METHODS AND APPARATUS FOR DETERMINING FOCUS

摘要

Disclosed are apparatus and methods for determining optimal focus for a photolithography system. A plurality of optical signals are acquired from a particular target located in a plurality of fields on a semiconductor wafer, and the fields were formed using different process parameters, including different focus values. A feature is extracted from the optical signals related to changes in focus. A curve is fitted to the extracted feature of the optical signals as a function of focus. An extreme point in the curve is determined and reported as an optimal focus for use in the photolithography system.

主权项

1. A method of determining optimal focus for a photolithography system, the method comprising:
using an inspection or metrology apparatus, acquiring a plurality of optical signals from a particular target located in each of a plurality of fields on a semiconductor wafer, wherein the fields were formed using different process parameters, including different focus values; extracting a feature of the optical signals that are acquired from each field and related to changes in focus; fitting a curve to the plurality of fields' extracted features as a function of focus; and on a display of the apparatus, determining and reporting an extreme point in the curve as an optimal focus for use in the photolithography system.