A Raman scattering study of H2 trapped near O in Si

Single-crystal silicon wafers exposed to a hydrogen plasma are studied by Raman scattering. Three Raman signals at 3727(1), 3733(1), and 3740(1)cm-1 (T→0K) are assigned to ro-vibrational modes of H2 bound to interstitial oxygen (O-H2). By monitoring the trapping kinetics of interstitial H2 at oxygen it is found that ortho- and para-H2 have similar diffusivities. At 77 K, an ortho-to-para conversion of H2 within the O-H2 complex is observed. This conversion occurs with similar kinetics as has been previously observed for isolated interstitial H2 in Si, and is suggested to be caused by interaction of H2 with the nuclear magnetic moment of 29Si.