All-Wet Stripping of FEOL Photoresist Using Mixtures of Sulphuric Acid

摘要

In today's semiconductor device fabrication flow, photoresist removal in front-end-of-line (FEOL)is most commonly achieved by applying a sequence of plasma ashing followed by a wet-clean step,usually with a sulfuric-peroxide mixture (SPM). This is followed by an aqueous ammoniumhydroxide-peroxide mixture (standard clean or SC1). However, changing design rules and theintroduction of new materials are creating a need for an all-wet resist removal process thateliminates the need for damaging plasma exposure. Neither batch (wet bench) systems, nor spraysystems that are typically used in FEOL wet cleans are ideally suited for all-wet resist stripping dueto the removed bulk resist residue, which tends to quickly block in-line filtration and subsequently,stays in the tank where it can redeposit on the cleaned wafer. Single-wafer cleaning systems havean inherent design advantage in that the amount of resist in the system per unit time is highlycontrollable as only one wafer at a time, per chamber, is being processed. Additionally, the fluid-flow characteristics and the chemical exchange rate on the wafer surface can be controlled withgreater precision in single-wafer than in batch systems. Ultimately, there are less defect transferpathways in a single-wafer system compared to a batch system.This paper discusses the capabilities of an all-wet resist removal process, using a sulfuric acid-basedmixture in a single-wafer Spin Processor. The effect of temperature and concentration of theoxidizing agent is examined. The impact on defectivity and material loss is also shown. The role ofrinsing as a method to avoid sulfate-based residues on the wafer surface is also discussed.