Patent ID: 7651873

Claim:
A method comprising: providing a semiconductor processing apparatus comprising at least a first processing body, the first processing body having a substantially flat surface, and the first processing body being provided with at least one gas conduit for discharging processing gas at said surface; providing a wafer, the wafer having a substantially flat, plate-like shape such that it comprises a first and a second main surface, and the wafer being positioned with its first main surface parallel to the surface of the first processing body, such that both surfaces face each other in proximity, thus defining a gap between them; effecting a flow of processing gas that extends through the at least one gas conduit and through the gap between the first processing body's surface and the wafer's first main surface; repeatedly measuring a pressure of the processing gas within the gas flow; and determining from the pressure measurements a occurrence of an event that is related to a variation in the position of the wafer's first main surface relative to the surface of the first processing body.