High temperature water as a clean and etch of low-k and SiO2 films

Water becomes more reactive as a function of temperature in part because the number of hydronium and hydroxyl ions increase. As one approaches the boiling point, the concentration of these species increases over seven times their concentrations at room temperature. At 150 °C, when the liquid state is maintained, these concentrations increase 15 times over room temperature. Due to its enhanced reactivity, high temperature water (HTW) has been studied as an etchant or clean of thermally grown SiO2 and low-k films. Ellipsometry, profilometry, infrared spectroscopy, and contact angle goniometry were used to study changes in film surface profiles, chemistries, and thicknesses. Interestingly, HTW demonstrated significant etching of SiO2 with minimal etching of the porous low-k. The temperature dependent etch rates of the thermal oxide were found to be in the range of reported results. To understand the reaction mechanisms of water with amorphous silica and low-k films, Reactive Force Field (ReaxFF) based molecular dynamics simulations of interface reactions of nanoporous organosilicate glass (OSG) low-k structure with water has been performed and the initial stage and steps of water/OSG reactions were identified. High temperature water could become a more selective and environmentally friendly etchant of thermally grown SiO2 layers.