- Aluminum metallizations up to 25,000 Å are vacuum deposited on the silicon slice, coated with a photoresist, and UV exposed using an appropriate photographic mask. The resist is developed to protect the aluminum where interconnections are desired. Then the unprotected areas of the aluminum are removed by etching with the aluminum etchant, followed by a water rinse.
- Etching time is dependent upon the etchant temperature and the aluminum film thickness. When etching thick aluminum films, a higher etch rate is required; thus a higher etchant temperature should be used. Likewise, for thinner aluminum films, slower etch rates are desired and a lower etchant temperature should be chosen.
- At a specific etchant temperature, the etching time is given by the following formula:
Etching time (second) + Film Thickness (Å)/ Etch Rate (Å/sec)
where Etch Rate at 25°C 30 Å/sec; at 40°C 80 Å/sec.