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

The various issues relating to the nature of high built-up stresses in diam ond like carbon (DLC) films are presented and analyzed and the utility of p ulse plasma technique in growing low residual stress DLC films is emphasize d. Subsequently, sufficiently thick (2.2 mu m) and hard (2000 kg/mm(2)) DLC films of significantly low stress (approximate to 0.1 GPa) were deposited by the pulse plasma enhanced chemical vapor deposition (PECVD) technique. S tress values were found to be less than 0.5 GPa even with wide variation in pulse parameters (power density 0.4-2.0 W/cm(2), dwell time 10-150 ms and duty cycle 10%-70%). A possible growth mechanism operating during pulse pla sma discharge of such low residual stress and hard DLC films appears to inv olve the three phenomena: (i) relaxation of adions/adatoms, (ii) control of the substrate temperature, and (iii) creation of a hard/soft multilayer st ructure. To examine the role of substrate heating during the pulse plasma d ischarge, films were also deposited on deliberately heated substrates, usin g pulse plasma discharge, by using methane, acetylene, and benzene as hydro carbon sources. An observation of direct correlation of the residual stress es and the degree of order of the film network has been made. Nitrogen dilu tion of the feedstock was also investigated, and further stress reduction h as 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 a lready approach close to a critical coordination number set by the fully co nstrained network (FCN) model. Other film properties like optical band gap (E-g), refractive index, and room temperature electrical conductivity (sigm a(RT)) have also been estimated. (C) 1999 American Institute of Physics. [S 0021-8979(99)02607-9].