Effect of MeV energy He and N pre-implantation on the formation of porous silicon

The effects of MeV energy He and N pre-implantation of Si substrate on the structure of porous silicon formed by anodic etching were studied by measur ing the depth profiles of N-15 decorating the pores walls, Radiation damage was recovered by annealing after the implantation. It was Found that the H e implant accelerates the etching process, probably due to the bubbles or t he remaining lattice damage, At a dose of 8 x 10(16) ions/cm(2) the He cont aining layer was formed with a significantly enhanced porosity due to the c ontribution of the large-sized bubbles. At the highest dose of 32.5 x 10(16 ) ions/cm(2) flaking took place during the anodic etching. In contrast to H e, N stopped the anodic etching at a depth of critical N concentration of s imilar to0.9 at.%. For the lowest implantation dose, where the peak concent ration was below this limit, the pores propagate through the implanted laye r with an enhanced speed. (C) 2001 Elsevier Science B.V. All rights reserve d.