B and Ga Co-Doped Si_1−xGe_x for p-Type Source/Drain Contacts

Abstract

Contact resistivity reduction at the source/drain contacts is one of the main requirements for the fabrication of future MOS devices. Current research focuses on methods to increase the active doping concentration near the contact region in silicon-germanium S/D epilayers. A possible approach consists in adding co-dopants during the epitaxy process. In the case of p-MOS, gallium can be used in addition to boron. In this work, the properties of in situ Ga and B co-doped Si0.55Ge0.45 layers are discussed. The surface morphologies, layer compositions, and structural and electrical material properties are described and compared with those of a B-doped Si0.55Ge0.45 reference layer. Ga segregation occurring at the growth surface is evidenced. Post-epi surface cleans are required to obtain the correct Ga profiles in the Si1-xGex layers from secondary ion mass spectrometry, otherwise altered by surface Ga knock-on. The layer morphologies, crystalline quality, and electrical properties show a progressive degradation with increasing Ga dose. Finally, specific titanium-Si1-xGex:B(:Ga) contact resistivity values have been extracted using the multi-ring circular transmission line method. The contact resistivity is lower for the Ga co-doped samples, with the lowest value (< 3 x 10-9 Ω.cm2) being obtained for the sample grown with the lowest Ga-precursor flow.

Low Temperature Epitaxy of In Situ GaDoped Si1-XGex: Dopant Incorporation, Structural and Electrical Properties

“…Gallium is a promising candidate, as it has already been used to fabricate highly doped semiconductor materials showing good contact properties with metals, both as a single dopant (6)(7)(8) and as a co-dopant (9). However, in Si1-xGex deposition, in situ doping normally results in a severe Ga segregation at the epilayer surface (10). Controlling this segregation is necessary to be able to study the physical properties of Ga doping in epitaxial Si1-xGex in view of its usage as a co-dopant.…”