Customized Index Optical Films by Pulsed Dual-Magnetron Co-Sputtering

David Christie, W. D. Sproul, D. Carter

Films with customized or graded index of refraction can be deposited by reactive co-sputtering. The optical coating designer may then use these options to create new classes of coatings. In reactive co-sputtering, two adjacent targets are sputtered so material from each target, and reactive gas, impinge on the work piece, making a compound on its surface. For example, if the targets are Al and Ti, and oxygen is the reactive gas, the index of the fi lm can be adjusted from about 1.66 to 2.4 by varying the magnetron powers. Previous barriers to reactive co-sputtering are overcome by current source pulsed supplies that can independently regulate power delivered to each magnetron (in dual magnetron sputtering), while eliminating disappearing anode effects. This is enabling technology for deposition of optical fi lms by reactive co-sputtering. We present optical films having a customized index of refraction deposited by pulsed mid-frequency reactive co-sputtering. We also show creation of films with a range of indexes by varying the relative power to each magnetron. This is accomplished by independent regulation of power to each magnetron by the pulsed power supply and appropriate reactive gas control.

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