PROCESS INTEGRATION

Planarization

Planarization is included among the pattern-transfer and micromachining methods in this part's fabrication toolbox.

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For now, the important concept is that multi-layer fabrication must manage the surface geometry produced by earlier steps.

Fabrication is not a collection of isolated steps. Each layer changes the starting condition for the next layer.

PROCESS THINKING

Add. Pattern. Remove. Repeat.

Deposit Add a material layer

Pattern Define selected regions

Etch Remove selected material

Modify Oxidize or dope material

Repeat Build complexity layer by layer

This is the mindset you should begin using when looking at any MEMS fabrication sequence:

What material exists now? What should remain? What should be removed? What must be added next?

LAYER-BY-LAYER MEMS

Build a free-standing structure.

Follow the logic of surface micromachining.

Step 1 Start with silicon substrate

Step 2 Deposit process layer

Step 3 Add sacrificial material

Step 4 Add and pattern structural layer

Step 5 Remove sacrificial material

Result Free-standing mechanical structure

STRUCTURE
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AIR GAP

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SILICON

This is the major transition: You're no longer memorizing process names. You're learning how to use processes together to manufacture a device.

WORKED EXAMPLE

Inside the cleanroom

Here's how a real device moves through a fabrication run, start to finish.

1. Design & layout CAD layout converted to GDSII, sent to a mask shop

2. Gown up Enter the cleanroom in a bunny suit and gloves

3. Wafer clean RCA clean removes organic and metallic contamination

4. Deposit LPCVD grows nitride, polysilicon, and PSG films

5. Coat & expose Spin-coat photoresist, expose through the mask

6. Etch & strip Pattern is etched into the film, resist is stripped

7. Inspect SEM checks the pattern at high magnification

8. Metallize Au/Cr contacts deposited, then lifted off

This is the same add → pattern → remove cycle you've been learning, run inside a real cleanroom, wafer by wafer.

UNIT 12 STUDY COMPLETE

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Ready for the Fab Challenges?

You've covered Process Integration & a MEMS Build.