Abstract:
A new designed carrier head for chemical mechanical polishing is disclosed. The carrier head has a non-rigid incision ring having a downwardly-projecting non-rigid incision and surrounding a support plate of the carrier head instead of conventional incision or rip disposed in a conventional support plate. The carrier head also has a flexible membrane extending around the edges of the support plate, wherein the edge of the flexible membrane is at predetermined distance from the incision.

Description:
This application claims the benefit of Provisional Application No. 60/336,382, filed Oct. 31, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a carrier head for chemical mechanical polishing, and more particularly to a carrier head for chemical mechanical polishing that can improve polishing uniformity. 
     2. Description of the Related Art 
     Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer. Therefore, there is a need to periodically planarize the deposited layer surface to provide a flat surface. 
     Chemical mechanical polishing (CMP) is one accepted method of planarization. This method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is then placed against a rotating polishing pad. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. In addition, the carrier head may rotate to provide additional motion between the substrate and polishing surface. 
     A polishing slurry, including an abrasive and at least one chemically-reactive agent, may be supplied to the polishing pad to provide an abrasive chemical solution at the interface between the pad and the substrate. CMP is a fairly complex process, and it differs from simple wet sanding. In a CMP process, the reactive agent in the slurry reacts with the outer surface of the substrate to form reactive sites. The interaction of the polishing pad and abrasive particles with the reactive sites on the substrate results in polishing of the substrate. 
     An effective CMP process not only provides a high polishing rate, but also provides a substrate surface which is finished (lacks small-scale roughness) and flat (lacks large-scale topography). The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad. The polishing rate sets the time needed to polish a layer. Because inadequate flatness and finish can create defective substrates, the selection of a polishing pad and slurry combination is usually dictated by the required finish and flatness. Given these constraints, the polishing time needed to achieve the required finish and flatness sets the maximum throughput of the CMP apparatus. 
     A recurring problem in CMP is non-uniformity of the polishing rate across the surface of the substrate. One source of this non-uniformity is the so-called “edge-effect”, i.e., the tendency for the substrate edge to be polished at a different rate than the center of the substrate. Another source of non-uniformity is termed the “center slow effect”, which is the tendency of center of the substrate to be underpolished. Yet another source of non-uniformity is termed as the fast band effect. The fast band effect causes an annular region of the substrate, the center of which is located approximately 15 millimeters to 20 millimeters from the substrate edge, to be significantly over-polished. This annular region may be about 20 millimeters wide. These non-uniform polishing effects reduce the overall flatness of the substrate and the substrate area suitable for integrated circuit fabrication, thus decreasing the process yield. 
     FIG. 1 shows a conventional carrier head for CMP. Carrier head  100  comprising a main frame  102 , a retaining ring  104 , an edge load ring  106 , a support plate  108  having a incision or lip  110 , and a flexible membrane  112  are shown. Generally, carrier head  100  holds a substrate such as a wafer in position against a polishing pad and distributes a force across the back surface of the substrate. Support plate  108  as well as incision  110  are composed of a rigid material, such as a stainless steel. During polishing, a bladder (not shown) is used to cause incision  110  of support plate  108  to press the edge of flexible membrane  112  against the wafer being polished, thereby creating a tight contact between the wafer and flexible membrane  112 . However, the rigidity of incision  110  and the winding phenomena of flexible membrane  112  during polishing would present non-uniformity of polishing such as the fast band effect and reduce the overall flatness of the wafer and the wafer area suitable for integrated circuit fabrication, thus decreasing the process yield. 
     Accordingly, it would be necessary to provide a CMP apparatus which ameliorates some, if not all, of these problems. The advantages of this invention are that it solves the problems mentioned above. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a modified carrier head which can effectively improve polishing uniformity. 
     It is another object of this invention to provide a carrier head which can overcome the fast band effect. 
     It is a further object of this invention to provide a carrier head which can provide a overall flatness of the substrate being polished and an improved process yield. 
