Characteristics improvement of HfO2/Ge gate stack structure by fluorine treatment of germanium surface

Chemical reactivity of fluorine molecule (F2)–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 F2-treated Ge(1 0 0) substrate and HfO2 film deposited by photo-assisted MOCVD. Interface state density observed as a hump in the C–V curve of HfO2/Ge gate stack and its C–V hysteresis were decreased by F2-treatment of Ge surface. XPS (X-ray photoelectron spectroscopy) depth profiling reveals that interfacial layer between HfO2 and Ge is sub-oxide layer (GeOx or HfGeOx), which is believed to be origin of interface state density. F was incorporated into interfacial layer easily by using F2-treated Ge substrate. These results suggest that interface defect of HfO2/Ge gate stack structure could be passivated by F effectively.