Contrast enhanced photoresists—processing and modeling

This paper will describe a new concept for the production of high contrast photopatterns. The method is designed to produce good quality patterns with very low contrast illumination through the use of photobleachable materials in conjunction with standard photoresists. A very thin bleachable layer is first applied to the photoresist surface. Following conventional exposure, the layer is removed and the resist developed in the ordinary way. As a result of the presence of the bleachable material, the contrast of the illumination that reaches the photoresist is increased. It is for this reason that the technique is called contrast enhancement. The degree to which the contrast is enhanced depends on both the photochemical properties of the bleachable material and the dose required to expose the underlying resist. The paper will discuss properties required of the bleachable material in order to make the technique feasible, such as the magnitudes of the extinction coefficient and the quantum yield. Bleaching experiments on candidate materials for the characterization of these parameters will be described. Also to be discussed is a model of the bleaching dynamics, which was used to calculate the improvements in contrast that are achieved as a function of base resist sensitivity. The extra processing steps required by the presence of the bleachable layer will be covered. Submicron resist patterns that demonstrate the resulting improvement in contrast will also be shown.