Abstract:
A system includes a chuck with a retaining ring on a first surface thereof. The first surface and the retaining ring are both circular, the retaining ring having a first inner circumference. The system also includes a platen with a second surface, and the second surface faces the first surface and is operable to move with the first surface. The system further includes an air zone circumscribed by the first inner circumference that provides an effective inner circumference different from the first inner circumference.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to a mechanical chuck with a retaining ring. Specifically, the present disclosure relates to systems and methods that provide an air zone at an inner diameter of a retaining ring within a chuck assembly. 
         [0002]    Many conventional systems use a chuck assembly for Chemical Mechanical Polishing (CMP). The polishing head is on top, and it has a circular shape in the horizontal plane. Around the circumference of the polishing head is a retaining ring. A round semiconductor wafer is loaded into the chuck by using a vacuum to hold the wafer to the polishing head, where the wafer sits within the retaining ring. The chuck system is then closed by contacting the exposed surface of the wafer to a polishing pad on a platen. The wafer is then moved relative to the polishing pad to perform polishing. 
         [0003]    In some embodiments the retaining ring is constructed of plastic. In conventional CMP systems, there is about 1 mm of clearance between the side of the wafer and the side of the retaining ring. In other words, the retaining ring is just a little larger in its inner diameter than is the wafer, and the purpose of this clearance is to facilitate loading of the wafer into the polishing head. 
         [0004]    As a result of the clearance, the wafer moves relative to the retaining ring during polishing. Such movement leads to contact stress during CMP processes that causes pitting on the inner circumference of the retaining ring. If byproduct builds up in the pits, it can result in increased scratch defect possibility, increased bevel damage possibility, and lower yield. Accordingly, a more effective technique for CMP is called for. 
       SUMMARY 
       [0005]    The present disclosure provides for many different embodiments. In a first embodiment, a system includes a chuck with a retaining ring on a first surface thereof. The first surface and the retaining ring are both circular, the retaining ring having a first inner circumference. The system also includes a platen with a second surface, and the second surface faces the first surface and is operable to move with the first surface. The system further includes an air zone circumscribed by the first inner circumference that provides an effective inner circumference different from the first inner circumference. 
         [0006]    In another embodiment, a method for holding a manufactured object in a chucking stage includes loading the manufactured object into a chuck. The chuck includes a retaining ring that surrounds the manufactured object and has a first inner circumference larger than a circumference of the manufactured object. A difference between the first inner circumference and the circumference of the manufactured object provides a first clearance. The method also includes applying a vacuum at the chuck to hold the manufactured object to the chuck and applying air to an air zone between a circumference of the manufactured object and the first inner circumference of the retaining ring, thereby making an effective first clearance that is different than the first clearance. 
         [0007]    In another embodiment, a system includes a chuck that has a vacuum system effective on a contact surface to hold a manufactured object to the chuck. The system further includes a retaining ring defining an area for holding the manufactured object to the contact surface, the retaining ring having a first inner circumference. The system also has means for applying pressurized air at the first inner circumference to reduce the first inner circumference to an effective inner circumference during a manufacturing process, the effective inner circumference being smaller than the first inner circumference. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
           [0009]      FIG. 1  is an illustration of an exemplary CMP system according to one embodiment. 
           [0010]      FIG. 2  is a conceptual top-down view not to scale showing a wafer circumference and a retaining ring inner circumference. 
           [0011]      FIGS. 3-5  show the use of the polishing head of  FIG. 1  according to one exemplary embodiment. 
           [0012]      FIG. 6  is an illustration of an exemplary method for polishing a semiconductor wafer, according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The present disclosure relates generally to manufacturing processes. Specifically, the present disclosure relates to systems and method reducing a clearance between a retaining ring and a manufactured product circumscribed by the retaining ring. While the examples herein discuss applying the techniques to a CMP process, it is noted that the techniques discussed herein can be applied generally to systems and methods that use chuck systems, whether in the semiconductor industry or otherwise. 
         [0014]    The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
         [0015]    With reference now to the figures,  FIG. 1  is an illustration of an exemplary CMP system  100  according to one embodiment.  FIG. 1  shows a cross-section of polishing head or chuck  110  and platen  150 . Polishing head  110  has an outer circumference illustrated in cross-section by diameter d 1 . Diameter d 1  also corresponds in this example to an outer circumference of retaining ring  120 . The inner circumference of retaining ring  120  is illustrated in cross-section by diameter d 2 . 
