Highly Stacked GeSn Nanosheets by CVD Epitaxy and Highly Selective Isotropic Dry Etching

The eight stacked Ge
_0.9
Sn
_0.1
ultrathin bodies down to 3 nm with high
${I}_{\text {ON}}/I_{\text {OFF}}$
and eight stacked Ge
_0.9
Sn
_0.1
thick nanosheets with high
${I}_{\text {ON}}$
per stack are demonstrated. For the eight stacked Ge
_0.9
Sn
_0.1
ultrathin bodies, the 50 epilayers, including Ge
_0.9
Sn
_0.1
channels, double Ge
_0.97
Sn
_0.03
/Ge (8 nm/3 nm) caps, heavily B-doped (~2E21 cm
⁻³
) Ge sacrificial layers (SLs), and undoped Ge buffer were epitaxially grown to reach high inter-channel uniformity with the co-optimization of epitaxy and radical-based highly selective isotropic dry etching (HiSIDE). The thin double Ge
_0.97
Sn
_0.03
caps can provide sufficient etching selectivity and stabilize the channel to prevent the channels from bending and buckling. The neutral radicals can isotropically etch the Ge
_0.97
Sn
_0.03
/Ge caps, Ge:B SLs, and Ge buffer to form the highly uniform eight stacked Ge
_0.9
Sn
_0.1
ultrathin bodies. The record
${I}_{\text {ON}}/{I}_{\text {OFF}}$
of 1.4
$\times 10^{{7}}$
at
${V}_{\text {DS}} \,\,=\,\,-0.05$
V is achieved among GeSn 3-D pFETs due to the quantum confinement. For the eight stacked Ge
_0.9
Sn
_0.1
thick nanosheets, the record
${I}_{\text {ON}}$
of 92
$\mu \text{A}$
per stack at
${V}_{\text {OV}} = {V}_{\text {DS}} = -0.5$
V is achieved among GeSn 3-D pFETs. Thick nanosheets can provide higher mobility than ultrathin bodies due to the reduced surface roughness scattering.