B show structures of pellicles according to a fifth embodiment of the present invention; 
     FIG. 8 is a top view of the pellicle according to the fifth embodiment of the present invention; 
     FIGS. 9A and 9B show structures of pellicles according to a sixth embodiment of the present invention; 
     FIGS. 10A-10C show the structure of a pellicle according to a seventh embodiment of the present invention; 
     FIGS. 11A and 11B show the structure of a pellicle according to an eighth embodiment of the present invention; 
     FIGS. 12A and 12B show the structure of a pellicle according to a ninth embodiment of the present invention; 
     FIGS. 13A and 13B show the structure of a pellicle according to a tenth embodiment of the present invention; and 
     FIGS. 14A-14C show the structure of a pellicle according to an eleventh embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described based on the preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention. 
     &lt;First Embodiment&gt; 
     A first embodiment of the pellicle according to the present invention is described below. 
     FIG. 2 shows the structure of the first embodiment. In the figure, two pellicles  25  are mounted on the mask  10 . However, the number of pellicles  25  mounted on the mask  10  is not limited to two. As will be described later, a single pellicle  25  may be mounted on the mask  10 . Because the configuration of the upper pellicle  25  and that of the lower pellicle  25  are the same even though their heights differ from each other, for ease of explanation and understanding, in the following only the upper pellicle  25  will be described and the description of the lower pellicle  25  will be omitted. 
     The pellicle  25  incorporates a pellicle frame  20  and a pellicle membrane  30 . The pellicle frame  20  supports the pellicle membrane  30 , wherein the pellicle frame  20  and the pellicle membrane  30  are adhered to each other by the second adhesive  50 . The pellicle  25  is mounted onto the mask  10  by the pressing of the pellicle mounting system  60 . More specifically, the pressing of the pellicle  25  toward the mask  10  using the pellicle mounting system  60  allows the pellicle  25  to be placed at a given position of the mask  10 . The pellicle  25  further incorporates a first adhesive  40 . The first adhesive  40  serves to fix the pellicle  25  on the mask  10 . 
     The feature of the first embodiment is described below. The above pellicle frame  20  comprises a first frame portion  20 A and a second frame portion  20 B. The first frame portion  20 A supports the pellicle membrane  30 , in which the first frame portion  20 A and the pellicle membrane  30  are adhered using the second adhesive  50 . The second frame portion  20 B is used for establishing contact with the pellicle mounting system  60 . Accordingly, when pressing the pellicle  25  to the mask  10 , the pellicle mounting system  60  makes contact with only the second frame portion  20 B, which does not cause a damage to the pellicle membrane  30 . 
     FIGS. 3A and 3B are a top views of the pellicle frame  20  of FIG.  2 . In FIG. 3A the outside corners of the first frame portion  20 A are rounded while in FIG. 3B the outside corners are sharpened. The sharp-corner shape is preferable in terms of ready manufacture of the pellicle frame  20  and can enable reduction of manufacturing costs and product price. 
     As described above, in a pellicle  25  according to the first embodiment, the pellicle frame  20  includes the first frame portion  20 A that supports the pellicle membrane  30  and the second frame portion  20 B that establishes contact with the pellicle mounting system  60 , thereby preventing the pellicle mounting system  60  from damaging the pellicle membrane  30 . 
     &lt;Second Embodiment&gt; 
     A second embodiment of the pellicle according to the present invention is described in the following. 
     FIG. 4 shows the structure of a pellicle according to the second embodiment. The structure of the pellicle of the second embodiment is very similar to that of the pellicle of the first embodiment while the mask  10  and the pellicle mounting system  60  in the second embodiment are the same as those in the first embodiment; therefore, only the unique features of the second embodiment will be made below for ease of description. 
