Record Low Contact Resistivity to Ge:B $(8.1\mathrm{x}10^{-10}\Omega-\mathrm{cm}^{2})$ and GeSn:B $(4.1\mathrm{x}10^{-10}\Omega-\mathrm{cm}^{2})$ with Optimized [B] and [Sn] by In-situ CVD Doping

Abstract

The record low contact resistivity $(\rho_{\mathrm{c}})$ of Ti contact to Ge:B $(8.1\mathrm{x}10^{-10}\Omega-\mathrm{cm}^{2})$ is achieved by in-situ doped CVD using the high-order Ge precursor $(\mathrm{Ge}_{2}\mathrm{H}_{6})$. The best achievable $[\mathrm{B}]_{\mathrm{act}}$. of $7\mathrm{x}10^{20}\mathrm{cm}^{-3}$ and extended epitaxial process window are obtained using $\mathrm{Ge}_{2}\mathrm{H}_{6}$. By optimizing the [B] and [Sn], 2% Sn addition into Ge epitaxy reaches the lowest $\mathrm{p}_{\mathrm{c}}$ of $4.1\mathrm{x}10^{-10} \Omega-\mathrm{cm}^{2}$. Further Sn addition (4.7% and 13.2%) increases $\rho_{\mathrm{c}}$ due to reduced [B], and degrades the thermal stability. The record low resistivity $(2\mathrm{x}10^{-4}\Omega-\mathrm{cm})$ among epitaxial p-type Ge and GeSn is also demonstrated. Optimized metal etching processes ($\mathrm{Cl}_{2}+\mathrm{BCl}_{3}$ for metal on $\mathrm{GeSn}:\mathrm{B}$, while $\mathrm{C}1_{2}$ for metal on Ge:B) are necessary to minimize etching of GeSn:B and Ge:B, and to fabricate the test structure. A two-sheet-resistance model is used to correctly extract the $\rho_{\mathrm{c}}$. B segregation $(> 1\mathrm{x}10^{21}\mathrm{cm}^{-3})$ at the metal/semiconductor interface enables the record low $\rho_{\mathrm{c}}$.