Rapid thermal processing of WSix contacts to InP in low-pressure N2:H2 and tertiarybutylphosphine ambients

Abstract

WSix thin films deposited on InP substrates have been investigated for possible use as refractory ohmic contact materials for self-aligned laser devices. The films have been rf diode sputtered using various Ar gas pressures from a single commercial target composed of W and Si with an atomic ratio of 1:1. Following the deposition, the WSix/InP samples were rapid thermal processed using a rapid thermal metalorganic chemical vapor deposition system in a controlled low-pressure ambient of N2:H2 (9:1) and tertiarybutylphosphine. The as-deposited films (∼100 nm thick) were amorphous but crystallized in the temperature range of 600–650 °C. The WSi2 phase forms first at 600 °C and then the W5Si3 nucleate with further heating at 650 °C. As a result of the crystallization, a reduction in the specific contact resistance to a value of 7.5×10−6 Ω cm2 and a decrease in the sheet resistance to values lower than 2 Ω/⧠ were observed. In addition, a significant reduction in the internal stress and an improvement in the WSix-to-InP adhesion were found, demonstrating the potential of WSix as a contact material for InP-based self-aligned devices.