Application of optical CD metrology for alternative lithography

Abstract

Directed self-assembly (DSA) and nanoimprint lithography (NIL) have been widely developed for low-cost nanoscale patterning. Although they are currently regarded as "alternative lithography," some papers show their potential to be candidates for next-generation lithography (NGL). To actualize the potential, the contribution of metrology engineers is necessary. Since the characteristics of the lithography techniques are different from those of conventional lithography, new metrology schemes correlated with each characteristic are required. In DSA of block copolymer (BCP), a guide is needed to control the direction and position of BCP. Therefore, it is necessary to monitor the relationship between the guide and the BCP pattern. Since the depth of guide or the coating thickness variation of BCP over guide influences the behavior of phase separation of BCP, 3D metrology becomes increasingly important. In NIL, residual resist thickness (RLT) underneath the pattern should be measured because its variation affects the CD variation of transferred pattern. 3D metrology is also important in NIL. Optical critical dimension (OCD) metrology will be a powerful tool for 3D metrology. In this work, some applications of OCD for alternative lithography have been studied. For DSA, we have tried to simultaneously monitor the guide and BCP pattern in a DSA-based contact hole shrinking process. Sufficient measurement accuracy for CD and shapes for guide and BCP patterns was achievable. For NIL, sufficient sensitivity to RLT measurement was obtained.