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As EUV direct patterning begins to hit its resolution limit, the need for EUV self-aligned double patterning (SADP) has arisen in order to reach sub-30 nm pitch. Currently, EUV resists suffer from several shortcomings, both in terms of roughness and resist budget. These constraints means using it directly as a mandrel material, as previously done for immersion lithography SADP is nearly impossible. Consequently, standard EUV SADP flows involve the transfer of the resist through a lithography stack and into a hard mandrel material, such as silicon nitride or amorphous silicon.1 Achieving line edge roughness (LER) and line width roughness (LWR) targets for an EUV SADP hard mandrel is significantly more challenging than for EUV direct print since the etch process needs to target a post etch CD of about half that of the lithographic CD. This aggressive shrink requirement usually involves degradation in roughness driven by high aspect ratios. To circumvent these issues, we have developed a new bottom up organic mandrel growth process, whereby the EUV resist can be grown to a height compatible with a resist mandrel SADP flow, while the roughness is improved and the critical dimension is controlled. This bottom up mandrel growth process is performed in an etch chamber and can therefore be easily coupled with other process steps. The mandrel height and critical dimensions can be easily tuned from the incoming lithography by changing the deposition and trim step times of the process. We have shown that this bottom-up grown mandrel can withstand typical ALD spacer process deposition. After spacer open, the organic material can be easily removed through an in-situ ash process before opening the underlayer. This integration will allow for the removal of the organic planarizing layer in the lithography stack, reducing the stack complexity, while also eliminating one of the major contributors to wiggling in the typical hard mandrel patterning scheme. In this paper, the performance of this new integration scheme was benchmarked against a more standard SADP flow. The roughness performance post mandrel formation and post spacer deposition for this new scheme is significantly improved over our standard EUV SADP baseline using a standard EUV SADP flow.
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