2 research outputs found
Self-Anchored Catalyst Interface Enables Ordered Via Array Formation from Submicrometer to Millimeter Scale for Polycrystalline and Single-Crystalline Silicon
Defying
text definitions of wet etching, metal-assisted chemical etching (MacEtch),
a solution-based, damage-free semiconductor etching method, is directional,
where the metal catalyst film sinks with the semiconductor etching
front, producing 3D semiconductor structures that are complementary
to the metal catalyst film pattern. The same recipe that works perfectly
to produce ordered array of nanostructures for single-crystalline
Si (c-Si) fails completely when applied to polycrystalline Si (poly-Si)
with the same doping type and level. Another long-standing challenge
for MacEtch is the difficulty of uniformly etching across feature
sizes larger than a few micrometers because of the nature of lateral
etching. The issue of interface control between the catalyst and the
semiconductor in both lateral and vertical directions over time and
over distance needs to be systematically addressed. Here, we present
a self-anchored catalyst (SAC) MacEtch method, where a nanoporous catalyst film is used to produce nanowires through the pinholes, which in turn
physically anchor the catalyst film from detouring as it descends.
The systematic vertical etch rate study as a function of porous catalyst
diameter from 200 to 900 nm shows that the SAC-MacEtch not only confines
the etching direction but also enhances the etch rate due to the increased
liquid access path, significantly delaying the onset of the mass-transport-limited
critical diameter compared to nonporous catalyst c-Si counterpart.
With this enhanced mass transport approach, vias on multistacks of
poly-Si/SiO<sub>2</sub> are also formed with excellent vertical registry
through the polystack, even though they are separated by SiO<sub>2</sub> which is readily removed by HF alone with no anisotropy. In addition,
320 μm square through-Si-via (TSV) arrays in 550 μm
thick c-Si are realized. The ability of SAC-MacEtch to etch through
poly/oxide/poly stack as well as more than half millimeter thick silicon
with excellent site specificity for a wide range of feature sizes
has significant implications for 2.5D/3D photonic and electronic device
applications
Enhanced Performance of Ge Photodiodes <i>via</i> Monolithic Antireflection Texturing and α‑Ge Self-Passivation by Inverse Metal-Assisted Chemical Etching
Surface
antireflection micro and nanostructures, normally formed
by conventional reactive ion etching, offer advantages in photovoltaic
and optoelectronic applications, including wider spectral wavelength
ranges and acceptance angles. One challenge in incorporating these
structures into devices is that optimal optical properties do not
always translate into electrical performance due to surface damage,
which significantly increases surface recombination. Here, we present
a simple approach for fabricating antireflection structures, with
self-passivated amorphous Ge (α-Ge) surfaces, on single crystalline
Ge (c-Ge) surface using the inverse metal-assisted chemical etching
technology (I-MacEtch). Vertical Schottky Ge photodiodes fabricated
with surface structures involving arrays of pyramids or periodic nano-indentations
show clear improvements not only in responsivity, due to enhanced
optical absorption, but also in dark current. The dark current reduction
is attributed to the Schottky barrier height increase and self-passivation
effect of the i-MacEtch induced α-Ge layer formed on top of
the c-Ge surface. The results demonstrated in this work show that
MacEtch can be a viable technology for advanced light trapping and
surface engineering in Ge and other semiconductor based optoelectronic
devices