Presented at the ASM technology seminar during the ALD-2016 conference, July 26th, 2016.
ALD was originally developed as a purely thermal process to deposit two-element films such as oxides and nitrides. Generally, thermal processes are easier to understand, and hence control and even model, when compared to plasma- assisted processes. A thermal ALD process would intrinsically give a better thickness uniformity and step coverage in an industrial (batch-type) reactor. However, ALD of single-element films (metals and semiconductors), with a few exceptions, is difficult to realize in thermal mode. PEALD becomes a solution, however, sometimes exhibiting inferior material properties to similar films deposited with competing techniques, for instance in terms of purity and conduction. PEALD can have a reduced step coverage compared to thermal ALD, cause damage to the wafer under treatment by the bombardment and UV photons and involve a large variety of chemical reactions. On the other hand, the bombardment and photons can play a positive role, influencing film crystallinity and enabling low-temperature processing. Alternatively, reactive species can be generated without plasma, by collisions of molecules with a hot tungsten wire (HW) heated up to a temperature in the range of 1600-2000 oC. This process excludes the additional bombardment and illumination with photons, is highly selective and purely chemical in terms of the radical formation.
6 Jul 2016
16th International Conference on Atomic Layer Deposition, ALD 2016