Spin-on trilayer scheme: enabling materials for extension of ArF immersion lithography to 32nm node and beyond
2008
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.
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