Magnetron sputtering of transparent conductive zinc oxide: relation between the sputtering parameters and the electronic properties

Magnetron sputtering of transparent conductive oxides (zinc oxide, indium t in oxide, tin oxide) is a promising technique which allows the deposition o f films at low temperatures with good optical and electronic properties. A special advantage is the scalability to large areas. The principles underly ing magnetron sputtering are reviewed in this paper. The growth process dur ing magnetron sputtering is characterized by the bombardment of the growing film with species from the sputtering target and from the plasma. In addit ion to sputtered atoms with energies in the eV range, ions from the plasma (mostly argon) and neutral atoms (also argon) reflected at the target hit t he growing film. Depending on the energy of these species and on the ion-to -neutral ratio the properties of the films vary. High energies (greater tha n or equal to 100 eV), which occur mainly at low sputtering pressures lead to damage of the growing film, connected with mechanical stress, small crys tallites and bad electrical parameters. Ion assisted growth with low ion en ergies (below about 50 eV) is advantageous as is a high ion-to-neutral rati o. A compilation of resistivities of magnetron sputtered zinc oxide films y ields a limiting resistivity of 2 x 10(-4) Ohm cm for polycrystalline films . Based on the correlation between plasma parameters and film properties ne w research fields are anticipated. (Some figures in this article appear in colour in the electronic version; s ee www.iop.org).