Wafer chuck featuring reduced friction support surface
Grinding, lapping and polishing basically work by making scratches in the body being ground, lapped or polished. The scratches typically are linear. The scratches gives rise to a directionality component of friction: the friction coefficient is less in the direction along the scratch than in a direction orthogonal, or across, the scratch. In a wafer handling/chucking situation, one wants the wafer to settle on the chuck, which involves the outer regions of the wafer moving radially with respect to the chuck. One can reduce friction in the radial direction by giving the lapping scratches a preferred orientation, namely, radial. This can be achieved by making the final passes of the lapping tool move predominantly in radial directions.
1. A wafer chuck for supporting a semiconductor wafer, comprising a surface configured to support the semiconductor wafer, said surface (i) inducting a plurality of regularly spaced pins of uniform height, thereby preventing drooping of the semiconductor wafer upon lowering of the semiconductor wafer onto said support surface, (ii) having a lower coefficient of friction in a radial direction than in a circumferential direction, and (iii) comprising scratches in a bearing surface of said pins, said scratches oriented predominantly radially.
2. The wafer chuck of claim 1 , produced by a lapping tool having about the same hardness as said wafer chuck.
3. The wafer chuck of claim 1 , produced by a lapping tool comprising SiC.
4. The wafer chuck of claim 1 , produced by a lapping tool having a toroidal shape.
5. The wafer chick of claim 4 , wherein said lapping tool has a diameter of about 28 millimeters, and applies a load of about 180 grams to said wafer chuck.
6. The wafer chuck of claim 5 , wherein said lapping tool is moved over said wafer chuck at a velocity of about 3 meters per minute.
7. The wafer chuck of claim 1 , wherein said support surface comprises SiC.
8. The wafer chuck of claim 1 , wherein said support surface comprises reaction bonded: silicon carbide.
9. The wafer chuck of claim 1 , wherein said predominantly radially oriented scratches are produced by a lapping tool comprising reaction bonded silicon carbide.
10. A wafer chuck for supporting a semiconductor wafer, comprising a surface configured to support the semiconductor wafer, said surface (i) having a center, (ii) featuring abrasion scratches that are oriented radially and pass through said center of said surface, and (iii) having a lower coefficient of friction in a direction along said radially oriented scratches than in a direction across said radially oriented scratches.