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

A vacuum chuck holds the wafer

Spin speed is set here

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

Exposure time set on timer

Wafer is held by vacuum, mask is placed on top and brought into contact with

wafer

Clear glass plates are

used to make sure the

transparency lays flat to the

wafer

UV light with filter

surrounding it

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 side conductor complete

Top conductor

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