Research on thickness uniformity correction of thin film by IBF

Abstract

Since it is difficult to control the lateral coating thickness with super high accuracy only in the depositing process, and the requirement of that is strict in deep ultraviolet lithography (DUV) objective or other systems, a method using Ion beam figuring (IBF) technique to correct lateral thickness non-uniformity of thin film has been developed, which can also be used to optimize optical elements’ surface profiles after it’s been coated. Experiments were done to test the correct effect of thickness non-uniformity by IBF. The substrate used in the experiments is a SiO 2 flat and the thin film material is TiO 2 . The thickness non-uniformity of the thin film is measured by interferometer and expressed as surface errors, which was about root mean square (RMS) value 1.2nm before IBF correction. After 2 iterative IBF process, the RMS value of TiO 2 thin film’s surface was reduced to about 0.5nm. The improvement of the surface profile indicates that the new proposed method is effective. The waviness and roughness of the TiO 2 thin film were also measured by white light interferometer and atom force microscope separately before and after IBF correction; the differences of the measured results indicate that the microstructure of the thin film doesn’t change too much. Finally the transmitted and reflection spectrums of the TiO 2 thin film were also measured and the variations of optical characteristics are discussed.