Efficient way of reducing contaminant induced by interactions between EUV photoresist and electron beam in CD-SEM: the route to carryover free SEM metrology

In SEM metrology, carbonaceous contamination is always troublesome because a SEM image is always influenced by non-zero carryover which mainly came from complex interactions between hydrocarbon and irradiated electron beam in the chamber. As device pattern design is getting shrunk, contaminant is getting more severe impact on the CDSEM metrology in terms of accuracy, precision, stability, and even tool to tool matching (TTTM) considering metrology budget of sub Å level. EUV lithography, dedicated to thinner pattern design, is widely utilizing chemically amplified resist (CAR) type EUV photoresists (PR) which contains photoacid generators (PAG). PAG interacts directly with the irradiated electrons during scanning (where, in practice, with cascaded low-energy electrons), which induces carbonaceous outgassing sources hindering accurate measurement of pattern surface – as a result, data fluctuations in the short term, and over time, may result in data trend issues, ultimately leading to chamber contamination and degradation of part quality. Previously, this non-invited contaminant was hindering EUV scanner lens’s durability and performance and now it’s started to invade SEM metrology tool as well. An efficient way of contamination control is critical for maintaining tool stability and long-term performance. In this work, we verified new way of reducing and controlling contamination both at R&D lab and HVM fab environment. In R&D lab, we mainly focused on whether the method is working as what we intended, and the operating condition was roughly optimized. In high volume manufacturing (HVM) fab environment, we identified efficiency and carefully verified whether there is any side effect. Verifying its efficiency, we intentionally contaminated the chamber and was monitored by slope -carryover value by iterated measurement on the same place-, quality control (QC) CD trend variation, and thermal desorption–gas chromatography–mass spectrometry (TD-GC-MS). It was verified that contaminant generated from interactions between electron beam and EUV PR is effectively removed by verifying slope, QC CD trend and TD-GC-MS results. We also explored impact of new method for the TTTM in the sub Å level and route to carryover free SEM metrology.