This study details low pressure and low temperature cleaning of Si(100) surfaces. The properties of Si surfaces exposed to variations in plasma generated H are described. The diagnostic techniques used to study the processing conditions are residual gas analysis (RGA) and emission spectroscopy. The surface is characterized by low energy electron diffraction (LEED) and angle resolved uv-photoemission spectroscopy (ARUPS). During the cleaning, Si complexes are formed which indicates the removal of species from the Si(100) surface. Plasma cleaning at 300°C results in a Si(100) surface with 2×1 surface diffraction patterns as detected by LEED. Measurements by ARUPS with He I radiation show the absence of Si surface states on the Hpassivated surface. The ARUPS measurements also indicate that the H begins to desorb from the Si(100) H-passivated surface at ∼500°C.
Wet chemical and in situ hydrogen plasma cleaning processes were studied and a low temperature cleaning process was developed for Si (100), Ge (100) and SixGe1−x (100) surfaces. A uv-ozone and HF based spin etch were used to initially remove contaminants and oxides from the Si (100) and SixGe1−x (100) surfaces. The Ge (100) surfaces were treated with deionized water prior to entry to UHV. Residual gas analysis (RGA) was used in the investigation of the surface removal process of the in situ H-plasma cleaning. Low Energy Electron Diffraction (LEED) and angle resolved UV-Photoemission Spectroscopy (ARUPS) were used to examine the surface structure and electronic states. The 2×1 LEED patterns were obtained for Si (100), Ge (100) and SixGe1−x (100) after cleaning at a maximum processing temperature of 300°C. By varying process conditions, the LEED showed the 1×1 and 2×1 surface diffraction patterns. The ARUPS spectra showed the electronic states and the chemistry of the cleaned surfaces.
This paper addresses the in-situ/in-vacuo preparation of Si (100) substrates by hydrogen plasma cleaning prior to low temperature deposition of SiO2, or epitaxial growth of Si or Ge. The paper emphasizes the effectiveness of this type of substrate surface preparation following ex-situ wet-cleaning procedures that include: i) conventional RCA cleans; ii) modified RCA cleans, which incorporate exposure of the Si substrate to ozone, O3; and iii) ozone exposure, with all of these terminated by the removal of sacrificial oxides by dilute HF. We conclude: i) all ex-situ surface cleaning of Si (100) substrates leaves behind sub-monolayer oxygen and carbon surface contamination; ii) that virtually all of the carbon can be removed by exposure of the Si surface to atomic hydrogen at a temperature of <300°C; and iii) that a necessary condition for: (a) the formation of Si/SiO2 interfaces with low defect densities, Dit<l−3×1010cm−2-eV−1, and (b) the growth of epitaxial films of Si; is that the processed Si surface exhibit a 2×1 reconstruction, as detected by LEED or RHEED, following the exposure to atomic hydrogen.
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