PROCESS THINKING

Why the order can't change

Anchor holes have to be etched before the layer that fills them is deposited. Dimples have to exist before Poly 1 is deposited over them. And every sacrificial layer has to survive every later masking step — right up until the moment it's dissolved in the HF bath.

Change the order, and the structure you designed simply doesn't form the way you intended.

In a fixed multi-mask process like this, sequence isn't a suggestion — it's the design.

WORKED EXAMPLE

From substrate to released motor

1. Wafer & doping 150 mm n-type wafer, phosphorus-doped surface

2. Nitride SiN isolation layer

3. Poly0 Patterned ground plane

4. PSG1 Dimples + ANCHOR1 etched

5. Poly1 Anchored to Poly0

6. PSG2 VIA + ANCHOR2 etched

7. Poly2 Anchored and connected to Poly1

8. Metal Contacts, routing, mirrors

9. Release HF dissolves PSG1 & PSG2 — moving parts are free

That's a complete PolyMUMPs run — the same nine steps behind real electrostatic motors and micromirrors shipped to customers every run.

UNIT 16 STUDY COMPLETE

🧩

Ready for the Fab Challenge?

You've covered Build a PolyMUMPs Device.