The minimum gate pitch for the 65nm device node will push 193nm lithography toward k1 ~ 0.35 with NA = 0.85. Previous work has analyzed the challenges expected for this generation. However, in the simplest terms, optical lithography for the 65nm node will be difficult. Lithographers are, therefore, looking into high-transmission attenuated phase shift mask (high-T attPSM), where T > 14%, to improve process margins. The benefits of a high-t attPSM are substantial, but drawbacks like inspection difficulty, defect free blanks manufacture, and sidelobe printing may make the use of such masks impractical. One possible solution to this problem is to employ medium transmission (med-T) attPSM, such as T = 9%, to image critical levels of the 65nm node with 193nm lithography. Earlier work shows that the problems High-T attPSMs face are manageable for med-T attPSM. Sidelobe printing in particular will be treated in this work with simulation and experiment. A primary goal of this effort is to determine if the lithographic benefit of moving from industry-standard 6% attPSM to 9% attPSM is worth the risks associated with such a transition. This goal will be met through a direct comparison of experimental 0.75NA 193nm λ results for 6% versus 9% attPSM on gate, contact/via, and metal layers at 65nm generation target dimensions with leading edge resists. Additional information on the inspectability and reticle blank manufacture of % AttPSM will also be given to provide a cohesive analysis of the transition tradeoffs.
Contact patterning for the 65nm device generation will be an exceedingly difficult task. The 2001 SIA roadmap lists the targeted contact size as 90nm with +/-10% CD control requirements of +/-9nm. Defectivity levels must also be below one failure per billion contacts for acceptable device yield. Difficulties in contact patterning are driven by the low depth of focus of isolated contacts and/or the high mask error (MEF) for dense contact arrays (in combination with expected reticle CD errors). Traditional contact lithography methods are not able to mitigate both these difficulties simultaneously. Inlaid metal trench patterning for the 65nm generation has similar lithographic difficulties though not to the extreme degree as seen with contacts. This study included the use of multiple, high transmission, 193nm attenuated phase shifting mask varieties to meet the difficult challenges of 65nm contact and trench lithography. Numerous illumination schemes, mask biasing, optical proximity correction (OPC), mask manufacturing techniques, and mask blank substrate materials were investigated. The analysis criteria included depth of focus, exposure latitude and MEF through pitch, reticle inspection, reticle manufacturability, and cost of ownership. The investigation determined that certain high transmission reticle schemes are strong contenders for 65nm generation contact and trench patterning. However, a number of strong interactions between illumination, OPC, and reticle manufacturing issues need to be considered.
The 65nm device generation will require steady improvements in lithography scanners, resists, reticles and OPC technology. 193nm high NA scanners and illumination can provide the desired dense feature resolution, but achieving the stringent overall 65nm logic product requirements necessitates a more coherent strategy of reticle, process, OPC, and design methods than was required for previous generations. This required integrated patterning solution strategy will have a fundamental impact on the relationship between design and process functions at the 65nm device node.
Semiconductor manufacturers are increasingly focusing on contact and via layers as the most difficult lithography pattern. Focus and exposure latitude, MEF, as well as iso-dense bias are challenges for contact patterning. This situation is only expected to worsen for the 65nm device generation where the 2001 SIA roadmap update lists the contact size as 90-100nm in 2004-2005. Thus, new contact pattern techniques with novel manufacturability are required. One possible avenue to meet these stringent process control requirements is the use of tri-tone high transmission attenuated phase shifting masks (tri-tone AttPSM) for the 65nm generation.
Multilayered SiN/TiN (9%-18%) EAPSM materials to manufacture advanced reticles were used in this investigation. Extensive study during the photomask processing (Front End and Back End) to access any issues related to the making of High %T tri-tone product types was performed.
Finally, the 2 prototype reticles were evaluated on a 193nm scanner (0.75NA) with various illumination settings to generate imaging to support the 65nm node technology generation.