Eugen Beck

Silicon Molecular Beam Epitaxy on Hydrogen-Plasma-Cleaned Substrates.

A process sequence for low-temperature in situ processing of silicon in an ultra-high vacuum (UHV) multichamber system is presented. For substrate cleaning, a hydrogen/argon discharge plasma was produced with an UHV-compatible plasma source. This low-energy plasma was used to remove, in a single step, native oxide and organic contaminations from the wafer surface at low substrate temperatures (\lesssim400° C). During the cleaning process the excitation energy of the gas atoms was determined by optical methods. The cleaning process was applied to patterned silicon substrates with micro-shadow masks. Local epitaxial growth by molecular beam epitaxy (MBE) on these substrates was used to fabricate triangular barrier diodes (TBD) to demonstrate the device quality for this cleaning procedure. The crystal quality of the grown layers and the interface was investigated by transmission electron microscopy (TEM). The electrical results for these diodes are in agreement with the grown layer sequence and the chosen dopings.

Single Step Low Temperature In-Situ Substrate Cleaning for Silicon Processing

Silicon wafers as obtained from the manufacturer are immersed in a large area argon/hydrogen plasma for surface cleaning. The plasma discharge is maintained between a heated cathode and the grounded process chamber at discharge voltages of about 30 V for which discharge currents up to 100 A can be chosen. In this regime, neither the chamber walls nor the substrates are sputtered. Chemical reactions at the wafer surface are assumed to be mainly stimulated by low energy electron bombardment. The etch rates for diamond-like carbon (DLC) on silicon wafers were determined for selected discharge parameters and compared with the previously obtained results for SiO 2 . It was found that 5 minutes in-situ cleaning prepares the silicon wafers for homoepitaxy at 500 °C and higher substrate temperatures, whereas a short anneal at 500 °C was necessary to obtain low temperature homoepitaxy at 300 °C on (100) and 400 °C on (111) silicon. This seems to be due to hydrogen passivation of silicon during the cleaning procedure.