         [0016]    Polishing head  110  also includes a vacuum assembly that has ports  111  and contact surface  114 . Ports  111  are used to create a vacuum to hold a wafer (not shown) to contact surface  114 . The ports  111  can also be used to neutralize the vacuum to “de-chuck” the wafer after a CMP process is completed. 
         [0017]    Ports  112  and  113  provide air passageways through the body of polishing head  110  and retaining ring  120 . Various embodiments apply pressurized air through ports  112  and  113  to create air zones  115  and  116 , thereby creating an effective inner circumference of retaining ring  120  illustrated in cross-section by diameter d 3 . In various embodiments, polishing head  110  and retaining ring  120  may include more than two ports, similar to ports  112  and  113 , that provide additional air zones around the inner circumference of retaining ring  120 . 
         [0018]    System  100  also includes platen  150  facing polishing head  110 . Platen  150  includes thereon polishing pad  160 , which when in use contacts the wafer held within the bounds of retaining ring  120 . Polishing head  110  and platen  150  may move relative to each other, in the z-axis to make contact, and rotate within the x-y plane. In one example, as a polishing process begins, polishing head  110  and/or platen  150  move in the z-axis direction so as to contact the wafer with polishing pad  160 . Polishing head  110  and/or platen  150  rotate so that there is abrasive motion applied to the wafer by polishing pad  160 . Polishing head  110  and/or platen  150  may also have translating motion in the x-y plane to increase the uniformity of abrasion across the surface of the wafer. Moreover, the wafer may rotate around more than one axis so as to increase the uniformity of abrasion as well. 
         [0019]    While not shown herein, system  100  may also include other pieces. For instance, other embodiments may include a pad conditioner, a slurry applicator, and the like, to facilitate CMP processes. Additionally, some embodiments include an air compressor/vacuum system in communication with ports  111 - 113  to provide vacuum for holding a wafer and for providing pressurized air in ports  112 ,  113 . Moreover, some embodiments may include a control system to control the movements of the system and the positioning of the wafer. Furthermore,  FIG. 1  is not shown to scale, and in some embodiments, the diameter of platen  150  may be several times larger than the outer diameter of polishing head  110 . 
         [0020]      FIG. 2  is an illustration of the concept of clearance, which helps to explain how a wafer fits with respect to a retaining ring according to one embodiment.  FIG. 2  is a conceptual top-down view not to scale showing wafer circumference  202  and retaining ring inner circumference  201 . In some embodiments,  202  is smaller than  201 , thereby allowing movement of the wafer relative to the retaining ring during the polishing process. 
         [0021]    Clearance is shown in  FIG. 2  as the maximum space between the wafer and the inner surface of the retaining ring. Various embodiments herein reduce the effective retaining ring inner diameter  201  to decrease clearance by using air zones during polishing. Such embodiments may reduce contact stress between the wafer and the retaining ring substantially enough to reduce pitting of the retaining ring. In one example, the effective inner circumference is reduced so as to reduce the clearance from 1 mm (typical of some conventional systems) to about 0.5 mm. 
         [0022]      FIGS. 3-5  show the use of polishing head  110  according to one exemplary embodiment. In  FIG. 3 , wafer  300  is positioned under polishing head  110 . In  FIG. 4 , vacuum is applied to hold wafer  300  to contact surface  114 . While not shown in  FIG. 4 , some embodiments include small holes in contact surface  114  to expose wafer  300  to the vacuum and facilitate the hold in  FIG. 4 . Ports  111  are used to reduce the air pressure within polishing head  110  to supply the vacuum. 
         [0023]    In  FIG. 5 , pressurized air is applied through ports  112 ,  113  to create air zones  115 ,  116  at the inner circumference of retaining ring  120 . Air zones  115 ,  116  include air pressurized to higher than ambient pressure to exert some force against the sides of wafer  300 , thereby reducing movement of wafer  300  during the polishing process. Thus, the pressurized air effectively reduces the inner circumference of retaining ring  120 , thereby effectively reducing the clearance between the retaining ring  120  and wafer  300 . 
         [0024]    Furthermore, air zones  115 ,  116  create a “seamless” surface from the perspective of polishing pad  160  ( FIG. 1 ). For example, without air zones  115 ,  116  the clearance between wafer  300  and retaining ring  120  creates a lack of smoothness where the polishing pad  160  contacts the gap formed by the clearance. However, air zones  115 ,  116  provide pressure at the gaps formed by the clearance, where the pressure affects the side of wafer  300  and the surface of the polishing pad as well. Air zones  115 ,  116  increase the smoothness so that the surface formed by retaining ring  120  and wafer  130  is approximately flush and smooth with respect to the polishing pad surface, even at the gaps between wafer  300  and retaining ring  120 . 
