Abstract:
An embodiment relates generally to an apparatus for reducing defects. The apparatus includes a spindle adapted to hold a wafer; and at least two light sources configured to direct light to a top-side and a back-side of the wafer

Description:
FIELD 
       [0001]    This invention relates generally to semiconductor fabrication processing, more particularly to apparatus and methods for reducing defects in the semiconductor fabrication process. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Resists are generally proprietary mixtures of a polymer or its precursor and other small molecules, e.g., photoacid generators, that have been specially formulated for a given lithography technology. For a typical semiconductor fabrication process, the resist is spin coated on a semiconductor substrate such as a silicon wafer, to form a thin uniform layer. The resist layer may be baked at a low temperature to evaporate residual solvents. A latent image is formed in the resist by using ultraviolet light through a photomask with opaque and transparent regions or by direct writing using a laser beam or an electron beam. Areas of the resist that have (or have not) been exposed are removed by rinsing with an appropriate solvent. Subsequently, there is another bake and processing through the resist pattern: wet or dry etching, lift-off, doping, etc., as known to those skilled in the art. Finally, the resist is removed. 
         [0003]    There are drawbacks and disadvantages associated with the previously described process. For example, resist accumulation on a bevel of the wafer in the photo track can cause yield loss, which is illustrated in  FIG. 3 . As shown in  FIG. 3 , the conventional edge exposure system  300  includes a single light source  305  with a fixed aperture focused on the area  330  that encompasses the edge  320  of the wafer  310 , where the edge  320  may be a bevel  325 . The wafer  310  may be supported by a spindle  315  that rotates the wafer  310  around the spindle  315 . 
         [0004]    During the resist coat process, the resist is spin coated to cover the top of the wafer  310 . The resist spreads to the edge  320  and can also coat or partially coast the bevel  325  and back edge of the wafer  310 . Since the single light source  305  directs light only to the top side of the wafer  310 , the resist on the bottom half of the bevel and underneath the wafer are unexposed, and thus remain. 
         [0005]    The remaining resist can break away on subsequent processing steps and become yield limiting defects. More particularly, the resist accumulation can be redistributed during subsequently processing. Moreover, the resist accumulation can cause blistering and de-lamination of deposited dielectrics and/or metals, which also contribute to yield loss. Accordingly, there is a need in the art to reduce the effects of resist accumulation. 
       SUMMARY 
       [0006]    An embodiment relates generally to an apparatus for reducing defects. The apparatus includes a wafer and a spindle configured to hold the wafer. The apparatus also includes multiple light sources configured to direct light to a top edge, a bevel, and a back-edge of the wafer. 
         [0007]    Another embodiment pertains generally to a method of reducing defects. The method includes depositing a layer of resist on a wafer and directing light from multiple light sources on a top edge, a bevel, and a back-edge of the wafer to reduce the layer of resist. 
         [0008]    Yet another embodiment relates generally to an apparatus for reducing defects. The apparatus includes a spindle adapted to hold a wafer; and at least two light sources configured to direct light to a top edge, a bevel, and a back-edge of the wafer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various features of the embodiments can be more fully appreciated, as the same become better understood with reference to the following detailed description of the embodiments when considered in connection with the accompanying figures, in which: 
           [0010]      FIG. 1  depicts an exemplary bevel exposure system in accordance with an embodiment; 
           [0011]      FIG. 2  depicts another exemplary bevel reduction system in accordance with another embodiment; and 
           [0012]      FIG. 3  depicts a conventional bevel exposure system. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0013]    For simplicity and illustrative purposes, the principles of the present invention are described by referring mainly to exemplary embodiments thereof. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented in, all types of semiconductor fabrication systems, and that any such variations do not depart from the true spirit and scope of the present invention. Moreover, in the following detailed description, references are made to the accompanying figures, which illustrate specific embodiments. Electrical, mechanical, logical and structural changes may be made to the embodiments without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense and the scope of the present invention is defined by the appended claims and their equivalents. 
         [0014]    Embodiments relate generally to apparatus and methods of reducing defects on a wafer induced by resist accumulation. More particularly, an edge exposure system may be configured to have light sources from multiple angles directed at a bevel and a back edge of a wafer as well as a top or front edge. The wafer may comprise of silicon or other similar material used in semiconductor manufacturing as known to those skilled in the art. On the edge or rim of the wafer, the rim of the wafer may comprise a top or front edge and a back or bottom edge, where a bevel may be formed between the edges. 
         [0015]    In one embodiment, multiple light sources generating a broad frequency of light to activate the resist are configured to direct light to the front edge, the bevel, and back edge of the wafer. After exposure, the resist on the top edge, bevel, and back edge becomes soluble, which then can be removed by subsequent develop processes. In another embodiment, a light source may be configured with a mirror, waveguide, or light guide, positioned to reflect and/or direct the light towards the bevel and back edge. Unlike conventional systems where the remaining resist can break-away on subsequent processing steps and become yield limiting defects, the removal of the resist on the bevel and back edge. 
