P‐6.4: Failure Analysis of Al Corrosion Issue at Complementary Metal Oxide Semiconductor Backplane Solder Process for 1980PPI Micro Light Emitting Diode Display

Abstract

Micro light emitting diode (LED) display fabricated on complementary metal oxide semiconductor (CMOS) backplane provide smaller size, higher contrast ratio and energy efficiency, can be accommodated to market applications such as augmented reality (AR)/virtual reality (VR). Hybridization of compound semiconductor Micro‐LED arrays with CMOS active matrix driver integrated circuit (IC) using flip‐chip technology is major solutions proposed, in which under bump metallurgy (UBM) and solder process is fabricated on CMOS backplane and followed by flip‐chip process with LED chips. In our experiment, AL corrosion issue at CMOS top metal electrode in UBM and solder process occurred during 1980PPI micro display fabrication. After scanning electron microscope (SEM) & focused ion beam (FIB) analysis, it's suspected that uneven passivation sidewall profile and poor bottom coverage of UBM metal at passivation sidewall induced developer liquid in following PR remove step penetrating to AL electrode surface and corrode it. Passivation etching recipe modification and UBM metal bottom coverage improvement could solve this issue