Impact of acid statistics on EUV local critical dimension uniformity

The goal of this work intends to explore the effects of different acid concentrations on LCDU and to utilize these experimental data to validate the LCDU analytical model for CAR with the final aim to predict the chemical limits of CAR. In this work, effects of acid deprotection, acid diffusion, acid-base interaction and PEB temperature on LCDU are studied by varying the PAG acidity, size, loading and quencher loading in chemically amplified resist. It was found PAG acidity, PAG anion size, quencher loading and PEB have significant influences on LCDU, while PAG loading has less significant influences. The EUV experimental results were then utilized to validate the LCDU analytical model. The model assumes that LCDU is directly proportional to normalized dose sensitivity (NDS) and photon-acid statistics, namely the photon or acid counting within blur range. In the above design of experience, PAG loading, quencher loading and PEB temperature affect resist sensitivity as well as diffusion length or blur length. Although acid diffusion reduction leads to shorter blur length thus smaller photon counting area, dose increment contributes to higher photon density in the counting area. Therefore overall acid and photon statistics is improved and LCDU generally decreased with reduced acid diffusion. However, such benefits disappear at certain level and the lower limit of LCDU of this resist platform is observed. Besides acid diffusion, NDS impacts LCDU through as well, which can be achieved by varying the PAG type. In summary, this work help to understand how to manipulate different resist compositions to impact NDS and acid diffusion in order to improve LCDU.