Patent ID: 6989683

Claim:
A method of controlling a process for wet etching a wafer, said method comprising: (a) providing a container with a liquid etch medium, (b) providing an apparatus for detecting a change in impedance in said liquid medium, said apparatus comprising an electrical circuit having a variable capacitor, at least two electrodes placed in said liquid medium, a source of alternating electrical current, and a detector for measurement of impedance across said electrodes as a function of time, (c) applying an alternating current to said circuit and adjusting said variable capacitor, (d) immersing at least one wafer in said liquid medium whereby said etching process is initiated, a surface of said immersed wafer being proximate to said electrodes, and (e) monitoring said detected impedance as a function of time said monitoring comprising providing a computing device for analyzing said detected impedance as a function of time and using said computing device to calculate a first derivative of said detected impedance with respect to time and to perform moving array calculations using moving array of detected impedance values to determine a rate of change of said impedance.