Investigations of ultrathin silicon nitride layers produced by low-energy ion implantation and EB-RTA

Ultrathin silicon nitride layers were produced by implanting 10 keV 15N+2 ions into left angle 100 right angle silicon at RT with fluences from 5.0 x 1016 at/cm2 to 5.0 x 1017 at/cm2. The 15N depth distributions were analysed by the resonant nuclear reaction 15N(p, αγ)12C. The NRA of the silicon nitride layers show understoichiometric, stoichiometric, and overstoichiometric N/Si ratios depending on the fluences. The implanted samples were processed by electron beam rapid thermal annealing (EB-RTA) between 900 and 1130 C under high vacuum conditions. The layer thicknesses and the 15N peak concentrations of EB-RTA samples varied with reference to non-annealed 15N layers. The alteration of the chemical bonds of SiNx layers by EB-RTA was investigated by XPS. NRA analyses of the EB-RTA samples at tilt angles from 65 to 83 indicated a shift of the low-energy edge which represents the sample surface. This shift is attributed to a shadowing effect of the SiNx surface. AFM analyses confirmed that the surfaces of EB-RTA samples were covered with irregularly distributed vertical very elastic, needlelike structures. Their average height was 16 nm (F = 5.0 x 1016 at/cm2, EB-RTA at 900 C for 15 s). (orig.)