Positive tone i-line photoresist with controlled undercut profile for advanced packaging

With the progress of advanced packaging, the RDL metal line and μBump stability and super electrical performance were highly concerned. The photoresist with undercut profile is required to obtain the RDL metal line and μBump with footing. The AZ® 3DT-400 series formulation is a chemically amplified positive-tone i-line photoresist developed by EMD Electronics which a special additive was introduced to generate the undercut profile. The undercut size and shape can be adjusted with the loading of the additive. After optimizing the formulation, the desired undercut length larger than 10% of the target CD and the undercut height less than 10% of target CD were achieved.