Abstract
SiO2 thin films are widely used in micro-electro-mechanical systems, integrated circuits and optical thin film devices. Tremendous efforts have been devoted to studying the preparation technology and optical properties of SiO2 thin films, but little attention has been paid to their mechanical properties. Herein, the surface morphology of the 500-nm-thick, 1000-nm-thick and 2000-nm-thick SiO2 thin films on the Si substrates was observed by atomic force microscopy. The hardnesses of the three SiO2 thin films with different thicknesses were investigated by nanoindentation technique, and the dependence of the hardness of the SiO2 thin film with its thickness was analyzed. The results showed that the average grain size of SiO2 thin film increased with increasing film thickness. For the three SiO2 thin films with different thicknesses, the same relative penetration depth range of ~0.4–0.5 existed, above which the intrinsic hardness without substrate influence can be determined. The average intrinsic hardness of the SiO2 thin film decreased with the increasing film thickness and average grain size, which showed the similar trend with the Hall-Petch type relationship.
Highlights
Tremendous efforts have been devoted to studying the preparation technology and optical properties of the SiO2 thin films [16,17,18,19], while little attention has been paid to their mechanical properties
The values of the surface roughness (Ra ), the root-mean-square (RMS) roughness and the height of irregularities at ten points (Rz ) of the three SiO2 thin films with different thickness were in the order of nanometer, which indicated that all three SiO2 thin films have good smoothness, ensuring the accuracy and consistency of the nanoindentation experimental results
It can be seen that the average grain size of SiO2 thin film increases with increasing film thickness, which is because it is easier for atoms to migrate on the surface of the silicon wafer, and the islands are gradually connected according to the thin film growth diffusion principle
Summary
Due to its good chemical stability, optical properties, dielectric properties, abrasion resistance and corrosion resistance, silicon dioxide (SiO2 ) thin films have received intensive attention within the technology and scientific community [1,2,3,4,5,6,7,8,9], and are widely used in micro-electro-mechanical systems, integrated circuits and optical devices [10,11,12,13,14,15]. Wang et al [35] studied the substrate effects on the mechanical properties of SiO2 thin films deposited respectively on K9 and two different of Y3 Al5 O12 (YAG) crystals by nanoindentation and nanoscratch tests, showing that the Young’s moduli of all films were similar, the damage mechanisms of SiO2 thin films on K9 and YAG were different, and the adhesive forces of the film on the films on YAG (100) and YAG (111) were much less than homologous film on K9. As the pressure changed from 0.27 to 1.33 Pa, the residual compressive stresses in the deposited films varied in the range from 440 to 1 MPa. The hardness and reduced elastic modulus values followed the same trend and declined with the increase of process pressure from 8.5 to 2.2 GPa and from 73.7 to 30.9 GPa, respectively. These research works rarely involve investigation of the thickness-dependent hardness of SiO2 thin films using the nanoindentation technique. The surface morphology, load-penetration depth curves and hardnesses of the SiO2 films with different thicknesses were evaluated
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