     Similar to the pellicle of the first embodiment, the pellicle of the second embodiment incorporates the pellicle frame  20  and the pellicle membrane  30 ; however, the pellicle frame  20  is shaped unlike the pellicle frame  20  of the first embodiment. More specifically, this pellicle frame  20  is L-shaped, where the first frame portion  20 A and the second frame portion  20 B construct the pellicle frame  20 . As illustrated in FIG. 4, the top surface of the first frame portion  20 A is higher than that of the second frame portion  20 B. The first frame portion  20 A serves to support the pellicle membrane  30  while the second frame portion  20 B acts to establish contact with the pellicle mounting system  60 . Similar to the first embodiment, when pressing the pellicle to the mask  10 , the pellicle mounting system  60  makes contact with the second frame portion  20 B rather than the pellicle membrane  30  and thereby avoids damaging the pellicle membrane  30 . 
     Since the first frame portion  20 A and the second frame portion  20 B are of different heights, the pellicle frame  20  includes a surface perpendicular to the mask  10  between the first and second frame portions  20 A and  20 B. When the pellicle is mounted onto the mask  10 , this surface maintains contact with the inner surface of the pellicle mounting system  60 . Accordingly, the pellicle can be set accurately at a given position on the mask  10 . In other words, the shape of the pellicle frame  20  matches the shape of the tip of the pellicle mounting system  60 , whereby they create no gaps in either the horizontal or the vertical directions. Thus, the pellicle can be arranged accurately at a predetermined position of the mask  10  by the pellicle mounting system  60 . 
     As described above, similar to the first embodiment, the pellicle in accordance with the second embodiment can prevent the pellicle mounting system  60  from damaging the pellicle membrane  30  when pressing the pellicle toward the mask  10 . In addition, the structure of the pellicle does not produce any gap between the pellicle and the pellicle mounting system  60 , whereby the pellicle can be deposited on the mask  10 . 
     &lt;Third Embodiment&gt; 
     A third embodiment of the pellicle according to this invention is described in the following. 
     FIG. 5A shows the structure of the pellicle of the third embodiment. As can be seen from this figure, this structure is extremely similar to that of the second embodiment. Therefore, the following explanation will focus upon the characteristic feature of the third embodiment. 
     Analogous to the first and second embodiments, the pellicle frame  20  includes a first frame portion  20 A and a second frame portion  20 B. The first frame portion  20 A supports the pellicle membrane  30  while the second frame portion  20 B makes contact with the pellicle mounting system  60 . The pellicle mounting system  60  does not come in contact with the pellicle membrane  30 , and therefore can not damage the pellicle membrane  30 . 
     In comparison with the first and second embodiments, the pellicle frame  20  has a different shape. More specifically, the first portion  20 A is higher than the second portion  20 B in the second embodiment; on the contrary, the latter portion  20 B is higher than the former portion  20 A in the third embodiment. The effect of this structure will now be explained hereinafter. 
     FIG. 5B shows the pellicle inspected by the particle inspection system. After the pellicle is mounted on the mask  10  using the pellicle mounting system  60 , the surface of the mask  10  is inspected. To determine whether or not any particle  90  is present on the mask  10 , the light source  60  irradiates a light or laser toward the mask  10  diagonally thereto so that the light detector  80  detects a laser scattered by the particle  90 . However, if the particle  90  lies near the pellicle frame  20  in FIG. 1 having a corner  20 X, the corner  20 X obstructs the path through which the scattered laser must pass, thus failing to arrive at the light detector  80 . Consequently, the particle  90  is not detected. To the contrary, since the configuration of the third embodiment does not have the corner  20 X of the first embodiment, the path is not obstructed, so that the scattered ray can reach the light detector  80  even if the particle  90  exists near the pellicle frame  20 . In this way, the particle  90  is detected. 
     As described above, with the configuration of the third embodiment, similar to the first and second embodiments, the pellicle membrane  30  is not damaged. Moreover, because the pellicle frame  20  requires no corner like corner  20 X, to secure the path that the ray scattered by the particle  90  lying near the pellicle frame  20  should pass along, it ensures accurate detection of such particles  90 . 
     &lt;Fourth Embodiment&gt; 
     A fourth embodiment of the present invention, very similar to the third, is described below. The principle difference between these two pellicles is the shape of the pellicle mounting system  60 . For ease of explanation and understanding, the distinguishing feature of the fourth embodiment will be explained below. 
