Tracing optimized condition for electron beam metrology of EUV photoresist pattern using low-landing energy

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 1^st 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 0_th and 1^st 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 0^th shrinkage and metrology uncertainty in lithography process is utilizing 1^st shrinkage (1^st CD – 2^nd 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.