Study of arsenic out-diffusion for buried plate formation in trench capacitors

We undertook a combined study of experiments and calibrated simulations to examine the arsenic diffusion from a solid source into Si for simulation of the buried plate (BP) of a trench capacitor. Arsenosilicate glass (ASG) deposited conformally in a Si deep trench has been used as a source to diffuse As into p-type Si to form a BP. Out-diffusion of As from ASG is studied for various two-step anneals consisting of an inert anneal followed by an oxidizing anneal. Effects of dry versus wet oxidation are contrasted. It was found that the junction depth decreases linearly with the oxide thickness grown from the second step of the ASG drive-in process. Arsenic surface concentration increases as more oxide is grown during the oxidation step, as long as the oxide thickness is less than the junction depth created by the anneal step of the ASG drive-in process. Effects of deposited As concentration and drive-in conditions on the trench capacitance are also investigated.