Effects of Deposition Plasma Power on Properties of Low Dielectric-Constant Plasma Polymer Films Deposited Using Hexamethyldisiloxane and 3,3-Dimethyl-1-butene Precursors

Abstract

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 15–60 W showed k values of 2.27–2.64. With increased deposition plasma power, the as-deposited and annealed films showed increased values of hardness and Young's modulus. For as-deposited films, deposited at a plasma power of 15–60 W, 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 15–60 W, showed a hardness of 0.05–2.07 GPa 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–Hx, Si–CH3, and Si–O related groups. The as-deposited and annealed PPHMDSO:DMB films showed decreased intensities of C–Hx 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.