Estimation of shot counts in VSB writer using GDSII design data

Abstract

Photomask pattern writer requires high-speed data processing that is conducted concurrently with the variable shaped beam (VSB) writing. As input electron beam (EB) mask data, trapezoid data format is generally used for EB writing because of the easier handling than polygon data format. Recent years, volume of photomask pattern data is growing as the increase of pattern density that is caused by additional various subsidiary patterns of optical proximity correction (OPC). OPC in design rules of 65nm and below is getting approximately 1.5 times more complex than that in the former generation, which increases the photomask pattern data volume approximately 3 times larger. VSB writing time is accurately estimated by counting the total number of which are primitive figures generated in the data processing of EB writer from the trapezoid patterns in EB mask data. However, no feedback and layout modification can be taken to LSI designs and OPC, even though problems regarding mask manufacturability such as explosion of EB writing time is recognized after starting EB writing process. We developed a simulator that estimates the number of in VSB EB writing by original shot division method using design data GDSII instead of EB mask data. This simulator outputs total counts and density map of shots of EB writing in photomask layout as well as chip layout in a short time using multi-processing. We can use this software as a core function in our Mask-DFM solutions offering to LSI designers and CAD engineers in order to estimate mask manufacturability before they finish mask data tape-out, and this work can reduce cost and improve TAT in mask manufacturing.