Stress evolution of sol-gel-derived silica coatings during heating: The effects of the chain length of alcohols as solvents

The effects of the solvent on in-plane stress evolution were studied on sol-gel-derived silica gel coatings during heating. Si(OC₂H₅)₄-H₂O-HNO₃-ROH (ROH = CH₃OH, C₂H₅OH, n-C₃H₇OH, and n-C₄H₉OH) solutions were prepared where the mole ratio Si(OC₂H₅)₄:H₂O:HNO₃ = 1:8:0.01 and the volume ratio Si(OC₂H₅)₄:ROH = 1:1.1. Silica gel films were deposited by spin coating on Si (100) wafers 4 in. in diameter, and heated at 5 °C/min up to 500 °C, where in situ stress measurement was conducted by measuring the substrate curvature. The stress was tensile and increased with increasing temperature. The stress was found to be identical below 200 °C between the films prepared with different alcohols while the stress above 200 °C was larger in the order, n-C₄H₉OH < n-C₃H₇OH ≈ C₂H₅OH < CH₃OH, namely in the order of the boiling points of the solvents.