Effect of surface hydrophobisation on the properties of a microporous phenylene-bridged organosilicate film

Abstract This study aims hydrophobisation of a microporous phenylene-bridged organosilicate film via its surface modification with hexamethyldisilazane (HMDS) vapour to adapt it for use as a low dielectric constant material for advanced microelectronics technology. The microporous organosilicate film was spin-coated with 1,4-bis (triethoxysilyl) benzene, followed by soft baking at 120–200 °C and annealing at 390 °C in N2. Subtractive porosity was added using a sacrificial template — Brij® L4. This 1,4-phenylene-bridged film possessed a large Young's modulus and small pore size. However, due to steric effects during the film formation, a large amount of unreacted silanol remained on the surface. The HMDS-induced hydrophobisation reduced the number of residual silanols and adsorbed water molecules, despite the small pore size. A decrease in the hydrophilicity of the film surface led to an increase in the WCA value as well as a decrease in the dielectric constant and dielectric loss tangent. Ellipsometric porosimetry showed that the open porosity decreased without changes in the pore size distribution as a result of silylation by the HMDS vapour. However, the Fourier transform infrared spectra showed limited time-dependant temperature stability of the –CH3 groups introduced by the HMDS vapour treatment. The decrease in open porosity during the heat treatment of the hydrophobised film was significantly reduced because of the strengthening of the pore walls. Consequently, this film demonstrated lower shrinkage and larger Young's modulus.