Laser-induced etching of titanium by Br2 and CCl3Br at 248 nm
Abstract
A quartz crystal microbalance (QCM) has been used to study the KrF* excimer laser-induced etching of titanium by bromine-containing compounds. The experiment consists of focusing the pulsed UV laser beam at normal incidence onto the surface of a quartz crystal coated with 1 μm of polycrystalline titanium. The removal of titanium from the surface is monitored in real time by measuring the change in the frequency of the quartz crystal. The dependence of the etch rate on etchant pressure and laser fluence was measured and found to be consistent with a two-step etching mechanism. The initial step in the etching of titanium is reaction between the etchant and the surface to form the etch product between laser pulses. The etch product is subsequently removed from the surface during the laser pulse via a laser-induced thermal desorption process. The maximum etch rate obtained in this work was 6.2 Å-pulse-1, indicating that between two and three atomic layers of Ti can be removed per laser pulse. The energy required for desorption of the etch product is calculated to be 172 kJ-mole-1, which is consistent with the sublimation enthalpy of TiBr2 (168 kJ-mole-1). The proposed product in the etching of titanium by Br2 and CCl3Br is thus TiBr2. In the etching of Ti by Br2, formation of TiBr2 proceeds predominantly through the dissociative chemisorption of Br2. In the case of etching with CCl3Br, TiBr2 is formed via chemisorption of Br atoms produced in the gas-phase photodissociation of CCl3Br. © 1990 Springer-Verlag.