Low voltage and temperature effects on SILC in stressed ultrathin oxide films

It is generally agreed that stress induced leakage current (SILC), in MOS d evices, is due to electrons tunneling through stress-induced neutral traps and that SILC has a steady-state component. However, it was observed that S ILC, created by positive or negative Fowler-Nordheim injection in 7 and 5 n m thick oxides, decays slowly but continuously when, after stress, the samp les are positively or negatively biased at low voltage. The decay is irreve rsible as long as the gate voltage is less than 4 V. To explain the SILC de cay, it has been proposed that some active traps in the tunneling process m ight possibly be deactivated. The present communication adds first compleme ntary observations on this subject: it shows that the above phenomenon is o bserved in 3.8 and 3.5 nm thick oxides after a positive stress; that this p henomenon is stable as long as the temperature remains below the SILC annea ling temperature threshold which is equal to 200 degreesC; and that during the SILC decay the interface state density does not diminish and can even i ncrease. This communication shows secondly that after a negative stress two SILC components exist in these thin oxides: one which has all the characte ristics of the SILC induced by a positive stress and another which does not exist in thicker oxides, which does not decay when a low voltage is applie d after stress and which is not annealed at 300 degreesC. (C) 2001 Publishe d by Elsevier Science Ltd.