Ion-Assisted Deposition (IAD)

Ion-assisted deposition: ion and molecule arrival rates, ions per deposited molecule, and ion energy and momentum per molecule from the ion current density, ion energy and deposition rate.

Model: Exact

Film materialMean ion energy (eV; not the anode voltage)Ion current density at the substrate (µA/cm²)Deposition rate (nm/s)Ion mass (u; Ar⁺ 40, O₂⁺ 32)Density set in the rate monitor (g/cm³; 0 = bulk)

SiO₂: M = 60.08 g/mol, bulk ρ = 2.20 g/cm³ (crystalline for TiO₂, Al₂O₃), 3 atoms per formula unit. Singly charged ions; the current density is the one measured at the substrate (Faraday cup), not the source current. A Faraday cup misses the fast neutrals made by charge exchange, and a doubly charged ion counts twice.

Ions per arriving molecule

0.283

ion-to-molecule arrival ratio

Ion energy per molecule

84.9 eV

28.3 eV per atom

Ion momentum per molecule

43.9 √(u·eV)

ratio × √(2 m_i E)

Ion flux

3.12e+18 m⁻² s⁻¹

J / e

Molecule arrival rate

1.10e+19 m⁻² s⁻¹

r ρ N_A / M, ρ = 2.20 g/cm³ (bulk)

Model

Φ_i = J/e; Φ_m = r ρ N_A/M; ratio = Φ_i/Φ_m

E per molecule = ratio × E_ion; momentum per molecule = ratio × √(2 m_i E_ion)

IAD results (packing density, index, stress) are reported against these numbers, but how a film responds depends on the material, the ion species and the chamber, so the page doesn't predict them. Φ_mneeds the mass rate: with a quartz-crystal monitor that is the displayed rate times the density set in it, whatever the film's porosity. For a rate from measured thickness and time, enter the film's own density, which is below bulk for a porous film.

Model and references

Exact. The equations are exact within the stated assumptions, or are a standard's tabulated values. The results are as good as the inputs. About the tiers

Arrival-rate bookkeeping: singly charged ions, current density measured at the substrate, sticking 1, mass rate = rate × monitor density. Packing density, index and stress depend on the process and are not predicted.

Martin P. J., Macleod H. A., Netterfield R. P., Pacey C. G., Sainty W. G. (1983). Ion-beam-assisted deposition of thin films. Appl. Opt. 22, 178. doi:10.1364/AO.22.000178
Ohring M. (2002). Materials Science of Thin Films, 2nd ed., ch. 5 (ion-beam-assisted deposition). Academic Press. doi:10.1016/b978-012524975-1/50008-2

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