Dark field Double Dipole Lithography (DDL) for 45nm node and beyond

Abstract

factors around 0.3. Double dipole lithography (DDL) is becoming a popular RET candidate for foundries and memory makers to pattern the poly gate active layer [2, 3, 4]. Double exposure method or double pattern technique (DPT), [5, 6, 7] using ternary 6% attenuated PSM (attPSM) is a good imaging solution that can reach and likely go beyond the 45nm node. In this work, back end of the line (BEO L) metal like test structures were used for developing a model-based dark field DDL method. We share our findings of using DDL for patterning 45nm node trench structures with binary intensity mask (BIM) on a dry high NA ArF scanner. Key words: double exposure technique, DET, Double Dipole Lithography, DDL, Double Pattering, Model based layout conversion, Dark field, trench patterning. 1. INTRODUCTION Clear field DDL with immersion and polarization is a good RET solution for printing the poly gate layer. The main advantages of the clear field DDL technique are that it [5]: 1. resolves the scalability and printability problem for scattering bars (SB) or assist features (AF); 2. allows printing devices using high contrast dipole illumination; and 3. enables to apply linear polarization for patterning device structures based on model based layout conversion method. The ITRS roadmap uses the metal1 pitch as one of the fundamental measures for successive device generations (Table 1). This is because the metal pitch defines the dens ity of integration and is therefore the dimension that is driven the hardest from a pitch shrinking perspective. Presently the back end metal interconnects processing all utilizes a low-k dielectric with copper damascene integrati on scheme that requires printing small dimension trenches at very tight pitches. Due to the inherent high contrast for dipole illumination, it is a good illumination choice for imaging dense trench. Figure 1 shows the simulated normalized image log slope (NILS=CD*ILS) NILS for 45nm half pitch where mask CD varies from 45 to 100nm under versus different k