Proceedings Article | 12 October 2018
Carmen Popescu, Alexandra McClelland, Guy Dawson, John Roth, Yannick Vesters, Dimitrios Kazazis, Yasin Ekinci, Wolfgang Theis, Danilo De Simone, Geert Vandenberghe, Alex P. Robinson
KEYWORDS: Line edge roughness, Extreme ultraviolet lithography, Molecules, Chemically amplified resists, Lithography, Optical lithography, High volume manufacturing, Photoresist materials, Diffusion, Stochastic processes
Recent tool and source advances make the introduction of EUV lithography into high volume manufacturing in the very near future inevitable. Whilst traditional chemically amplified resists will likely support the initial insertion, a wide range of materials options are being examined for future nodes, aiming to identify a photoresist that simultaneously meets the resolution, line edge roughness and sensitivity requirement. However, this issue represents a fundamental trade-off in lithography (the RLS triangle) and it is difficult to overcome. For instance, addition of quenchers in chemically amplified resists reduces the acid diffusion length and increases the resolution of the patterned features, but decreases the sensitivity, and impacts on material stochastics affecting the line edge roughness.
In this study we present results obtained with Irresistible Materials’ Multi Trigger Resist. The multi trigger concept enables high sensitivity patterning but also incorporates a quenching behaviour into the chemistry to improve resolution. The standard material consists of a base molecule – EX2, a crosslinker and a PAG. EUV light generates photoacids, as with a traditional chemically amplified resist, but the response of the resist matrix implements a logic-type function. Where two resist molecules are activated by two acids, in close proximity to each other, then the resist molecules will react catalytically and release both acids. When a resist molecule encounters a single acid in isolation then it will hold on to the acid, without itself reacting, thus removing the acid from the reaction. This behaviour allows a high sensitivity response at a certain dose threshold but turns the resist response off much more quickly (as a 2nd order reaction) as the dose decreases, leading to sharper lines and lower line width roughness.
We present results where the molecular structure was modified to create enhanced versions of the standard resin. This will offer higher cross-linking capability and better mechanical strength to reduce the LER, wiggling and defects, and thus ultimately higher resolution. We present the lithography performance of the MTR2 resist series which shows 16nm half pitch lines patterned with a dose of 38mJ/cm2, giving a LER of 3.7 nm when patterned using an NXE3300. We also present a new resist formulation using a crosslinker with a high opacity non-metallic atom attached, which has patterned 13nm lines at the Paul Scherrer Institute (14nm half pitch) and also 13nm lines on the MET tool at Berkeley (20nm half pitch) with an LER of 4.24nm. We also present the lithographic performance of the MTR3 resist series which is 10% faster than the MTR2 series when patterning with EUV lithography at PSI, and has achieved a 2.95nm LER at 16nm half pitch, and 3.80nm LER at 14nm half pitch at PSI. Performance across various process conditions is also discussed, including process conditions to reduce wiggling and improve LER.
