Mock CMOS Processing Update: Oxide Etch

MEMS course structures: Polymerization removal

Note: These are using large feature mask, not 1.6um mesh structure.

Using the new knowledge of how to perform the wet aluminum etch, we proceeded to pattern the remaining TiW using hydrogen peroxide, thus leaving oxide. Instead of going for the fine 1.6um freatures, Matte and I used large features.

Matte then performed an oxide etch. As you can see, 1) the aluminum etch was too long, undercutting the photoresist. 2) the titanium/tungsten etch was also a bit too long, 3) the oxide etch went beyond the oxide and started to etch the silicon. There is some type of polymerization that is occurring. Next step is to try a oxygen plasma to remove the polmyer film.

Here is what the processing steps were:
Photoresist Patterning
Photoresist used: AZ 4210
Approx. thickness: 1.5 um
Hard Bake: 5 minutes at 200C on hot plate

Aluminum Etch
Type of etch: Wet Isotropic Etch
Chemical used: Transene Type APre-mixed Aluminum Etch
Machine used: None
Temperature of etch: 45-50 degrees Celsius
Advertised etch rate: 100 Angstroms/minute
Etch time: 40 seconds

Titanium/Tungsten Etch
Type of etch: Wet Isotropic Etch
Chemical used: Hydrogen Peroxide
Machine used: None
Temperature of etch: 45-50 degrees Celsius
Advertised etch rate: 60 Angstroms/minute
Etch time: 2 minutes

Oxide Etch
Type of etch: Dry Anisotropic Etch
Chemical used: CF4
Machine used: Technics RIE system
Etch time: 30 minutes

Aluminum etch (Click to enlarge)

Titanium/Tungsten etch (Click to enlarge)


Oxide etch (Click to enlarge)

Oxide etch, center of wafer (Click to enlarge)