Diffusion of acid and amine at resist/BARC interface

In chemically amplified (CA) resist process, photo-chemically generated acid is needed to diffuse in resist matrix to induce the de-blocking reaction. The concentration of acid in resist matrix should be constant during the post-exposure-bake (PEB) treatment. Organic bottom anti-reflective coating (BARC) is essentially important to provide reflectivity control for resist patterning. In some cases, the photochemically generated acid and amine added as a quencher can diffuse from resist layer to BARC layer, which causes the footing or undercut of resist patterns. In this study, we have devised novel concept to qualitatively observe the diffusion of acids and amines from resist layer to BARC layer and vice versa. The rate of de-blocking reaction of CA resist was used to estimate the amount of acid in resist layer. It was found that the acid in resist layer can diffuse into BARC layer and the acid in BARC layer can also diffuse into resist layer during PEB treatment. Diffusion efficiency of the acid at resist / BARC interface was dependent on the chemical structure of resist and crosslinking density of BARC materials. Diffusion of amines from resist layer to BARC layer was negligible.