CFX (X=1-3) Radical Measurements in ECR Etching Plasma Employing C4F8 Gas by Infrared Diode Laser Absorption Spectroscopy

CF, CF2 and CF3 radical densities were investigated in electron cyclotron resonance (ECR) plasma employing C4F8 (octafluoro-cyclobutane) and C4F8/H2 gases using infrared diode laser absorption spectroscopy. It was found that CF2 radical density in ECR C4F8 plasma was on the order of 1013 cm-3 at microwave power below 300 W and pressure of 0.4 Pa, which was quite high compared to CF and CF3 radical densities. With addition of H2 to C4F8 plasma, CF radical density increased markedly and the CF radical became dominant along with the CF2 radical. The mechanisms of these behaviors of radicals are discussed on the basis of these experimental results.