Specific Process Knowledge/Etch/Aluminum Oxide/Al2O3 Etch using HF

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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 using Ellipsometer VASE, and the thickness as function of time has been plotted as shown in the graph below.

• 
  Different etching rates for different HF concentrations.

The etch rates:

• 5% HF → 1.74 nm/s

• 1vol. H₂O : 1vol. 5% HF → 1.05 nm/s

• 2vol. H₂O : 1vol. 5% HF → 0.72 nm/s

Be aware of that the 5% HF etches quite fast. Actually, so fast that it can be tricky to control. Taking the sample out of the solution and placing it in a bigger water container to rinse, resulting a time delay due to the movement and the etch continues. It means the handling things around the fumehood can be a source of errors in this case.

Evgeniy Shkondin, DTU Nanolab, June 2019