     FIG. 6A shows a structure of the pellicle mounting system  60  while FIG. 6B shows another such structure. In FIGS. 6A and 6B, the pellicle mounting system  60  is so shaped as to agree with the shape of the pellicle frame  20 . More specifically, in FIG. 6A, the pellicle mounting system  60  has a portion  60 A for maintaining contact with the second frame portion  20 B. The portion  60 A ensures that there is no gap between the pellicle mounting system  60  and the pellicle frame  20 , thus enabling the pellicle mounting system  60  to tightly hold the pellicle. Similarly, in FIG. 6B, the pellicle mounting system  60  further comprises a portion  60 B for maintaining contact with the first frame portion  20 B, where the portion  60 B acts in the manner of the portion  60 A. 
     As described above, according to the fourth embodiment, the pellicle mounting system  60  has a shape that matches that of the pellicle frame  20 , whereby the pellicle mounting system  60  can press the pellicle toward the mask  10 , with no resulting gap produced. 
     &lt;Fifth Embodiment&gt; 
     A fifth embodiment of the present invention will next be described. The distinguishing feature of the fifth embodiment is the shapes of the pellicle frame  20  and the pellicle mounting system  60 . FIGS. 7A and 7B show the structure of the fifth embodiment. In FIGS. 7A and 7B, the pellicle frame  20  has contact portions  20 S while the pellicle mounting system also has contact portions  60 S. Here, the pellicle mounting system  60  serves to mount the pellicle on the mask  10 , and serves to demount or remove the pellicle from the mask  10 . Therefore, the system  60  may be referred to as the pellicle mounting system  60 , the pellicle demounting system  60 , or the pellicle mounting/demounting system  60  in the following explanation. The contact portions  20 S are inclined and the contact portions  60 S are also inclined, wherein they face to each other. The mask  10  on which the pellicle should be mounted is fixed by the mask fixing members  70 . The other elements are the same as those of the above described embodiments. 
     FIG. 8 is a top view of the apparatus shown in FIGS. 7A and 7B. In the figure, the pellicle is supported by the pellicle mounting system  60  on all sides. In other words, all of the contact portions  20 S establish contact with the respective contact portions  60 S. 
     In the configuration shown in FIG.  7 A and FIG. 8, in order to seize the pellicle, the pellicle mounting system  60  is moved toward the height of the contact portions  20 S vertically so that the contact portions  60 S face to the respective contact portions  20 S, that is to say, so that the contact portions  60 S surrounds the contact portions  20 S. Next, the contact portions  60 S approaches the respective contact portion  20 S horizontally, whereby the pellicle mounting system  60  seizes the pellicle frame  20 . As both the contact portions  60 S and the contact portions  20 S are sloped, they readily establish contact with each other. Stated another way, the pellicle mounting system  60  readily grasps the pellicle frame  20 . 
     As described above, because the pellicle frame  20  has contact portions  20 S and the pellicle mounting/demounting system  60  has contact portions  60 S, the pellicle mounting/demounting system  60  can readily seize the pellicle frame  20 . More specifically, the shapes of the contact portions  60 S and the contact portions  20 S enable the pellicle mounting/demounting system  60  and the contact portion  20  to easily establish contact with each other. Therefore, the accuracy in the movement of the pellicle mounting/demounting system  60  is not required to the extent of the prior art. In other words, the pellicle mounting/demounting system  60  of this embodiment is permitted to move or slide more roughly compared with the prior art, which can reduce the cost of manufacturing the semiconductor devices. 
     In FIG. 7B, to remove the pellicle from the mask  10 , the pellicle demounting system  60  seizes the pellicle frame  20  as outline above. Next, the pellicle demounting system  60  lifts up the pellicle while the mask  10  remains at the same position. 
     As described above, because the pellicle demounting system  60  lifts up the pellicle by maintaining contact with all the sides of pellicle frame  20 , the removal force of the pellicle demounting system  60  is uniformly applied to the pellicle frame  20 , whereby the pellicle is readily removed from the mask  10 . In addition, as shown in FIG. 7B, heating the adhesive by which the pellicle frame  20  and the mask  10  are adhered with each other enables removing the mask  10  with less force. 
