Transient plasma-induced emission analysis of laser-desorbed species during Cl2 plasma etching of Si

Abstract

The surface during the etching of Si in a Cl2 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, SiCl2, and possibly other species was detected in situ using this LD-PIE method as a function of rf power, substrate bias, and pressure. 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 ion density was changed by varying the rf power supplied to the ICP, confirming the observation made using laser-induced fluorescence (LIF) detection (LD-LIF). The LD-PIE signal is related to the density of species desorbed from the surface and subsequently excited by electrons. LD-PIE analysis of the surface is 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 collision-induced excitation of the laser-desorbed species.