Fabrication of Ge MOS with low interface trap density by ALD of Al₂O₃ on epitaxially grown Ge

Effects of initial surface conditions on interface characteristics of Al₂O₃/GeOx/Ge gate stacks are studied. As a clean surface condition prior to atomic layer deposition (ALD), a non-terminated Ge surface is realized by the insertion of an epitaxial Ge layer are grown on a Ge substrates in a MBE chamber which is directly connected to an ALD chamber. For these structures, the fixed charge density (Q _f) and interface trap density (D _it) are evaluated from the C-V characteristics and conductance method. Q _f reduction of about 17% and 90% are achieved by insertion of the epi-Ge layer and additional GeOx formation using plasma post-oxidation, respectively. A 90% reduction of D _it is also confirmed. These results indicate the importance of the initial Ge surface conditions before ALD and the Al₂O₃/GeOx/Ge gate stacks are very promising for high mobility Ge based CMOS applications. (paper)