Resputtering

Resputtering is the process in vacuum thin-film deposition in which atoms that have been deposited on a surface are ejected again by energetic bombardment, typically by ions from a plasma. It is the reverse of sputtering and occurs in many sputtering and ion-assisted deposition systems. As energetic ions strike the surface, they transfer momentum and energy, causing surface atoms to leave the surface if the incident energy exceeds the surface binding energy. The sputter yield depends on ion energy, ion species, target material or film material, incidence angle, and surface bonding.

Resputtering can influence film thickness and composition, sometimes leading to thinning of the deposited layer or to preferential removal of certain elements in multi-component films, causing stoichiometry shifts. It can also increase surface roughness or densify the film depending on conditions; high-energy bombardment may cause damage or defect formation.

Resputtering is common in magnetron sputtering, ion beam assisted deposition, and reactive sputtering, especially when substrate bias or gas ions are used. In many processes, resputtering is undesirable when precise thickness control is needed; process parameters such as lower ion energy, reduced bias, higher pressure to thermalize ions, or using heavier inert gases can mitigate it. Conversely, controlled resputtering can be used to improve film density and adhesion or to sculpt microstructures.

Surface and film properties affected include stoichiometry in compounds, density, roughness, and adhesion. Accurate modeling of resputtering informs process design and thickness budgeting.