The importance of less damaged and surface sensitive metrology to identify true EUV process monitoring

The adoption of EUV technology in DRAM fabrication is primarily driven by the pursuit of higher device densities, improved performance, and increased energy efficiency. EUV's shorter wavelength (13.5 nm) enables enhanced resolution and finer patterning, enabling the production of smaller memory cells with reduced feature sizes. As the target patterning size is becoming sub-10nm, line edge/width roughness (LER/LWR) is the centerpiece in controlling uniformity of pattern going through the lithography process. Accordingly, it is essential to figure out the dedicated CDSEM metrology method for EUV step without any image quality degradation, charging issue, and e-beam damage that can hinder accurate diagnosis of the real process status. Empirically, it is highly difficult to predict the best metrology condition that fits to the specific resist material, dimension, and geometry due to complex stochastic effect caused by secondary electron inside photoresist (PR) material. Here we represent experimental results of PR damage caused by electron beam irradiation with different landing energy for both line and space (LS) pattern and contact hole (CH) pattern. The results enabled us to define the effect of the landing energy and geometry of pattern on the critical dimension (CD) and roughness. We examined electron irradiation induced damage by comparing etch bias of fresh location and e-beam exposed location on etch process step to fully understand shrinkage and deformation behavior. For the roughness measurement of CH pattern, we adopted new metric which enables us to quantify contact edge roughness and shape of contact. Utilizing various metrics, it was possible to observe damage on the process, which was not observed only by CD changes, and it was confirmed that the primary beam with low landing energy could be used to not only reduce damage but also enhance surface sensitivity of metrology without bias which is crucial for stochastic effect monitoring on the EUV process.