In this example we examine the "classic" dome coater. Here the spherical dome has a radius of curvature of 100 cm. The rim of the dome is 65 cm above the source. The source is offset by 50.7 cm from the rotation center.
Without the aid of any masks, the thickness on the dome surface is remarkably uniform with a peak-to-valley nonuniformity of 0.69%, as shown in the display below. The thickness displayed is again in units of "nanometers per gram of material evaporated," assuming the material is magnesium fluoride with a density of 3.15 gram/(cubic centimeter). The material collection is a respectful 36.9%.
The thickness uniformity can be further improved with the use of correction masks. We now insert three uncoupled masks that are optimized through the mask-optimization program of V-Grade 5. They are positioned 40 cm above the source plane and at 0 degree, 120 degrees and 240 degrees on the azimuth angle, respectively, to accommodate three sources. These masks are very narrow, a mere 1 cm across in the widest position, as shown in the following mask panel.
With the masks, the thickness uniformity on the dome is further improved with a peak-to-valley nonuniformity of 0.08%; the associated material-collection efficiency is 36.6%.
The good uniformity exhibited here, with or without mask, could be misleading and unlikely to be realized unless the job is to coat very small flat substrates or to coat the dome surface itself. In the cases that follow, we will examine the coating of curved surfaces in the same coater.
