Illuminating the Edge: Why Sidewall Imaging is Critical in MicroLED Inspection

As microLED devices continue to shrink in size and expand in application, new frontiers of failure analysis and quality assurance are emerging. Among the most critical, and often overlooked, is the microLED sidewall. These vertical edges, formed during the etching process, can be deceptively small yet disproportionately influential in determining device performance. Advanced sidewall imaging is no longer a luxury for R&D teams; it’s an essential capability for any manufacturer aiming to optimize yield, efficiency, and reliability.

What Are Sidewall Defects?

Sidewall defects arise during microLED fabrication, particularly in plasma or chemical etching steps used to define individual pixels. These processes can introduce roughness, physical damage, or residues on the vertical facets of each emitter. At the micro- and nanoscale, these imperfections become highly consequential: they create surface states that act as non-radiative recombination centers, reducing the device’s light output and operational lifetime. As microLED pixel sizes fall below 10 µm, these effects are magnified – making precise sidewall analysis a strategic imperative.

Why Traditional Imaging Falls Short

Most standard inspection techniques, such as photoluminescence (PL) or electroluminescence (EL), are designed to evaluate the emission profile from the top surface of the device. While effective for detecting central defects or assessing uniformity, these approaches are blind to issues lurking on the sides. That’s where sidewall imaging comes into play.

Sidewall measurements, i.e. characterizing the structural and optical properties of the vertical side edges of microLED devices, can be highly indicative of LED health and functionality. By analyzing the sidewall morphology and emission, researchers can assess the quality of the etching process, identify any defects or irregularities that may affect device performance, and optimize fabrication techniques. Additionally, sidewall measurements can provide valuable information about light extraction efficiency, as the sidewall roughness and angle can influence the amount of light emitted from the device. By carefully controlling the sidewall parameters, engineers can maximize light output and improve overall microLED efficiency (Fig. A).

Fig. A: A combined image of 3D topographic AFM map of a microLED sidewall, with high-resolution EL map, revealing structural asymmetries and optical intensity variations. Scale represents range of relative optical power.

InZiv’s Approach to Sidewall Imaging

At InZiv, we’ve integrated sidewall imaging capabilities directly into our OmniPix 3.0, using our proprietary nano-EL imaging with resolution of 100nm and resulting in optical power distribution, not only from the top, but also at configurable angles to capture sidewall data. Our systems reveal both topographical and emission-based sidewall characteristics, helping engineers:

• Identify defects missed by standard PL/EL techniques
• Evaluate process-induced damage
• Quantify edge roughness and slope
• Optimize passivation layers and etching chemistries

These insights support more precise process tuning, and ultimately, higher-yield manufacturing.

In the microLED world, performance isn’t just about what you see on the surface. Sidewalls – though literally on the edges – are at the center of many key challenges in microLED reliability and efficiency. Advanced sidewall imaging not only reveals hidden failure modes but also empowers smarter fabrication. At InZiv, we’re proud to lead the way in making this critical measurement accessible and actionable.