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.

Evaluation of Subretinal Implants Coated with Amorphous Aluminum Oxide and Diamond-like Carbon

“…Moreover, initially a film thickness of 150 nm (10,000 pulses) was targeted and yielded an actual film thickness of 110 nm, as determined by profilometry. However, this coating was not adhesive and tended to buckle and peel off easily indicating a high degree of internal stress in the film, which agrees with results published by Kumar [44]. When the target film thickness was lowered to 60 nm (5,000 pulses), pinhole free coatings were obtained.…”

Studies of nanostructured copper/hydrogenated amorphous carbon multilayer films

“…It appears that one can obtain thick a-C:H films with a multilayer structure of Cu/a-C:H, because interfacial layers present in the multilayer structure reduce the residual compressive stress in the films as the soft/hard structure provides the needed relaxation in the overall structure. The pulsed plasma grown soft/hard DLC layer and Si containing DLC multilayer structure concept for the relaxation of the residual stress has been reported by Kumar et al [26,27]. The soft Cu layer present in the multilayer structure acts as a metallic substrate for subsequent a-C:H layers and prevent the delamination of the multilayer structure.…”

Structurally Driven Enhancement of Resonant Tunneling and Nanomechanical Properties in Diamond-like Carbon Superlattices

“…32,33 However, the generation of high compressive stress is one of the mechanisms proposed for the growth of high sp 3 bonded DLC films. 34 Ferrari et al, 35 on the other hand, suggested that it is not only the stress that influences the sp 3 carbon bonding and vice versa but also that stress can be manipulated by rearranging the sp 2 C phase.…”