HOT-CARRIER EFFECTS IN MOSFETS WITH NITRIDED-OXIDE GATE-DIELECTRICS PREPARED BY RAPID THERMAL-PROCESSING

Hot-carrier effects are studied for n- and p-channel MOSFET's with nanometer-range thin (re-annealed) nitrided oxides prepared by rapid thermal processing (RTP) at 910-1080-degrees-C for 15-200 s. For typical 0.5-mu-m n-FET's with a reannealed nitrided oxide, substrate, current I(SUB) is smaller only by approximately 15%, while gate current I(G)'s for holes and electrons are reduced by approximately 95% and 20%, respectively, from those of a pure oxide. At the peak I(SUB) condition (stressing gate voltage V(Gstr) = 2 V), nitridation alone is found to reduce hot-carrier-induced threshold voltage shift DELTA-V(T) markedly while scarcely changing transconductance degradation DELTA-g(m(max))/g(m(max0)). On the other hand, as the subsequent re-annealing proceeds, both DELTA-V(T) and DELTA-g(m(max))/g(m(max0)) vary in a similar manner; both decrease very rapidly and saturate to respective values, which are not dependent on the re-annealing atmosphere (O2 or N2) but are smaller as the starting nitridation is heavier. When V(Gstr) is as high as the stressing drain voltage, DELTA-V(T) is found to be influenced by nitridation and re-annealing quite differently from the peak I(SUB) case; as nitridation proceeds, DELTA-V(T) decreases rapidly in the early nitridation stage and then increases showing a turnaround. As the subsequent re-annealing proceeds, DELTA-V(T) increases drastically and saturates to a value over a pure oxide, which is larger as the starting nitridation is heavier. Such undesirable DELTA-V(T) enhancement at high V(Gstr) is found to be greatly alleviated by changing the re-annealing atmosphere from O2 to N2. However, the most critical factor determining device lifetime is always the DELTA-g(m(max))/g(m(max0)) at the peak I(SUB) condition even for a dielectric film subject to the largest high V(Gstr) DELTA-V(T) in the lightly nitrided-oxide system studied, and so both rapid reoxidation and inert annealing strikingly improve n-FET hot-carrier reliability by achieving approximately 100-times longer device lifetime as compared with oxide n-FET's. In contrast with the n-FET case, hot-carrier immunity as well as I(SUB) and I(G) for p-FET's are found to be substantially unchanged by nitridation and subsequent re-annealing. Furthermore, as well as the above n-FET improvements with respect to conventional ON-state degradations, the hot-carrier-induced increase of gate-induced drain leakage (GIDL) observed fro oxide n-FET's is markedly suppressed for typical (re-annealed) nitrided oxides, and the improvement in OFF-state hot-carrier immunity is enhanced as V(Gstr) is lower. To explain the behaviors of hot-carrier-induced n-FET degradations, a two-factor model is proposed; DELTA-V(T) and DELTA-g(m(max))/g(m(max0)) at the peak I(SUB) condition are enhanced by one factor of increasing hydrogen concentration [H], while both are reduced by the other factor of increasing nitrogen concentration [N]int. From the experimental data, we also derive the following semi-empirical formula: DELTA-V(T), DELTA-g(m(max))/g(m(max0)) is-proportional-to [H]n/(1 + K(N) . [N]int(m)), where n, m, and K(N) are constants. Thus the striking improvement of n-FET hot-carrier immunity by rapid re-annealing cn be explained bv the observed reduction of [H] while keeping [N]int unchanged.