edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 27 NO. 3 16 SPECTROSCOPIC CHARACTERIZATION AND DETECTION OF YIELD-KILLING DEFECTS IN MICRO-LED WAFERS Praveena Manimunda HORIBA, Irvine, California praveena.manimunda@horiba.com EDFAAO (2025) 3:16-19 1537-0755/$19.00 ©ASM International® INTRODUCTION The burgeoning demand for high-performance displays with enhanced brightness, reduced power consumption, and extended operational lifetimes has positioned micro-LED (µLED) technology as a leading contender to supersede existing organic light-emitting diode (OLED) and liquid crystal display (LCD) technologies.[1] The market for µLED displays is projected to reach USD 21 billion by 2028, driven by applications in automotive panels, smartwatches, mobile devices, and augmented reality (AR) glasses. Achieving the high pixel densities required for wearable and AR applications necessitates the fabrication of µLEDs with dimensions of 3 µm or smaller. However, the transfer of these micron-scale dies to the backplane and the inherent challenges in maintaining high production yields at such small dimensions remain significant hurdles to full commercialization.[2] Low yields directly translate to increased production costs, hindering the widespread adoption of µLED displays. The conventional µLED display manufacturing process (Fig. 1) involves two primary stages: the growth of an epitaxial wafer (epi-wafer) and the subsequent dicing and processing of this wafer to create individual LEDs with contact pads. Imperfections or defects introduced during the epitaxial growth stage critically impact the final performance of the fabricated µLEDs, leading to issues such as uneven color uniformity, reduced brightness, and the presence of nonfunctional (dead) pixels. Early identification and characterization of microscopic defects at the wafer level are therefore paramount for enhancing die yield and reducing manufacturing costs. While macroscopic defects and surface contaminants can often be identified using conventional imaging inspection tools, the detection and analysis of structural defects and epitaxial growth imperfections necessitate the application of advanced spectroscopic techniques. This article describes the utility of HORIBA’s multimodal spectroscopic metrology tools, specifically the LabRAM Odyssey and SMS320 systems, in characterizing µLED epi-wafers and identifying yield-killing microscopic defects through Raman spectroscopy, photoluminescence (PL) mapping, high-resolution PL spectroscopy, and time-resolved photoluminescence (TRPL). METHODS AND MATERIALS This study utilized commercially available 2-inch GaN-based epitaxial wafers emitting blue (~450 nm) and green (~532 nm) light. For defect identification and characterization, full wafer PL mapping was performed using a HORIBA SMS 320 system, integrated with 375 nm excitation source. The spatial resolution of the mapping was optimized to identify regions of nonuniformity. High-resolution PL spectroscopy was conducted on selected defect regions Fig. 1 Schematic illustration of µLED-based display production process.[2]
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