Nuclear microprobe ion-channelling analysis of total dielectric isolation structures in silicon

The production of isolated device islands by high dose oxygen implantation into silicon followed by high temperature annealing has been termed total dielectric isolation (TDI). Higher packing densities, higher frequency performance and radiation hardness are the three potential advantages of fabricating very large scale integrated circuits by this method. Because of the microscopic size of the silicon islands, they cannot be analysed using conventional ion-channelling apparatus. However, some nuclear microprobes are now available which produce small diameter, low convergence MeV ion beams suitable for microscopic ion-channelling analysis. Thus, a technique which has proved very useful in analysing the near surface region in bulk semiconductor samples can now be applied to semiconductor device structures. The authors report on a preliminary study of TDI structures using the Surrey scanning microprobe. Measurements of crystalline quality, silicon thickness and buried oxide thickness were obtained from isolated islands. Secondary electron and optical microscopy were used to assess beam damage, and the feasibility of nuclear microprobe analysis of TDI structures is discussed.