     &lt;Sixth Embodiment&gt; 
     A sixth embodiment of the present invention is described below. 
     FIGS. 9A and 9B show the structure of the sixth embodiment. Similar to the pellicle mounting/demounting system  60  in the fifth embodiment, this pellicle mounting/demounting system  60  is vertically moved toward the pellicle and is horizontally moved to seize the pellicle, thus mounting the pellicle onto the mask  10 . In addition, Similar to the fifth embodiment, the pellicle frame  20  and the pellicle mounting/demounting system  60  have contact portions  20 S and contact portions  60 S, respectively. However, the relationship between the contact portion  20 S and the contact portions  60 S in this embodiment is inverse to that of the fifth embodiment. That is to say, the pellicle mounting/demounting system  60  in the fifth embodiment seizes the pellicle from the outside of the pellicle while the pellicle mounting/demounting system  60  in the sixth embodiment seizes the pellicle from the inside of the pellicle. 
     In the configuration shown in FIG. 9A, similar to that of FIG. 7A, when mounting the pellicle on the mask  10 , the pellicle mounting system  60  is moved so that the contact portions  60 S are closer to the contact portions  20 S. Subsequently, the contact portions  60 S are slid on the corresponding contact portions  20 S while the height of the pellicle mounting system  60  is kept almost unchanged, thus allowing the contact portions  60 S and the contact portions  20 S to establish contact with each other. As a result, the pellicle mounting system  60  can securely seize the pellicle. Maintaining this seizure, the pellicle mounting system  60  mounts the pellicle on the mask  10 . 
     In the apparatus of FIG. 9B, similar to that of the fifth embodiment, when removing the pellicle from the mask  10 , first the pellicle demounting system  60  seizes the pellicle. Next, the pellicle demounting system  60  lifts up and removes the pellicle from the mask  10 . Analogously to FIG. 7B, heating the adhesive serving between the pellicle and the mask  10  eases removal of the pellicle from the mask  10  because the adhesion force of the adhesive is weakened. 
     As described above, in accordance with the sixth embodiment, the contact portions  20 S of the pellicle frame  20  and the contact portions  60 S of the pellicle mounting/demounting system can give the same effect as that of the fifth embodiment. 
     &lt;Seventh Embodiment&gt; 
     A seventh embodiment of the pellicle according to the present invention is described below. 
     FIG. 10A is a perspective view showing the pellicle frame of the seventh embodiment. In FIG. 10A, the pellicle frame  20  has two hooks  100  paired with two respective recesses. One pair is made on a side surface of the pellicle frame  20 , while the other pair is made on the side surface opposite to the above side surface. These hooks  100  and recesses are used for holding a string  120  that supports the pellicle membrane  30 , as detailed below. 
     FIG. 10B is a perspective view showing the pellicle frame  20  holding the string  120 . In the figure, both the ends of the strings  120  are fixed at the respective hooks  100 , and are specifically tied into the hooks  100 , wherein the string  120  is stretched over the pellicle frame  20  through the recesses  110 . From the viewpoint of the influence upon exposure of the wafer, the string  120  preferably has a width of less than  50  microns, while the number of strings  120  is not limited to one; a plurality of strings  120  may be employed. 
     FIG. 10C is a cross sectional view showing the complete structure of a pellicle covered with the pellicle membrane  30 . In FIG. 10C, on the string  120  lies the pellicle membrane  30 . The pellicle membrane  30  is prone to bend due to its weight, but the string  120  resists the bending of the pellicle membrane  120 , and thereby maintains the shape of the pellicle membrane  120 . 
     As described above, in accordance with the seventh embodiment, the string  120  is arranged over the pellicle frame  20  to support the pellicle membrane  30 , thereby preventing the pellicle membrane  30  from bending downward due to its weight. As the desire to employ larger pellicle membranes  30  has sharply increased, the advantage offered by this embodiment can meet that demand. 
     &lt;Eighth Embodiment&gt; 
     An eighth embodiment of the pellicle in accordance with this invention is explained below. 
