Abstract:
A container is provided for storing a lithographic printing mask. A first container section is formed of a sturdy material which defines a central inner recess area that is shaped to house a mask and to hold outer edges of a mask without touching a pattern on the mask. A second identical container section is placed against the first container section with a mask housed within recesses of, both to form a container which has a common pressure level all around and therein. A higher pressure level is then applied outside the container causes the first and second sections of the container to be held together. To remove the mask from the container, the pressure outside the container is reduced to substantially the pressure level inside the container and the first and second sections are pulled apart.

Description:
This application is a continuation application of application Ser. No. 09/757,715, filed Jan. 9, 2001 ABN. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a container useful for holding (storing) mask, e.g., a Next Generation Lithography (NGL) mask, and preventing dust or other particles from reaching the mask, and to a method of using the container. 
     BACKGROUND OF THE INVENTION 
     Keeping a mask used in the fabrication of integrated circuits clean is critical. Dust or other particles on a mask can cause corresponding spots to be formed on the substrate of an integrated circuit being formed when the mask is illuminated. Such spots will produce an inaccurate reproduction of the mask on the substrate and thereby can reduce yield. 
     In prior art optical projection printing systems, light is generally projected from a light source through a lens arrangement and then a mask having a predetermined pattern formed thereon that is stored in a pellicle. The image projected from the mask is incident on a substrate having a light sensitive layer, e.g., photoresist, formed on a surface thereof. In this regard, see, for example, U.S. Pat. No. 4,131,363 (Shea et al.), issued on Dec. 26, 1978. The pellicle in such printing systems generally comprises a solid frame for holding a mask, and a transparent thin film that covers an upper opening of the frame. To print a mask pattern, the substrate and the mask within the pellicle are cleaned to remove any dust or particles thereon, and the bottom of the pellicle frame is securely mounted above the substrate around a light sensitive layer thereon to be irradiated. The pattern on the mask within the pellicle is then irradiated to transfer the pattern of the mask onto the light sensitive layer on the substrate. Generally, dust or other particles on the transparent thin film stretched over the pellicle frame is of no concern. This is because the film is positioned a sufficient distance above the mask so that dust or other particles on the film are out of focus when the surface of the substrate is irradiated through the mask with the type of radiation (e.g., Ultraviolet (UV), deep UV, or X-ray radiation) used in the prior art systems. Therefore, such dust or other particles on the surface of the pellicle itself do not affect the printed-pattern on the substrate. 
     Pellicles used in the prior art photolithography systems are generally secured to the substrate by various techniques such as using an adhesive, vacuum chucking techniques, magnets, and spring loading arrangements to protect the mask area from dust or other particles. In this regard see, for example, U.S. Pat. No. 4,833,051 (Imamura), issued on May 23, 1989. Prior art pellicles also have included various passageways through the sides of the pellicle frame for equalizing atmospheric pressure changes that occur between the protected area within the pellicle and outside of the pellicle while still protecting the protected area within the pellicle from dust or particles. Such passageway arrangements prevent the thin film covering the frame of the pellicle from deforming and contacting the surface of the mask when the pellicle is transported via different altitudes and/or environments. These passageways in the pellicle frame can include serpentine channels or a straight through passageway with filters mounted therein. In this regard see, for example, the Imamura patent cited above, and U.S. Pat. No. 6,055,040 (Sego), issued on Apr. 25, 2000. 
     For all Next Generation Lithography (NGL) systems where a narrow beam of radiation is used as, for example, electron beam printing technology, keeping a mask clean is critical. However, known pellicle materials are not transparent enough to radiation, e.g., electron beams and extreme ultraviolet radiation, used with NGL systems. 
     It is desirable to provide a container for holding a, mask that is to be used with NGL systems during transportation, storage, etc. to keep dust and/or particles from depositing on the mask. The design of the container should also reduce the chance of dust and/or particle being deposited on a mask during mask loading and unloading into and out of the container. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a container and use thereof for temporarily storing a Next Generation Lithography (NGL) mask in order to keep such a mask clean prior to it being used with, for example, electron beam printing technology. 
     A first apparatus aspect of the present invention is a container for housing a lithographic mask. The apparatus comprises a first section and a second section. The second section is in contact with the first section with the contacting first and second sections defining a cavity having a size-which is sufficient to house a lithographic mask and provide an air tight seal around the cavity when pressure within the cavity is less than pressure outside the container such that dust and other particles cannot reach a lithographic mask housed in the cavity. 
     A second apparatus aspect of the present invention is a container for storing a lithographic printing mask. The container comprises a first container section formed, of a sturdy material and a second container section formed of a sturdy material. When the first and second container sections are placed together they define a cavity therein having a size to fixedly house a mask while not contacting a mask pattern on the mask and provide an air tight seal around the cavity when pressure within the cavity is less than pressure outside the container such that dust and other particles cannot reach the mask housed in the cavity. 
