Sputtered amorphous carbon films: Micro-structure, density, optical and mechanical properties

Amorphous carbon (a-C) films, single and multilayered were deposited by rf magnetron sputtering, from graphite, on c-Si substrates. In-situ and real-t ime Spectroscopic Ellipsometry (SE) was used to determine the optimum depos ition conditions where the formation of controllable sp(3) sites on be achi eved The growth mechanisms of sputtered a-C films and their properties (opt ical, compositional, density and mechanical) were studied using a variety o f novel characterization techniques. SE data analysis provides: (i) the sp( 3) and sp(2) volume fractions and (ii) the optical properties, that are com bined well with the density, the internal stresses and the elastic properti es of ultra-thin to thick a-C films. In sputtering, the applied substrate b ias voltage V-b (up to -200V) controls the energy 30 less than or equal to E less than or equal to 230 eV) of the Ar+ ions bombarding the growing film surface, affecting all film properties and responses and classifying the f ilms in three types. The films developed with E approximate to 30 eV (rich in sp(2) sites) and 30<E less than or equal to 130 eV (rich in sp(3) sites) are defined by type I and II respectively. Type III is defined by films de veloped with E>130 eV, where the formation of a new and dense carbon phase is detected, exhibiting a semi-metallic optical behaviour. The experimental results show: a) in films of type I and II the stress, density, hardness a nd elastic modulus are directly related with the sp(3) content and describe d well with the so far proposed models on the formation mechanism of tetrah edral carbon, and b) the density and the elastic properties, in type III fi lms, depend not only on the sp(3) content but also on the new carbon phase. a-C films deposited by sputtering exhibit unique properties that can be ta ilored to meet specific application requirements. For example, the combinat ion of single a-C films of type I and Il in developing multilayered films r esulted to the growth of stable, thick and highly sp(3) bonded films with i mproved elastic properties.