Abstract:
A shadow frame and framing system for semiconductor fabrication equipment comprising a rectangular frame having four edges, the edges forming an interior lip with a top surface and an bottom engagement surface; and a cross beam disposed between at least two edges of the frame, the cross beam having a top surface and a bottom engagement surface, the engagement surface of the cross beam configured to be flush with the engagement surface of the lip; wherein one or more of the engagement surfaces are configured to cover metal interconnect bonding areas on a carrier disposed below the frame. The shadow frame is particularly useful in plasma enhanced chemical vapor deposition (PECVD) applications used to make active matrix liquid crystal displays (AMLCDs) and solar cells.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    The invention pertains to the field of semiconductor processing equipment, and more particularly to a shadow framing system for use in semiconductor manufacturing over a large substrate or carrier.  
           [0003]    2. Background Information  
           [0004]    Large panel displays, such as those manufactured with thin film technology (hereinafter “TFT”), are used in a wide variety of electronic applications as a display device for presenting information to a user. Such displays, for instance active matrix liquid crystal displays (hereinafter “AMLCDs”) are often manufactured on a glass substrate (or over a carrier, which supports a substrate) of approximately 550 by 650 centimeters in dimension. In an exemplary environment, the displays comprise arrays of red, blue and green electronic cells that are driven through one or more grids of control lines.  
           [0005]    The control lines are driven by control electronics elements, which are mounted to the substrate in one or more contact regions (metalization regions) on the upper surface of the substrate. The contact regions are generally free of semiconductor materials, such as SiN, a-Si, n+ Si, and Si films, these having been removed in semiconductor processing steps when the cell electronics were formed.  
           [0006]    As the control electronics elements drive the control lines, the control lines in turn send signals to the cells. The signals electrically charge transistor lines in the cells, which cause a colored beam of light to be emitted. When several cells are combined, a spectrum of colors representing a discernable image will be created.  
           [0007]    A shadow frame is occasionally employed in the semiconductor equipment that creates the large panel displays (that is, the equipment that deposits and etches semiconductor materials onto a substrate to create the TFT cells). In known systems, the shadow frame is a rectangularity shaped rim or lip that extends over the outer edges of a substrate and into the central deposition area approximately three to five millimeters. The shadow frame helps to hold the substrate in place and, in some cases, protects the substrate from warping and from deposition of material on the edges and backside of the substrate.  
           [0008]    Some semiconductor equipment includes a shadow frame, while other equipment does not. For instance, the AKT, Inc., an of Applied Materials company, currently ships large panel display manufacturing units (e.g. the AKT 1600, 3500, 4300 and 5500 systems) that include a shadow frame, similar to what is described above, in the plasma enhanced chemical vapor deposition (hereinafter “PECVD”) process chamber.  
         SUMMARY  
         [0009]    A shadow frame for a semiconductor fabrication comprising a rectangular frame having four edges, the edges forming a lip with a top surface and an bottom engagement surface; and a cross beam disposed between at least two edges of the frame, the cross beam having a top surface and a bottom engagement surface, the engagement surface of the cross beam configured to be flush with the engagement surface of the lip; wherein one or more of the engagement surfaces are configured to cover metal interconnect bonding areas on a substrate disposed below the frame.  
           [0010]    According to a preferred embodiment, the shadow frame of claim 1, wherein the cross beam is constructed of a thin, glass-like material including sapphire, while the frame is constructed of aluminum in which the outer surface has been anodized. According to another embodiment, the edges of the cross beam and lips are beveled to promote a smooth laminar flow of materials over a substrate disposed beneath the frame.  
           [0011]    In another embodiment, the shadow frame is part of an overall framing system for a plasma enhanced chemical vapor deposition chamber, which further includes a susceptor disposed below the frame and configured to support the substrate against the frame, the susceptor including apertures, the apertures positioned below the engagement surfaces of the frame; and support elements including an engagement surface, the support elements configured to protrude through the apertures and contact a lower surface of the substrate at the engagement surface of the support elements.  
           [0012]    These and other embodiments are described in the detailed description below and set forth in the claims that follow the detailed description. 
       
    
    
     DESCRIPTION OF THE FIGURES  
       [0013]    [0013]FIG. 1 is a perspective drawing of the improved shadow framing system.  
         [0014]    [0014]FIG. 2 is a side view of a PECVD process chamber.  
