RETENTION OF PHOSPHORUS IN SILICON BENEATH TUNGSTEN SILICIDE CONTACTS DURING HIGH TEMPERATURE CYCLES
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2001-Oct-19
After metal contacts and short-range interconnects are deposited on silicon, there is often the need to carry out processing at high temperatures. Compound formation, grain size enhancement, contact improve- ment, and glass reflow for tapering of via holes in thick doped glass layers all can require exposure to temperatures in the 900.1000°C range for best results. To withstand such high temperatures, refractory metals or compounds are necessary. Of these, tungsten silicide (WSi>) with a melting temperature of 2164°C is a promising candidate! WSh can easily withstand temperatures above 1100°C if sufficient excess Si is available to satisfy the needs of any oxidation cycle, which produces asurface layerof SiOz, without lowering theSi content below that need- ed to maintain WSiz stoichiometry. To accomplish this, and to promote adhesion to SiOz, WSh is often deposited silicon-rich and onto a layer of poly SP; this is referred to as a polycide. To obtain a deposited WSh layer in its most conductive (<40pgcm) large grain form, a high temperature cycle, e.g., lo-120 minutes at lOOo"C, is needed.