مطالعات شبیه سازی تصادفی مقاومت مولکولی

The influence of resist molecular weight as well as its architecture becomes important in lithographic scales aiming at sub-45 nm resolution. The effects of processing and resist molecular geometry on line-edge roughness (LER) should be well understood in order to meet the ITRS lithographic specifications. In this work, two-dimensional simulations and comparisons of the LER between films of molecular resists and resist films made of oligomers with the same molecular diameter, showed that in all cases molecular resists have lower LER. Explanations of this behavior are proposed based on molecular architecture and the free volume distribution in the resist film. It was also found that the size of free volume regions is less in molecular resist than in the corresponding oligomers.

As resist feature sizes get smaller towards the sub-45 nm nodes, resist thickness become less than 100 nm, which introduces non-bulk behavior on the physicochemical properties of the resist films, due to interfaces and also the decreasing number of polymer chains which comprise the film itself. Therefore, the influence of resist molecular weight as well as its architecture becomes important in these lithographic scales [1], [2], [3], [4] and [5]. Experiments [6], [7], [8], [9], [10] and [11] and simulations [3], [4] and [5], have shown that low molecular weight resist materials could result in low line-edge roughness (LER) which is a critical parameter for the next technology nodes. Fig. 1 shows the effects of average degree of polymerization (for linear polymer chains) on LER as obtained from stochastic lithography simulations for a conventional type resist and a chemically amplified one [3]. It is seen that low LER levels are accomplished with short polymer chains and low acid diffusion lengths Motivated from this behavior, several molecular resists based on anthracene or other polycarbocycle derivatives, newly synthesized by our group, have been tested experimentally and characteristic main resist components are modeled with the stochastic lithography simulator in order to predict their LER behavior. One of the studied molecular resin architectures is shown in Fig. 2a and has code name M21. This molecule is one of a large series of similar polycarbocycles designed and synthesized by the Demokritos group [10], to be used as main components of molecular resists. Similar molecules had been also proposed few years ago as etch resistance additives [11]. Experimentally M21 molecular resist formulation resulted in sub-45 nm resolution under EUV exposure, [unpublished results; to be presented at MNC 2006]. In the current modeling level, only material properties closely related to dissolution are accounted explicitly and not other intermolecular or intramolecular properties, other than the excluded volume constraints. The effects of molecular geometry and size on LER will be investigated. Comparisons of the LER between films of molecular resists and resist films made of oligomers with the same molecular diameter will be presented

Two-dimensional simulations with a stochastic lithography simulator aimed at comparisons of the LER between films of a molecular resist model and resist films made of oligomers with the same molecular size or radius of gyration. The results showed that molecular resists have much lower LER. This was true both under no acid diffusion and with acid diffusion. This behavior is attributed, apart from the small and more compact size of the molecular resist, also to the distribution of the free volume in the films made from such materials, because, in their case, free volume size distribution is shifted in very small areas and mainly inter-molecularly, prohibiting easy acid diffusion.