John Rönn, Sauli Virtanen, Philipp Maydannik, Sami Sneck, Beneq Oy, Espoo, Finland
Since its invention 50 years ago, atomic layer deposition (ALD) has shown tremendous performance in depositing thin film structures for various applications in physical, chemical, biological, and medical sciences. Due to the unique layer-by-layer growth mechanism of ALD, thin films with exceptional uniformity, conformality and quality can be deposited not only on planar substrates, but also on the most complicated surfaces. Despite its superior advantages, traditional ALD, or temporal ALD, suffers from relatively low deposition rates (~20-50 nm/h), which has greatly limited ALD’s application in many systems where thin films with thicknesses of several hundreds or even microns are required. Such examples are often found in optical coatings that are widely used in our everyday lives in the form of self-driving cars, augmented reality glasses or mobile phones, to name a few.
In this work, we present a new-generation ALD technology that revolutionizes the production of conformal thin-film coatings: the spatial ALD. In spatial ALD, the substrate is rotated across successive process zones to achieve ultra-fast and high-precision thin film deposition. We present our latest results, which include ultra-fast production of SiO₂, Ta₂O₅ TiO₂, HfO₂, and Al₂, O₃, with deposition rates reaching up to 2 µm/h. In addition, we show that the deposition of these films can be controlled in such a way that no coating induced stress is obtained on the substrate, ultimately allowing extremely thick layer configurations to be deposited. Finally, we show that these films exhibit low optical losses which make them very advantageous especially in novel optical applications where conformal, thick, and low-loss coatings are highly desirable.