         [0015]    FIGS.  3 A-E are views of embodiments of the shadow frame with cross beams. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    A shadow framing system is disclosed. According to an aspect of the system, an improved shadow frame comprises a rectangular perimeter yielding a generally open area, and one or more cross beams extending across the open area, dividing it into a plurality of smaller open regions. Each of the smaller open regions is configured to allow deposition of semiconductor materials so that an individual display can be created.  
         [0017]    According to one embodiment, the perimeter is constructed of anodized aluminum and the cross beam of thin, rigid, glass-like material, such as sapphire. A planar surface of the shadow frame is configured to intimately engage a planar surface of the substrate. According to an aspect of the inventions, the cross beam is positioned so that it covers a metal interconnect bonding area where control circuitry will be connected to the display.  
         [0018]    According to one embodiment, the shadow framing system further includes a susceptor. The susceptor is disposed below the shadow frame and is configured to support the substrate (or carrier supporting the substrate) and place the substrate intimately against the engaging surface of the shadow frame. The susceptor includes a plurality of apertures through which support elements can extend. The apertures are positioned such that they do not reside below any critical open area of the frame.  
         [0019]    In the susceptor&#39;s disengaged state, the engaging surface of the susceptor is positioned below the engaging surface of the support elements. As the substrate is moved into the process chamber of the semiconductor fabrication equipment, it is robotically placed on top of the engaging surface of the support elements. The susceptor is then moved in an upwardly direction until the engaging surface of the susceptor is flush with the engaging surface of the support elements. From this position, the substrate is thrust upward farther still until a top surface of the substrate intimately engages the engaging surface of the shadow frame. As the susceptor continues upwardly, so too do the support elements, so that the engaging surfaces of the susceptor and support structures maintain their flush alignment with a bottom surface of the substrate.  
         [0020]    These and other aspects of embodiments of the shadow framing system are disclosed in greater detail below, with reference to accompanying figures. The embodiments, like the figures, are meant to be illustrative of embodiments of the methods and systems described herein, but not their only embodiments. Further, we note that the embodiments shown in the figures are not to scale and the dimensions provided are not intended to be limiting, except as specifically recited in the claims.  
         [0021]    Turning first to FIG. 1, it depicts an embodiment of the improved shadow frame system, shown here in representative chamber  10 . (We note that not all the parts or elements of a chamber are shown, rather only those needed to conceptually understand our disclosure are depicted.) The system includes a shadow frame  14  and a susceptor  18 . According to an aspect of the invention, the shadow frame  14  has a rectangular profile with overlapping edges (or “lips”)  30  that extend, preferably, approximately two centimeters (as opposed to two to five millimeters) into the interior/central area of the frame  14 . The overlapping edges  30  preferably have a beveled cross section at their edges, as is shown in FIG. 2 (described below).  
         [0022]    Between opposing edges  30 , lie one or more cross beams  34 . The cross beams  34  define a plurality of open regions  16 , into which semiconductor materials can be deposited onto a substrate. While not shown in FIG. 1, the bottom surfaces of the edges  30  and cross beams  34  are preferably coplanar, so that they act as a flush engaging surface to the top surface of a substrate  26 , which will be pressed against the frame  14  by the susceptor  18 .  
         [0023]    According to one embodiment, the cross beams  34 , like the edges  30 , can be beveled. An objective here, as was the case with the edges  30 , is to provide a configuration of the area above the top surface of the substrate  26  that allows for an even flow of materials from the showerhead (FIG. 2), over the frame  14 , and onto the top surface of the substrate  26 .  
         [0024]    According to one embodiment, the cross beams have a width of, preferably, approximately two centimeters and a thickness of less than approximately  1  millimeter, or more preferably a width of less than 2.0 centimeters and a thickness of less than 0.7 millimeters. Our experiments have found that the thinner the cross beam  34 , the better the performance of the equipment. Further, we have found that anodized aluminum is an acceptable material for the major portions of the frame  14 , e.g. the edges  30 , while a ceramic or glass-like material is acceptable for the cross beam  34 . However, the cross beam  34  should be generally rigid and capable of withstanding the environmental conditions known to the PECVD process chamber. One material that can be acceptable and conform to this preference is sapphire.  
