Kinetics and thermodynamics constraints in Pt gettering by P diffusion in Si

We have explored the mechanisms underlying the gettering of Pt atoms dissolved in crystalline Si. By using Pt implantation at different fluences followed by a thermal process at 970 degrees C for 5 h we were able to prepare crystalline silicon wafers containing a uniform Pt concentration in the range 2x10(12)-2x10(14) atoms/cm(3). Subsequently, a heavily 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 temperature range 700-970 degrees C and for annealing times ranging from 30 min to 48 h. Lifetime measurements by means of a contactless technique were used to detect the depletion of Pt in the bulk of the wafer due to the gettering process. The large range of initial Pt concentrations that we have explored allowed us to identify and separate the kinetics and thermodynamics constraints that determine the gettering efficiency and to propose a phenomenological model for the gettering of Pt. In particular, it has been found that the kinetics of the gettering process are driven by the dissolution of immobile substitutional Pt atoms into interstitial sites. This process is assisted by Si self-interstitials 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 gettering efficiency, decrease when the temperature of the gettering process is increased and is described by an activation energy of 2.5 eV. (C) 1996 American Institute of Physics.