Wafer focusing measurement of optical lithography system based on Hartmann–Shack wavefront testing

• A technique for the wafer focusing measurement in optical lithography system is introduced.
• The measurement principle based on Hartmann–Shack wavefront is explained detailed.
• An experiment is processed to prove the feasibility and the focus measurement precision is indicated.

To improve the focusing measurement precision of wafer in optical lithography instrument (OLI), a method based on Hartmann–Shack (HS) testing principle is introduced. Defocus of wafer is immediately detected by measuring the image change between plane and spherical wavefront. As defocus is measured by every sub-lens of microlens array (MLA), serials of defocus position are calculated at single shot of CCD sensor. Choose the average in this measurement the outstanding advantage of this technology is the high accuracy and efficiency. With an experiment to validate the feasibility, the accuracy of focusing measurement is indicated as 20 nm.