SPUTTERED AMORPHOUS CARBON FILMS: MICRO-STRUCTURE, DENSITY, OPTICAL AND MECHANICAL PROPERTIES

Abstract

Amorphous carbon (a-C) films, single and multilayered, were deposited by rf magnetron sputtering, from graphite, on c-Si substrates. In-situ and real-time Spectroscopic Ellipsometry (SE) was used to determine the optimum deposition conditions where the formation of controllable sp 3 sties can be achieved. The growth mechanisms of sputtered a-C films and their properties (optical, compositional, density and mechanical) were studied using a variety of novel characterization techniques. SE data analysis provides: (i) the sp 3 and sp 2 volume fractions and (ii) the optical properties, that are combined well with the density, the internal stresses and the elastic properties of ultra-thin to thick a-C films. In sputtering, the applied substrate bais voltage Vb (up to -200V) controls the energy (30≤E≤230 eV) of the Ar+ ions bombarding the growing film surface, affecting all film properties and responses and classifying the films in three types. The film developed with E≈30 eV (rich in sp 2 sites) and 30<E≤130 eV (rich in sp 3 sites) are defined by type I and II, respectively. Type III is defined by films developed with E>130 eV, where the formation of a new and dense carbon phase is deteched, exhibiting a semi-metallic optical behavior. The experimental results show: a) in films of type I and II the stress, density, hardness and elastic modulus are directly related with the sp 3 content and described well with the so far proposed models on the formation mechanism of tetrahedral carbon, and b) the density and the elastic properties, in type III films, 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 tailored to meet specific application requirements. For example, the combination of single a-C films of type I and II in developing multilayered films resulted to the growth of stable, thick and highly sp 3 bonded films with improved elastic properties.