Dynamic images of plasma processes: Use of Fourier blobs for endpoint detection during plasma etching of patterned wafers

By monitoring various process parameters (e.g., applied rf power, flow rate of gases, etc.) as a function of time, we show that Fourier series decomposition of the values of those parameters, at each time step, plotted on polar coordinates, gives closed curves representing the state of the plasma and the activity on the wafer. A change of the shape of the “blob” is a signature of the endpoint. The technique was successfully applied on TiN/poly-Si, $WSix,$ and doped poly-Si gate etch, and contact etch processes. Moreover, the method is reproducible from wafer to wafer and can be used easily by inexperienced operators to spot endpoint in plasma processes.