Sunday, March 6, 2016

Photochemical atomic layer deposition and etching - Open Access Review

Here is a interesting review paper on photochemical activation of ALD and ALE processes by Prof. Paul Chalker from University of Liverpool [Thanks to Henrik Pedersen for this one]. The paper presents a review of the exploitation of light in ALD to stimulate photochemical processes. The use of light for area selective deposition for patterning methods is also reviewed and finally the potential for photo-etching in Atomic Layer Etching is assessed.


A range of radiation sources, which emit radiation at wavelengths below the visible (λ < 400nm) spectrum and into the UVA (315–400 nm, 3.10–3.94 eV), UVB (280–315 nm, 3.94–4.43 eV) and UVC (100–280 nm, 4.43–12.4 eV) ranges. [Surface & Coatings Technology 291 (2016) 258–263 Under a Creative Commons license]

ALE is the reverse process of ALD, i.e., the controlled layer-by-layer removal of material. Two examples are give of previous studies an photochemical ALE:
  • Photo-induced atomic layer etching of GaAs has been demonstrated using molecular chlorine (Cl2) coupled with KrF excimer laser irradiation (λ = 248 nm, 5 eV).
  • Etching of the reconstructed silicon, Si(111) 7 × 7 surface  using KrF excimer laser irradiation with Cl2 as the etchant.

Photochemical atomic layer deposition and etching

P.R. Chalker
Surface & Coatings Technology 291 (2016) 258–263
Under a Creative Commons license

Conventional atomic layer deposition (ALD) is a thermo-chemical process that is now used extensively in the manufacture of ultrathin films. In addition to substrate heating, various forms of other “assisted” ALD processes are actively being developed, where supplementary energy is supplied for example, from a plasma discharge or from light. This paper presents a critical review of the exploitation of light in ALD to stimulate photochemical processes. The range of light sources that are exploitable for photochemical ALD processes is considered and the chemical mechanisms that are stimulated in the ultraviolet spectrum are interpreted. The use of light as an excitation source lends itself to area selective deposition using lithographic methods or focused beams. The exploitation of photochemical processes for the deposition of patterned ALD films is reviewed in the context of the current alternatives. Finally, the potential for photo-etching is introduced. Atomic layer etching is a complimentary process to ALD and the application of photochemistry in layer-by-layer subtraction processes is considered.