         [0016]      FIG. 1  depicts an exemplary edge exposure system  100  in accordance with an embodiment. It should be readily apparent to those of ordinary skill in the art that the edge exposure system  100  depicted in  FIG. 1  represents a generalized schematic illustration and that other components may be added or existing components may be removed or modified. 
         [0017]    As shown in  FIG. 1 , the edge exposure system  100  may include multiple light sources  105 A and  105 B, a wafer  110  and a spindle  115 . The wafer  110  may be substrate where semiconductor fabrication can be directed thereon. The wafer  110  may be silicon or other substrate known to those skilled in the art of semiconductor processing. The spindle  115  may be configured to support the wafer  110  in a generally perpendicular to the paths of light from light sources  105 A-B. The spindle  115  may include a platen (not shown) to support the wafer in some embodiments. 
         [0018]    The wafer  110  may also comprise a top surface  110 A and a bottom surface  110 B along with an edge or rim  120 . The rim  120  may comprise a top edge  130 A, a back edge  130 B and a bevel  125  formed between the edges  130 A,  130 B, respectively. The top edge  130 A and the back-edge  130 B may be an area determined by the user or by the requirements of the fabricated device. 
         [0019]    The light source  105 A may be aligned to direct light to the top edge  130 A and a top half of the bevel  125 . The light source  105 B may be aligned to direct its light to the back edge  130 B and a bottom half of the bevel  125 . The frequency range of the light from light sources  105 A-B may be broad to ensure activation of any applied resist. In some embodiments, the frequency range may from 440 nm to 193 nm. In other embodiments, the frequency range may change due to the type of resist being used. The illumination source may alternately be a monochromatic source, such as a laser, of a frequency appropriate to the resist being used in the system. This may be used instead of or in addition to a broadband source. 
         [0020]    The light sources  105 A-B may have a fixed aperture to focus the light. The width of the fixed aperture may range from 5 mm to 0.1 mm in accordance with some embodiments. In other embodiments, light sources  105 A-B may be implemented as a fiber optic tip, a light source with a waveguide or other light sources that can focus a broad frequency of light to a small location. The light sources  105 A-B may be positioned using support structures (not shown) as known to those skilled in the art. 
         [0021]    Although the embodiment depicted in  FIG. 1  shows two light sources aligned to direct light at the top and back edges along with the bevel, other embodiments may include a third or more light sources to direct light at the bevel. Yet other embodiments may configure the light sources at various angles to cover the top and back edges along with the bevel. 
         [0022]    Accordingly, embodiments of the edge exposure system  100  can expose light to both edges  130 A,  130 B along with the bevel  125 . The light may then make soluble substantially all the resist coating the top and back edges  130 A,  130 B of the bevel  125 , which then can be removed by a subsequent develop process. 
         [0023]      FIG. 2  illustrates another exemplary embodiment of the edge exposure system  200 . It should be readily apparent to those of ordinary skill in the art that the bevel exposure system  200  depicted in  FIG. 2  represents a generalized schematic illustration and that other components may be added or existing components may be removed or modified. 
         [0024]    As shown in  FIG. 2 , the edge exposure system  200  may include light sources  205 , a mirror  210 , a wafer  215  and a spindle  220 . The wafer  215  may be substrate where semiconductor fabrication can be directed thereon. The wafer  215  may be silicon or other substrate known to those skilled in the art. The spindle  120  may be configured to support the wafer  215  in a generally perpendicular to the paths of light from light sources  105 A-B. The spindle  115  may include a platen (not shown) to support the wafer in some embodiments. 
         [0025]    The wafer  215  may also comprise a top surface  215 A and a bottom surface  215 B along with an edge or rim  225 . The rim  225  may comprise a top edge  235 A, a back edge  235 B and a bevel  230  formed between the edges  235 A,  235 B, respectively. The top edge  235 A and the back-edge  235 B may be an area determined by the user or by the requirements of the fabricated device. 
         [0026]    The light source  205  may be aligned to direct its light to the top edge  235 A and a top half of the bevel  230 . The mirror  210  may be aligned to direct the light from the light source  205  to the bevel  230 , the back edge  23 B and/or a combination thereof depending on the configuration of mirror  205 . The configurations of mirrors to direct light at the aforementioned areas are known to those skilled in the art. The frequency range of the light from light sources  205  may be broad to ensure activation of any applied resist. In some embodiments, the frequency range can be from 440 nm to 193 nm. In other embodiments, the frequency range may change due to the type of resist being used. 
         [0027]    The light sources  205  may have a fixed aperture to focus the light. The width of the fixed aperture may range from 5 mm to 0.1 mm in accordance with some embodiments. In other embodiments, light source  205  may be implemented as a fiber optic tip, a light source with a waveguide or other light sources that can focus a broad frequency of light to a small location. The light source  205  and mirror  210  may be positioned using support structures (not shown) as known to those skilled in the art. 
         [0028]    While the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments without departing from the true spirit and scope. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. In particular, although the method has been described by examples, the steps of the method may be performed in a different order than illustrated or simultaneously. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope as defined in the following claims and their equivalents.