Variation in In‐Plane Stress during Densification and Crystallization of Titania Gel Coatings Deposited on Different Substrate Surfaces

Abstract

Titania gel films were prepared from a coating solution with a starting mole ratio of Ti(OC3H7i)4:H2O:HNO3:C2H5OH=1:1:0.2:30 on Si(100) wafers by spin coating, with and without sol–gel‐derived, fired silica, and titania underlayers. In situ measurement was conducted on the in‐plane stress in the titania gel films during heating up to 500°C at 5°C/min. Basically, for all the gel films, the in‐plane, tensile stress increases once with increasing temperature, and then decreases around the temperature of crystallization. The increase in stress was thought to result from the capillary pressure due to solvent evaporation and from the densification of the coatings. The reduction in stress around the temperature of crystallization was ascribed to the accelerated atomic diffusion in the coatings and to the difference in thermal expansion coefficient between the coatings and the Si wafer. However, when the stress–temperature curves were examined more in detail, differences were found in the variation in stress, depending on the underlayers. Then, the question of how the underlayers could induce the crystallization and relax the strain in the coatings was discussed.