Dual Damascene BEOL processing using multilevel step and flash imprint lithography

摘要

Step and Flash Imprint Lithography (S-FIM) in conjunction with Sacrificial Imprint Materials (SIM)shows promise as a cost effective solution to patterning sub 45 nm features and is capable ofsimultaneously patterning two levels of interconnect structures, which provides a high throughputand low cost BEOL process. This paper describes the integration of S-FIL into an industrystandard Cu/low-k dual damascene process that is being practiced in the ATDF at Sematech inAustin. The pattern transferring reactive ion etching (RIE) process is the most critical step andwas extensively explored in this study. In addition to successful process development, the resultsprovide useful insight into the optimal design of multilevel templates which must take into accountthe characteristics of both the imaging material and the dielectric layer. The template used in this study incorporates both the via and trench levels of an M2 (Metal 2) testvehicle that incorporates via chains with varying via dimensions, Kelvin test structures,serpentines, etc. The smallest vias on the template are 120 nm vias with an aspect ratio of 2.0and the smallest dense lines are 125 nm/175 nm with an aspect ratio of 2.9. Two inter-leveldielectrics (ILD), Coraland Black Diamond~were studied. No trench etch stop was incorporatedin the ILD film stack. A multi-step, in-situ etching scheme was developed that achieves faithfulpattern transfer from the sacrificial imprint material (SIM) into the underlying low k ILD withsurprisingly wide process latitude. This multi-step scheme includes the following etch steps: aresidual layer open, a via etch, a trench descum, a trench etch, and an SIM removal ash. Amongthese steps, the trench etch was found to be the most challenging to develop and it holds the keyto producing high aspect ratio dual damascene features. An etching chemistry based on twofluorocarbon gases, CF_4and C_4F_8, was found to be very effective in delivering the desired etchprofiles with optimal sidewall angle, minimal facet formation. The optimized etch process can beexploited to provide substantial size reduction and/or increased aspect ratio relative to thetemplate. In this way structures with final critical dimensions of 95 nm in vias with aspect ratio of3.0 and 67 nm/233 nm in dense lines with aspect ratio of 3.6 were demonstrated with wideprocess latitude. This enables manufacturing of the template at larger dimensions, whichsimplifies both fabrication and inspection. The successful development of the dual damascene RIE process at the second metal (M2) levelwas demonstrated in a mixed and matched build with an ATDF standard first layer metal (M1)process. The M1 dielectric was TEOS and was patterned by 248 nm lithography. The M2 and Vialevels used Coral as ILD and both levels were patterned simultaneously by S-FIL using MolecularImprint Imprio 55 and lmprio 100 imprint tools. This electrical test vehicle provided solid evidencethat S-FIL is fully compatible with industry standard dual damascene process.