Solid solubility of As in CoSi2 and redistribution at the CoSi2/Si interface

The solid solubility of As in CoSi2 and the redistribution of As at the CoS i2/Si interface at temperatures between 650 and 950 degrees C have been inv estigated. As was implanted in the cap Si layer of mesotaxy samples (epitax ial CoSi2 layers buried in a Si substrate). The As profiles after annealing were measured by secondary ion mass spectrometry. The solubility of As is lower in the cobalt disilicide than in silicon. A detailed description of t hermodynamic equilibrium between the solution of As in CoSi2 and the soluti on of As in Si shows that the distribution coefficient is dependent on the concentration. Within the experimental accuracy, the enthalpy of solution, deduced from the distribution coefficient, is constant in the temperature r ange and equal to 0.28 eV. The solution of As in CoSi2 can thus be describe d by Henry's law, which is valid for dilute solutions. Accumulation of As a t both interfaces of the buried CoSi2 layer has been observed and is discus sed in terms of segregation and precipitation. A transient enhancement of t he As diffusion in the Si substrate has also been found. Simulation of the redistribution process shows that this enhancement is not due to the diffus ion of As in CoSi2 but more likely associated with the excess of point defe cts resulting from ion implantation or from the silicide film. On the basis of both ternary phase diagram calculations and experimental results, it is shown that there is a ternary equilibrium between Si(As), CoSi2, and SiAs in contrast to the equilibrium between Si(As), CoSi2, and CoAs reported pre viously by other authors. It is shown that the latter equilibrium should de crease the solubility of As in Si, but such a decrease has never been obser ved experimentally. (C) 1999 American Institute of Physics. [S0021- 8979(99 )08121-9].