Verticle's Wet Etching Technology Ready for Mass Production of AlGaInP Red Micro-LEDs
US-based R&D company Verticle has announced that its wet etching technology is now ready for mass production of AlGaInP red micro-LEDs. A major hurdle in the commercialization of high-resolution micro-LED displays is reducing the size of LED chips while maintaining efficiency, with red micro-LEDs being particularly susceptible to efficiency drops compared to their blue and green counterparts.
The primary cause of this efficiency reduction is sidewall defects created during plasma-based mesa dry etching. Up until now, no viable alternatives to dry etching have been developed, so efforts have largely focused on mitigating damage through post-dry-etching techniques such as chemical treatment, annealing, and passivation. However, these methods offer only partial recovery and are less effective for the tiny chips required for high-resolution displays, where sidewall defects can penetrate deep into the chip, sometimes exceeding its size.
Because of this, the search for "defect-free" etching methods has been ongoing for years. Wet etching has long been considered a potential solution due to its defect-free nature, but its isotropic characteristics can lead to undesirable undercutting, making it unsuitable for the etching of small chips like micro-LEDs.
However, Verticle, a San Francisco-based firm specializing in LED and display technologies, has recently made a significant breakthrough. The company has developed a defect-free wet chemical etching process for AlGaInP red micro-LEDs, specifically targeting the challenges of mesa etching.
CEO Mike Yoo has stated that Verticle is prepared to scale this wet etching technology for mass production, accelerating the commercial adoption of micro-LED displays for applications ranging from large screens to near-eye displays.
Comparing Sidewall Defects in Wet and Dry Etching
To better understand the impact of sidewall defects, Verticle compared wet and dry etched AlGaInP red micro-LEDs using Cathodoluminescence (CL) analysis. In CL, an electron beam generates electron-hole pairs within the micro-LED surface, and radiative recombination in the undamaged crystal produces bright emission images. Conversely, non-radiative recombination in damaged areas leads to little to no luminescence.
CL images and spectra reveal a stark contrast between the two etching methods. Wet-etched AlGaInP red micro-LEDs exhibit much brighter emissions, with the emission area being more than three times larger than that of dry-etched LEDs, according to Mike Yoo.
Most notably, the sidewall defect penetration depth for dry-etched micro-LEDs is around 7 µm, while the depth for wet-etched micro-LEDs is nearly nonexistent, measuring less than 0.2 µm. Consequently, the effective mesa area of dry-etched red micro-LEDs is just 28 percent of that of wet-etched ones. These CL findings suggest that there are few, if any, sidewall defects present in the wet-etched AlGaInP red micro-LEDs.
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