Abstract: A method, apparatus, and computer program product for flattening a warped substrate. The substrate is placed on a planar surface of a clamping apparatus in direct mechanical contact with the planar surface. The substrate comprises surface regions S1, S2, . . . , SN having an average warpage of W1, W2, . . . , WN, respectively, wherein W1?W2? . . . ?WN and W1?WN. Zones Z1, Z2, . . . , ZN of the planar surface respectively comprise vacuum port groups G1, G2, . . . , GN. Each group comprises at least one vacuum port. N is at least 2. A vacuum pressure PV1, PV2, . . . , PVN is generated at each vacuum port within group G1, G2, . . . , GN, at a time of T1, T2, . . . , TN to clamp surface region S1, S2, . . . , SN to zone Z1, Z2, . . . , ZN, respectively. The vacuum pressure PV1, PV2, . . . , PVN is maintained at the vacuum ports of group G1, G2, . . . , GN, respectively, until time TN+1. T1<T2< . . . <TN<TN+1.