Material Properties, Thermal Stabilities and Electrical Characteristics of Ge MOS Devices, Depending on Oxidation States
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1155-C02-04
Material Properties, Thermal Stabilities and Electrical Characteristics of Ge MOS Devices, Depending on Oxidation States of Ge Oxide: Monoxide [GeO(II)] and Dioxide [GeO2(IV)] Yoshiki Kamata1, Akira Takashima2, and Tezuka Tsutomu1 1 MIRAI-Toshiba, 1, Komukai-Toshiba-cho, Saiwaiku, Kawasaki, 212-8582, Japan 2 Toshiba Corporation, 1, Komukai-Toshiba-cho, Saiwaiku, Kawasaki, 212-8582, Japan ABSTRACT Ge monoxide [GeO(II)] and dioxide [GeO2(IV)], which are selectively formed on Ge substrate by controlling pH and redox potential in pretreatment solution, have been confirmed by XPS. ΔEC in GeO(II)/Ge and GeO2(IV)/Ge are almost the same, whereas ΔEV in GeO(II)/Ge is smaller than that in GeO2(IV)/Ge, resulting in smaller Eg of GeO(II). GeO(g) desorption is suppressed in LaAlO3/Ge gate stack, whereas GeO(g) desorbs through LaAlO3 layer when there is an intentional interfacial GeO(II) layer, leading to a large increase in Jg. GeO(g) desorption temperature in Ge oxide/Ge gate stacks decreases with the increase in the ratio of GeO(II) in Ge oxide and is independent of the oxidation techniques. Since GeO(g) desorption is accompanied by H2O(g) desorption, a new model to explain the GeO(g) desorption phenomena is proposed, in which Ge(OH)2 decomposes into GeO(g) and H2O(g). Highly effective etching methods of Ge oxide, using HCl solution and HCl vapor at higher temperature than boiling point of Ge (hydro)chloride have been demonstrated. INTRODUCTION High-k/Ge MISFETs are very promising for future nanoscale LSIs[1, 2]. The most important technical issue concerning high-k/Ge gate stacks is the passivation of the Ge surface, or the control of the interfacial Ge oxide. Although Ge oxide consists of GeO(II) and GeO2(IV) [1, 2], little has been reported about influences of GeO(II), distinguishing them from those of GeO2(IV), on thermal stability and electrical characteristics of Ge MOS devices. In this study, we investigate material properties, thermal stabilities and electrical characteristics of Ge MOS devices, depending on the type of Ge oxide: GeO(II) and GeO2(IV). In particular, we report on (i) a selective formation of GeO(II) or GeO2(IV) that is confirmed by XPS, (ii) band alignments of GeO(II)/Ge and GeO2(IV)/Ge, (iii) relationship between Jg and GeO(g) desorption in LaAlO3/Ge gate stacks with or without intentional interfacial Ge oxide, (iv) universality of GeO(g) desorption depending on GeO(II) ratio in Ge oxide and independent of oxidation technique, (v) a new GeO(g) desorption model explaining GeO(g) desorption accompanied by H2O(g) desorption, and (vi) highly effective etching methods of Ge oxide using HCl solution and HCl vapor at higher temperature than boiling point of Ge (hydro-)chloride. EXPERIMENTAL LaAlO3 film of 10nm was deposited at 200oC by using MBE apparatus on Ge substrates (Sb, ~0.3Ωcm) with or without intentional interfacial Ge oxide layer. X-ray photoelectron spectroscopy (XPS) analyses were performed with monochromatic-Al Kα source. Thermal desorption spectroscopy (TDS) was performed for LaAlO3/
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