Studies on Desorption Dynamics of Laser Induced Chemical Etching Reactions Using Time-Resolved Mass Spectrometry

The desorption dynamics of reaction products in laser induced chemical etching of Si（111）, GaAs（100） and InP（l00） surfaces by chlorine molecules is studied using a CW supersonic molecular beam and a time-resolved mass spectrometry. The time-of-flight （TOF） spectra of the major desorbed species have been measured as a function of laser flunce （E_L） under 560 nm and 355 nm pulsed laser irradiations and it is found that there exist laser fluence thresholds for the investigated reaction systems. The analysis shows that the measured TOF spectra of desorbed species fit a Maxwell—Boltzmann distribution pretty well. It is pointed out that the laser—induced desorption of the reaction intermediates is the rate—limiting step of the chemical etching reactions under molecular beam and pulsed laser conditions, and the desorption process may be described as the laser induced thermal desorption.