Applied Surface Science 46 (1990) 435-440 North-Holland 435 Hydrogen plasma treatment of silicon surfaces studied by in-situ spectroscopic ellipsometry P. Raynaud, J.P. Booth * and C. Pomot Laboratoire de Physique et Chimie des ProcedPs Plasma, CNRS URA 844, CNS-CNET, BP 98, 38243 Meylan CPdex, France Received 29 May 1990; accepted for publication 26 June 1990 The use of H, and Ar plasmas for the cleaning of crystalline Si surfaces has been investigated by in-situ spectroscopic ellipsometry (SE), LEED and Auger spectroscopy. H2 plasma treatment, followed by annealing at 700°C to desorb the adsorbed hydrogen, was found to produce high-quality clean crystalline surface. SE was shown to be sensitive not only to surface oxide layers and micro-roughness, but also to monolayer adsorption of hydrogen. The desorption of hydrogen as a function of temperature from H, plasma treated Si(100) and Si(ll1) surfaces was investigated. The presence of different phases of adsorbed hydrogen is distinguished by SE, in agreement with UPS and EELS studies. The clean (plasma treated and annealed) Si(100) and Si(ll1) surfaces show differences in their apparent dielectric constants, which may be due to the nature of the surface reconstruction. zyxwvutsrqponmlkjihg 1. Introduction zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Plasma-assisted epitaxial growth of Si layers has been achieved with SiH, multipolar micro- wave plasmas (MMP) [l-3]. However, the Si sub- strate must have a very clean crystalline surface, particularly if low defect density is required. The removal of the native oxide layer and of other surface impurities, of which carbon is particularly problematical, has been achieved previously with argon and H, plasmas [4-71. A detailed study is needed to establish the plasma conditions neces- sary to achieve high cleanliness, whilst minimizing damage to the crystal structure and avoiding ex- cessive heating of the substrate (which may cause dopant diffusion). Spectroscopic ellipsometry (SE) is a very sensitive probe for surface perturbations, including oxide layers, amorphization, absorbed atoms in the sub-monolayer range [8] and micro- roughness [9]. Comparison of argon and H, plasma treatments allows physical sputtering to be distinguished from chemical reaction. The H, cleaning results stimulated a study of hydrogen * European Commission post-doctoral research fellow. desorption from the surface. Comparative studies of desorption from Si(100) and Si(lll) surfaces, combined with the findings of previous UPS, EELS or IR reflection studies [13-181, have elucidated the desorption mechanisms. 2. Experimental The experimental apparatus consists of a plasma reaction chamber equipped for vacuum transfer to a load-lock and a high-vacuum analysis chamber. The residual gas pressure is about 10e9 and lo- lo Torr in the p lasma and analysis cham- bers, respectively. The plasma is excited by dis- tributed electronic cyclotron resonance (DECR) [lo] which produces highly dissociated plasmas at low pressure and enables independent control of the substrate bias relative to the plasma. Measure- ment of the complex reflectivity ratio of the sub- strate surface, p = tg( \k) exp(iA), over the photon energy range (1.55-4.6 eV) is achieved with an in-situ SE installed on the plasma chamber. The Si substrate temperature is measured with an optical pyrometer [12] which monitors the surface temper- 0169-4332/90/$03.50 0 1990 - Elsevier Science Publishers B.V. (North-Holland)