Measurement of thickness of silicon carbide using multi-frequency analysis in the inductively coupled plasma

The focus ring plays an essential role in improving the plasma uniformity at the edge of the wafer in the semiconductor etching. However, as etching proceeds, erosion of the focus ring occurs by ion bombardment. When the focus ring is eroded, the tilting of the incident ions distorts the wafer profile. Silicon carbide (SiC), which has high heat resistance and durability, is used as material for the focus ring. To measure the thickness of SiC, we applied multi-frequency sinusoidal voltages to a metal plate in contact with SiC in plasma. The impedances are measured from the multi-frequency currents, and we can obtain the thickness using the capacitance of SiC from a SiC equivalent circuit model. The measurement is in good agreement with the actual SiC thickness. Our result is expected to be applied to erosion monitoring of the focus ring in plasma etching processing.