Current EUV lithography pushes photoresist thickness reduction to sub-30 nm in order to meet resolution targets and mitigate pattern collapse. In order to maintain the etch budgets in hard mask open, the adhesion layer in between resist and hard mask has to scale accordingly. We have reported a grafted polymer brush adhesion layer used in an ultrathin EUV patterning stack and demonstrated sub-36 nm pitch features with significant improvement over existing adhesion promotion techniques . This paper provides further understanding of this class of materials from a fundamental point of view. We first propose a hypothesis of the adhesion mechanism, and probe key factors that could affect adhesion performance. The grafting kinetics study of polymer brush that contains different functional groups to the substrate shows grafting chemistry, time, and temperature are key factors that affect the printing performance. We then conduct a systematic study to understand printing capability at various pitches for different silicon-based substrates. By comparing the process window, we gain comprehensive understanding of the printing limits and failing modes with this approach. We provide a comparative study of a grafted adhesion layer vs. a conventional spin on BARC type material, including defectivity. Pattern transfer to hard mask with varied etch chemistry is conducted to understand the performance of polymer brush during etch.
The thin nature of EUV (Extreme Ultraviolet) resist has posed significant challenges for etch processes. In particular, EUV patterning combined with conventional etch approaches suffers from loss of pattern fidelity in the form of line breaks. A typical conventional etch approach prevents the etch process from having sufficient resist margin to control the trench CD (Critical Dimension), minimize the LWR (Line Width Roughness), LER (Line Edge Roughness) and reduce the T2T (Tip-to-Tip). Pre-etch deposition increases the resist budget by adding additional material to the resist layer, thus enabling the etch process to explore a wider set of process parameters to achieve better pattern fidelity. Preliminary tests with pre-etch deposition resulted in blocked isolated trenches. In order to mitigate these effects, a cyclic deposition and etch technique is proposed. With optimization of deposition and etch cycle time as well as total number of cycles, it is possible to open the underlying layers with a beneficial over etch and simultaneously keep the isolated trenches open. This study compares the impact of no pre-etch deposition, one time deposition and cyclic deposition/etch techniques on 4 aspects: resist budget, isolated trench open, LWR/LER and T2T.