Patent ID: 7871830

Claim:
A method for controlling a plasma processing chamber, wherein the plasma processing chamber includes an RF generator, the RF generator providing a drive signal to an electrode to generate a gas plasma, and an RF sensor for sensing operating characteristics of the drive signal, wherein the plasma processing chamber processes a single semiconductor wafer at a time, the method consisting of: (1) selecting a mathematical model equation of the form X(ti)=A+Be(exp (−λ*ti)), wherein X(ti) is an instant electrical reactance of the plasma processing chamber; (2) commanding the plasma processing chamber to begin processing the wafer according to a predetermined plasma etching recipe; (3) receiving a plurality of data sets from the RF sensor, each data set comprising a representation of RMS voltage, RMS current, and phase angle between the RMS voltage and RMS current during a first time period, wherein each data set corresponds to a unique time point; (4) saving the data sets received from the RF sensor and their corresponding time points; (5) calculating the variable parameters A, B, and λ using the data set values; (6) receiving an additional data set from the RF sensor during a second time period; (7) saving the additional data set received from the RF sensor and its corresponding time point; (8) using the values of the variable parameters A, B, and λ from the first time period, calculating a value of the mathematical model for a time point corresponding to the same time point of the additional data set; (9) calculating a residual between the additional data set and the value of the mathematical model for the time point corresponding to the time point of the additional data set; (10) if and the residual is greater than a predetermined threshold, commanding the plasma processing chamber to stop processing; and (11) if the residual is not greater than the threshold, repeating the process steps beginning with the operation (6) above, thereby extending the second time period.