LONDON -- Reverse engineering and analysis consultancy ChipworksInc has posted microscopecross-sections of parts of the 22-nm Ivy Bridge processor from Intel that hasrevealed that the FinFETs, which Intel calls tri-gate transistors, are in facttrapezoidal, almost triangular, in cross-section.
The ICs were 64-bit, four-core Xeon E3-1230 CPUs intendedfor the server market, which Chipworks (Ottawa, Ontario) said it obtained inHong Kong, China.
The triangular section is markedly different to theidealized 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-criticalmanufacturing artifact or are deliberately engineered by Intel and have acritical impact on electron mobility or yield.
Gold Standard Simulations Ltd (or GSS base in Glasgow,Scotland), a spin-off from the University of Glasgow led by Professor AseAsenov as CEO, responded by saying on its Web site: "There is a lot ofspeculation about the possible advantages and disadvantages of the trapezoidal,or almost triangular, shaped 'bulk' FinFET." GSS has performed asimulation analysis of the FinFET using its statistical 3-D TCAD simulatorcalled Garand.
Comparison of the TEM image of one of the FinFETs fromFigure 6 of the Chipworks blog (linked above) with the Garand simulation domainof Gold Standard Simulations. GSS' simulation was used to explore the dependence ofthreshold voltage on gate length for the trapezoidal Intel transistor and anequivalent rectangular-fin transistor. "Clearly the rectangular fin hasbetter short channel effects. Still, the million-dollar question is if thealmost-triangular shape is on-purpose design, or is this, what bulk FinFETtechnology can achieve in terms of the fin etching?"
The comparisons between dimensionally comparable rectangularand trapezoidal FinFETs are not markedly different but as GSS had no knowledgeof doping profiles it assumed a lightly doped channel. At the same time GSSacknowledged that there is a high doping concentration stopper below the fin inthe shallow trench isolation (STI) region. "Clearly FinFETs are morecomplicated devices in terms of understanding and visualization compared to theold bulk MOSFETs," GSS concluded.
This story was originally posted by EETimes.
