Optical Monitoring of Capacitance in Hemispherical Grain Polycrystalline Silicon for Advanced Dynamic Random Access Memory Application

A novel approach for monitoring the capacitance using optical data from the material characteristics of hemispherical grain (HSG) polycrystalline silicon film is reported. This noncontact optical method provides indirect measurement of electrical capacitance for advanced dynamic random access memory (DRAM) applications using HSG material. By a simple statistical analysis of the microscopic HSG structure, the actual electrical capacitance is estimated to better than 90% confidence level through correlation of the optically measured thickness and the void content of the HSG film. Data from broad band spectrop otometry (190-750 nm) with beam profile reflectometry are fitted in the context of the Bruggeman effective medium approximation (EMA) model to give HSG thickness and void content. The actual capacitance obtained from the electrical probe technique using an intrusive electrode on finished DRAM devices indicates good agreement with our approach.