Development of Two-Layer Resist Technology for the Halftone Mask

Abstract

A halftone mask was used in a lithography process to reduce the number of steps required in semiconductor device manufacturing. Resist patterns with different film thicknesses were produced at same time using the halftone mask. When the halftone mask is used, the resist is exposed in the area where the sensitivity curve rises. Therefore, it is difficult to make the resist films with thicknesses of several tens of percent. Previously, we fabricated the three layer structure by inserting an intermediate layer composed of a water-soluble polymer between the two resist layers with different sensitivity. We realized that the film thickness of several tens of percent was obtained stably with only the lower layer resist remaining. However, three layer structure is not expected to much reduce the number of steps in lithography process because the coating repeated for three times is needed for fabrication of three layer structure. In this study, we demonstrated a two-layer coating without mixing using two kinds of i-line resist (hydrophilic negative-tone water-soluble resist and hydrophobic negative-tone chemical amplification resist) with different solubility values. Both were dissolvable into an alkaline developer. We thus accomplished a novel two-layer resist technology for the halftone mask.