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Title: Formation of Low-Resistivity Germanosilicide Contacts to Phosporous Doped Silicon-Germanium Alloy Source/Drain Junctions for Nanoscale CMOS
Authors: Mo, Hongxiang
Advisors: Douglas Barlage, Committee Member
Gregory Parsons, Committee Member
Mehmet Ozturk, Committee Chair
Veena Misra, Committee Member
Keywords: SiGe
contact reistance
silicon germanium
source drain
Issue Date: 30-Dec-2003
Degree: PhD
Discipline: Electrical Engineering
Abstract: Conventional source/drain junction and contact formation processes can not meet the stringent requirements of future nanoscale complimentary metal oxide silicon (CMOS) technologies. The selective Si[subscript 1-x]Ge[subscript x] source/drain technology was proposed in this laboratory as an alternative to conventional junction and contact schemes. The technology is based on selective chemical vapor deposition of in-situ boron or phosphorus doped Si[subscript 1-x]Ge[subscript x] in source/drain areas. The fact that the dopant atoms occupy substitutional sites during growth make the high temperature activation anneals unnecessary virtually eliminating dopant diffusion to yield abrupt doping profiles. Furthermore, the smaller band gap of Si[subscript 1-xGe[subscript x] results in a smaller Schottky barrier height, which can translate into significant reductions in contact resistivity due to the exponential dependence of contact resistivity on barrier height. This study is focused on formation of self-aligned germanosilicide contacts to phosphorous-doped Si[subscript 1-x]Ge[subscript x] alloys. The experimental results obtained in this study indicate that self-aligned nickel germanosilicide (NiSi[subscript 1-x]Ge[subscript x]) contacts can be formed on Si[subscript 1-x]Ge[subscript x] layers at temperatures as low as 350°C. Contacts can yield a contact resistivity of 1E-8 ohm-cm² with no sign of germanosilicide induced leakage. However, above a threshold temperature determined by the Ge concentration in the alloy, the NiSi[subscript 1-x]Ge[subscript x]/Si[subscript 1-x]Ge[subscript x] interface begins to roughen, which affects the junction leakage. For phosphorus doped layers considered in this study, the threshold temperature was around 500°C, which is roughly 100°C higher than the threshold temperature for NiSi[subscript 1-x]Ge[subscript x contacts formed on boron doped Si[subscript 1-x] Ge[subscript x] layers with a Ge percentage of ~ 50%. Nickel and zirconium germanosilicides were also considered as contact candidates but they were found to result in a contact resistivity near 1E-7 ohm-cm².
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