March 9, 2006 – Sematech has begun work on a project to investigate alternative materials to silicon in MOSFET channels, in an effort to develop process technologies that achieve enhanced mobility without compromising reliability.
The effort, originally announced at a workshop in December 2005, aims to combine data and methods from other projects using high-mobility, high-k materials, and dual-metal gate stacks to explore the compatibility of silicon germanium (SiGe) and germanium as channel materials. Initial work will focus on evaluating the most promising variations of SiGe for low defect density and performance enhancement, developing and characterizing the performance of SiGe and Ge source and drain junctions, and finding a suitable interface between a Ge-based channel and a high-k dielectric material in an advanced gate stack.
“As a channel material for current geometries, silicon is still the best — in many ways, it’s been nature’s gift to electrical engineers,” stated Hsing-Huang Tseng, manager of the new CMOS extension program in Sematech’s frontend processes division (FEP), in a statement. “But continued CMOS scaling means we need to find new materials to replace silicon in these functions. Germanium and silicon-germanium, and potentially III-V compounds in the longer term, could provide even bigger benefits for mobility enhancement.”
The project was conceived at a workshop in December 2005, which identified four or five material combinations, which were referred to participating universities for more examination, Tseng said. Sematech currently is targeting SiGe and Ge for development use in volume manufacturing. The alternate-materials projects will be cross-linked with strategic efforts on suitable gate stack and source-drain junction development, as well as corollary programs with tool suppliers.
Ge shares several elemental properties with silicon, and was once seen on par with Si as a basic semiconductor material, but integration issues hampered Ge adoption. Renewed interest in Ge has meant going back to the history books (including publications from 1954) to learn more about its capabilities, noted Larry Larson, FEP associate director at FEP.
“Our goal is not to replace silicon entirely, but to apply higher-mobility channel materials selectively on tried and trusted silicon-based technology for continued CMOS scaling,” said Raj Jammy, Sematech’s FEP director, noting that this will require not only new processing techniques to put down alternate channel materials on silicon with low defect densities, but also new ways to form compatible source-drain junctions and gate stacks. “The need for solutions with alternate channel materials and other high performance materials options has become critically important as we finally encounter the limits of silicon,” he explained.