Improving Thickness Uniformity of Mo/Si Multilayers on Curved Spherical Substrates by a Masking Technique

• Published in: Coatings (Basel) Vol. 9; no. 12; p. 851
• Main Authors: Zhang, Zhe, Qi, Runze, Yao, Yiyun, Shi, Yingna, Li, Wenbin, Huang, Qiushi, Yi, Shengzhen, Zhang, Zhong, Wang, Zhanshan, Xie, Chun
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 2019
• Subjects: Bandwidths; Deviation; Direct current; Experiments; Laboratories; Magnetron sputtering; Masking; Microscopes; Motion systems; Multilayers; Nonuniformity; Numerical aperture; Planetary rotation; Radiation; Radius of curvature; Shadow masks; Telescopes; Thickness measurement
• ISSN: 2079-6412; 2079-6412
• DOI: 10.3390/coatings9120851

In this work, a masking technique was used to improve the thickness uniformity of a Mo/Si multilayer deposited on a curved spherical mirror by direct current (DC) magnetron sputtering with planetary rotation stages. The clear aperture of the mirror was 125 mm with a radius of curvature equal to 143.82 mm. Two different shadow masks were prepared; one was flat and the other was oblique. When using the flat mask, the non-uniformity considerably increased owing to the relatively large gap between the mask and substrate. The deviation between the designed and measured layer thickness and non-uniformity gradually reduced with a smaller gap. The second mask was designed with an oblique profile. Using the oblique mask, the deviation from multilayer thickness uniformity was substantially reduced to a magnitude below 0.8% on the curved spherical substrate over the clear aperture of 125 mm. Multilayers still achieved a smooth growth when deposited with obliquely incident particles. The facile masking technique proposed in this study can be used for depositing uniform coatings on curved spherical substrates with large numerical apertures for high-resolution microscopes, telescopes, and other related optical systems.