(Invited) Role of Low-Energy Ions during Plasma-Enhanced Atomic Layer Deposition

Abstract

This contribution will discuss the role and impact of ions during plasma-enhanced atomic layer deposition (ALD), in the context of the latest trends in nanoelectronic device fabrication. Due to the ongoing downscaling of semiconductor device structures, atomic-scale processing techniques such as plasma ALD are becoming increasingly important and more widely applied. Detailed insight into the role of ions is essential, now more than ever, for further advancing the atomic-level precision that plasma ALD offers.Among others, it will be presented that even ions with a low energy of <20 eV, as typical when using a grounded substrate and a remote plasma source, can considerably influence plasma ALD processes. This will be illustrated using plasma ALD of SiO2 and TiO2 as industry-relevant case studies. Specifically, it is observed that (low-energy) ions contribute to the film quality of SiO2,1 can induce crystallization during plasma ALD of TiO2,2 and can alter the growth per cycle by a factor of up to ~2 (for both SiO2 and TiO2). These effects can have important consequences for applications, for instance on the film conformality obtained on 3D nanostructures.Furthermore, the mechanisms governing the influence of ions on an elementary level will be discussed. An important topic here is the combined effect of ion energy, ion flux and plasma exposure time. These parameters can all have a different impact, depending on the plasma and material system. For plasma ALD of SiO2 and TiO2 the combined effect can be universally described by the ion energy dose (i.e., ion energy × flux × exposure time),3 where a minimal effect is obtained when supplying a dose of <1 eV nm-2 cycle-1, or a strong effect when supplying a dose of >100 eV nm-2 cycle-1.1,2 In conclusion, general insights into the role of ions during plasma ALD will be presented, which are particularly important for advancing the level of control over film thickness and material properties in the fabrication of (next-generation) nanoelectronics. Arts et al., Appl. Phys. Lett. 117, 031602 (2020).Arts et al., Impact of ions on film conformality and crystallinity during plasma-assisted atomic layer deposition of TiO2 (to be published).Faraz et al., Plasma Sources Sci. Technol. 28, 024002 (2019). Figure 1