Shawn Whaley

COMPARATIVE STUDY ON DRY OXIDATION OF HETEROEPITAXIAL SI1-XGEX AND SI1-X-YGEXCY ON SI(100)+

The goal of this study is to investigate the effect of carbon incorporation upon thermal oxidation of Si1−xGex alloys and its role on strain compensation in Si1−xGex alloys. Si1−xGex and Si1−x−yGexCy alloys on Si(100) are grown by combined ion and molecular beam deposition and are then oxidized at 1000 °C in a dry oxygen ambient for two h. The thickness and the composition of all samples before and after oxidation are measured by Rutherford backscattering spectrometry (RBS) combined with ion channeling at 2.0 MeV and carbon nuclear resonance analysis at 4.3 MeV using 4He++ ions. In agreement with previously reported results of dry oxidation on Si1−xGex thin films, 2.0 MeV RBS analysis shows that a layer of SiO2 is formed on the top surface of both Si1−xGex and Si1−x−yGexCy thin films, while Ge segregates towards the top surface and at the SiO2/Si1−xGex and SiO2/Si1−x−yGexCy interfaces. However, it is observed for the first time that dry oxidation rates of Si1−xGex thin films decrease with increasing Ge fr...

Hydrogen passivation of Si( 100) wafers as templates for low temperature ( T < 600°C) epitaxy '

Epitaxial growth requires an initial surface that is ordered and as free as possible of contaminants such as C, 0, or metallic impurities. Wet chemical etching of Si( 111) wafers by a solution of HF in alcohol after a modified RCA clean, has been shown to produce (1 X 1) H-terminated hydrophobic Si surfaces that are ordered at room temperature and can be desorbed at 200°C in UHV. Less is known about a similar treatment on Si(lO0) wafers, more commonly used in semiconductor technology. However, high temperature (T> 800°C) thermal desorption of the native oxide on Si(lO0) is known to induce detrimental effects such as surface roughness, precipitation and dopant segregation. Therefore, this study is motivated by the development of a low-temperature (T < 600°C) surface cleaning method for Sit 100). RBS combined with ion channeling and nuclear reaction analysis is conducted to measure the coverage of C, 0, and H as well as the residual disorder at the surface at different steps of wet chemical cleaning prior to low temperature desorption. Hydrogen is detected by the forward elastic recoil of H by 4He2+ at 2.8 MeV. 0 and C are detected by nuclear reaction analysis (NRA) at 3.05 and 4.265 MeV, respectively, in combination with ion channeling along the Si( 111) direction to increase the detection sensitivity for C and 0 as well as to measure the Si surface peak to correlate it to surface disorder. Atomic force microscopy of these surfaces has shown different degrees of roughness in addition to defect formation and is correlated to the ion beam analysis results. Our results indicate a strong dependence of final H-passivation on the pretreatment of the Si surfaces before the final dip in the HE/alcohol solution.

Heteroepitaxial properties of Si1−x−yGexCy on Si(100) grown by combined ion- and molecular-beam deposition

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1−x−yGexCy on Si(100), has been investigated. The epitaxial quality of Si1−x−yGexCy is found to be inferior to that of Si1−xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank–van der Merwe to Stranski–Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1−x−yGexCy material, as determined by Vegard’s law, and the equilibrium Si–C bond length, weakens the Si–C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier ...

Ion Beam Analysis Of Silicon-Based Surfaces And Correlation With Surface Energy Measurements

The water affinity of Si‐based surfaces is quantified by contact angle measurement and surface free energy to explain hydrophobic or hydrophilic behavior of silicone, silicates, and silicon surfaces. Surface defects such as dangling bonds, surface free energy including Lewis acid‐base and Lifshitz‐van der Waals components are discussed. Water nucleation and condensation is further explained by surface topography. Tapping mode atomic force microscopy (TMAFM) provides statistical analysis of the topography of these Si‐based surfaces. The correlation of the above two characteristics describes the behavior of water condensation at Si‐based surfaces. Surface root mean square roughness increasing from several A to several nm is found to provide nucleation sites that expedite water condensation visibly for silica and silicone. Hydrophilic surfaces have a condensation pattern that forms puddles of water while hydrophobic surfaces form water beads. Polymer adsorption on these surfaces alters the water affinity as ...