Ion Beam Sputter Deposition of Dielectric Films on Large Optical Substrates
Homogeneous deposition on large, planar optical substrates using state of the art electron beam evaporation sources has been challenging due to point-type sources and the lack of a sophisticated movement system for them. Alternatively, the utilization of ion beam sputtering (IBS) has the advantage of higher energy of the sputtered material (i.e. temperature) arriving at the substrate, compared to competing techniques. Therefore, IBS commonly yields denser films with properties closer to the respective bulk materials.
Al2O3 was deposited as an anti-reflective coating on an optical glass. The process was conducted reactively from the metallic aluminum target. Oxygen was added as a reactive background gas. The substrates dimension was 500 mm x 300 mm. Uniformity was controlled by a constant velocity linear movement of the substrate stage and by the use of shapers. Static deposition rate of Al2O3 was 7 nm/min. The deposited film thickness was in-situ monitored by a software integrated quartz crystal oscillator and used as an end point signal. Film thickness measurements were conducted on a Sentech SE400 ellipsometer. Measurement of the large sample area was done on five 150 mm substrates. Reproducibility was determined from three subsequent process runs (see Fig. 1).
Static deposition rates of different materials:S
ilicon (Si): 3.0 nm/min, aluminum (Al): 5.5 nm/min, molybdenum (Mo): 3.5 nm/min, titanium (Ti): 2.8 nm/min, aluminum oxide (Al2O3): 7.0 nm/min
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- IBS on large substrates up to 500 mm x 300 mm or 300 mm diameter
- Translation and/or rotation of substrate stage fully CAM controlled for creation of gradient layers etc.
- Target drum for 6 water-cooled targets for automated deposition of multilayer films
- Recipe selectable shaper for target specific control of homogeneity
- Uniformity up to 2 % on large substrates and 0.5 % on 200 mm wafers