KINETICS AND THERMODYNAMICS CONSTRAINTS IN PT GETTERING BY P DIFFUSION IN SI

We have explored the mechanisms underlying the gettering of Pt atoms d issolved in crystalline Si. By using Pt implantation at different flue nces followed by a thermal process at 970 degrees C for 5 h we were ab le to prepare crystalline silicon wafers containing a uniform Pt conce ntration in the range 2x10(12)-2x10(14) atoms/cm(3). Subsequently, a h eavily doped n-type region was produced on one side of the wafer by P diffusion at 900 degrees C. Following this deposition process we have studied the kinetics of Pt gettering to the P-doped region in the temp erature range 700-970 degrees C and for annealing times ranging from 3 0 min to 48 h. Lifetime measurements by means of a contactless techniq ue were used to detect the depletion of Pt in the bulk of the wafer du e to the gettering process. The large range of initial Pt concentratio ns that we have explored allowed us to identify and separate the kinet ics and thermodynamics constraints that determine the gettering effici ency and to propose a phenomenological model for the gettering of Pt. In particular, it has been found that the kinetics of the gettering pr ocess are driven by the dissolution of immobile substitutional Pt atom s into interstitial sites. This process is assisted by Si self-interst itials and characterized by an activation energy of 0.4 eV. Moreover, the equilibrium distribution of Pt is thermodynamically determined by a segregation coefficient of the Pt atoms between the gettering sites and the silicon matrix. This segregation coefficient, and hence the ge ttering efficiency, decrease when the temperature of the gettering pro cess is increased and is described by an activation energy of 2.5 eV. (C) 1996 American Institute of Physics.