Imec stacks Gate-all-Around Si nanowires vertically in CMOS MOSFETs

December 07, 2016 // By Julien Happich
At San Francisco's International Electron Devices Meeting 2016 (IEDM), imec researchers reported the CMOS integration of vertically stacked gate-all-around (GAA) silicon nanowire MOSFETs. Key to their integration scheme is a dual-work-function metal gate, enabling matched threshold voltages for the n- and p-type devices.

As well as building the GAA nanowire MOSFETs, the researchers also reported their findings on how the intrinsic ESD performance of the MOSFET is impacted by the novel nanowire architecture, proposing the integration of two different ESD protection diodes, a gate-structure defined diode (gated diode) and a shallow-trench isolation defined diode (STI diode).

“GAA nanowire transistors enable ultimate CMOS device scaling, with low degree of added complexity compared to alternative scaling scenarios,” stated Dan Mocuta, Director Logic Device and Integration at imec. The proposed integration scheme for Si GAA CMOS technology and the results on ESD protection are important achievements towards realizing these 7nm and beyond technology nodes. Future work will focus, among others, on further optimizing individual process steps, for example through the co-optimization of the junction and nanowire formation.”

(a) Top view SEM image after PWFM etch form the n-FETs, and (b) – (d) cross-sectional TEM images of p- and n-FETs at the end of process (LG = 30nm).

In a horizontal configuration, GAA nanowire transistors are seen as a natural extension of today’s mainstream FinFET technology. In this configuration, the drive current per footprint can be maximized by vertically stacking multiple horizontal nanowires.

Earlier this year, imec scientists demonstrated GAA FETs based on vertically stacked 8nm diameter Si nanowires. These devices showed excellent electrostatic control, but were fabricated for n- and p-FETs separately.

Namely, the two papers presented at IEDM 2016 were: "Vertically stacked gate-all-around Si nanowire CMOS transistors with dual work function metal gates", and "ESD diodes in a bulk Si gate-all-around vertically stacked horizontal nanowire technology".
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