Real-time observation of self-limiting SiO2/Si decomposition catalysed by gold silicide droplets

The thermal decomposition of thin SiO2 layers on silicon substrates draws significant attention due to its high technological importance in the semiconductor industry and in all relevant fields where silicon is employed as a substrate or part of an active device. Understanding of the underlying processes on silicon surfaces is therefore of fundamental importance. Here we show that the presence of gold silicide (AuSi) catalytically enhances the decomposition of SiO2 layers on a Si substrate, which proceeds via void nucleation under the positions of Au nanoparticles and subsequent lateral growth of the void. Our real-time secondary electron microscopy data reveal that the presence of a AuSi droplet within the void enhances the reaction rate due to an increased pre-exponential factor of the rate limiting step (i.e., SiO desorption at temperatures beyond 700 degrees C). While the SiO2 is decomposed the silicon surface in the open voids is covered by an Au monolayer. Consequently, as the void grows, the AuSi droplet is depleted of gold and the reaction rate enhancement is terminated when the supply of gold stops. Hence, the size of the pits is determined by the initial size of the Au nanoparticle. Our work thus provides insight into Au-enhanced SiO2 decomposition and its self-limiting nature offers a way for the preparation of nanoscale features with nanometer precision.