Effect of the Amount of Water for Hydrolysis on Cracking and Stress Evolution in Alkoxide-Derived Sol-Gel Silica Coating Films

Abstract

Silica sols were prepared by hydrolyzing tetraethoxysialne (TEOS) under acidic conditions at H₂O/TEOS mole ratios (r) of 2 - 10, and gel films were deposited on single-crystal silicon substrates by spin-coating. The gel films prepared were heated at a constant rate, where in situ observation was made with an optical microscope. Cracking occurred in the heating-up stage, and higher r′s resulted in cracking at lower temperatures. In situ measurement was also made on the stress in gel films subjected to heat-treatment by measuring the substrate bending with a laser beam. Tensile stress developed in the plane of the substrate in the course of heating, and higher r′s gave rise to higher stress, which was thought to be the origin of the cracking at lower temperatures.