Apparatus, system, and methods for weighing and positioning wafers

A method for characterizing a lot of wafers following a first device fabrication process step performed on the wafers, the method comprising:

• a) prior to the process step, weighing a first reference wafer selected from the lot of wafers to obtain a pre-step reference weight;
• b) following the process step, weighing the first reference wafer to obtain a post-step reference weight;
• c) subtracting the pre-step reference weight from the post-step reference weight to define a pre/post reference weight;
• d) prior to the process step, weighing another wafer selected from the lot of wafers and defined as a test wafer to obtain a pre-step weight;
• e) following the process step, weighing the test wafer to obtain a post-step weight;
• f) subtracting the pre-step weight from the post-step weight to obtain a pre/post test weight of the test wafer;
• g) comparing the pre/post reference weight of the reference wafer with the pre/post test weight of the test wafer;
• h) if the pre/post test weight of the test wafer is within a pre-determined tolerance range for the first process step extending from above and below the pre/post reference weight of the reference wafer, delivering the test wafer to a subsequent device fabrication process step;
• and
• i) if the pre/post test weight of the test wafer is outside of the pre-determined tolerance range for the first process step extending from above and below the pre/post reference weight of the reference wafer, performing at least one of imaging the test wafer, inspecting the test wafer, performing a further test of the test wafer, or discarding the test wafer.