Surface and Bulk Properties which Influence Ion-Beam Hydrogenation of Silicon
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SURFACE AND BULK PROPERTIES WHICH INFLUENCE ION-BEAM HYDROGENATION OF SILICON ROBERT A. ANDERSON AND CARLETON H. SEAGER Sandia National Laboratories, Albuquerque,
NM 87185
ABSTRACT The time evolution of dopant passivation in p and n-type silicon Schottky and MIS barriers has been investigated for low-energy H ions implanted directly into the silicon through a 400-A front-electrode metallization. Knowledge of the dependence of the near-surface hydrogen concentration on time and experimental parameters is crucial to the analysis of these experiments. Hydrogenation effects are observed to vanish at ion energies below 800 eV, which suggests that the front electrode, rather than being a source of H, will behave as a sink for H diffusing in the silicon. Accordingly, we show that a steady-state H concentration proportional to the ion-deposition flux and deposition depth is established in a time interval less than a second near the electrode. Although some of the mobile H appears to be in a positively charged state, we calculate that the bias voltage applied to samples has only a small influence on the near-surface H concentration. An extensive study of the effects of sample temperature, beam flux, and ion energy supports these concepts and has revealed no evidence of ion-damage induced H trapping. The possible importance of H.H recombination is suggested by data obtained at the higher H concentrations.
INTRODUCTION We are studying hydrogen motion and bonding in silicon by means of rapid 1 MHz capacitance-voltage profiling of Schottky and MIS barriers [1]. Our results display the time evolution of charge density (dopant passivation) when low-energy H ions are implanted directly into the silicon through the frontelectrode metallization. These data can be compared with numerical transport simulations and simple analytic approximations to deduce the charge state, diffusivity, and trapping parameters appropriate to the hydrogenation process in p and n-type material [2]. Such an analysis, however, relies on a knowledge of the surface boundary condition and bulk processes which affect the H concentration at the implantation depth; this hydrogen concentration is the source of mobile H that transports into the silicon bulk. Therefore, we have performed an extensive study of the effects of varying the sample temperature and the beam current and energy from our ion source, in order to deduce the simplest physical models which are consistent with observed behavior. Results from this study support our approach and, furthermore, give important insight into the role of implantation-induced damage and direct H.H interactions.
SURFACE BOUNDARY CONDITION Previously we postulated that H implanted into the front metallization of our Schottky-barrier diodes was diffusing into the silicon [1]. Highresolution TEM and SEM examinations of these early samples have revealed numerous small pinholes in the metallizations, so that some H was being implanted directly into the silicon even at low ion energies. The hydrogenation of these samples is l
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