Abstract:
A mask pellicle removal apparatus for separating a mask pellicle from a glass reticle to which it is bonded by prying against its releasable bond. The apparatus includes a table support for nesting the glass reticle and for supporting a manually operated prying mechanism having only the necessary degrees of freedom for prying free the mask pellicle without damaging the glass reticle.

Description:
This is a division of patent application Ser. No. 08/813,567, filing date Mar. 7, 1997 now U.S. Pat. No. 5,953,107, Mask Pellicle Remove Tool, assigned to the same assignee as the present invention. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Technical Field 
     This invention applies generally to methods of photo-printing microcircuit patterns on photosensitive coated substrates used in the manufacture of semiconductor slices and more particularity, to a method and apparatus for removing a pellicle frame from a surface of a photomask consisting of an array of enlarged circuit patterns. 
     (2) Description of the Prior Art 
     The following three documents relate to various methods dealing with pellicle mounting apparatus. 
     U.S. Pat. No. 4,637,713 issued Jan. 20, 1987 to Shulenberger et al, discloses a pellicle mounting apparatus having a pair of pellicle holder assemblies positioned on either side of a photomask holder assembly. 
     U.S. Pat. No. 5,311,250 issued May 10, 1994 to Suzuki et al, shows another pellicle mounting apparatus. 
     U.S. Pat. No. 5,422,704 issued Jun. 6, 1995 to D. Sego discloses a pellicle frame. 
     A wafer for the manufacture of a semi-conductive elements is subjected to numerous sequenced operations which enable the fabrication of all its circuit elements. The use of a photo resist material in conjunction with photograhic masks provides the means to transfer the various pattern layers to the semiconductor wafer. The photo mask carries an enlarged pattern which is optically reduced upon each wafer&#39;s surface by projection printing. The layers upon which these images are to be reproduced are either a semiconductor, an oxide on a semiconductor, or a metal film covering the semiconductor. 
     The image formed in the photo resist can not be better than the photomask used to determine the exposed and unexposed areas. The most important characteristics that the image must possess are; dimensional correctness, uniform density in both clear and opaque areas, and sharp definition between clear and opaque areas. 
     In most applications, thousands of images are formed on a single photomask. A sequenced series of photomasks is required to complete a given semi-conductive device. Each mask controls the exposure of window patterns on wafers coated with photo sensitive resist material. This resist material is processed (developed) to wash away the exposed resist which permits access through the windows for depositing, implanting, or etching a variety of materials. 
     Multiple mask images which make up a mask series are produced with a defined, closely controlled spacing. In most semiconductor manufacturing operations, a series of photomasks are required to produce finished semi-conductive devices. Since the series of masks are used sequentially, mask alignment and the center to center spacing between features produced by successive masks must conform to preceding mask images to form a coherent array of materials in the layers of the devices being built. 
     It is well known that during the manufacture of semiconductive devices the goal is to achieve defect free exposures of circuit patterns. As integrated circuits evolved from small scale integration to very large scale integration the need for ultra clean manufacturing space became increasingly critical. As an example, a single airborne particle landing on the photomask surface during exposure can ruin the circuit exposed on the wafer below it. 
     To help solve this problem, the photolithographic industry developed pellicles to intercept particulates and protect the surfaces of photomasks against all forms of contamination. Pellicles include a thin, transparent membrane stretched across a frame. The frame holds the membrane in tension and keeps it away from the mask surface by the thickness of the frame. An adhesive is used to bond the frame to a surface of the photomask. 
     Because of the obvious inherent simplicity of this device, it has found use over a very wide range of the electromagnetic spectrum. The pellicle concept has been used in the optical industry for many years. A transparent membrane would have the effect of increasing the number of wavelengths in an optical path, or as a beam splitter in interferometry. Its application has been extended to photolithography by intercepting dust particles and other contaminents from reaching the focal plane of photomasks. 
     Many difficulties have been fronted in properly removing pellicle assemblies from photomasks. This procedure is necessary when cleaning or replacing damaged pellicle membranes. Presently, this job is done manually with the aid of simple hand tools and a stereomicroscope. Techniques for removing pellicle assemblies from photomasks vary widely. Each technician developes their own procecure and craftiness therefore, at times, cause costly miscues. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide apparatus for removing pellicle assemblies from a photomask without damaging the photomask&#39;s image quality. 
     Another object of the present invention is to standardize the removal process of pellicle assemblies by eliminating the crafty dependance of an operator. 
     In accordance with the objects of this invention, a new method and apparatus is provided to standardize the removal of pellicle assemblies from photomasks. This invention describes an apparatus that requires less skill and training with little chance of damaging the photomask or producing inbedded particulates on the plane of the mask&#39;s circuit pattern causing repeating shorts or opens during a wafer&#39;s exposure process. 
     Briefly, the invention describes a mechanical apparatus that permits only the degrees of freedom necessary for removing the pellicle assembly from the photomask. The mechanical apparatus is positioned inline with a pellicle/photomask nesting station. A mask is placed within the nesting station, the apparatus is then moved towards the pellicle/photomask assembly until a pair of prying arms come into contact with adjacent corners of the pellicle at the bonded interface between the pellicle frame and photo mask. The materials making contact with the pellicle assembly and photomask especially in the area of prying are delicate in composition and non-obtrusive to the photomask&#39;s glass surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the present invention shown in its working position for removing a mask pellicle. 
