Plasma Immersion Ion Implantation of Nitrogen into Porous Silicon Layers

Nitrogen plasma immersion ion implantation (PIII) (with bias voltage, pressure and duration up to 1000 V, 1 mbar and 240 seconds, respectively) was applied to modify the composition of porous silicon layers prepared on p and p(+) type single crystal Si substrates. The amounts of nitrogen and other impurities like O and C were determined using the N-14(d,alpha)C-12, N-14(alpha,alpha)N-14, P-16(d,p(1))O-17* and C-12(d,p)C-13 nuclear reactions. For a 30 sec immersion, the obtained nitrogen amount in the 2 mu m thick columnar-type porous layers increased with plasma pressure and bias voltage. To introduce nitrogen into sponge-like porous layer, nitrogen PIII with bias voltage of 1000 V and 1 mbar pressure was applied. As measured by Rutherford Backscattering Spectrometry (RBS), the introduced nitrogen is always in the near surface region and its amount reaches a saturation value after similar to 30 sec treatment of direct PIII. An example is shown for remote PIII (1000 V, 1 mbar and 180 sec) that is able to introduce nitrogen into the whole porous layer.