New method for the deposition of thin films on the inner walls of a deep blind hole: Application to semiconductor doping

A novel method for the deposition of thin films of dopant elements on the inner walls of a hole with a high aspect ratio aimed at doping germanium is here described. GeAlx and Sb were evaporated from a W filament inserted inside a hole 10 mm in diameter and 80 mm deep (aspect ratio 8:1). The filament was previously coated by sputtering with either GeAlx or Sb film. The filament heating process is fast enough to ensure very limited temperature increase on the inside walls of the hole as demonstrated by a heat balance calculation, thus preventing the introduction of contaminant species in the doped semiconductor. The filament was inserted in a purpose-built sample holder where planar substrates acted as the inner walls of the hole. The thickness distribution of the films evaporated on these substrates was characterized and correlated with the thickness distribution of the sputtered films deposited on the filament. In view of the final application of this process, i.e., doping of coaxial Ge-based gamma radiation detectors, GeAlx and Sb films were evaporated on Ge substrates and then subjected to pulsed laser melting to induce metal diffusion and doping of Ge surface. Measurements of the electrical activation of the laser melted samples pointed out the successful doping by both elements, i.e., p + doping for Al and n + doping for Sb.