     FIG. 11A is a perspective view of the pellicle frame  20  of the eighth embodiment. Whereas the pellicle frame  20  of the seventh embodiment comprises recesses  110 , the pellicle frame  20  of this embodiment has no recesses. Accordingly, similar to the seventh embodiment, the string  120  is stretched over the pellicle frame  20 , but without assistance of recesses. 
     FIG. 11B is a cross sectional view showing the eighth embodiment of the pellicle frame  20 . In the figure, in contrast with the seventh embodiment, the string  120  lies on the pellicle membrane  30 , being adhered thereto with an adhesive. In this way, the string  120  supports the pellicle membrane  30 . 
     As described above, according to the eighth embodiment, the string  120  arranged over the pellicle frame  20  supports the pellicle membrane  30 , thus preventing the pellicle membrane  30  from bending due to its own weight. 
     &lt;Ninth Embodiment&gt; 
     Hereinafter, a ninth embodiment of the pellicle according to the present invention is described in detail. As explained above, the pellicle frame  20  of the seventh and eighth embodiments comprises both hooks  100  and recesses  110 . To the contrary, the structure of the pellicle frame  20  of the ninth embodiment is simplified to comprise neither hooks nor recesses. 
     FIG. 12A is a perspective view showing the pellicle frame  20  of the ninth embodiment, and FIG. 12B is a cross sectional view of the pellicle. In FIG. 12A, the ends of the string  120  are soldered on the pellicle frame  20 , wherein the string  120  is stretched over the pellicle frame  20 . In FIG. 12B, the pellicle membrane  30  lies on, and this is supported by, the string  120 . 
     As described above, in accordance with the ninth embodiment, similar to the preceding embodiment, the string  120  stretching over the pellicle frame  20  can prevent the pellicle membrane  30  from bending under its own weight. In addition, the string is directly fixed on the pellicle frame  20  using only the solder, which simplifies the structure of the pellicle in comparison with those embodiments. 
     &lt;Tenth Embodiment&gt; 
     A tenth embodiment of the pellicle according to the present invention is described below. 
     FIG. 13A is a perspective view of the tenth embodiment of the pellicle, and FIG. 13B is a cross sectional view thereof. Whereas the pellicle of the previous embodiments employ the string  120  to support the pellicle membrane  30 , the pellicle of this embodiment employs a net  130  in lieu of the string  120  of the ninth embodiment, as shown in FIG.  13 A. This net  130  is directly attached on the pellicle frame  20  using solder or the like. Like the string  120 , the width of the net  130  is preferably smaller than 50 microns. 
     In FIG. 13B, the pellicle membrane  30  lies on, and is supported by the net  130 . 
     As described above, in accordance with the tenth embodiment, the net  130  is deposited on the pellicle frame  20  to thereby prevent the pellicle membrane  30  from bending due to its weight. 
     &lt;Eleventh Embodiment&gt; 
     An eleventh embodiment of the pellicle according to the present invention is explained below. 
     FIG. 14A is a perspective view of the pellicle membrane, FIG. 14B is a perspective view of the pellicle frame, and FIG. 14C is a cross sectional of the pellicle. 
     While the pellicle membranes  30  of the preceding embodiments are flat, the pellicle membrane  30  of the eleventh embodiment has a thick portion  30 A. The portion  30 A serves to support the pellicle membrane  30  itself, which characterizes this embodiment. Other elements including the pellicle frame  20  shown in FIG. 14B are the same as those in the previous embodiments. 
     In FIG. 14C, the membrane  30  is attached on the pellicle frame  20 , wherein the portion  30 A stretches over the pellicle frame  20 . Since the thickness of the portion  30 A is larger than those of other portions, the portion  30 A resists the bending force produced by the weight of the pellicle membrane  30 . Therefore, according to this embodiment, the thick portion  30 A provided in the pellicle membrane  30  supports the pellicle membrane  30  itself. Thus, the pellicle membrane  30  does not bend downward due to its own weight. 
     Although the present invention has been described by way of exemplary embodiments, it should be understood that many changes and substitutions may be made by those skilled in the art without departing from the spirit and the scope of the present invention which is defined only by the appended claims.