A study of deblocking reaction of chemically amplified positive DUV resists

Deblocking reaction mechanisms and lithographic performance in chemically amplified positive KrF resist were investigated by analyzing acid concentration and blocking level. The resists consist of tetrahydropyranyl (THP) or tert-butoxycarbonyl (t-BOC) blocked polystyrene as the base resin and 2,4-dimethylbenzenesulfonic acid derivative as a photoacid generator (PAG). The deblocking reaction mechanisms and activation energy of the deblocking reaction were evaluated from Arrhenius plots of the deblocking reaction rate constant k d . It was found that the deblocking reaction is ruled by two rate-determining steps; it is reaction-controlled in the low-temperature region and acid-diffusion-controlled in the high-temperature region. The activation energy of THP blocked resists (THP resists) in the low-temperature region was lower than that of the t-BOC blocked resists (t-BOC resists). The THP groups were deblocked even at room temperature. Then the THP resist was hardly affected by air contamination. This is one of the reasons why the THP resist had good PED stability. Moreover, the linewidth difference between the isolated line and the dense line (iso-dense bias) of the THP resist was much larger than that of the t-BOC resist. It was concluded that the resist with a high deblocking reaction rate at room temperature had a clear advantage for PED stability, and that the activation energy of the deblocking reaction should be high at PEB (post-exposure bake) temperature to reduce iso-dense bias.