ELECTRICAL-STRESS SIMULATION OF PLASMA-DAMAGE TO SUBMICRON METAL-OXIDE-SILICON FIELD-EFFECT TRANSISTORS - COMPARISON BETWEEN DIRECT-CURRENTAND ALTERNATING-CURRENT STRESSES

The study reported herein is aimed at establishing signatures of metal -oxide-silicon field-effect transistors (MOSFETs) damage induced by al ternating current (ac) stressing applied at conditions that simulate p lasma processing environment and the comparison of the ac stress induc ed damage to damage from an equivalent direct current (de) stress. We also examine the response of stress induced damage to annealing that e mulates postmetallization annealing in complementary metaloxide-silico n processing. We apply sinusoidal and de voltage stress signals to 0.5 mu m n- or p-MOSFETs with 90-Angstrom-thick gate oxides and anneal th e stressed transistors in forming gas ambient (6% H-2 and 94% N-2) at 400 degrees C for 30 min. We assess damage on MOSFETs by measuring tra nsconductance, threshold voltage, and subthreshold swing. We find out that the onset of damage to devices subjected to ac stressing occurs a t voltage amplitudes as low as 6 V, whereas in de stressing damage bec omes significant only at voltages larger than 10 V. We also show that the forming gas annealing is able to eliminate both types of damage an d recover transistor characteristics. It is proposed that carrier hopp ing is primarily responsible for oxide current and, hence, device dama ge observed following the ac stress in contrast to Fowler-Nordheim tun neling current which causes the damage produced by our de stress. (C) 1997 American Vacuum Society.