View source for Specific Process Knowledge/Etch/Aluminum Oxide/Al2O3 Etch using HF

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A wet chemical etch of Al<sub>2</sub>O<sub>3</sub> can be done with HF. The etch rate depends on the HF concentration. 

=== Experiment and results ===

Si samples with about 100 nm of [[Specific_Process_Knowledge/Thin_film_deposition/ALD_Picosun_R200|ALD]] deposited Al<sub>2</sub>O<sub>3</sub> (1000 cycles at 300<sup>o</sup>C) has been etched in different HF concentrations. After the etching, the thickness of the Al<sub>2</sub>O<sub>3</sub> layer has been measured using [[Specific_Process_Knowledge/Characterization/Optical_characterization#Ellipsometer|Ellipsometer VASE]], and the thickness as function of time has been plotted as shown in the graph below.

<gallery caption="" widths="600px" heights="500px" perrow="1">
image:Al2O3_HF_20190826.png| Different etching rates for different HF concentrations.
</gallery>


The etch rates:
<ul>
<li><p>5% HF &#8594; <b>1.74 nm/s</b></p></li>
<li><p> 1vol. H<sub>2</sub>O : 1vol. 5% HF &#8594; <b>1.05 nm/s</b></p></li>
<li><p> 2vol. H<sub>2</sub>O : 1vol. 5% HF &#8594; <b>0.72 nm/s</b></p></li>
</ul>

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''