A SUPERSONIC MOLECULAR-BEAM STUDY OF THE CHEMISORPTION OF PH3 ON THE SI(100) SURFACE

The dissociative chemisorption of phosphine, PH3, on the Si(100) surfa ce has been examined with supersonic molecular beam scattering techniq ues. The effect of phosphorus adatoms, P(a), formed by the dissociativ e chemisorption of PH3, on the reaction of SiH4 and Si2H6 with Si(100) has also been characterized. All reactions have been examined at subs trate temperatures characteristic of steady-state Si thin film growth, i.e. T-s greater than or equal to 450 degrees C. The reaction probabi lity, S-R, for PH3 on Si(100) decreases with increasing substrate temp erature and the kinetic energy of the incident molecule, suggesting th at chemisorption proceeds via a trapping precursor-mediated dissociati on channel. The dependence of PH3 dissociative chemisorption on the fr actional coverage of P(a) and H(a) has been deduced under conditions w here the desorption of H-2 and P-2 are finite. The dependence of the d issociative chemisorption of both SiH4 and Si2H6 on the coverage of P( a) has also been determined. For reaction conditions under which P(a) is the dominant surface species, the reaction probabilities of PH3, Si H4 and Si2H6 are proportional to the quantity 1 - theta(P)(2), where t heta(P) is the fractional coverage of the adsorbed phosphorus atoms. I n addition, the presence of phosphorus adatoms has also been found to have a significant influence on the reaction pathway of Si2H6 on Si(10 0). Our results have been employed to formulate a predictive model for the kinetics of Si thin film growth in presence of PH3(g).