Dopant profiling in vertical ultrathin channels of double-gate metal-oxide-semiconductor field-effect transistors by using scanning nonlinear dielectric microscopy

Nanometer-scale dopant profiling in the vertical ultrathin channels (UTCs) of double-gate metal-oxide-semiconductor field-effect transistors has been performed by using scanning nonlinear dielectric microscopy. UTCs 18-58 nm thick and 175 nm high were formed on a bulk silicon substrate by orientation- dependent wet etching. An n⁺/p junction was fabricated on the top of the UTC by angled ion implantation. By beveling the UTC with an ultragentle angle, the vertical size of the UTC was amplified by a factor of 86. Using the beveled samples, the channel thickness dependence of the dopant depth profile in the UTC was quantitatively investigated. It was found that a significant dopant loss occurs when the channel thickness is reduced to 18 nm.