2.1 The problem of imaging
The basic problem of imaging is shown in Fig. 2.1. Light from an illumination source passes through a photomask, which defines the patterns. The simple photomask illustrated here consists of two types of complementary areasâone type that is opaque, while the other is transparent. In this example, the transparent (or âclearâ) area is a long space of uniform width, and the optical and resist profiles shown in Fig. 2.1 are cross sections for this geometry. Some of the light that passes through the mask continues through a lens, which projects an image of the mask pattern onto a wafer.
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