Studies of Photo Resist Profile Improvement in 28 nm Implanting Layer’s Lithography Process without BARC

Abstract

Implant layer patterning at 28nm node is becoming challenging , due to decreasing CD and usage of non-uniform substrates without BARC. Nevertheless a prevalent LDD loop will not introduce BARC for the concern of cost and process complication. The considerable bottom reflectivity not only causes standing wave in photo resist but also introduces slight PR footing if the substrate topography is rough. In this paper, several factors of the implant litho process which impacts the PR profile and line width roughness (LWR) are studied. Firstly we changed the mask bias and simultaneously modified the exposure dosage, which is based on our previous study and will result in better photo resist profile. Secondly we studied the PR profile dependence on temperature of post exposure baking (PEB), we tried out the best temperature setting to improve PR footing. Thirdly we slightly shifted the focus offset during exposure away from the best focus defined by process FEM results, so that the photoresist profile is improved and meanwhile maintaining a large enough depth of focus for the process.