ANNEALING OF IONIZING-RADIATION INDUCED DEFECTS IN INSULATED GATE FIELD-EFFECT TRANSISTORS USING ELEVATED PRESSURE

Intrinsic and extrinsic bulk defects (generated using Al-Kalpha x-rays ) were characterized using optically assisted electron injection into the SiO2 gate insulator of completed insulated gate field effect trans istors. Following labeling of neutral defects or annihilation of charg ed defects, the resulting threshold voltage shift due to charge collec tion at defect sites was used as a measure of the density of such bulk defects. The present study focuses on the effectiveness of reducing e xtrinsic defect densities (fixed positive charge and large neutral ele ctron traps) as a function of gate insulator thickness using various h igh pressure anneals, and on the effect of annealing on defect centroi d. A unique high pressure annealing system is described. The system is a specially modified commercial tool and has its own dedicated gas su pply for the high pressure process. Extensive modifications to the ann ealing system and to the gas supply system are described including the addition Of safety interlocks and a thermal conductivity gas analyzer . Radiation-induced defect densities decreased following all anneals, including high pressure pure argon. However, hydrogen-containing atmos pheres were far superior, with the effectiveness of an anneal directly related to the partial pressure of hydrogen employed. (The partial pr essure of hydrogen is equal to the hydrogen concentration multiplied b y the total pressure.) For the first time, dry oxide thicknesses in th e range of 6 to 50 nm, grown in 0 and 4.5% HCI at 1000-degrees-C, have been examined.