2510332 - February 2009
There is a strong dependence between the angle of illumination and the amount of light scattered into a projection pupil by multiple reflections from underneath the device mirrors when they are off. This is due to shape and reflectivity of the structure and materials used for constructing the layers under the mirrors, which tend to behave specularly. As the mirrors tilt to off, they expose more of this area under the mirror to the incoming illumination light.
Scattered light from the edges of the mirrors and mirror vias enters the projection lens pupil as a function of the illumination angle (see Figures 9 and 10).
Cone of constant elevation
θ = elevation angle φ = azimuth angle
Plane of constant azimuth
Figure 9. Scattering Incident-Beam Geometry
Azimuth angle (deg)
Elevation angle (deg)
Figure 10. Scattered Light Into Projection Pupil for Off-State Mirror, 10-Degree Device
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