Interaction of Pb defects at the (111)Si/SiO2 interface with molecular hydrogen:: Simultaneous action of passivation and dissociation

The simultaneous action of passivation and dissociation during thermochemical interaction of trivalent interfacial Si traps (P-b's;Si-3=Si .) with molecular hydrogen has been analyzed. A unified description is attained through solution of the simultaneous set of the first-order rate equations describing passivation and dissociation, under the restriction that the H-2 concentrations at the interface and in the ambient are continuously equal. The analysis is given allowance by the recently attained physically consistent pictures for each of the separate steps of passivation in H-2 and dissociation in vacuum, incorporating the existence of distinct spreads sigma(Ef) and sigma(Ed) in the respective activation energies. The assessment of heat treatment in H-2 shows that, as compared to the fictitious case sigma(Ef)=sigma(Ed)=0, the effect of the existence of the spreads, for usual anneal times of 10-60 min in 1 atm H-2, is to reduce the passivation efficiency by two orders of magnitude, while enhancing the optimum anneal temperature T-an from similar to 330-360 to the range 400-430 degrees C-the latter being commonly used. The optimum anneal time-T-an curve is established. The analysis, and as experimentally verified, shows that the P-b passivation level is not decreased (P-b regenerated) by successive annealings at successively lower T-an, in contrast with previous reports on annealing of electrically detected interface traps in atomic H. The results are discussed within technological context. A general inference is that P-b may be readily optimally passivated (in 1 atm H-2) to sub-1-ppm levels, rendering negligible their role in the typically attained residual interface trap densities of (2-10)x10(9) cm(-2); at these levels, the interface traps left must be of different type, as concluded previously. During passivation in H-2, the P-b system appears as an efficient atomic H mill. (C) 2000 American Institute of Physics. [S0021-8979(00)10313-5].