Novel isolation process using selective polysilicon filled trench technology for high speed bipolar circuits

Zero encroachment variable-width trench isolation (ZERO) with selective polycrystalline refill has been developed for emitter coupled logic (ECL) circuits. Subsequent oxidation of the selective polysilicon film produces a box-type oxide isolation with vertical sidewalls, no faceting, and zero encroachment. From the planarization point of view, selective polysilicon growth reduces the process complexity of LPCVD (low-pressure chemical vapor deposition) polysilicon-filled single-width trench technology. The selective polysilicon growth also facilitates variable-width trench isolation. Furthermore, it eliminates the faceting problem associated with selective monosilicon trench refill. Bipolar devices were built with variable-width trenches of 1 μm depth. Gate delay performance was improved by 40-45% as compared to recessed LOCOS isolated circuits