Atomic layer deposition in fabrication of micro- and nanodevices

Atomic layer deposition (ALD) has become a widely used thin film deposition method in fabrication of many micro- and nanodevices. In this thesis, the reasons for this are investigated by studying what ALD has enabled for the applications based on available literature. In addition to reviewing existing applications, ALD was used in selected experimental case studies to enable better performing thin films and/or new improved device designs. Based on the literature review the most important advantages that ALD offers are conformal deposition and precise thickness control combined with relatively low deposition temperatures. As the device dimensions and required film thicknesses have decreased, and the devices have turned from planar to three-dimensional, ALD has gained more momentum. However, due to the the biggest downside of ALD, slow deposition rate, ALD is selected as the depositon method only when other deposition methods fail to meet the requirements. In the first experimental case, AlN deposition was studied from less used AlCl3 precursor with aim of depositing pure and crystalline AlN thin films. The AlN deposition from AlCl3 showed promise and enabled deposition of relatively pure AlN films. However, more work is still needed in order to determine whether it is a better precursor option for the deposition than the more commonly employed AlMe3. Additionally, the possibility to control residual stress of the AlN film was observed. In the second experimental case, ALD was used to deposit heterogenous catalyst into microreactors. ALD enabled deposition of even distribution of Pt nanoparticles in microreactor walls with controllable size, which showed high activity in hydrogenation of propene.In the third experimental case, ALD Al2O3 and AlN was studied as thin free-standing membranes. The thin ALD Al2O3 membranes showed exceptional mechanical properties. Membranes of 400-µm diameter were fabricated as thin as 15 nm. The amorphous Al2O3 membranes were found more durable than polycrystalline AlN membranes. In the final experimental case, ALD was used to enable new designs for fabrication of superomniphobic surfaces. Superomniphobic surfaces that could repel all room temperature liquids were realized with the help of ALD SiO2. Role of ALD in the fabrication of the superomniphobic surfaces could increase if the dimensions of the surface features are shrunk further. This could also enable decreasing the temperature budget of the process to <120 °C.