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Analysis reveal Intel finFETs' triangular structure

Posted: 23 May 2012 ?? ?Print Version ?Bookmark and Share

Keywords:finFET? Ivy Bridge? tri-gate transistors?

An analysis made by reverse engineering and analysis consultancy firm Chipworks Inc. has revealed microscope sections of some parts of Intel Corp.'s 22nm Ivy processor showing that the FinFETS are in fact trapezoidal, or almost triangular in cross-section. Intel calls these FinFETs tri-gate transistors.

The ICs were 64-bit, four-core Xeon E3-1230 CPUs intended for the server market, which Chipworks said it obtained in Hong Kong, China.

The triangular section is markedly different to the idealized rectangular section that Intel had shown previously in 2011. However, it is not clear whether the non-vertical sides to the fins are a non-critical manufacturing artifact or are deliberately engineered by Intel and have a critical impact on electron mobility or yield.

Gold Standard Simulations Ltd, led by Prof. Ase Asenov as CEO, has said that "There is a lot of speculation about the possible advantages and disadvantages of the trapezoidal, or almost triangular, shaped 'bulk' FinFET." GSS has performed a simulation analysis of the FinFET using its statistical 3D TCAD simulator called Garand.

FinFET comparison

Comparison of the TEM image of one of the FinFETs from the Chipworks blog with the Garand simulation domain of Gold Standard Simulations.

GSS's simulation was used to explore the dependence of threshold voltage on gate length for the trapezoidal Intel transistor and an equivalent rectangular-fin transistor. "Clearly the rectangular fin has better short channel effects. Still, the million-dollar question is if the almost-triangular shape is on-purpose design, or is this what bulk FinFET technology can achieve in terms of the fin etching?"

The comparisons between dimensionally comparable rectangular and trapezoidal FinFETs are not markedly different but as GSS had no knowledge of doping profiles it assumed a lightly doped channel. At the same time GSS acknowledged that there is a high doping concentration stopper below the fin in the shallow trench isolation (STI) region. "Clearly FinFETs are more complicated devices in terms of understanding and visualization compared to the old bulk MOSFETs," GSS concluded.

- Peter Clarke
??EE Times

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