AVS 60th International Symposium and Exhibition
    Surface Science Wednesday Sessions
       Session SS+EM-WeA

Paper SS+EM-WeA11
Monolayer Doping via Arsenic Acid Grafting on Silicon Surfaces

Wednesday, October 30, 2013, 5:20 pm, Room 201 A

Session: Semiconductor Surfaces and Interfaces
Presenter: A. Vega, The University of Texas at Dallas
Authors: A. Vega, The University of Texas at Dallas
W. Cabrera, The University of Texas at Dallas
R. Longo, The University of Texas at Dallas
Y. Lu, The University of Texas at Dallas
P. Thissen, Karlsruhe Institute of Technology, Germany
Y.J. Chabal, The University of Texas at Dallas
Correspondent: Click to Email
Density scaling and subsequent device dimension reduction continue to drive significant advances in the materials, processing, and architecture of advanced transistors. As gate lengths approach the sub-10 nm regime, junction doping has become an increasing concern due to its importance in controlling short channel effects. Source/drain junction depths must be extremely shallow and abrupt, typically around 1/3 of gate length (Lg). Unfortunately, the conventional technique for junction doping, ion implantation and anneal, is incapable of producing uniform and abrupt junctions shallower than 10 nm in depth due to random dopant fluctuations and ion-induced damage leading to broadened dopant profiles. Monolayer doping (MLD) is a promising technique for creating ultra-shallow junctions (USJs). The self-limiting nature of self-assembled monolayers (SAMs) of MLD provides uniform coverage of a specific quantity of dopant containing molecules. Subsequent high temperature anneals drive the dopant atoms into the semiconductor via diffusion mechanism.

In this work we explore how methyl arsonic acid molecules can be grafted on H-terminated Si(111) surfaces. This approach has recently been demonstrated for alkylphosphonic acids by Longo et al.1, showing that the weak link of a molecule such as octadecylphosphonic acid (ODPA), is the P-C bond, with typical release of the carbon ligand around 500°C. First-principles calculations predict that the dissociation of the As-C bond occurs at lower temperature (barrier is 1 eV lower) and shallower junctions can be achieved due to the lower diffusion rate of arsenic compared to phosphorus. We have further used infrared absorption spectroscopy to determine the extent of chemisorption of the methyl arsonic acid molecules by quantifying the amount of H remaining and directly detecting the monolayer-Si bond (Si-O-As) at ~1080cm-1. The final stage of the process (dopant diffusion) is characterized in-situ with Low Energy Ion Scattering (LEIS) with angstrom resolution, and supported by first-principles calculations.

(1) Longo, R. C.; Cho, K.; Schmidt, W. G.; Chabal, Y. J.; Thissen, P. Advanced Functional Materials 2013.