     A third apparatus aspect of the present invention is a container for storing a lithographic printing mask. The container comprises first and second sections. The first container section is formed of a sturdy material and defines a first cavity which is shaped for contacting an edge section of a mask to be stored in the container and covers, but does not contact an area of a mask pattern on the mask when the edge section of the mask is placed in the cavity. The second container section is formed from a sturdy material and defines a second cavity therein having a size which contacts an edge section of a mask to be stored in the container wherein when the first and second container sections are placed together they fixedly house the mask in the first and second cavities and provide an air tight seal around the cavity when pressure within the first and second cavities is less than pressure outside the container such that dust and other particles cannot reach the mask housed in the cavity. 
     A fourth apparatus aspect of the present invention is a container for storing a lithographic printing mask. The container comprises first and second container sections. The first container section is formed of a sturdy material and defines a first cavity which is shaped for contacting an edge section of a mask to be stored in the container and covers, but does not contact an area of a mask pattern on the mask when the edge section of the mask is placed in the cavity. The second container section is formed from a sturdy material and defines a second cavity therein having a size which contacts an edge section of a mask to be stored in the container wherein when the first and second container sections are placed together they fixedly house the mask in the first and second cavities and provide an air tight seal around the cavity when pressure within the first and second cavities is less than pressure outside the container such that dust and other particles cannot reach the mask housed in the cavity. 
     A method aspect of the present invention is a method of storing a mask in a container comprising first and second sections which are both cleaned to remove particles thereon. The method comprising the steps of: placing first and second cleaned sections of the container and a cleaned mask in a chamber and reducing the pressure within the chamber to a first pressure level; while the mask is in the chamber which is at the first pressure level, placing the mask in a cavity defined by portions of the first container section such that a mask pattern on the mask does not contact any portion of the first container; while the mask is in the cavity, placing the second container section in contact with the first container section to form the container and to seal the cavity therein from dust and particles and any pressure changes outside the container; and raising the first pressure level surrounding the container to a second higher pressure level to seal and hold the first and second container sections together. 
     The invention will be better understood from the following more detailed description taken with the accompanying drawing and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross-sectional side view of a container with a Next Generation Lithography (NGL) mask stored (housed) therein in accordance with the present invention; 
     FIG. 2 shows a cross-sectional schematic view of a vacuum chamber with the container (shown in perspective view) of FIG. 1 housing a NGL mask in accordance with the present invention; and 
     FIG. 3 shows a cross-sectional side view of an other container with NGL mask stored (housed) therein in accordance with the present invention. 
     The drawings are not necessarily to scale. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is to be understood that corresponding elements having the same function in the several views of the drawings are provided with the same designation numbers. 
     Referring now to the FIG. 1, there is shown a cross-sectional side view of a container  10  for storing (housing) a mask  12  in accordance with the present invention. The container  10  is particularly suited for housing (storing) a mask  12  of the type used in Next Generation Lithography (NGL) systems including electron beam lithography and may be used for housing conventional lithographic masks. The storage container  10  comprises an upper half  14  and a lower half  16 . In a preferred embodiment the halves  14  and  16  are identical. The upper half  14  and the lower half  16  of the storage container  10  are formed of a sturdy material such as, for example, a metal, plastic, or other sturdy composition material (i.e., a material capable of esentially not deforming with a vacuum applied to portions thereof). Each of the upper and lower halves  14  and  16  defines first and second inner recess sections (cavities)  18   a  and  18   b  in a portion of the first and second halves  14  and  16  when the two halves  14  and  16  are placed together. The first inner recess section (cavity)  18   a  is formed around an outside edge of the overall inner recess area for contacting and holding edge portions of the mask  12  when it is stored therein. The second inner recess section (cavity)  18   b , which is deeper than the first inner recess section  18   a , is in a central area of the overall inner recess area so that it does not contact, and is over the area of the mask  12  where a mask pattern is actually found. A compressible O-Ring  19  is positioned around a surface  15  of one of the upper and lower halves  14  and  16  where the halves  14  and  16  where the upper and lower halves  14  and  16  come together to prevent air leakage into the first and second inner recess section  18   a  and  18   b  when the container  10  is subsequently vacuum sealed with a mask  12  stored therein. The compressible material can comprise any suitable material such as, rubber, which will seal the first and second inner recesses  18   a  and  18   b . Optionally, small channels (not shown) can be formed in both the upper and lowers halves  14  and  16  of container  10 . These channels are in communication with each other at least one location where the upper and lower halves  14  and  16  contact each other so as to help ensure that pressures in recesses  18   b  of both halves are equal. 
