Laser-induced thermal desorption as an in situ surface probe during plasma processing

We report a new technique for detecting adsorbates in real time during plasma processing. During etching of Si(100) in a ${\mathrm{Cl}}_2$ plasma, pulsed XeCl excimer laser irradiation of the surface induces thermal desorption of ${\mathrm{SiCl}}_{\mathit{x}}$ (x=0–4). Desorbing products are detected by either laser-induced fluorescence (for SiCl) excited by the same laser pulse, or by plasma-induced emission (for SiCl and Si) from electron impact excitation. The technique has a time resolution of <0.1s and submonolayer sensitivity, and should be applicable to processes at high ambient pressure.