Silicon Wafer-Scale
Micro-Fabrication Factory
Using Scanning Probe Micro-Robots
This is an abstract
for a poster to be presented at the
Fifth
Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is
available on the web.
Information processing and material technologies play a
crucial role in nanofabrication and molecular assembly
technologies. The tendencies of atoms to stick together in a
certain way to form solids, is directly dictated by their
electronic orbitals and interaction between electrons in these
orbitals. Calling this "tendency" the information
content of the atoms, nanotechnology can either go along with
this content or it can attempt to manipulate it. The manipulation
against the natural tendency of the atoms can only be done under
non-equilibrium conditions. The other issue is the manipulation
process itself and methods that can be used to achieve the
desired structure. A very appealing scheme is to design a
molecular blueprint by which the assembly can be affected. This
requires a building block composed of many atoms with an overall
different information content. Direct manipulation at the atomic
level requires local probes or nearly autonomous micro-robots
with built-in programming to build structures. All the materials
and structures that can be built this way can be called
"hierarchical structures and materials" because in
hierarchical structures the overall structure is optimized for a
given functionality while each sub-unit or sub-assembly may not
be individually optimal and there is a mechanical hierarchy with
identifiable layering.
Taking the route of direct manipulation, we propose a
microelectronics "factory" that is entirely contained
on a 400 cm2 area. Equipped with micro-reaction
chambers with dedicated environmental controls and scanning
probes for local deposition, the proposed
"Micro-Factory" is capable of fabricating a few million
devices simultaneously without any need for masks or lithography.
Using an electric field, the scanning microprobes deposit
materials from gas phase using a process that is very similar to
the chemical vapor deposition. Due to the confinement of electric
fields at the tip of the probes to a few tens of angstroms,
devices as small as 10 Å x 10 Å can be fabricated. Using
gas-phase metal-organic precursors, semiconductors such as Si,
GaAs, GaN, and SiC, metals such as Al, Cu, Mo, W, and Pt, and
oxides such as SiO2, and Al2O3,
and other insulators such as Si3N4 can be
deposited. These precursor gases are carried over the local tip
area where relatively large electric fields (106 V/cm:
field emission mode) are generated by applying a few volts to the
probe. In the tip region, the electric field decomposes the
precursor molecules and deposits the desired material over the
substrate. By choosing the tip to substrate polarity
appropriately, deposition over the tip is avoided. The rest of
the decomposed precursor molecule remains in the gas phase and is
carried away by the carrier neutral gas. A novel approach, that
involves laterally vibrating the local probe, is used to achieve
line-widths in the wide range of 10 Å to 10 µm. Local probes,
depositing in parallel, efficiently cover large areas needed in
integrated circuits. The speed of deposition by our proposed
local probes is only limited by the rate of the material delivery
by the carrier gas. In this novel approach, the deposition
chamber encloses a volume that is slightly larger than the local
tip-substrate volume. Thus, the whole fabrication facility is
fabricated on silicon using bulk and surface micromachining used
in micro-electro-mechanical systems (MEMS) technologies. All the
valves, flow meters, pressure gauges and analysis tools are also
fabricated using MEMS technologies and constitute an integral
part of the micro-fabrication facility.
The proposed "Micro-Fabrication" facility bridges
the gap between micro-technologies and nano-technologies. We will
discuss the above issues and the role of interfaces and present
preliminary calculations regarding the feasibility of our
proposed wafer scale "Micro-Fabrication" facility.
Figure 1 shows the bottom view of a wafer-scale
deposition facility. Scanning probes are enclosed in a
micro-chambers with their own supply lines as shown in Figure 2.
Micro-pumps and valves are all fabricated on silicon using MEMS
technology already demonstrated during the past 5-10 years.
Parallel local probes deposit patches of semiconductors, metals,
and insulators over the substrate. These probes, combined with
the linear motion of the substrate underneath them have four
degrees of freedom.
Figure 1: Different micro-chambers enclosing
groups of local probes can be used to deposit different materials
in parallel.
[2] Figure 2: Overall view of the fabrication
facility.
*Corresponding Address:
Massood Tabib-Azar, Associate Professor, Case Western Reserve
University, Cleveland, Ohio 44106, ph: 216-368-6431, fax:
216-368-6039, email: mxt7@po.cwru.edu
|