PLASMA ETCHING APPARATUS

PURPOSE:To settle a problem about inequality in plasma on the face of a wafer, by using a clamp ring made of conductive material with no fear of corrosion or pollution, and keeping the plasma at an electric potential equal to that of the surface of a wafer. CONSTITUTION:A wafer 3 is mounted on a lower electrode 4, and an edge part of the wafer 3 is fixed by a clamp ring 1. The clamp ring has a ringed shape having a reverse L-shaped cross section. The clamp ring is made up of a conductive aluminum core 11 and an insulating alumina part 12. The aluminum core 11 is covered with the alumina part 12, but a part of the aluminum core 11 adjacent to the wafer 3 is exposed. The electric potential and the heat at the wafer 3 are transmitted through the aluminum 11 as a conductive and good heat-conductive material. In this way, the electric potential of the clamp ring 1 is made equal to that of the wafer 3, and the surface temperature of the wafer 3 is made stable. Moreover, the aluminum 11 and alumina 12 used together are preventive against corrosion, so a sample (wafer) can be protected from a contamination.