III-V Gate-wrap-around field-effect-transistors with high-k gate dielectrics (2014)

As MOSFETs continue scaling down for low power logic applications, non-planar multi-gated field-effect-transistors have been brought out to overcome the electrostatics control issue. To achieve the ultimate gate electrode control, great efforts have been devoted to investigate nanowire and GWAFETs or gate-all-around (GAA) FETs devices. Nanowires can be constructed using bottom-up synthesis method where various materials can be used but huge manufacture challenges, or by top-down machining approach. The gate-wrapped-around structure was applied to higher-electron-mobility III-V material in order to achieve a combination of improved subthreshold characteristics and higher current drive capability. Much works on III-V multi-gated FETs and GWAFETs have shown promising results including better SCE control and increased integration density. However, several challenges remain, such as current degradation from quantum effect, leakage current, high-k/III-V interface quality, external contact resistance, and fabrication difficulties. In this work, we fabricated the lateral In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As GWAFETs using the top-down method, that is, the devices were patterned by e-beam lithography and nanowires were constructed by dry and wet etching process. We will present (a) novel device and layout design such that the resulting fin structure is more robust, (b) an optimized fin-etching process in order to achieve smooth sidewalls of the InGaAs channels, (c) high-quality high-k dielectrics and metal gate stack to enhance the interface and bulk oxide quality and (d) device modeling and simulation results to explain device characteristics. The layer structure of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As GWAFET device, grown by MBE on the semi-insulating InP substrate, consists of 500 nm InP buffer layer, 50 nm In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As channel layer, 1 nm InP barrier layer and 20 nm In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As cap layer. All these layers were designed to be undoped, except for the top In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As layer which is a heavily N-doped (Si 3e19cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) layer intended for source/drain (S/D) contact. Fig. 1 illustrates the device layer structure of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As GWAFET with the channel wrapped around by ALD Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiN gate. InP was chosen as the buffer layer to enable selective wet etch between In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As and InP for releasing the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As fin structure. The key fabrication steps and improved layout design are illustrated in Fig. 2 and 3, respectively. The transfer characteristics of a typical In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As GWAFET with W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fin</sub> =40 nm, L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> =140 nm, and 7 parallel channels demonstrate excellent behavior (Fig. 4). Drive currents are normalized to the perimeter of InGaAs channels W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tot</sub> = (2W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fin</sub> +2H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fin</sub> )×(No. of channels). The gate leakage is lower than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> μA/μm in the voltage range. The on/off current ratio of this device is around 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> =1 V. The off current is at 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> μA/μm level at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> =-0.2 V and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> =0.5 V. The off current is limited by the bulk leakage current. Detailed device characteristics will be shown in the presentation. Fig. 4 illustrates the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> characteristics of InGaAs planar MOSFETs and non-planar InGaAs GWAFETs. 10X drop on DIBL was observed from planar InGaAs MOSFETs at around 200mV/V to 20mV/V for GWAFETs. By apply gate wrapped around structure SS also reduced 33%. Fig. 5 shows the DIBL vs. gate length for 10 nm, 5 nm-thick InGaAs channel MOSFETs and InGaAs GWAFETs with W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fin</sub> 200 nm, 100 nm, 60 nm and 40 nm. Better scalability was achieved by non-planar GWAFETs compare to planar structure with lower DIBL, SS and higher drive current.