ON-AXIS AIR GAGE FOCUS SYSTEM

摘要

A lithography tool having an improved focus system. The focus system comprises a lens mounted in a nosepiece which defines a chamber. The chamber defines an onifice through which the lens system may see a workpiece. An air supply is provided to supply a regulated and measured air flow to the chamber. By measuring the air flow into the chamber, the rate of air flow through the orifice may be determined. The rate of air flow through the orifice is proportional to the gap between the orifice and a workpiece.