DESIGN AND EXPERIMENTAL PROCEDURE
Our traditional anemometer design and the cross-section
diagrams indicate the post CMOS process of the flow sensor
are shown in Figure 1 (a), (b), (c), and (d) sequentially. The
anemometer is mainly composed by the M4, P2 and Oxide
layers. Figure 1 (a) illustrates our past anemometer designed
after receiving from the foundry. Followed by the post CMOS
etching processes, figure 1 (b) indicates that etching the M4
aluminum layer by commercial Al etchant. After that,
NH4OH+±h02 solution are adopted to etch the TiN. Repeating
upper processes, step (b) progress can be achieved. In figure 1
(c), apply AOE to etch the passivation layer and XeF2 or
TMAH solution to etch the silicon substrate isotropically to
form the basic anemometer structure. Figure 1 (d) illustrates
the pad opening process. However, this anemometer violates
the design rule for the CMOS foundry and this violation can
cause the unpredictable low yield results e.g. the residual
oxide layer leaves a small layer on the metal surface while
etching back in Chemical Mechanical Polishing (CMP)
process. Therefore, this design can impede the following
etching process and reduce the yield of anemometers after the
post CMOS machining.