Possible solution to the problem of high built-up stresses in diamond-like carbon films

Abstract

The various issues relating to the nature of high built-up stresses in diamond like carbon (DLC) films are presented and analyzed and the utility of pulse plasma technique in growing low residual stress DLC films is emphasized. Subsequently, sufficiently thick (2.2 μm) and hard (2000 kg/mm2) DLC films of significantly low stress (≈0.1 GPa) were deposited by the pulse plasma enhanced chemical vapor deposition (PECVD) technique. Stress values were found to be less than 0.5 GPa even with wide variation in pulse parameters (power density 0.4–2.0 W/cm2, dwell time 10–150 ms and duty cycle 10%–70%). A possible growth mechanism operating during pulse plasma discharge of such low residual stress and hard DLC films appears to involve the three phenomena: (i) relaxation of adions/adatoms, (ii) control of the substrate temperature, and (iii) creation of a hard/soft multilayer structure. To examine the role of substrate heating during the pulse plasma discharge, films were also deposited on deliberately heated substrates, using pulse plasma discharge, by using methane, acetylene, and benzene as hydrocarbon sources. An observation of direct correlation of the residual stresses and the degree of order of the film network has been made. Nitrogen dilution of the feedstock was also investigated, and further stress reduction has been observed, but not to the extent that occurs in continuous wave (cw) discharge grown films. This may be because constituent atoms in the film already approach close to a critical coordination number set by the fully constrained network (FCN) model. Other film properties like optical band gap (Eg), refractive index, and room temperature electrical conductivity (σRT) have also been estimated.