Characteristics improvement of HfO 2/Ge gate stack structure by fluorine treatment of germanium surface

Abstract

Chemical reactivity of fluorine molecule (F 2)–germanium (Ge) surface and dissociation of fluorine (F)–Ge bonding have been simulated by semi-empirical molecular orbital method theoretically, which shows that F on Ge surface is more stable compared to hydrogen. Ge MIS (metal insulator semiconductor) capacitor has been fabricated by using F 2-treated Ge(1 0 0) substrate and HfO 2 film deposited by photo-assisted MOCVD. Interface state density observed as a hump in the C– V curve of HfO 2/Ge gate stack and its C– V hysteresis were decreased by F 2-treatment of Ge surface. XPS (X-ray photoelectron spectroscopy) depth profiling reveals that interfacial layer between HfO 2 and Ge is sub-oxide layer (GeO x or HfGeO x ), which is believed to be origin of interface state density. F was incorporated into interfacial layer easily by using F 2-treated Ge substrate. These results suggest that interface defect of HfO 2/Ge gate stack structure could be passivated by F effectively.