Proceedings Article | 16 October 2017
KEYWORDS: Line edge roughness, Lithography, Molecules, Extreme ultraviolet, Electron beam lithography, Chemically amplified resists, Electron beams, Diffusion, Stochastic processes, Metals
As the minimum lithographic feature size continues to shrink, the development of techniques and resist materials capable of high resolution (R), high sensitivity (S) and low line edge roughness (L) has become increasingly important for next generation lithography. However, the issue represents a fundamental trade-off in lithography (the RLS triangle) and it is difficult to overcome. Addition of quenchers in chemically amplified resists reduces the acid diffusion length and improves the line edge roughness and increases the resolution of the patterned features, but decreases the sensitivity, and impacts on material stochastics increasing the line edge roughness. One current approach to boost the sensitivity in organic resists has been the addition of metals by incorporating organometallic complexes or metallic clusters in the resist, but again this can impact the line edge roughness.
In this study we will introduce and explain the multi-trigger mechanism concept employed in our system. This enables high sensitivity without the need for additional metallic components in the resist, but also incorporates a quenching behaviour in to the chemistry to improve resolution. The standard material consists of a proprietary molecule – xMT, together with 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 subsequently 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 second order reaction) as the dose decreases, leading to sharper lines and lower line width roughness.
We present results where the xMT molecular structure was modified to create enhanced versions of the standard resin that will offer higher cross-linking capability, better mechanical strength to reduce the LER and ultimately higher resolution. The impact of high Z additives was also evaluated. The materials were patterned in electron beam lithography at 100 kV and also using EUV lithography at the Paul Scherrer Institute in Switzerland, and their lithographic properties were analyzed in comparison with our standard resist. Dense line and spaces at 14nm and 16nm half pitches were patterned, and results show with a dose to size of 25mJ/cm2 with LER of 3.3nm at 16nm half pitch with an enhanced version. The same half pitch is patterned at a dose of 17mJ/cm2 when a high Z additive is introduced, but with a higher LER value. Results from the MET are also presented. Isolated pillars and holes with a diameter of 25nm, and line and space patterns at 11 nm half pitch have been patterned using ebeam lithography in the enhanced xMT resist.
