Laser Chemical Vapor Deposition Rapid Prototyping System

1
Laser Chemical Vapor Deposition Rapid Prototyping
System
Supported by Dr. Julie Chen Dr. Delcie Durham
W. Jack Lackey, David W. Rosen, Ryan W. Johnson,
Scott N. Bondi, Jian Mi, Josh Gillespie, Jae
Park, and Elizabeth Richter George W. Woodruff
School of Mechanical Engineering Georgia
Institute of Technology Atlanta, Georgia
30332-0405
Overview
Features and Process Control
Operation of Georgia Techs LCVD system
began in 1999. The system has a cylindrical
build envelope 3 cm high by 3 cm in diameter in
which arbitrarily shaped devices may be
fabricated from metals, ceramics, or composite
materials. The system uses a 200 µm CO2 laser
spot to generate bulk features with dimensions on
the order of 50 µm, while an Ar ion laser is
focused to 10 µm to generate finer details. The
chamber design incorporates many unique features,
including Gas-Jet Reagent Supply System
Rotating-Translating Stage Assembly
Dual Laser System Bimodal Substrate
Heating Heated Reagent Supply Line
On-Line Dimensional Control Laser
Triangulation Device On-Line Temperature
Control Thermal Imaging Device
The LCVD Rapid Prototyping system utilizes
the thermal energy of a laser beam to initiate
localized chemical vapor deposition of metals and
ceramics. By controlling the path of the laser
beam, complex two and three dimensional
components can be fabricated. The goal of the
current research is to identify
process-structure-property relationships and
conduct process planning in order to permit
efficient operation of the LCVD Rapid Prototyping
system and to demonstrate the usefulness of this
system by fabricating advanced electronic devices
and structural materials.
Conventional CVD generates a uniform deposit
over a uniformly heated substrate. By contrast,
Laser CVD uses the localized thermal energy of a
laser beam to confine deposition to a micron
scale. Georgia Techs LCVD system is capable of
both general forms of deposit growth fiber
growth and direct writing.
The chamber design allows the corrosive
gases to be isolated to the upper chamber, while
the lower chamber houses the delicate stage
assembly. Typically, reagent gases are supplied
locally by a gas-jet that aids mass transport and
increases deposition rates. Georgia Techs
system is flexible to allow for three separate
modes of operation for comparison purposes.
LCVD Modeling
In a laser-heated process such as LCVD, the
temperature field varies significantly over the
diameter of the laser spot. Deposition rates
typically follow an Arrhenius relationship, so it
is critical to document and understand these
two-dimensional temperature variations.
Therefore, it is imperative to study and
accurately model the temperature variations in
and around the laser spot.
100 µm
LCVD Deposits
Georgia Techs LCVD system has deposited
materials such as carbon, silicon carbide, boron,
boron nitride, and molybdenum onto various
substrates including graphite, grafoil, zirconia,
alumina, tungsten, and silicon. Direct write
patterns as well as fibers have been successfully
deposited. A 200 µm laser spot was used for all
deposits, while the laser power varied from 20 to
130 Watts.
LCVD Applications
Georgia Techs LCVD system is uniquely
suited for the fabrication of a spherically
concave, thermionic electron source incorporating
an integral control grid structure. The design
shown below offers advantages of higher power,
higher frequency, and miniaturization compared to
current technology. The design incorporates BN
layers which support and isolate the molybdenum
grids from the emitter. The presence of the BN
layers permits using smaller distances between
the tungsten emitter and the metal grids which,
along with the concave surface provides
advantages in beam geometry and control required
for high-frequency devices to be realized. The
BN layers also support the grids and prevent
their distortion--which is a source of
degradation in gridded electron guns.
Fiber Measurement
Single Layer Carbon Line