2.2.2 Alignment
Pattern alignment plays a major role in photo-lithography for making controlled
feature sizes and shapes. The pattern transferred to a wafer has a set of alignment
marks which have highly precise features. These marks are used as reference for
positioning other patterns at different layers with respect to a pattern of one layer
each alignment mark should be labelled for easy identification, positioning and time
saving [ 17 ]. Complex MEMS features are mostly multi-level and use multiple
masks for different operations related to micromachining on a single chip platform.
Fig. 2.3 Pattern transfer
process
Fig. 2.4 (a) Pattern in positive photoresist, (b) Pattern in negative photoresist
2 Microfluidics Overview 39