Coupled effects of bombarding ions energy on the microstructure and stress level of RFPECVD a-C:H films: correlation with Raman spectroscopy

In this work a-C:H films have been prepared in a capacitively coupled RF-PECVD device (ν=13.56 MHz) from methane as the gas source. By the use of ERDA, IRTF and X-Ray reflectometry techniques, we have first investigated the structural evolutions of the films as a function of the ion energy. In the second part, we have measured mechanical properties (hardness and Youngʹs modulus) by nanoindentation. Concerning the stress level, according to Stoneyʹs equation, the magnitude of the internal stress has been determined by substrates deflection measurements: this finally leads to a quantification of the adhesion through the calculation of the interfacial fracture energy (Gic). Raman spectroscopy has been used as a probe of both film quality and mechanical properties. The position of the G band is correlated with the sp3 carbon content and the stress level. One observes that the G peak position moves to high frequencies when the ion energy increases, indicating a graphitization of the samples. The relationship linking the Raman wavenumber shift to stress is discussed.