THE ADSORPTION AND THERMAL-DECOMPOSITION OF PH3 ON SI(111)-(7X7)

The adsorption of PH3, on Si(111)-(7 × 7) has been studied by Auger electron spectroscopy and temperature programmed desorption. PH3 was found to exhibit two kinds of behavior on the surface. A small surface coverage of molecularly adsorbed PH3 desorbs without any dissociative surface chemistry. For the majority of the adsorbed PHx species (3 ≥ x ≥ 1) dissociation occurs to form P(a) and H(a). At 120 K, PH3 initially adsorbs as the reactive species with a sticking coefficient of S ≅ 1 up to ∼75% saturation. The reactive PHx species surface concentration saturates at (1.9 ± 0.3) × 1014 PHx cm-2. Surface H(a), produc thermal decomposition, desorbs as H2(g) at T > 700 K., and P(a) desorbs as P2(g) at T > 900 K. Capping the Si-dangling bonds with atomic deuterium prevents PH3 adsorption, indicating that the dangling bonds are the PH3 adsorption sites. Isotopic studies involving Si-D surface species mixed with adsorbed PHx species indicate that PH3 desorption does not occur through a recombination process. Finally, additional PH3 may be adsorbed if the surface hydrogen produced by dissociation of PH3 is removed. Evidence for P penetration into bulk Si(111) at 875 K is presented. © 1990.