Gradient chuck method for wafer bonding employing a convex pressure

Abstract

An apparatus and method for improved wafer bonding by scrubbing, spin drying, aligning, and pressing the polished wafers together. The first wafer (13) is mounted on a flat wafer chuck (11) and a second wafer (14) is mounted on a convex pressure gradient chuck (10). Wafers are scrubbed until a polished contamination free surface is obtained and pressed together. The convex pressure gradient chuck exerts a higher pressure at the center of the wafer than at the periphery of the wafer.

We claim: 
     
       1. A method for bonding a first and a second semiconductor wafer together, which comprises: mounting the first semiconductor wafer on a flat chuck and mounting the second semiconductor wafer on a convex pressure gradient chuck;   scrubbing a surface of the first and second semiconductor wafer to obtain polished surfaces; and   pressing the polished surfaces of the first and second semiconductor wafers together by using the flat chuck and the convex pressure gradient chuck to press them together by applying a convex pressure gradient by using pressurized fluid across a surface of the second semiconductor wafer that is in contact with the convex pressure gradient chuck, thereby applying a greater pressure centrally located which gradually decreases to a periphery of the convex pressure gradient chuck by interconnecting a series of pressure reduction orifices, plenums, and channels which create a convex pressure gradient on the second semiconductor wafer during the pressing of the polished surfaces together.   
     
     
       2. The method of claim 1 further including spin-drying the semiconductor wafers after the scrubbing step. 
     
     
       3. The method of claim 1 further including providing the convex pressure gradient chuck with a soft malleable head. 
     
     
       4. The method of claim 2 further including accomplishing all steps sequentially. 
     
     
       5. A method of bonding a first and a second semiconductor wafer together, comprising: polishing a surface of the first semiconductor and a surface of the second semiconductor wafer to obtain clean surfaces;   pressing the clean surfaces of the first and the second semiconductor wafer together by applying a convex pressure gradient across at least a surface opposite the clean surface of the first semiconductor wafer; and   creating the convex pressure gradient by using a pressurized fluid through orifices and channels to create a greater pressure centrally located which gradually decreases to a periphery of the convex pressure gradient chuck to bond the first and second semiconductor wafers together.   
     
     
       6. A method for bonding a first and a second semiconductor wafer together which comprises the steps of: scrubbing a surface of the first semiconductor wafer and a surface of the second semiconductor wafer to obtain clean surfaces;   spin drying the surface of the first and the second semiconductor wafer to obtain at least a monolayer of liquid left on the surface of at least one wafer;   pressing the surface of the first and the second semiconductor wafer together by exerting a convex pressure gradient on at least the first semiconductor wafer; and   creating the convex pressure gradient by using a pressurized fluid through orifices and channels to create a greater pressure centrally located which gradually decreases to a periphery of the convex pressure gradient chuck to bond the first and second semiconductor wafers together. .Iadd.   
     
     
       7.  A method for processing a semiconductor wafer comprising the steps of: providing the semiconductor wafer, the semiconductor wafer having a frontside and a backside;   providing a rotatable polishing chuck for holding the semiconductor wafer;   mounting the semiconductor wafer on the rotatable polishing chuck by applying a vacuum to the backside of the semiconductor wafer;   placing the rotatable polishing chuck next to a surface such that the frontside of the semiconductor wafer is in contact with the surface; and   exerting a positive pressure on the backside of the semiconductor wafer by exposing the backside of the semiconductor wafer to a pressurized fluid, while the frontside of the semiconductor wafer is pressed against the surface by the rotatable polishing chuck..Iaddend..Iadd.8. The method of claim 7, wherein the step of exerting the positive pressure is further characterized as exposing the backside of the semiconductor wafer to a gas..Iaddend..Iadd.9. The method of claim 7, wherein the step of exerting the positive pressure is further characterized as exposing the backside of the semiconductor wafer to a liquid..Iaddend..Iadd.10. The method of claim 7, wherein the step of exerting the positive pressure is further characterized as applying a convex pressure gradient to the backside of   
     
     
        the semiconductor wafer..Iaddend..Iadd.11.  A method for processing a frontside of a semiconductor wafer comprising the steps of: providing the semiconductor wafer, the semiconductor wafer having a frontside and a backside;   providing a rotatable polishing chuck for holding the semiconductor wafer;   mounting the semiconductor wafer onto the rotatable polishing chuck;   using the rotatable polishing chuck to press the frontside of the semiconductor wafer against a surface;   exposing the backside of the semiconductor wafer to a pressurized fluid to apply a positive pressure to the backside of the semiconductor wafer, wherein the rotatable polishing chuck continues to press the frontside of the semiconductor wafer against the surface while the pressurized fluid is applied to the backside of the semiconductor wafer..Iaddend..Iadd.12. The method of claim 11, wherein the step of exposing the backside of the semiconductor wafer to the pressurized fluid is further characterized as exposing the backside of the semiconductor wafer to a gas..Iaddend..Iadd.13. The method of claim 11, wherein the step of exposing the backside of the semiconductor wafer to the pressurized fluid is further characterized as exposing the backside of the semiconductor wafer to a liquid.