Analysis of Diffusion at Buried Interfaces Following Area-Selective Atomic Layer Deposition For Dopant-Containing Small Molecule Inhibitors
Date
2025-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
With further scaling of transistors to the sub-5 nm regime, photolithography is
becoming less feasible in favor of bottom-up methods such as area-selective atomic
layer deposition (AS-ALD). This thesis reports on the investigation of 4-
fluorophenylboronic acid (FPBA) as a small molecule inhibitor (SMI) for selective
doping at buried interfaces. Titania thin films were deposited on silicon substrates
functionalized with FPBA and subsequently subjected to a variety of thermal
treatments including both vacuum tube furnaces and rapid thermal annealing (RTA).
Characterization methods, such as XPS, AFM, SEM, ellipsometry and ToF-SIMS
were employed to assess surface integrity, dopant preservation and depth profiles.
Diffusion was modeled using simple one-dimensional Fickian diffusion with an
Arrhenius-type temperature-dependent diffusion coefficient. Through the
experiments, it was found that boron preferentially diffused into the titania as opposed
to the silicon, with fitted Gaussian profiles showing a finite amount of broadening for
both annealing processes. However, for multiple experiments, intensive thermal load
resulted in significant enough surface damage to compromise the quantification of
some samples. Low heat RTA anneals preserved surface quality and led to controlled,
albeit slow diffusion, showing the sensitivity of the process. This work presents a
proof-of-concept for the incorporation of area-selective surface chemistry with
monolayer doping techniques and reveals the tradeoffs involved in process tuning.