Method of clamping a wafer during a process that creates asymmetric stress in the wafer
View Patent ↗This invention relates to electrostatic clamping and associated clamps. A particular method is described of clamping a wafer, during the process that creates asymmetric stress in the wafer, to an electrostatic chuck having a concave portion in its clamping surface characterized in that the wafer is initially clamped around its periphery in a generally flat orientation and then is bowed into the concavity as the asymmetric stress is created in the wafer. It is particularly preferred that the degree of concavity of the chuck is such as to maintain a gas seal between the wafer and the chuck sufficient to allow backside cooling of the water.
1. A method of clamping a wafer during a process that creates asymmetric stress in the wafer to an electrostatic chuck having a concave portion in its clamping surface, the method comprising:
initially clamping the wafer around its periphery in a generally flat orientations, and
etching an outer layer of the wafer so that the wafer is bowed into the concavity as asymmetric stress is created in the wafer.
2. A method as claimed in claim 1 wherein the degree of concavity of the chuck is such as to maintain a gas seal between the wafer and chuck sufficient to allow back-side cooling of the wafer.
3. A method as claimed in claim 1 wherein the process is etching.
4. A method as claimed in claim 2 wherein the process is etching.
5. A method as claims in claim 1 , wherein the outer layer is an oxide layer.