         [0025]      FIG. 6  is an illustration of exemplary method  600 , for polishing a semiconductor wafer, according to one embodiment. Method  600  may be performed in some instances by one or more persons and/or machines in a single manufacturing site or multiple manufacturing sites. 
         [0026]    In block  610 , the wafer is loaded onto a chuck. In this example, the chuck has a retaining ring that has an inner diameter that is larger than the circumference of the wafer. The clearance between the retaining ring and the wafer allows for reliable loading of the wafer to the chuck. In some examples, the clearance is about one millimeter, though the scope of embodiments is not limited to any particular range of clearance. 
         [0027]    In block  620 , a vacuum is applied at the chuck to hold the semiconductor wafer to the chuck. For instance, as shown in  FIGS. 3-5 , a vacuum system with ports applies a vacuum through the ports to hold the wafer to a contact surface within the retaining ring. 
         [0028]    In some embodiments, the vacuum system is controlled to keep the wafer at an even profile during the polishing process. Using  FIG. 4  as an example, the wafer is shown edge-on and aligned in an x-y plane. However, it is possible that the wafer may become unaligned and tilt in the z-direction, which leads to uneven wear during polishing. In some embodiments, the profile alignment can be controlled using the vacuum ports so that by adjusting the vacuum at the various ports individually, a precise profile alignment can be achieved. 
         [0029]    In block  630 , an air zone is applied between the inner circumference of the retaining ring and the edge of the wafer. The air zone applies a force to the edge of the wafer, effectively reducing the inner circumference of the retaining ring and effectively reducing the clearance. In one example, the clearance is reduced to one-half millimeter, though the scope of embodiments is not limited to any range of effective clearance. 
         [0030]    As mentioned above, some embodiments control the profile of the wafer using the vacuum system so as to achieve an even polishing on the whole surface of the wafer. Some embodiments additionally use the air zones to add further control to the profile alignment by moving the wafer relative to the retaining ring in the x-y plane. 
         [0031]    While the examples herein refer to an air zone, the scope of embodiments is not limited to using atmospheric air. Various embodiments may use any suitable gas in an appropriate pressure for reducing the effective clearance between the wafer and the retaining ring. 
         [0032]    Block  640  includes in some embodiments polishing the semiconductor wafer by moving the chuck relative to a polishing surface. As the chuck moves, the wafer may also move relative to the retaining ring. The air zones operate to reduce such movement by applying force at the edges of the wafer in the x-y plane, thereby reducing contact stress. Furthermore, the air zones create a more smooth and even surface at the gap between the wafer and retaining ring. 
         [0033]    In block  650 , the wafer is removed from the chuck. For instance, in some embodiments the pressurized air at the air zones is eliminated, as is the vacuum at the contact surface of the chuck. When the pressure at the air zones returns to ambient pressure, the effective clearance returns to the original clearance, thereby facilitating reliable removal of the wafer. 
         [0034]    Method  600  is exemplary, and the scope of embodiments is not limited only to that shown in  FIG. 6 . Other embodiments may add, omit, modify, or rearrange actions. For instance, some embodiments include further processing of the wafer, such as deposition, etching, and further polishing steps. In another example, a manufactured object is positioned in a chuck using air gaps, and the process does not include a semiconductor polishing process. For example, an optical disc (e.g., a DVD) may be held in place in a chuck assembly during one or more portions of the manufacturing process, and the object may be held using air zones as illustrated above. In fact, the scope of embodiments includes chucking any manufactured object for any of a variety of purposes. 
         [0035]    Various embodiments may include advantages over other techniques that employ a retaining ring with no air zone. For instance, some embodiments provide an effectively seamless surface for contacting the polishing pad. Such surface may reduce contact stress between the wafer and the retaining ring. Reduced contact stress may help to increase the lifespan of a retaining ring. 
         [0036]    Additionally, contact stress can lead to damage at the relatively thin edges of the wafer (i.e., bevel damage). Various embodiments reduce incidents of bevel damage by reducing the contact stress. 
         [0037]    Furthermore, some embodiments may increase wafer profile control by providing additional adjustment in the x-y plane. In some instances, adding the air zone may increase the wafer profile control by two or more millimeters for some conventional-sized wafers (e.g., from 145 mm to 147 mm). 
         [0038]    The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.