     Referring now to FIG. 2, there is shown a perspective view of a vacuum chamber  26  with the container  10  of FIG. 1 therein. To mount a mask  12  in the container  10 , the first and second halves are separated and placed within the vacuum chamber  26  (shown within a dashed line rectangle) which is dust and particle free. A selectively operated vacuum source (not shown) reduces the pressure in the chamber  26  to a predetermined vacuum level via a port  28 . The surfaces of the mask  12  and especially the inner recess areas  18   a  and  18   b  are then cleaned to make sure that no dust or particles remain thereon. The mask  12  is then placed in the inner recess section  18   a  of the second half  16  of the container  10 , and the first half of the container  10  is symmetrically placed onto the second half  16  and in contact with the O-ring  19 . At his point in time, the predetermined pressure (vacuum) level in the chamber  26  is the same inside the first and second inner recess areas  18   a  and  18   b  and outside the container  10 . The pressure in the chamber  26  is then increased to atmospheric pressure outside of the chamber  26 . The pressure outside the container  10  is now greater than the pressure level inside the first and second inner recess sections  18   a  and  18   b . This holds the first and second halves together. Additionally, the O-ring  19  is compressed by the holding force of the vacuum in the first and second inner recesses  18   a  and  18   b  to prevent air from leaking into the first and second inner recess sections  18   a  and  18   b . The container  10  storing (housing) a mask  12  can then be then removed from the chamber  26  and shipped to where it will be used. 
     In use, a container  10  housing a mask  12  is placed in a clean chamber  26  where a lithographic machine (not shown) is located. The pressure in the chamber  26  is reduced to the predetermined vacuum level so that the container  10  can be opened, i.e., the sections  14  and  16  can be separated. Once the container  10  in opened in the clean chamber  26 , the mask  12  is removed from the container  10  and transferred for use in the lithographic machine to print a plurality of circuit substrates (not shown). It is to be noted that the upper  14  and lower  16  halves are not connected together at all by a hinge or other type of coupling device. This means that there are no surfaces that rub against each other when the two halves  14  and  16  are separated. Accordingly, there are no particles formed from a coupling device that can fall onto the mask  12  stored in the container  10  of FIG. 1 or the container  10   a  of FIG.  2 . 
     Referring now to FIG. 3, there is shown a cross-sectional side view of a container  10   a  for storing (housing) a mask  12  in accordance with the present invention. The container  10   a  is similar to the container  10  of FIG. 1 but comprises a different outside configuration without extra protrusions, and has a somewhat different internal recess configuration. The storage container  10   a  comprises an upper half  14   a  and a lower half  16   a  which have a rectangular shape. Each of the upper and lower halves  14   a  and  16   a  defines first and second inner recess sections  18   aa  and  18   bb  in a portion thereof when the two halves  14   a  and  16   a  are placed together. The first inner recess section  18   aa  is formed around an outside edge of the overall inner recess area for contacting and holding edge portions of the mask  12  when the mask  12  is stored in the upper and lower halves  14   a  and  16   a . This avoids movement of the mask  12  during any movement of the container  10   a  which can cause the possible release of particles from the rubbing of the mask  12  with the container  10   a . The second inner recess section  18   bb , which is deeper than the first inner recess section  18   aa , is in a central portion of the overall inner recess area so that it does not contact and is over the area of the mask  12  where a mask pattern (not shown) is actually found. 
     A layer of a compressible material  20  is positioned around the circumference of the container  10   a  outside the first inner recess section  18   aa  where the upper and lower halves  14   a  and  16   a  come together to prevent air leakage into the first and second inner recess section  18   aa  and  18   bb  when the container is subsequently vacuum sealed with a mask  12  stored therein. The upper half  14   a  and the lower half  16   a  of the container  10   a  are formed of a sturdy material such as, for example, a metal, plastic, or other sturdy composite material and define first and second inner recess sections  18   aa  and  18   bb  when the two halves  14   a  and  16   a  are placed together. The recess section  18   aa  is formed around the recess section  18   bb  and is sized to hold edge portions of the mask  12  when it is stored therein. The inner recess section  18   aa  is sized such that it does not contact the area of the mask  12  where the mask pattern is actually found. The layer of a compressible material  20  is positioned around a surface  15   a  of at least one of the upper and lower halves  14   a  and  16   a  where the halves  14   a  and  16   a  come together to prevent air leakage into the first and second inner recess sections  18   aa  and  18   bb  when the container  10   a  is subsequently vacuum sealed with a mask  12  therein. The compressible material  20  can comprise any suitable material such as, rubber, which will seal the first and second inner recesses  18   aa  and  18   bb.    
     The mask  12  can be inserted and removed from container  10   a  using the vacuum chamber  26  of FIG. 2 in essentially the same manner as container  10  of FIG. 1 has a mask  12  inserted and then removed therefrom. 
     It is to be appreciated and understood that the specific embodiment of the invention described hereinbefore are merely illustrative of the general principles of the invention. Various modifications may be made by those skilled in the art which are consistent with the principles set forth. More particularly, the first and second halves  14 ,  14   a  and  16 ,  16   a  can have any other shape as, for example, a rectangular outside shape with or without external protrusions from that shown in FIGS. 1-3.