OXIDATION OF SILICON-GERMANIUM ALLOY FILMS
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-11
Silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) have recently demonstrated their high- speed capability over conventional bipolar-devices. Besides the low-temperature processing constraints required for maintaining the strained properties of SiGe films, oxidation remains the major difference between SiGe and Si processing. Conventional wet (or dry) ther- mal oxidation and rapid thermal oxidation of the SiGe films have resulted in oxide layers with Ge piling up at the oxide-silicon interface. This piling up of Ge at the interface can produce leakage paths, resulting in poor isolation between electrodes or devices. University research has shown high pressure oxidation at 680 atm. (and 550°C in dry 02) to be effective in reducing Ge pile up at oxide-silicon interfaces when oxidizing single crys- tal SiGe iilms. Unfortunately, a high pressure oxidation system operating at 680 at*. is not commercially available.