Formation of Doping Profiles in Float Zone Silicon by Helium Implantation and Plasma Hydrogenation

Abstract

By means of two-point-probe Spreading Resistance (SR) analyses, the formation and evolution of hydrogen-related and vacancy-related donor and acceptor states were studied in helium implanted and subsequently hydrogen plasma-treated n-type Float-Zone (FZ) silicon wafers. He + -implantation was carried out at 3.75 MeV and 11 MeV, applying fluences of 1⋅10 14 cm -2 and 2⋅10 13 cm -2 . After 15-min post-implantation H-plasma exposures at substrate temperatures between 350 °C and 500 °C, distinct surplus doping profiles were observed in the subsurface layers of the treated FZ Si samples. Also acceptor-like states occurred, at least partially compensating for the initial n-type doping, so that even buried p-type layers could be created under appropriate process conditions. The nature of the involved defect complexes will be discussed.

Distribution of Hydrogen- and Vacancy-Related Donor and Acceptor States in Helium-Implanted and Plasma-Hydrogenated Float-Zone Silicon

“…To provide mirrorpolished surfaces for these measurements, the samples were beveled at a low angle (α ≈ 1° and 3° for implantations at E = 3.75 MeV and 11 MeV, respectively) on a rotating quartz plate with diamond paste (0.1-µm grains) and Buehler IsoCut Fluid ® . As was briefly discussed already in [7,8], down to a depth of ∼20 µm below the surface, such processes resulted in a significant modification of the subsurface layers of the FZ Si samples. Due to the small bevel angles, resistance profiles with fairly high depth resolution were obtained.…”

“…At higher applied substrate temperatures (400 °C), the implantation-damaged area was partly annealed during plasma hydrogenation, and the damage layer became somewhat nar- rower. Such acceptor-like defect states might be associated with a deep acceptor level of multi-vacancy-oxygen complexes, V n -O m , or hydrogenated divacancy complexes, V 2 -H 2 [6][7][8]. However, in case of 15-min H-plasma exposure at substrate temperatures up to 400 °C, the in-diffused hydrogen concentrations were not high enough to transform the radiation damage into donor-like defect states around R p , as was observed for H + -implanted and H-plasma treated FZ Si (a more detailed discussion can be found in [6,8]).…”

“…Furthermore, at moderate temperatures up to 500 °C, hydrogen-plasma treatments can cause n-type doping in Si wafers under appropriate conditions. We also observed and briefly discussed similar but more complex formation of electrically active defect states for He + -implanted and plasma hydrogenated FZ Si [7,8]. With this background, we have been interested in two-step processes based on H + -or He + -implantations and successive hydrogen-plasma treatments.…”

“…Further details can be found in [6][7][8]. To provide mirrorpolished surfaces for these measurements, the samples were beveled at a low angle (α ≈ 1° and 3° for implantations at E = 3.75 MeV and 11 MeV, respectively) on a rotating quartz plate with diamond paste (0.1-µm grains) and Buehler IsoCut Fluid ® .…”

“…Hence, light-ion implantation is a powerful tool in semiconductor device technology for device optimization; this is true in particular for silicon devices. Subsurface layer modifications down to quite deep wafer regions via the tailoring of doping profiles by light-ion implantation and subsequent hydrogen-plasma exposure could be a promising technological approach for power devices [6][7][8]. Therefore, substrate modifications by light-ion implantation can follow rather deep profiles if desired.…”