Uniform 4-Stacked Ge<sub>0.9</sub>Sn<sub>0.1</sub> Nanosheets Using Double Ge<sub>0.95</sub>Sn<sub>0.05</sub> Caps by Highly Selective Isotropic Dry Etch
Chien-Te Tu, Yu-Shiang Huang, Chun-Yi Cheng, Chung-En Tsai, Jyun-Yan Chen, Hung-Yu Ye, Fang-Liang Lu, C. W. Liu
Abstract
The undoped 4-stacked Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> nanosheets sandwiched by double Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.95</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> caps without parasitic Ge channels underneath are realized by a radical-based highly selective isotropic dry etching. Highly inter-channel uniformity of the stacked GeSn nanosheets is realized by thin Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> (5 nm) channels and thick Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.95</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> caps to achieve high I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . The caps are the barriers to separate the holes from the dielectrics/cap interface to reduce the surface roughness scattering. The double caps with small strain also stabilize the channels to prevent the channel buckling. The undoped GeSn nanosheets with [B] below the detection limit ( <; 1 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) and heavily doped ( ~ 2 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) Ge at S/D can suppress the impurity scattering to increase the channel mobility and can reduce the S/D resistance, respectively. The high I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> = 73 μA per stack (86 μA/μm, normalized by the total perimeter of nanosheets) at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OV</sub> = V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = - 0.5 V is achieved for the device with the sheet width of 80 nm and the Lg of 80 nm. The quantum mechanical simulation shows that there is heavy hole population at the two ends of nanosheets.