Photolithography

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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.

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Starting material is a 100mm (4 inch) wafer of
silicon - shown in an edge view
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Wafers are cleaned first
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Silicon Dioxide (SiO2 ) is grown on the silicon
creating a dielectric or insulating layer
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High temperature tube furnace for the formation
of silicon dioxide (SiO2)
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A conductor metal (student choice) is vacuum
deposited on to the wafer
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Conductor vacuum deposition tools in the ECE
Microelectronics Clean Room
CVC 601-sputter deposition
Cooke-thermal deposition
Varian 3125 e-beam deposition
CHA Mark 50 e-beam deposition
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UV light sensitive material called photoresist is
spin coated on to the conductor side of the wafer
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Wafers are spin coated with Shipley 1813 UV
sensitive photoresistspin coating produces a
uniform coating
Spin speed is set here
Light sensitive material is stored in amber
dropper bottles Use 1813
A vacuum chuck holds the wafer
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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.
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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
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Ultraviolet light is projected down on to the
photoresist coated wafer
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HTG mask aligner and UV light source The UV
light source is a mercury vapor lamp at 436nm
wavelength
UV light with filter surrounding it
Clear glass plates are used to make sure the
transparency lays flat to the wafer
Exposure time set on timer
Wafer is held by vacuum, mask is placed on top
and brought into contact with wafer
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The wafer is developed, leaving photoresist where
no UV light has penetrated the mask
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Solitec automatic developer
Vacuum switch
Start switch
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Conductors are etched using chemicals specific to
the metal
Gold, silver, nickel, and copper etch
Chrome etch
Aluminum etch
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After etching, the antenna pattern, in the
conductor of choice, will be left on the wafer
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In the clean room

• Complete one wafer first
• Determine the number of complete antennas on the
  wafer. Partial antenna can not be counted.
  Record this number. It is needed for the cost
  analysis.
• Consider cost cost analysis will be next lesson
  
• Redesign if appropriate

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Homework

• Find Excel and PowerPoint programs on Mosaic
• Begin learning how to use both programs
• A cost analysis for your antenna design will be
  due shortly
• Your project presentation will be done on
  PowerPoint