Challenges of Manufacturing Capacitor Oxide in Mixed Signal ASICS

Deposited PECVD oxides are used as the dielectric in polysilicon-polysilicon capacitors for a variety of mixed signal applications. Wafers using highly doped substrates showed good thickness uniformity. Variation across the wafer increased along with increasing substrate resistance. This variation was correlated to electrostatic charge imparted to the wafer from poorly grounded wafer handling robotics. Charging caused plasma instabilities that promoted localized adsorption and reaction of the TEOS intermediates in the initial phase of the deposition. Plasma instabilities were confirmed by measuring fluctuations in the RF power and DC bias levels.