Transient Plasma-Induced Emission Analysis of Laser-Desorbed Species During Cl sub 2 Plasma Etching of Si

The surface during the etching of Si in a Cl sub 2 inductively-coupled plasma (ICP) was analyzed by laser desorption (LD), followed by detection of the desorbed species by monitoring the transient changes by plasma- induced emission (PIE). Optical emission from Si, SiCl, SiCl sub 2 and possibly Si sub 2 or SiCl sub 3 was detected in situ using this LD-PIE method. The surface coverage of chlorine was determined by normalizing the LD-PIE signal by either of two ways: by the electron density, as measured by microwave interferometry, or by using the background PIE signal. Little change in surface coverage was observed as the electron density was changed by varying the rf power supplied to the ICP, confirming the observation made using laser-induced fluorescence (LIF) detection (LD-LIF). LD-PIE analysis of the surface is seen to be more versatile than LD-LIF- sometimes it can detect the desorbed species while LD-LIF cannot; still, it requires calibration to account for the electron-induced excitation of the laser-desorbed species.