| 摘要 |
Apparatus and methods are disclosed for performing microlithography of a pattern defined by a reticle that is divided (segmented) into multiple exposure units. During exposure of each exposure unit, appropriate focal-point corrections are made according to variations in feature density and feature distribution within individual exposure units. Each exposure unit is divided into multiple subregions. The proportion of the area of each subregion occupied by actual pattern features is determined. A mean (average) feature density in the exposure unit is calculated based on the minimum (not zero) surface area of features and the maximum surface area of features. Based on the result of such a calculation, the focal point for the exposure unit is adjusted as required using a focal-point correction lens.
|
