Because of equipment
availability, cost, and
time, we will use
aluminum as the top side
conductor
Top Side Conductor vacuum deposition
Aluminum sputter deposit in Argon plasma
CVC 601-sputter deposition tool
A conductor metal is vacuum deposited on
to the wafer
Because of cost and equipment, aluminum
will be used instead of silver
Sputtered aluminum
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 is 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.
Top side conductor grid needs
to be designed
Pattern is created on a transparency sheet
to keep cost low
Once top side conductor grid is finalized, a
chrome on glass professional mask can be
made
Typical top side conductor
Because of tester limitations (100mA) – cell
size to be 10 cm2 max
UV light sensitive material called photoresist
is spin coated on to the conductor side of he
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
Transparency is used as a photomask
Cells can be
of
various
sizes but must
line up for saw
cutting
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.
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
The conductor is disolved (etched) with the
appropriate chemical
Aluminum is etched using the
aluminum etchant at about 750C
Aluminum
etch
After etching, the top conductor grid pattern,
will be left on the wafer
Top conductor
Top side conductor complete
Once the top side conductor
grid is complete, the back side
conductor can be deposited
For this fabrication run, aluminum
will also be sputtered as the back
side contact
Assignment
Complete your top
side conductor grid
pattern and submit