Specific Process Knowledge/Etch/Aluminum Oxide/Al2O3 Etch using HF: Difference between revisions

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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''
+=== Photoresist adhesion ===
+Experiments in April 2025 as shown bad adhesion of AZ 5214E on Al2O3. Total delamination occurred in less than 120 seconds on 50nm and 100nm of Al2O3 deposited using ALD.
+Thus wetetch is unsuitable to structure an Al2O3 for use as hard-mask for dryetching.
+<br>
+Systematic studies have not yet been done as of April 2025.
+<br>
+Following parameters were tested:
+{| class="wikitable"
+|+ Process parameters
+|-
+!style="max-width:7em;"| ALD Parameters
+||
+* Cycles: 500 and 1000
+* Temperature: 200°C
+* TMA pulse: 0.1s
+* H2O pulse: 0.1s
+|-
+!style="max-width:7em;"| Lithography parameters
+||
+* Pretreatment: HMDS
+* Resist type: AZ 5214E
+* Resist thickness: 1.5µm
+* Exposure parameters:
+** Tool: MLA3
+** Dose: 100 mJ/cm2
+** Defocus: 1
+** Mode: Fast
+* Development: TMAH, SP60
+* Post treatment: Hardbake 120s@120C
+|}
+''Jesper Pan, DTU Nanolab, April 2025''