Advanced Wet-Etch-Only Process for Complete Tri-Layer Rework

A tri-layer patterning is used for high numerical aperture immersion lithography at 28 nm node. The tri-layer consists of a photoresist (PR) deposited on silicon containing anti-reflective coating (SiARC) above an organic planarization layer (OPL). Defective PR layer (e.g. overlay, over-exposure, residues) are repeatedly being reworked in high volume manufactories. Since selective PR removal has some disadvantages for the remaining SiARC (residues, roughness increase, thickness loss, optical properties modification) commonly, the complete tri-layer stack is removed and reprocessed. Due to the different chemical composition of the three layers, multiple etch processes (e.g. dry-wet-dry) are necessary.

In this work we investigate a wet-etch-only tri layer rework approach that takes advantage of a lower material damage, cost reduction and an increased throughput possibility. A complete removal and low defect levels on patterned 300 mm wafers have been required.

The screening of various ULSI chemicals according to their removal ability and selectivity to functional layers (TiN hardmask and TEOS cap) enabled a wet-etch-only process on an industry standard single wafer tool. Ellipsometric spectroscopy, cross-section scanning electron microscopy (X SEM), Transmission Electron Microscopy (TEM) and defect scans confirm these results.