Specific Process Knowledge/Etch/Wet Chromium Etch

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Wet etching of Chromium

Fume hood 01 or 02 (for acids and bases) in cleanroom D-3 can be used for wet chromium etching.

Wet etching of chromium at Danchip is done making your own set up in a beaker in a fume hood - preferably in cleanroom B-1 or D-3. You can see the APV here.

We have two solutions for this:

1. Commercial chromium etch (Chrome Etch 18). You can see the KBA here
2. HNO₃:H₂O:cerisulphate - 90ml:1200ml:15g

Etch rate are depending on the level of oxidation of the metal.

How to mix the Chromium etch 2:

1. Take a beaker and add 15g of cerisulphate.
2. Add a little water while stirring - make sure all lumps are gone.
3. Add water until 600 ml - keep stirring (use magnetic stirring)
4. Add 90 ml HNO₃
5. When the cerisulphate is completely dissolved (clear liquid) you can add the other 600 ml of wafer.

Comparing the two wet chromium etches

	Chromium etch 1	Chromium etch 2
General description	Etch of chromium	Etch of chromium
Link to safety APV and KBA	see APV here. see KBA here	see APV here
Chemical solution	Chrome Etch 18	HNO3:H2O:cerisulphate - 90ml:1200ml:15g
Process temperature	Room temperature	Room Temperature
Possible masking materials	Photoresist (1.5 µm AZ5214E)	Photoresist (1.5 µm AZ5214E)
Etch rate	~ ? nm/min	~40-100 nm/min
Batch size	1-7 4" wafers at a time	1-7 4" wafers at a time
Size of substrate	Any size and number that can go inside the beaker in use	Any size and number that can go inside the beaker in use
Allowed materials	No restrictions. Make a note on the beaker of which materials have been processed.	No restrictions. Make a note on the beaker of which materials have been processed.