1Key Laboratory of Material Science and Technology for High Power Lasers, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
2Graduate School of Chinese Academy of Sciences, Beijing 100049, China
Ming Fang, Dafei Hu, Jianda Shao. Evolution of stress in evaporated silicon dioxide thin films[J]. Chinese Optics Letters, 2010, 8(1): 119
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The evolution of stress in evaporated SiO<sub>2</sub>, used as optical coatings, is investigated experimentally through in situ stress measurement. A typical evolution pattern consisting of five subprocedures (thin film deposition, stopping deposition, cooling, venting the vacuum chamber, and exposing coated optics to the atmosphere) is put forward. Further investigations into the subprocedures reveal their features. During the deposition stage, the stresses are usually compressive and reach a stable state when the deposited film is thicker than 100 nm. An increment of compressive stress value is observed with the decrease of residual gas pressure or deposition rate. A very low stress of -20 MPa is formed in SiO<sub>2</sub> films deposited at 3×10<sup>-2</sup> Pa. After deposition, the stress increases slightly in the compressive direction and is subject to the stabilization in subsequent tens of minutes. In the process of venting and exposure, the compressive component increases rapidly with the admission of room air and then reaches saturation, followed by a logarithmic decrement of the compressive state in the succeeding hours. An initial discussion of these behaviors is given.