Spin-on trilayer scheme: enabling materials for extension of ArF immersion lithography to 32nm node and beyond

Trilayer stacks with alternating etch selectivity were developed and extensively investigated for high NA immersion lithography at 32nm node and beyond. This paper discusses the fundamental aspects of the Si-containing BARC (Si-BARC) materials with ultra-high silicon content and carbon-rich underlayers that we developed. Designing of materials at a molecular level is presented. It was demonstrated that this fundamental understanding assisted in achieving satisfactory shelf life and excellent coating defect results. Prolith^® simulations using trilayer stacks showed superior reflectivity control for hyper-NA immersion lithography. The impact of high incident angles on substrate reflectivity was analyzed and this paper demonstrated that trilayer scheme provides wider process windows and is more tolerant to topography than conventional single layer BARC. Extensive resist compatibility investigation was conducted and the root causes for poor lithography results were investigated. Excellent 45nm dense lines performance employing the spin-on trilayer stack on a 1.2 NA immersion scanner is reported. In addition, pattern transfers were successfully carried out and the Si-BARC with high silicon content demonstrated outstanding masking property. In comparison to the theoretical %Si values, better correlation with etch selectivity was observed with experimental %Si. Furthermore, this paper addresses the wet rework of trilayer materials and results using Piranha rework are presented. Clean 12in wafers were obtained after reworking trilayer stacks, as evidenced by defect analysis.