     FIG. 1A is an isometric view of the present invention illustrating the upper mask pellicle removal apparatus. 
     FIG. 2 is an abbreviated top view illustration of the present invention. 
     FIG. 3 is a top view of a typical 5× photomask, of the prior art, with a mask pellicle in place showing a layout of an array of reticle cells. 
     FIG. 3A is a fragmentary view of an attached mask pellicle of the prior art. 
     FIG. 4 is a top view representation of a six inch, 5× photomask showing the lens image exposure area relative to the pellicle frame. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described with reference to the drawings. Referring briefly to FIGS. 3 and 3A an array of reticle cells  18  is etched through a thin metal plating deposited on the surface of a glass substrate  10  and protected from particulates and other forms of contamination by a pellicle frame assembly  12 . Assembly  12  consists of an aluminum frame  19  with a pellicle membrane  13  having an anti-reflection coating thereof. The pellicle membrane is stretched and adhered with an adhesive  16  to the top surface  14  of frame  19  effecting a transparent and protective top enclosure. Assembly  12  is placed on the glass substrate and aligned to encompass the reticle array. The bottom edge of the aluminum frame  15  is bonded with adhesive  16  to the image side of the glass substrate. The bonding of the pellicle membrane to the aluminum frame and the pellicle frame assembly to the glass reticle is done off line,and prior to a lithographic exposure. 
     All references to the pellicle frame assembly will hereafter be referred to as mask pellicle. 
     The present invention is utilized when the mask pellicle requires cleaning or is damaged. The bonded mask pellicle must be removed from the glass photomask without damaging the reticle pattern. 
     FIGS. 1 and 1A are illustrations showing a mask pellicle removal apparatus according to the embodiment. With reference to FIG. 1, a base  30  is a heavy, flat plate which provides stability for a prying mechanism  20  shown in FIG. 1A. A pair of bearing plates  21  and  22  having one end slidably engaged with parallel dovetail guides  23  and  24  are spaced apart and recessed in the base said bearing plates extend upward to a rotatable shaft  34  which is transversely placed through journal bearings  31  and  32  located at the other end of the bearing plates. L shaped Lever  33  is disposed intermediate the bearing plates and the horizontal lever member fixed horizontally to the pivot shaft with a locking screw  38 . The vertical member of the lever is bifurcated to limit the lever rotation by the space between members  26  and  27  with base  30 . Making member  26  shorter relative to member  27  permits a greater downward rotation of the horizontal member. A right arm  35  and a left arm  36  are each mounted with two screws  39  at opposite ends of the pivot shaft. The arms designed to converge downward are mounted parallel to each other on opposite ends of the pivot shaft and extend forward horizontally to midway its length are then angled downward while converging as best illustrated in FIG.  1 . Blade insert  37   a  is mounted with two screws  39  to the forward end of arm  35  and blade insert  37   b  is mounted with two screws  39  to the forward end of arm  36 . The blade inserts are made of a teflon base material, polyvinylidenefluoride, having sufficient strength for prying off the mask pellicle from the glass reticle yet resilient not to cause damage to the glass or reticle array. The blade inserts are shaped to fit under a recessed front portion of the arms, and tapered in two steps. The first step is to allow visual access for positioning of the blade inserts towards the bottom edge of the mask pellicle and the second tapered step forms a sharp edge that is used for prying the mask pellicle from the glass reticle. 
     Base  30  with the manually operated prying mechanism that is used to remove the mask pellicle is positioned, aligned, and secured to a table surface  40  with 4 corner screws  25  behind a pattern of raised dowel pins  19  pressed into a plurality of holes in the table surface forming a bordered nest for the glass reticle as illustrated in FIG.  1 . 
     FIG. 4 shows the positions of blade inserts  37   a  and  37   b  relative to the reticle pattern and the edge of the glass reticle. As pictured, the operating space for removing the mask pellicle is limited by both the glass edge at the outside of the frame and the reticle pattern at the inside of the frame. Care must be taken to avoid damage to the reticle pattern and the glass surface. 
     During photolithography, an exposing apparatus is used in semi-conductor manufacturing. A lens exposure field  9  is shown in FIG. 4 during a typical exposure of a pellicle shielded retical array. 
     The operating procedure for the use of apparatus  20  will be discussed with primary reference to FIGS. 1 and 2. The procedure begins with the placement of the glass reticle  10 , with its mask pellicle attached, onto a table  40  within a bounding location defined by pins  19 . Lever  33  is depressed to lift the blade inserts above the top surface of the glass reticle while the upper portion of assembly  20  is moved slidably towards the mask pellicle while lowering the blade inserts to gently rest on the glass reticle until contact is made between the blade inserts and the bottom edge of the mask pellicle. Forward pressure is applied to the upper assembly  20  while depressing lever  33 . The pressure angle imposed on the bottom edge of the mask pellicle by the blade inserts and its angle of rotation will generate shear and tensile force components sufficient to dislodge the adhesion bond between the mask pellicle and glass substrate. The mask pellicle is then carefully lifted away from the glass reticle. Both translating and rotating motions are limited by preset mechanical stops, not shown, to avoid overtravel that may excessively push or lift the loosened mask pellicle thereby causing damage to the unprotected reticle pattern or to the glass surface. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.