18.6: A Study on Micro‐LED Laser Lift‐off (LLO) Technology Based on Excimer Lasers

Abstract

Micro‐LED is considered the next generation of display due to several advantages, such as long‐life, high contrast and brightness, splicing screen, etc. Mass transfer is the bottleneck that limits the manufacturing of Micro‐LED display at large volume, in terms of factors like temporary bonding‐laser lift off (LLO), pick‐up and metal bonding, and so on, among which the temporary bonding‐LLO is the first step yet has a defining impact to the final panel yield and cost. Temporary bonding‐LLO, to elaborate, is the process to bond LED chips onto a temporary substrate via a layer of glue, which holds the LEDs during the next step of LLO where laser blasts shot onto the buffer layer between the LED epitaxy layer and the epitaxy wafer, in order to separate the LED dies and the epitaxy wafer and leave on the temporary substrate. Based on the stickiness of the temporary bonding glue, temporary substrate (TS) can be categorized as strong bonding and weak bonding type, the former of which would have a stronger bonding force and a larger process window for LLO yet leaves difficultyfor pick‐up at a later stage. The latter, on the contrary, has a weaker bonding force and makes it easier to pick‐up, but during LLO the process window is smaller and demands higher LLO equipment stability, spot uniformity, accuracy, etc. We believe excimer laser, with such fine qualities, is the most promising candidate to achieve the required 4 high LLO yield.