The Influence of Back End Processing on the Fixed Charges Density in the Si ‐ SiO2 Interface

Abstract

Variations in the density of fixed surface charges at the interface during back end processing steps are reported. After the deposition of phosphosilicate glass (P‐glass) films (LPCVD at 630°C, from TEOS, phosphine, and oxygen), measured on aluminum gate capacitors is in the range of . Densification of the P‐glass by means of heat‐treatment affects in a similar fashion to previously reported post thermal oxidation treatments. The effectiveness of the densification ambient in reducing can be ranked in the order: steam > oxygen > argon > steam + argon. After polycrystalline silicon/aluminum metallization, which involves polysilicon deposition followed by heat‐treatment (doping) and aluminum deposition, depends very strongly on the premetallization treatment. When this metallization is applied over undensified glass, can be higher than . It increases with increasing the doping time, the doping temperature, the glass thickness, or the phosphine to oxygen flow rate ratio during the P‐glass deposition. Polysilicon/aluminum metallization applied over densified glass yields much lower , with the final value depending strongly on the densification conditions. For example, densification in steam or oxygen at 950°C for 10 min yields of less than after the silicon/aluminum metallization. The results can be explained on a basis of oxygen deficiency in as deposited P‐glass films and rearrangement of the interface in the presence of a polysilicon cap film over the glass.