DAMAGE TO N-MOSFETS FROM ELECTRICAL STRESS RELATIONSHIP TO PROCESSINGDAMAGE AND IMPACT ON DEVICE RELIABILITY

The study reported herein examines and compares damage to n-channel an d p-channel metal-oxide-silicon field-effect transistors (MOSFETs) fro m direct current (d.c.) and alternating current (a.c.) electrical stre sses as well as the relationship of this damage to plasma processing d amage in MOSFETs. The lightly-doped drain (LDD) MOSFETs used are of 0. 5 mu m channel length and with a 90 Angstrom thick thermally grown gat e oxide Fabricated using a full flow CMOS process up to and including metal-1 processes and post-metallization annealing (PMA). The damage t o MOSFETs is assessed using transistor parameter characterization and charge-to-breakdown measurements on the gate oxide. It is found that m anifestations of d.c. stress-induced damage and a.c. stress-induced da mage to transistors are fairly similar in that both forms of damage ar e passivated by PMA and are reactivated by a subsequent d.c. electrica l stress. However, a.c. stress-induced damage is observed to occur at much lower electric fields across the gate oxide than those necessary for d.c. stress-induced damage to be significant. This is attributed t o a.c. currents, caused by carrier hopping, occurring at relatively lo w electric fields. One implication of our results is that plasma-charg ing damage, often attributed to d.c. electrical stress alone, may comp rise an a.c. electrical stress component too. (C) 1996 Elsevier Scienc e Ltd. All rights reserved.