Directed self-assembly of medium-chi and high-chi block copolymers for DRAM C/H patterning

State of the art DRAM devices utilize crosshatch self-aligned quadruple patterning (X-SAQP) as the primary process method to create the contact hole (C/H) patterns of the capacitor array. However, X-SAQP requires many process steps resulting in long cycle times and added costs. In addition, SAQP suffers from line-wiggling and pitch-walking defects as the geometry size is scaled down. One cost effective alternative to X-SAQP is to apply directed Self-assembly (DSA) materials as a pattern pitch splitting method to significantly reduce the number of processing steps. DSA shows great promise at solving the CD variance problem that impacts SAQP at a much-reduced cost; however, being a radically different type of process, it has a separate set of failure modes—namely, Dislocation defect and Pattern Placement Error (PPE). In this study we review the progress of block copolymers (BCP) development for C/H patterns covering a range of pitch sizes in a DRAM device. First-generation BCP comprised of PS-PMMA block copolymers were limited in performance at larger pitch sizes due to the slower kinetics of the system. For large pitch CH layouts, the modified PS-PMMA BCP and the effect of kinetic additives was studied to improve the dislocation defects and the pattern placement error. For smaller CH patterns of 30nm pitch, a new medium-chi (MChi) and high-chi BCP was developed to improve the local CD uniformity (LCDU) and pattern placement error. Finally, the paper will look ahead to pitch scaling below 30nm and the materials supply readiness of DSA.