Antenna Project
in Cameron clean room
Wafer preparation, conductor
deposition, photolithography
Dilbert
The starting material for the antenna project
is a silicon wafer
It is also the starting material for most
microelectronic devices
Silicon is a group 4 element, meaning it has
4 electrons in its outer electron band
Group 4
Why is silicon an excellent
microelectronics material?
1. It is very abundant
2. It can be grown into a single orientation crystal
3. It can be made electrically active easily by
“doping” with group 3 and group 5 elements
4. It can be made to conduct electrons with a
small applied potential
5. It has a naturally forming oxide that acts as an
insulating and diffusion barrier
Two
dimensional
schematic of
three
dimensional
crystal
Group 3 Elements
P type doping –
Positive, electron
short, also called
a hole
Group 5 elements
N-type doping
– N is
negative,
electron rich
Combing n-type
silicon and ptype silicon
gives a pn
junction
The whole microelectronics
revolution can be traced to this
fundamental characteristic of
silicon – a semiconductor material
Silicon is the most common
semiconducting material for
today’s microelectronics
Many other semiconducting
materials like GaAS, and GaN are
used for specific applications
Creating an antenna on the
silicon wafer
Starting material is a 100mm (4 inch) wafer
of silicon - shown in an edge view
Wafers are chemically cleaned
first
Silicon Dioxide (SiO2 ) is grown on the silicon
creating a dielectric or insulating layer
The antenna must sit on an insulating layer
High temperature tube furnace for the
formation of silicon dioxide (SiO2)
Once the insulating layer is
formed, a conductor needs to
be chosen
Conductivity of metals
1. Silver
• Expensive, used for solar cells
2. Copper
• Moderate cost, used in electrical wiring,
antennas
3. Gold
• Very expensive but very useful in that it will not
oxidized. Used in most high quality connections
4. Aluminum
• Low cost, easy to use, used for most
microelectronics devices
For this antenna project
Copper will be used
A copper metal is vacuum deposited on to
the wafer
Conductor vacuum deposition tools in the ECE
Microelectronics Clean Room
Cooke-thermal deposition
CHA Mark 50 e-beam deposition
CVC 601-sputter deposition
Varian 3125 e-beam deposition
Photolithography
• Photolithography is the transfer of patterns,
circuits, device structures, etc. to a substrate or
wafer using light and a mask or stencil to stop
the light.
• Photolithography was used extensively in the
progression of microelectronics.
• Today, because of the sizes involved in current
computer microprocessor devices, other
methods like direct patterning using electron
beams are used.
• Photolithography is still used for dimensions
down to about 0.5um. The wavelength of UV
light is .35-.45 um.
UV light sensitive material called photoresist
is spin coated on to the conductor side of
the wafer
Wafers are spin coated with Shipley 1813
UV sensitive photoresist
spin coating produces a uniform coating
Spin speed
is set here
A vacuum chuck
holds the wafer
Light sensitive
material is stored in
amber dropper bottles
– Use 1813
The antenna design, arrayed on a transparency sheet, is
placed on top of the wafer. This transparency is called a
photo mask. Production photo masks would be made on
glass plates with high precision patterns.
The antenna pattern, arrayed and printed on
a transparency paper, is used as a
photomask
The array of
antenna will
be cut to just
larger than the
wafer
Ultraviolet light is projected down
on to the photoresist coated wafer
HTG mask aligner and UV light source
The UV light source is a mercury vapor lamp at 436nm
wavelength
Clear glass
plates are
used to make
sure the
transparency
lays flat to the
wafer
UV light with
filter
surrounding it
Exposure
time set
on timer
Wafer is held by vacuum,
mask is placed on top and
brought into contact with
wafer
The wafer is developed, leaving photoresist
where no UV light has penetrated the mask
Solitec automatic developer
Vacuum
switch
Start switch
Conductors are etched using
chemicals specific to the metal
Aluminum
etch
Chrome etch
Gold, silver,
nickel, and
copper etch
After etching, the antenna pattern, in the
conductor of choice, will be left on the wafer
Homework
•Complete dimension drawing and printing
of transparency mask – submit dimension
drawing
•Find PowerPoint programs on Mosaic
•Begin learning how to use it
•Your project report will be done on
PowerPoint
•Photos of your team working in the clean
room are required for the PowerPoint report