Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...

spin coating. A layer of light sensitive AZ 5214 positive photoresist from AZ Electronic
Materials was coated onto the oxidized surface of the wafer using the spin coating
method. The wafer was held on a vacuum chunk, the photoresist was dispensed and the
wafer was spun at 3000 rpm for 30 seconds to obtain a 1 μm thick uniform layer. After
the photoresist application, the wafer was soft baked at 105 o C for 1 minute to remove the
solvents from the photoresist coating. For die B, before step 3, a layer of 1μm aluminum
metal was deposited by E-beam on the oxidized wafer to form the bump pads.
4. Mask alignment and UV exposure: The mask was aligned with the wafer to transfer the
designed pattern onto the wafer surface. Once the mask was accurately aligned, the
photoresist was exposed through the pattern on the mask with a high intensity ultraviolet
light. 12 seconds continuous exposure time was used for all the wafers.
5. Development: The resist in the patterned area that had been exposed to the ultraviolet
light was washed away using a 1:3 AZ 400K developer-to-water solution for 30-35
seconds, leaving other areas still covered with photoresist. The exposed part without the
resist was the exact pattern layout on the wafer surface.
6. Post-development inspection: The inspection is to ensure the resist processing steps
conducted earlier had produced the desired results. This was done using an optical
microscope.
7. Descum process: Descumming is the process to ensure full removal of resist from
uncovered areas after development through gentle oxygen plasma cleaning. Oxygen
plasma etching is a more controlled process than wet chemical etching, able to remove
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