Investigation of the notching effect for single layer deep ultraviolet resist processing

In order to extend the application limit of single layer resist processing to 0.25 μm pattern formation, the influence of resist thickness on reflective notching effects was investigated, using a two-dimensional resist profile simulator with the vector model. As the resist thickness increased, the reflective notching was varied periodically. Resist profile degradation due to reflective notching was maximum at the resist thickness where resist sensitivity was maximum (Emax), and was minimum at the resist thickness where resist sensitivity was minimum (Emin). The reflective notching was strongly dependent on the effective exposure dose Eeff at the bottom of the resist film, defined as the product of resist transmittance and optimum exposure dose Eopt. These simulation results were verified experimentally. It was concluded that the resist thickness should be set to minimize exposure dose for the reduction of reflective notching effects.