Effects of deposition plasma power on properties of low dielectric-constant plasma polymer films deposited using hexamethyldisiloxane and 3,3-dimethyl-1-butene precursors

We investigated the effects of deposition plasma power on the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of hexamethyldisiloxane and 3,3-dimethyl-1-butene as the precursor, which are referred to as plasma polymerized hexamethyldisiloxane:3,3- dimethyl-1-butene (PPHMDSO:DMB) films. As the deposition plasma power was increased from 15 to 60 W, the relative dielectric constants k of PPHMDSO:DMB films, increased from 2.67 to 3.19. After annealing at 450 °C, the films deposited at a deposition plasma power of 15-60W showed k values of 2.27-2.64. With increased deposition plasma power, the asdeposited and annealed films showed increased values of hardness and Young's modulus. For as-deposited films, deposited at a plasma power of 15-60W, the films showed a hardness of 0.13-2.0 GPa, and a modulus of 2.25-17.27 GPa. Annealed films, deposited at a plasma power of 15-60W, showed a hardness of 0.05-2.07GPa and a modulus of 1.66-14.4 GPa. The change in the k value and hardness of plasma polymer films as a function of deposition plasma power was correlated with fourier transform infrared (FT-IR) absorption peaks of C-H_x , Si-CH₃, and Si-O related groups. The as-deposited and annealed PPHMDSO:DMB films showed decreased intensities of C-H_x and Si-CH₃ peaks as the deposition plasma power increased. The reduction in the dielectric constant after annealing is mainly due to hydrocarbon removal in the film. Deconvolution of Si-CH₃ bending peaks of PPHMDSO:DMB films was performed to relate mechanical properties to chemical structures. The relative oxygen content in the O-Si-(CH₃)_x structure is analyzed in detail. Improvements in hardness and modulus of our films are attributed to an increased amount of O₃Si-(CH₃) in the Si-CH₃ structure.