Patent ID: 7214548

Claim:
A method for flattening a warped substrate, comprising: placing the warped substrate on a planar surface of a clamping apparatus such that an external surface of the substrate is in direct mechanical contact with the planar surface, wherein the external surface of the substrate comprises N surface regions S 1 , S 2 , . . . , S N having an average warpage of W 1 , W 2 , . . . , W N , respectively, wherein W 1 ≦W 2 ≦ . . . ≦W N and W 1 <W N , wherein zones Z 1 , Z 2 , . . . , Z N of the planar surface respectively comprise vacuum port groups G 1 , G 2 , . . . , G N , wherein each vacuum port group comprises at least one vacuum port, and wherein N is at least 2; and generating a vacuum pressure P V1 , P V2 , . . . , P VN at each vacuum port within group G 1 , G 2 , . . . , G N , at a time of T 1 , T 2 , . . . , T N to clamp surface region S 1 , S 2 , . . . , S N to zone Z 1 , Z 2 , . . . , Z N , respectively, wherein the vacuum pressure P V1 , P V2 , . . . , P VN is maintained at the vacuum ports of group G 1 , G 2 , . . . , G N , respectively, until time T N+1 , and wherein T 1 <T 2 < . . . <T N <T N+1 .