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.
With the extreme ultraviolet (EUV) lithography and its pitch scaling, the resist shrinkage from electron beam has returned to an important critical dimension (CD) control issue—unlike multi-patterning where the smallest CD is larger than 40nm. The resist height reduces to maintain the aspect ratio below 2:1 which is critical factor for the prevention of the resist collapse. This leads to huge challenges to minimize the shrinkage of resist during the scanning electron microscope (SEM) measurement. Accurate and precise metrology of chemically amplified resist (CAR) type EUV photoresist processed pattern utilizing classical beam energy for lithography pattern such as 500V is great challenging as electron beam exposure of 1st measurement already fully shrunk the pattern. Moreover, occurrence of carbonization along with shrinkage hinders finding best conditions for not only metrology optimization but also minimized process impact. In this work, we evaluated the magnitude of shrinkage of CAR type EUV photoresists with several approaches including 0th and 1st shrinkage estimation utilizing line & space pattern and contact hole pattern as a function of landing energy dose and static/dynamic repeatability method to distinguish behaviors of shrinkage and carbonization by controlling interaction time of photoresist to its environment. One approach to trace minimized 0th shrinkage and metrology uncertainty in lithography process is utilizing 1st shrinkage (1st CD – 2nd CD) analysis together with plotting absolute value of the 1st CD as a function of dose. The other approach to trace optimization condition was comparing exposed area with electron beam and non-exposed area achieved by comparing litho/etch consecutive process on the same area. Furthermore, model fits, a simulation study were also performed.
With the extreme ultraviolet (EUV) lithography and its pitch scaling, the resist shrinkage from electron beam has returned to an important critical dimension (CD) control issue - unlike multi-patterning where the smallest CD is larger than 40nm. The resist height reduces to maintain the aspect ratio below 2:1 which is critical factor for the prevention of the resist collapse. This leads to huge challenges to minimize the shrinkage of resist during the scanning electron microscope (SEM) measurement. Accurate and precise metrology of chemically amplified resist (CAR) type EUV photoresist processed pattern utilizing classical beam energy for lithography pattern such as 500V is great challenging as electron beam exposure of 1st measurement already fully shrunk the pattern. Moreover, occurrence of carbonization along with shrinkage hinders finding best conditions for not only metrology optimization but also minimized process impact. In this work, we evaluated the magnitude of shrinkage of CAR type EUV photoresists with several approaches including 0th and 1st shrinkage estimation utilizing line & space pattern and contact hole pattern as a function of landing energy dose and static/dynamic repeatability method to distinguish behaviors of shrinkage and carbonization by controlling interaction time of photoresist to its environment. One approach to trace minimized 0th shrinkage and metrology uncertainty in lithography process is utilizing 1st shrinkage (1st CD – 2nd CD) analysis together with plotting absolute value of the 1st CD as a function of dose. The other approach to trace optimization condition was comparing exposed area with electron beam and non-exposed area achieved by comparing litho/etch consecutive process on the same area. Furthermore, model fits, a simulation study were also performed.
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