     In one embodiment of this invention, the invention provides a carrier head for chemical mechanical polishing, said carrier head comprising: a main frame; a support plate disposed in said main frame having a non-rigid incision ring surrounding said support plate, said incision ring having a downwardly-projecting non-rigid incision; and a flexible membrane disposed under said support plate extending around the edges of said support plate, wherein said flexible membrane applies a load from said main frame on a substrate being polished against a polish pad. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 shows a conventional carrier head for CMP; and 
     FIG. 2 shows a carrier head for CMP of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It is to be understood and appreciated that the structures described below do not cover a complete structure. The present invention can be practiced in conjunction with various conventional CMP apparatus fabrication techniques that are used in the art, and only so much of the commonly practiced structures are included herein as are necessary to provide an understanding of the present invention. 
     The present invention will be described in detail with reference to the accompanying drawings. It should be noted that the drawings are in greatly simplified form and they are not drawn to scale. Moreover, dimensions have been exaggerated in order to provide a clear illustration and understanding of the present invention. 
     Referring to FIG. 2, carrier head  200  comprising a main frame  202 , a retaining ring  204 , an edge load ring  206 , a support plate  208 , a incision ring  210  having a incision  212 , and a flexible membrane  214  are shown. During actual polishing, carrier head  200  lowers a substrate such as a wafer having deposited layers thereon into contact with a polishing pad. Generally, carrier head  200  holds the substrate in position against the polishing pad and distributes a force across the back surface of the substrate. The carrier head  200  also transfers torque from the drive shaft to the substrate. Main frame  202  may be generally circular in shape to correspond to the circular configuration of the substrate to be polished. A cylindrical bushing (not shown) may fit into a vertical bore (not shown ) through the main frame  202 , and two or more passages may extend through the main frame  202  for pneumatic control of the carrier head  200 . 
     Main frame  202  can be connected to a drive shaft (not shown) to rotate therewith during polishing about an axis of rotation (not shown) which is substantially perpendicular to the surface of the polishing pad during polishing. A loading chamber (not shown) of main frame  202  located above support plate  208  applies a load, i.e., a downward pressure, to support plate  208 . The vertical position of support plate  208  relative to the polishing pad is also controlled by the loading chamber. 
     Retaining ring  204  may be a generally annular ring secured at the outer edge of main frame  202 , e.g., by bolts (not shown). When fluid is pumped into the loading chamber, retaining ring  204  is pushed downwardly to apply a load to polishing pad. A bottom surface of retaining ring  204  may be substantially flat, or it may have a plurality of channels to facilitate transport of slurry from outside the retaining ring to the substrate. An inner surface of retaining ring  204  engages the wafer to prevent it from escaping from beneath the carrier head. 
     Edge-load ring  206  is a generally annular body located between retaining ring  204 . Edge-load ring  206  includes a base portion having a substantially flat lower surface for applying pressure to a perimeter portion of the wafer being polished. Edge-load ring  206  is composed of a material, such as a stainless steel, ceramic, anodized aluminum, that is relatively rigid compared to the flexible membrane  214 . A layer of compressible material (not shown), such as a carrier film, may be adhesively attached to lower surface of edge-load ring  206  to provide a mounting surface for the wafer being polished. 
     Support plate  208  may be a generally disk-shaped rigid member having a plurality of apertures formed therethrough. Incision ring  210  having incision or downwardly-projecting lip  212  at its outer edge is mounted at the outer edge of support plate  208 . Incision ring  210  preferably comprises a non-rigid ring such as a colloid ring. Incision or downwardly-projecting lip  212  also preferably comprises a non-rigid incision or lip composed of the same material of incision ring  210 . 
     Flexible membrane  214  is a generally circular sheet formed of a flexible and elastic material, such as neoprene, chloroprene, ethylene propylene or silicone rubber. Flexible membrane  214  extends around the edges of support plate  208 . The edge of flexible membrane  214  is at a predetermined distance from incision  212 , and it is preferably about 1 centimeter. During polishing, a bladder (not shown) of main frame  202  is used to cause support plate  208  to press flexible membrane  214  against the wafer being polished, thereby creating a tight contact between the wafer and flexible membrane  214 . Because incision  212  is non-rigid and the edge of flexible membrane  214  is at a predetermined distance from incision  212 , the annular region on the edge of the substrate being polished will not be over-polished and flexible membrane  214  will not wind, so that the non-uniformity phenomena such as the fast band effect can be avoided and the process yield can be improved. 
     Other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples to be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.