Organosilicate Spin-on Glasses II. Effect of Physical Modification on Mechanical Properties

Abstract

Porous copolymer films were synthesized from a methylsilsequioxane:1,2-bis(trimethoxysilyl)ethane (MSSQ:BTMSE) matrix and either an aromatic-core or aliphatic-core porogen at 10, 20, or 30 wt % porogen loading. Films were characterized using scanning electron microscopy (SEM), IR spectroscopy, and ellipsometry. Depth-sensing indentation experiments were performed to measure apparent film modulus, E, and hardness, H. Indentation load-displacement traces and SEM images were used to determine the threshold load for cracking, Pc. The aliphatic-core porogen produced a greater porosity film than the aromatic-core porogen for 10 wt % loading and smaller porosity films for 20 and 30 wt % loadings. IR spectra, normalized for film thickness and density, indicated decreased O-Si-O networking in porous MSSQ:BTMSE films. The combination of increased porosity and decreased O-Si-O networking led to a decreased apparent E and H relative to the unmodified MSSQ:BTMSE film. However, low-porosity (approximately 7%), aliphatic-porogen MSSQ:BTMSE films are optimized relative to unmodified MSSQ with smaller dielectric constant and greater E and H.