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A wet chemical etch of Al₂O₃ can be done with HF. The etch rate depends on the HF concentration.

Experiment and results

Si samples with about 100 nm of ALD deposited Al₂O₃ (1000 cycles at 300^oC) has been etched in different HF concentrations. After the etching, the thickness of the Al₂O₃ layer has been measured, and the thickness as function of time has been plotted as shown in the graph below.

The etch rates:

5% HF: 1.74 nm/s
1vol. H₂O : 1vol. 5% HF 1.05 nm/s
2vol. H₂O : 1vol. 5% HF 0.723 nm/s

Be aware of that the 5% HF etches quite fast - Actually so fast that it can be tricky to control the etch. Just imagine, you take a sample out of solution and place it in a bigger water container to rinse, and during that movement, the etch continues… So the handling things around the fumehood can be a source of errors.

Evgeniy Shkondin, DTU Nanolab, June 2019

@@ Line 14: / Line 14: @@
 The etch rates:
-<ol type="a">
+<ul>
 <li>5% HF: 1.74 nm/s</li>
-*'''1vol. H<sub>2</sub>O : 1vol. 5% HF 1.05 nm/s'''
+<li>1vol. H<sub>2</sub>O : 1vol. 5% HF 1.05 nm/s</li>
-*'''2vol. H<sub>2</sub>O : 1vol. 5% HF 0.723 nm/s'''
+<li>2vol. H<sub>2</sub>O : 1vol. 5% HF 0.723 nm/s</li>
-</ol>
+</ul>
 Be aware of that the 5% HF etches quite fast - Actually so fast that it can be tricky to control the etch. Just imagine, you take a sample out of solution and place it in a bigger water container to rinse, and during that movement, the etch continues… So the handling things around the fumehood can be a source of errors.
 ''Evgeniy Shkondin, DTU Nanolab, June 2019''