Application of two-wavelength optical heterodyne alignment system in XS-1

Abstract

ABSTRACT This article presents the alignment performance of the two-wavelength optical heterodyne alignment system in the x-raystepper XS-1. The alignment accuracy (mean+3) obtained by the double-exposure method with a single mask and a Sitrench wafer was better than 20 nm. The dependence of the alignment accuracy on Si trench depth indicated that the twowavelengths compliment each other and ensure a 3a of less than 20 nm. The alignment capabilities for other processed testwafers were also investigated by mix-and-match exposure. For etched Si02, and poly-Si film on a Si trench, an accuracybelow 20 nm (3cr) was obtained. For A1SiCu film sputtered on etched Si02, there appeared systematic alignment offsets (i.e.,die shift and rotation errors) depended on die position, which are thought to be due to a wafer-induced shift. The systematicoffset errors were eliminated by the use of a send-ahead wafer and corrections for individual offsets on each die, and thusthe alignment accuracy was improved to 20-40 urn (3cr) for each alignment axis. The two-wavelength heterodyne alignmentsystem ofthe XS-1 has sufficient potential for 130-nm lithography and below.Keywords: proximity x-ray lithography, stepper, two-wavelength optical heterodyne alignment, alignment accuracy,systematic alignment offset, processed wafers, wafer-induced shift