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Wet ething of aluminium can be done using many different acids and bases. Using dilute phosphoric acid gives reasonably good control and compatibility with photoresists. Etching with dilute phosphoric acid is suitable for etching pure aluminium. If the aluminium is alloyed with other metals, other etchants may be better suited. Previously, aluminium with 1,5% silicon was used at DTU Danchip. This alloy is no longer in use at DTU Danchip but a suitable etchant (PES 77-19-04) for this alloy is included below.

Wet Aluminium Etch

Aluminium Etch bath located in left side of Wet bench 05 in cleanroom D-3

Wet etching of aluminium is done with two different solutions:

H₂O:H₃PO₄ 1:2 at 50 ^oC
Pre-mixed etch solution: PES 77-19-04 at 20 ^oC

Both solutions are used in the Aluminium etch bath shown to the right. It must be written on which one is in. Solution no. 1 is the most used solution for etching aluminium. Solution no. 2 is primarily for etching aluminium mixed with a small percentage of silicon.

The user manual and contact information can be found in LabManager:

Al-etch info page in LabManager

Comparing the two solutions

	Aluminium Etch	Etch with PES 77-19-4
General description	Etch of pure aluminium	Etch of aluminium + 1.5% Si
Location	'Aluminium Etch' bath in Wet Bench 05	Beaker in Fumehood 01 or 02
Link to KBA	see KBA here	see KBA here
Chemical solution	H₂O:H₃PO₄ 1:2	PES 77-19-04 77 vol% H₃PO₄ 85% 19 vol% CH₃COOH 100% 4 vol% HNO₃ 70%
Process temperature!	50 ^oC	20 ^oC
Possible masking materials!	Photoresist (1.5 µm AZ5214E)	Photoresist (1.5 µm AZ5214E)
Etch rate	~100 nm/min (Pure Al)	~60 nm/min
Batch size!	1-25 wafers at a time	1-25 wafer at a time
Size of substrate	4" wafers	4" wafers
Allowed materials	Aluminium Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist	Aluminium Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist