Comprehensive Analysis of an Isolation Area Obtained by Local Oxidation of Silicon Without Field Implant

Abstract

Isolation area, obtained by local oxidation of silicon (LOCOS) without field implant, naturally shows a high sensitivity of the leakage current to fixed charges in metal oxide semiconductor (MOS) parasitic transistors. It has been shown that during the deposition of the nitride capacitor insulator-layer, fixed charges are generated in the underlying plasma-deposited oxides. The behavior of the P-channel MOS (PMOS) parasitic transistor can be well accounted for by considering fixed charge creation in the thick part of the gate insulator. In the case of the N-channel MOS (NMOS) transistor, the leakage current is controlled by the bird's beak region where a high interface state density exists. The NMOS behavior has been explained taking into account the charge creation as well as a decrease in interface state density during nitride deposition. A new “recipe” for the nitride deposition based on a very low thermal budget has been established. Finally, a high threshold voltage and a reasonably low leakage current have been achieved for both the NMOS and PMOS parasitic transistors.