An evaluation of FUROX isolation technology for VLSI/nMOSFET fabrication

A defect-free near-zero bird´s beak, fully recessed oxide (FUROX) field-isolation technology has been evaluated through the fabrication of VLSI/nMOSFETs. The FUROX process mainly consists of: (1) a thin nitrided oxide as the stress buffer layer and the interface sealing layer for local oxidation enhancement; and (2) a novel more-reliable nitride masking structure for a two-step field oxidation and a self-aligned field implantation. The elimination of the necking effect on positive photoresist and the improvement of critical dimension control for polysilicon gates using the planarized isolation have been demonstrated. Through electrical characterization of n⁺-p diodes and field and active transistors, the FUROX devices have been shown to provide low leakage-current level, good isolation property, and large recovery of the effective channel width (1.4 μm). Therefore, the serious narrow-width effects that exist in conventional LOCOS (local oxidation of silicon) isolated have been effectively reduced. Using histogram analysis, the reliability of the masking structure had hence good uniformity of device properties for FUROX isolation have been exhibited. The successful fabrication of FUROX devices with W_eff=0.6 μm clearly demonstrates that FUROX isolation technology is greatly superior to conventional LOCOS