High-resolution infrared spectroscopy applied to powder formation, plasma transport and surface processes

Infrared absorption spectroscopy using both a Fourier transform spectrometer and a tunable diode laser arrangement has been performed to study the growth of particles in an rf (13.56 MHz) plasma at pressures from 25 to 200 mTorr in mixtures of CF4, CF2Cl2 and CHF3 with argon. A planar configuration has been used, with a silicon wafer on the powered electrode. Absorption bands at 750–1300 cm-1 have been found and attributed to C-F, Si-F, C-Cl and Si-C absorption. Furthermore continuous extinction due to Rayleigh and Mie scattering has been observed. The CF2 concentration appears to decrease strongly when powder growth begins. The SiF4 concentration shows a maximum then. Considering all these results, we arrive at the conclusion that particle growth is initiated by micromasking at the Si surface combined with a highly directional etching process. Due to residual isotropic etching the particles are released from the surface and enter the plasma. Furthermore, it has been found that the powder production continues and even accelerates after the freon flow is stopped, due to sputtering of remaining structures on the surface