Moore's law continues to drive the semiconductor industry to create smaller transistors and improve device performance. Smaller transistors require shallower junctions, especially for the non-planar geometries such as FinFETs and nanowires which are becoming more common. Conventional doping techniques such as ion implantation and spin-on diffusants have difficulty producing shallow junctions, especially for conformal doping of non-planar structures. Molecular monolayer doping (MLD) is presented as an alternative doping method with the capability to produce ultra-shallow junctions with low sheet resistances for planar and non-planar structures. MLD relies on the formation of a self-assembled monolayer of a dopant-containing compound which is annealed to diffuse dopants into the substrate, forming an ultra-shallow junction with a high surface concentration. This work fabricates and characterizes field effect devices using MLD to dope the source and drain regions.
To support this goal, a low-cost reaction chamber for MLD is developed using materials that are commonly found in chemistry stockrooms and local home goods stores. The results of the MLD process are quantified using four point probe measurements and SIMS profiles, with diffused layers measured to have sheet resistances on the order of 1000 Ω/□ and surface concentrations on the order of 1020 cm-3. MLD is demonstrated to be patternable using SiO2 as a masking layer, verified with four point probe measurements, electrical testing, and thin oxide growth over a wafer with heavily doped and lightly doped areas to reproduce the original doping pattern. A fabrication process and mask design compatible with the MLD process is created to fabricate NMOSFETs. The NMOSFETs are electrically tested and show field effect behavior with threshold voltages around -0.3 V and subthreshold swing of 150 mV/dec. The devices do show high series resistance, due to an unintended 13.1 Å interfacial layer of SiO2 in the contact cuts, discovered by STEM images. Future work proposes process revisions to mitigate this issue and scale down the size of the FETs to further explore MLD's potential for creating cutting edge field effect devices.
Library of Congress Subject Headings
Field-effect transistors; Semiconductor doping; Phosphorus; Silicon
Materials Science and Engineering (MS)
Department, Program, or Center
School of Chemistry and Materials Science (COS)
Doran, Jenna L., "Self-Assembled Monolayers for Phosphorus Doping of Silicon for Field Effect Devices" (2018). Thesis. Rochester Institute of Technology. Accessed from
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