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Oxide tub isolation (OTI) is an attractive alternative for bipolar and complementary metal-oxide-semiconductor (BiCMOS) technologies. OTI is a variation of shallow trench isolation in which the trenches reach the buried diffusion layers. This isolation technology affords increased BiCMOS device density and latch-up suppression compared to junction isolation and affords cost advantages over deep trench isolation. Furthermore, this isolation technology affords an increase in bipolar junction transistor device performance due to the reduction of collector-to-substrate capacitance. However, trench-related stress is a formidable challenge in the effective implementation of OTI. Both physical and electrical evidence shows that a Si 3 N 4 trench liner significantly reduces trench-related stress. The Si 3 N 4 trench liner thus affords increased device array yield, as well as improved resistor and metal-oxide-semiconductor field-effect transistor matching.

A study of the use of reactive chlorine species for etching silicon and silicon dioxide in a plasma etching process has been made with a gas mixture in a cathode‐coupled diode system. A key advantage of the gas mixture is the ability to achieve high etch rate ratios between silicon and silicon dioxide (≥ 20:1) coupled with no mask undercutting, which tends to be prevalent with fluorinated gas systems. Etching characteristics of Si as a function of process parameters ( concentration, pressure, system loading) and material parameters (e.g., Si conductivity, edge shape of mask) have been evaluated. These parameters can influence the silicon etch rate, the etch rate ratio, as well as the etched edge shape.