         [0025]    The cross beams  34  and edges  30  can be mechanically coupled through a variety of connection means. For instance, the edges  30  can have recesses into which the ends of the cross beams  34  rest, the cross beam  34  ends themselves capable of having recessed regions so that a flush joint is formed on the engagement surface of the frame. A fastening, clamping, or bonding mechanism, which is capable of withstanding the environmental conditions of the chamber and not disrupting the gaseous flow, can secure that cross beams  34  to the edges  30 . As well, a support structure (not shown) can be included above the cross beams  34  to add rigidity where the weight of the cross beam  34  may be more than the cross beam&#39;s  34  physical structure can safely support.  
         [0026]    According to one embodiment, the frame  14  is secured in a fixed position within the process chamber  10 , while the susceptor  18  and other substrate engaging components move relative to the frame  14 .  
         [0027]    Turning to the susceptor  18 , it is typically a resistively heated plate upon which the substrate  26  is supported. According to one embodiment, the susceptor includes a plurality of apertures  38 . Extending through each aperture  38  is a support element  22  (or “lift pin”), the support elements  22  resembling a golf tee. The support elements have a flat upper surface (also called an “engagement surface”) with a support rod beneath the engagement surface.  
         [0028]    When a substrate  26  is robotically placed into the chamber  10 , the susceptor  18  is in its disengaged, or lowest position. The support elements  22 , however, are erect—protruding through the apertures  38 . The robotic placement mechanism (not shown) places the substrate over the engagement surfaces of the support elements  22 . (This placement typically occurs as the substrate  26  is transferred from the vacuum robot end effector (also not shown) to the susceptor  18 .) Once the substrate  26  is in place, the susceptor  18  is forced in an upwardly direction until the top surface (or engagement surface) of the susceptor  18  makes intimate contact with the bottom surface of the substrate  26 . At this point, the engagement surfaces of the support elements  22  and the susceptor  18  are coplanar.  
         [0029]    Experimental results identified transistor issues (e.g., non-uniformities in SiN, a-Si and n+ Si films) in areas on the substrate  26  directly over the support elements  22 . The non-uniformities, in turn, caused inconsistencies in the threshold voltages of the TFTs in the effected areas. However, we discovered that by placement of the support elements  22  in areas beneath the cross beams  34  and edges  30 , these issues were resolved. Preferably, and so that the ultimate product is of the highest quality, the support elements  22  should be likewise placed in an area where a non-uniformity will not be of significance, if of any significance at all. For example, the support elements  22  and aperture  38  placement can be along the cut lines of the substrate  26 .  
         [0030]    In order to accommodate various configurations of the frame  14 , namely the cross beam  34  positioning, it can also be preferable to not locate the support elements  22  in the central areas of the susceptor  18 , but rather to place them on the peripheral areas of the susceptor  18 . In such an embodiment, the peripheral support elements  22  should be lengthened to accommodate additional sag caused by the weight of the substrate  26 .  
         [0031]    Further, a power lift step, which can reduce static charge between the substrate  26  and the susceptor  18 , can be modified, as well the transfer height of the substrate  26  can be adjusted. One embodiment of a power lift step is disclosed in U.S. Pat. No. 5,380,566, issued Jan. 10, 1995, and entitled “METHOD OF LIMITING STICKING OF BODY TO SUSCEPTOR IN A DEPOSITION TREATMENT”, invented by Robert Robertson, et al., and commonly assigned with the subject application. U.S. Pat. No. 5,380,566 is incorporated herein by reference in its entirety.  
         [0032]    Returning to the susceptor  18 , it continues the upward drive of the substrate  26  until the top surface of the substrate  26  makes intimate contact with the lower surface (the engagement surface) of the cross beams  34  and edges  30 . At this point, gravity secures the substrate  26  between the shadow frame  14  and the susceptor  18 . Once secured in place, the PECVD process begins and materials (e.g. gate silicon nitride and amorphous silicon film) are deposited onto the substrate  26 .  
         [0033]    When the deposition process is complete, the susceptor  18  is lowered into its disengaged state and the substrate  26  is remove from the chamber  10  in a process similar to the manner in which it was placed into the chamber  10 . After the manufacture of the display is complete, the substrate  26  will be cut along cut lines on the substrate  26 . Preferably, these cut lines are directly below the regions where the cross beams  34  covered the top surface of the substrate  26 .  
