Alignment method of self-aligned double patterning process

Abstract

Double patterning technology (DPT) is the best alternative to achieve 3x NAND flash node by 193nm immersion lithography before entering EUV regime. Self-aligned double patterning (SADP) process is one of several DPT approaches, and most likely be introduced into NAND flash manufacture. The typical single exposure process in 40nm node flash will become into multiple exposure job in 32nm node by DPT or SADP, and the overlay control among these multiple exposure will be highly restricted than single exposure process. To reach tight overlay spec. mainly relies on the contribution of alignment system of scanner, but the well alignment mark design with high contrast signal and outstanding sustainability are essential factor as well. Typically, the feature size patterned in SADP around 3x nm that is too narrow to form essential signals that is qualified to be the alignment mark and the overlay mark either. This paper, we will discuss 1. the performance of alignment algorithm on direct alignment and indirect alignment 2. different alignment mark design and 3. film scheme dependence (layer dependence). And experiment result show the new mark design performs sufficient contrast and signal for subsequent layer aligning process.