Mid-Frequency Dual Magnetron Reactive Co-Sputtering for Deposition of Customized Index Optical Films

Reactive co-sputtering is a means to create films of customized or graded index of refraction. This gives the optical coating designer new options, and enables practical realization of new classes of coatings. Two neighboring targets may be sputtered such that material from both targets and reactive gas are incident on the workpiece, depositing a film consisting of a compound. For example, if one target is Si and the other Ti, with oxygen as the reactive gas, then the index of the film may be adjusted over a range of approximately 1.5 to 2.4 by varying the power to each magnetron. Factors limiting application of reactive co-sputtering include the disappearing anode effect when DC supplies are used, and difficulty adjusting the relative power to the magnetrons when mid-frequency AC supplies are used in dual magnetron sputtering. However, current source pulsed supplies can independently regulate power delivered to each magnetron (in dual magnetron sputtering), while eliminating disappearing anode effects. This enables reactive co-sputtering of optical films. We present optical films, having a customized index of refraction deposited by mid-frequency dual magnetron reactive co-sputtering, with independent target power regulation and show the ability to create films with a range of indexes.