Abstract: The invention is a method of fabricating a self-aligned, sub-minimum guard ring for a Schottky diode device wherein the sub-minimum guard ring is positioned at the inside edges of adjacent isolation structures and is self-aligned to the intrinsic base implanted regions. In this particular invention, illustrating the guard ring fabrication technique, an improved Schottky diode is fabricated at minimum groundrules which utilizes a frequency-doubling resist and an appropriate mask to provide the implant mask for a p- or n-type guard ring. This shallow implant near the surface prepares a guard ring that minimizes the electric field at the interface where the deposited metal or silicide joins the STI structure. Additional ion implants with energies greater than and less than the guard ring implantation energy may be deposited to tailor the substrate surface and reduce the parasitic capacitance of the diode.

Abstract: An isolation method in which an isolation ring is formed to isolate a semiconductor device from other semiconductor devices on a common substrate. The method is suitable for isolating bipolar devices from CMOS or other devices formed on the same substrate and for preventing base current from being injected into the substrate. The method starts with a substrate having a buried sub-collector and a first isolation region that surrounds the portion of the surface to contain the semiconductor device. The first isolation region extends only part of the distance from the surface towards the buried sub-collector. Layers of polysilicon and dual-tone resist are applied, and a first mask is used with an opaque area aligned over the portion of the surface to contain the semiconductor device. The edge of the opaque region terminates above the first isolation region. After exposure, the properties of the dual-tone resist allow a narrow sub-minimum width trench to be removed from the resist to define an isolation ring.