Modification of DLC films for MEMS applications

SiO_x-containing DLC films are deposited by plasma enhanced chemical vapor deposition on Si substrate. The effect of SiO_x dopants on the stress, adhesion and hydrophobicity of the DLC films are studied. The incorporation of SiO_x in the DLC films deposited by using hexamethyldisiloxane (HMDSO) and CH₄ mixture reduces the residual stress as well as enhances adhesion of the film on the substrate. Besides, the thermal stability of the film also improves. The incorporation of SiO_x in the DLC film, as deposited by using HMDSO/CH₄ mixture, can raise the water contact angle from 95°, as for the pure DLC film, to 110°. IR results show that the increase of contact angle is mainly due to the incorporation of a higher concentration of -CH₃ group in the HMDSO-deposited films. By adding O₂ with HMDSO, the contact angle of the deposited film can be reduced to 27°, showing hydrophilic property. By enhancing the surface roughness, the water contact angle can be further increased to 145° for the hydrophobic films deposited using HMDSO/CH₄, and the water contact angle can be further reduced to 3° for the hydrophilic films deposited using HMDSO/O₂.