| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS+TF-WeM |
| Session: | Atomic Layer Etching |
| Presenter: | Nicholas Johnon, University of Colorado at Boulder |
| Authors: | NJ. Johnon, University of Colorado at Boulder H. Sun, University of Colorado at Boulder K. Sharma, University of Colorado at Boulder S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Thermal atomic layer etching (ALE) has been recently demonstrated for a variety of oxides such as Al2O3, HfO2 and ZrO2 using sequential, self-limiting fluorination and ligand-exchange reactions. In this work, the thermal ALE of aluminum nitride, a III-V metal nitride, was performed for the first time. Crystalline aluminum nitride (AlN) films were etched using hydrogen fluoride (HF) and tin(II) acetylacetonate (Sn(acac)2) as the reactants. The AlN films were in the crystalline wurtzite phase with the (0001) plane parallel to the surface. Film thicknesses were monitored versus number of ALE reaction cycles at 275°C using in situ spectroscopic ellipsometry (SE). A low etch rate of 0.07 Å/cycle was measured during etching of the first 40 Å of the film. These small etch rates corresponded with the AlOxNy layer on the AlN film. The etch rate then increased to 0.36 Å/cycle for the AlN films. In situ SE experiments established the HF and Sn(acac)2 exposures that were necessary for self-limiting surface reactions. In the proposed reaction mechanism for thermal AlN ALE, HF fluorinates the AlN and produces an AlF3 layer on the surface. The metal precursor, Sn(acac)2, then accepts fluorine from the AlF3 layer and transfers an acac ligand to the AlF3 layer in a ligand-exchange reaction. The volatile etch products are SnF(acac) and either Al(acac)3 or AlF(acac)2. Adding a H2 or Ar plasma exposure to the reaction sequence enhanced the etching rates. A H2 or Ar plasma exposure after the Sn(acac)2 exposure increased the AlN etch rate from 0.36 Å/cycle to 1.96 Å/cycle or 0.9 Å/cycle, respectively, at 275°C. The enhanced etch rates are believed to result from either H radicals or photons from the H2 plasma or ions or photons from the Ar plasma. The H radicals may be able to remove acac surface species that may limit the etch rate. The photons or ions may also lead to the desorption of surface species or substrate excitation that enhances the etch rate.