Selection of attenuated phase shift mask compatible contact hole resists for KrF optical lithography

Abstract

Multiple contact hole resist samples from a variety of DUV resist suppliers, including both acetal and ESCAP chemistries are evaluated on an organic anti-reflective under layer (ARC) using an attenuated phase shift mask (APSM). One sample exhibited excellent surface inhibition and superior lithographic performance for patterning contact holes of 0.2 μm imaging size. For most of resists, the process windows are limited by unwanted sidelobe printing through focus. The sensitivity of sidelobe printing to focus can be attributed to lens aberrations. For the first time, we propose to use Depth-of-focus (DOF) loss PWLdof and Exposure latitude (EL) loss PWLel to characterize resist surface inhibition, as we discovered that DOF loss is a sensitive measure of surface inhibition. Similar lithographic performance is obtained from acetal and ESCAP based materials. The two ESCAP resists EB3 and EA2 have better oxide etch resistance than the acetal resist AC1. The top surface reticulation is observed on ESCAP resists EB3 and EA2 during the oxide etch, but not on the acetal resist AC1. 110 nm underexposed resolution is achieved with the resist EA4 at a mask size of 250 nm. Faster resists generally exhibit better resolution but have smaller process windows when side lobe printing is included as a criterion. Selection of a resist formulation for attenuated phase shift applications has to face a compromise between resolution, photospeed, process window and surface inhibition. Finally, ARC operational modes and optical properties had little effect on sidelobe printing, and optimization of PEB temperature is important in suppressing sidelobe printing.