Continuous monitoring of temperature and rate of plasma etching of semiconductor wafers

We propose an original algorithm for processing of low-coherence tandem interferometer signals, enabling identification of small changes in the geometric thickness of sample against major changes in its optical thickness, caused by temperature variations. Possibilities for simultaneous monitoring of the changes in sample thickness and temperature are demonstrated during chemical plasma etching of a Si wafer highly heated by a plasma discharge. The attained absolute accuracy of temperature measurements is 3 °C. The noise level (3σ) at measurements of thickness/temperature variations was 20 nm and 3 °C, respectively.