Specific Process Knowledge/Etch/Wet Aluminium Etch

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Wet etching 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 Nanolab. This alloy is no longer in use at DTU Nanolab 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:

1. H₂O : H₃PO₄ (1:2) at 50°C
2. Pre-mixed etch solution: Aluminum etch 80-15-3-2 at 20°C

The first solution is always available ready made in the Aluminium Etch bath. The second solution can be mixed manually or bought pre-mixed and ready for use. Please contact DTU Nanolab if you need to use the Aluminum etch 80-15-3-2 etch mixture. Since it is used only very rarely it will probably have to be ordered when needed. The table below summarizes possibilities and parameter for the two etch mixtures.

Comparing the two solutions

	Aluminium Etch	Etch with Aluminum etch 80-15-3-2
General description	Etch of pure aluminium	Etch of aluminium with 1.5% Si
Location	Bath inside Wet Bench 05 in D-3	Beaker in Fumehood 1 or 2 in D-3
Link to SDS	Kemibrug SDS: Phosphoric acid >25%	Kemibrug SDS: Phosphoric acid etch slution
Chemical solution	H2O:H3PO4 1:2	Aluminum etch 80-15-3-2: 60-90 vol% H3PO4 85% 5-20 vol% CH3COOH 100% 1-5 vol% HNO3 70%
Process temperature	50°C	20°C
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	Flexible
Size of substrate	4" wafers 6" wafers	Any size that fits in beaker
Allowed materials	See the Cross Contamination Sheet for Aluminium Etch bath	Any material allowed in cleanroom