With a continuous pursuit of making semiconductor devices and integrated
circuits (ICs) faster, better, and more energy efficient, the shrinking of device
dimensions became imminent. Today we are approaching the ångström era,
where the manufacturability of such devices is becoming challenging. As a
result, atomic level processing (ALP) is now most desired. Atomic layer
deposition (ALD) and atomic level etching are two such ALP methods that
take full advantage of surface chemistry and allow growth and removal of
atomistically thin layers of material on a substrate, respectively. Atomic level
etching broadly describes the etching that maintains the ångström-level (i.e.
below 1 nm) etched-thickness control and uses sequential gas-surface
reactions that may be self-limiting. Atomic level etching can be either plasma
based (plasma atomic layer etching - PALE), or thermal based (thermal
atomic layer etching - ALEt, gas-phase pulsed etching - GPPE). PALE has
existed at least for three decades. Although thermal atomic level etching is
relatively new, it has evolved rapidly over the last seven years.
In this thesis work, new thermal atomic level etching processes based on
NbF5 , HF, CCl4 , SOCl2 , O2 , and O3/O2 reactants were developed. The materials that were removed selectively over SiO2 and Si3N4 are Al2O3, TiN, and HfO2 . Two types of etching processes were investigated, the first one uses
sequential exposures of two or more reactants (ALEt), and the second uses
pulsing of a single reactant (GPPE) to etch the target. The processes
explored here show that the novel etch chemistries are capable of removing
the material in the ångström regime isotropically from 3D structures.
Thermochemical analyses of possible reactions based on the atomic-scale
surface-gas models were carried out using first-principles calculations in
density functional theory (DFT) as well as molecular dynamics (MD)
simulations. In addition, potential etch reactions were also evaluated using
conventional thermodynamic calculations. Finally, the post-etched surfaces
were characterized using various surface sensitive techniques such as
spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS),
X-ray reflectivity/diffraction (XRR/XRD), transmission electron microscopy
(TEM), atomic force microscopy (AFM), and weighing balance.With a continuous pursuit of making semiconductor devices and integrated
circuits (ICs) faster, better, and more energy efficient, the shrinking of device
dimensions became imminent. Today we are approaching the ångström era,
where the manufacturability of such devices is becoming challenging. As a
result, atomic level processing (ALP) is now most desired. Atomic layer
deposition (ALD) and atomic level etching are two such ALP methods that
take full advantage of surface chemistry and allow growth and removal of
atomistically thin layers of material on a substrate, respectively. Atomic level
etching broadly describes the etching that maintains the ångström-level (i.e.
below 1 nm) etched-thickness control and uses sequential gas-surface
reactions that may be self-limiting. Atomic level etching can be either plasma
based (plasma atomic layer etching - PALE), or thermal based (thermal
atomic layer etching - ALEt, gas-phase pulsed etching - GPPE). PALE has
existed at least for three decades. Although thermal atomic level etching is
relatively new, it has evolved rapidly over the last seven years.
In this thesis work, new thermal atomic level etching processes based on
NbF5 , HF, CCl4 , SOCl2 , O2 , and O3/O2 reactants were developed. The materials that were removed selectively over SiO2 and Si3N4 are Al2O3, TiN, and HfO2 . Two types of etching processes were investigated, the first one uses
sequential exposures of two or more reactants (ALEt), and the second uses
pulsing of a single reactant (GPPE) to etch the target. The processes
explored here show that the novel etch chemistries are capable of removing
the material in the ångström regime isotropically from 3D structures.
Thermochemical analyses of possible reactions based on the atomic-scale
surface-gas models were carried out using first-principles calculations in
density functional theory (DFT) as well as molecular dynamics (MD)
simulations. In addition, potential etch reactions were also evaluated using
conventional thermodynamic calculations. Finally, the post-etched surfaces
were characterized using various surface sensitive techniques such as
spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS),
X-ray reflectivity/diffraction (XRR/XRD), transmission electron microscopy
(TEM), atomic force microscopy (AFM), and weighing balance
