Measurement of acid diffusion from PAG in photoresists by using TOF-SIMS with GCIB

摘要

The role of photoresist has become more important for down scaling of electric devises. One of the key factors which identify the photoresist is a diffusion of acid through the lithography process. The 'top coat method' was proposed for measuring the distance of diffusion of acid which was generated from PAG and calculating the diffusion coefficient. In this method, top coat material containing PAG (2nd layer) is coated on a PAG-free resist (1st layer), then the exposure and PEB processes are performed. The generated acid in 2nd layer during the exposure diffuses into 1st layer when the PEB is performed. After that, we can obtain the acid diffusion length based on the quantity of film removed by the development. In this work, we applied TOF-SIMS measurement with gas cluster ion beam (GCIB) etching to the samples that were prepared for top coat method. This measurement has revealed the distribution of diffusing PAG and residual protecting groups of the resin in the resist (1st layer). The diffusion length of the acid which is obtained by the top coat method has corresponded to the depth profile of the acid and the deprotection rate which is acquired by TOF-SIMS with GCIB. We can estimate the marginal deprotection rate which is needed for the development by the result of these two methods. It has also been clear that the distributions of acid shifted into the resist according to the PEB temperature.