Effects of carbon nanoparticle insertion on stress reduction in hydrogenated amorphous carbon films using plasma chemical vapor deposition

Stress reduction in hydrogenated amorphous carbon (a-C:H) films is of considerable interest for improving their performance as protective films. Herein, we reduced the compressive stress of the films by inserting carbon nanoparticles (CNPs) between two a-C:H layers to form an a-C:H/CNP/a-C:H sandwich structure using a system of plasma chemical vapor deposition (CVD). We measured the deposition features of the CNPs via transmission electron microscopy (TEM) and assessed the dependence of the stress on the thickness of the second a-C:H layer as a parameter of surface coverage, C p . We represented the stress reduction as a function of C p ; mean size of large CNPs, and thickness of the first and second a-C:H layers. In addition, the surface and film morphologies were investigated using atomic force microscopy (AFM) and cross-sectional scanning electron microscopy (SEM). Compared with films without CNPs, those containing CNPs with 8.9 % C p showed 36 % lower stress when the thickness of the second a-C:H layer was similar to that of the first (154 nm). The deposited CNPs exhibited two size groups, with mean sizes of the small and large CNPs of 5 and 16 nm, respectively. Stress reduction was strongly correlated with the distance between large CNPs. The insertion of CNPs between a-C:H films affects the surface morphology of the second layer, and the stress decreases when the growth stage of the film starts transitioning from three-dimensional (3D) to two-dimensional (2D). (a) Capacitively coupled plasma chemical vapor deposition reactor (CVD). (b) Deposition procedure of a-C:H/CNP/a-C:H sandwich films using plasma CVD. a-C:H, hydrogenated amorphous carbon; CNP, carbon nanoparticles. (c) Dependence of the stress reduction, R , on coverage of CNP C p . Dashed line represents theoretical curve. (d) Cross-sectional scanning electron microscopy images of a-C:H films for each coverage of CNP ( C p = 0 %, 8.9 %). • Incorporating carbon nanoparticles into carbon films reduce the film stress. • Distance between nanoparticles is related to the stress reduction of the films. • Stress reduction ratio are formularized with features of nanoparticle deposition. • Film morphology are modified by nanoparticles, resulting to the stress reduction.