| 摘要 |
A process and apparatus are described for a projection system having improved depth of focus. This has been achieved by introducing into a standard projection system, of the type suitable for photolithography, both a quadrupole mask in the pupil plane of the illuminator lens and a phase-type filter in the pupil plane of the projection lens. Detailed data for the design of both these filters is provided. If these guidelines are followed the result is a projection system whose depth of focus has been increased to a sufficient degree to allow the formation, in a single exposure, of a photoresist wafer suitable for simultaneously etching both isolated and densely packed contact holes.
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