Stress analysis of high reflective multilayers fabricated by magnetron sputtering

In order to fabricate high reflective multilayer mirrors for 6.7 nm wavelength near B absorption edge, a series of Mo, B4C, Mo2C thin films and Mo/B4C, Mo2C/B4C multilayers were deposited using direct current (DC) magnetron sputtering technology. The thickness for all of the thin films is 30 nm, and the bi-layer number for both multilayer is 30. The period thickness is 3.5 nm, which were measured by grazing incidence-X-ray reflection(GIXR). Surface profiles before and after deposition were measured with a stylus profiler and the stresses were calculated by Stoney formula. The results indicate that all of the thin films show compressive stress, in which the B4C layer shows the biggest stress, and the compression stress of Mo2C layer is larger than that of the Mo layer. Both of the multilayer films show the compressive stress. Mo2C/B4C periodic multilayers have a smaller stress than Mo/B4C multilayers with a sharp interface and are a good material combination for extreme ultraviolet multilayer optics with a large number of bilayers.