         [0034]    Turning next to FIG. 2, it is a cross section of a PECVD process chamber  10 , including attendant components. We note again that the drawing is not to scale and certain editorial changes are made to emphasize different components. For instance, the engagement surfaces of the frame  14 , that is the edges  30  and cross beams  34 , are not shown making intimate contact with the top surface of the substrate  26 —this is just to draw out the components. Of course, such a view may look as is shown in FIG. 2 prior to the susceptor  18  pressing the substrate  26  against the engagement surfaces of the frame  14 .  
         [0035]    A remote plasma source  44  and a gas supply are combined in a chamber  48 , from which materials flow to the process chamber  10  through a showerhead  40 . As the materials exit the showerhead  40 , the flow may first encounter the top surfaces of the cross beams  34  and edges  30  of the frame  14 . It is from this angle that the bevel  32  on the edges of the crossbeams  34  and edges  30  is best seen.  
         [0036]    The material flow will then be deposited through the open regions  16  created between the cross beams  34  and edges  30  of the frame  14  and onto the top, exposed surfaces of the substrate  26 , as well as onto the top, exposed surfaces (the non-engagement surfaces) of the cross beams  34  and edges  30 .  
         [0037]    As the processes continue, materials will build up on the substrate  26  forming electronic circuitry. However, material will not be deposited on the portions of the substrate  26  that are intimately mated with the engagement surfaces of the frame  14 . According to an aspect of the inventions, the cross beam  34  and edge  30  engagement surfaces cover the metal interconnect bonding areas where control circuitry will be mounted.  
         [0038]    This deposition characteristic, that is of protecting the metal interconnect bonding area, has several advantages. First, the metal contact areas of the gate metal and source/drain metal are not covered with a passivation layer. Thus, direct bonding contact can be made to the metal connection pads at the periphery of the display by bonding to the metal patterning the passivation layer though lithography and etching. Second, it reduces the number of steps involved in the semiconductor manufacturing process. For instance, a typical process to manufacture a back channel TFT involves four to six photolithography masks. These masks include a gate metal mask, an active layer mask, a contact mask, a source/drain conductor mask, and a passivation mask. Improvement is found in our systems in that a passivation masking step can be eliminated from the manufacturing process. This, in turn, can increase the yield of process, as fewer steps lead to fewer defects, can reduce the number of the photolithography printing tools required, and can reduce the production time (or increase the throughput) of the production process.  
         [0039]    To complete the description of the chamber  10 : the substrate  26  is held between the engagement surfaces of the frame  14  and the susceptor  18 . The susceptor  18 , which is resistively heated, is connected to a shaft  52 , which moves in a vertical direction and electrically couples the susceptor  18  to ground.  
         [0040]    There will be a build up of materials on the cross beams  34  and edges  30  of the frame  14 . To prevent this build up from interfering with or adding impurities to the semiconductor processing steps, it is recommended that the process chamber  10 , namely the non-engagement surfaces of the frame  14  be cleaned to prevent material buildup. Such a cleaning should take place each time the buildup reaches two to three microns in thickness. While semiconductor processes vary, this will typically occur between three and ten depositions and can be set by control software monitoring the fabrication process.  
         [0041]    To clean the chamber, we recommended that reactive fluorine atoms from a remote plasma discharge of NF 3  be forced through the showerhead  40 . The fluorine atoms will react with the deposition material and can be pumped out of the chamber  10  with a vacuum pump.  
         [0042]    Depicted in FIGS.  3 A-E are exemplary embodiments of the improved shadow frame with one or more cross beams. We only show an overall view of the improved shadow frame with the understanding that one of skill in the art could modify the interconnection or precise dimensions in accordance with the description provided above, or in accordance with a particular application in which the inventions can be employed.  
         [0043]    Above, we have described a shadow framing system with reference to a PECVD process chamber used in the manufacture of AMLCDs. This, however, should not limit the application of the claims below to other processes or applications, unless otherwise specifically limited therein.  
         [0044]    For example, the systems and methods described above can be equally well applied to the manufacture of solar cells with semiconductor fabrication equipment. In such systems, the solar cells are manufactured on a substrate (or a carrier supporting a substrate), in which 25-50 wafers are cut from the carrier after processing. The above shadow framing system can be configured with cross beams to frame each of the wafers and protect the wafers from the deposition of, for instance, an amorphous silicon film.