A Novel Large-Area Photoresist Removal Process for Multi-wafer in Advanced Packaging by Surface Wave Plasma

With the wide application of redistribution layer (RDL) technology in advanced packaging, RDL structures become more sophisticated, the efficient and uniform removal of photoresist is increasingly critical to packaging quality. Traditional single-wafer methods struggle to meet the demands of large-scale, fine-pitch processing, highlighting the need for multi-wafer solutions. This study develops an optimized photoresist stripping process by combining surface wave plasma (SWP) with radio-frequency (RF) bias, using a waveguide-coupled microwave source and water-cooled design to support large-area treatment. Through Taguchi design and single-factor analysis, the effects of microwave power, bias power, oxygen concentration and gas flow rate on photoresist removal efficiency are evaluated. The stripping rate is most influenced by bias power, while non-uniformity is most strongly affected by oxygen concentration. Optimal results can be achieved under the conditions of 2600 W microwave, 1800 W bias and 90% O₂, with which a maximum stripping rate of 4592.1 Å/min is attained and a minimum within-wafer non-uniformity of 5.5% is obtained. Pure oxygen under moderate power is beneficial for achieving the lowest non-uniformity, and a higher gas flow rate brings about improvement of wafer-to-wafer non-uniformity (from 12.5% to 7.6%) but reduction of the stripping rate (~30.4%). The process combining SWP with RF bias provides an effective solution for multi-wafer photoresist removal, which is crucial for balancing the photoresist stripping rate and non-uniformity.