Laser Lift-Off of the Sapphire Substrate for Fabricating Through-AlN-Via Wafer Bonded Absorption Layer Removed Thin Film Ultraviolet Flip Chip LED

Anil Kawan,Soon Jae Yu

doi:10.1007/s42341-020-00273-1

Abstract

In this study we report chip fabrication process that allows the laser lift-off of the sapphire substrate for the transfer of the GaN based thin film flip chip to the carrier wafer. The fabrication process includes 365-nm ultraviolet flip chip LED wafer align bonding with through-AlN-via wafer and sapphire laser lift-off. n-holes with the diameter of 100 µm were etched on the GaN epilayers for accessing n-type GaN. Through-AlN-via size was 110-µm and filled by Cu electroplating method for the electrical connection. Mechanical stabilization to prevent the GaN epilayers cracking and fragmentation during laser lift-off was achieved by utilizing epoxy based SU-8 photoresist support.

Highlights

Light emitting diode (LED) based on GaN has been intensively studied for longer period, as a result of which, visible LEDs based on GaN have higher light extraction efficiency [1]
Chip and pad isolation areas can be damaged by the relived stress and N 2 vaporization pressure formed by decomposition of GaN during the laser lift-off process [23, 24] because they are free standing without bonding to the carrier wafer
GaN epilayer on chip isolation was totally etched until sapphire substrate was exposed and SU-8 was filled in chip isolation trench as well as pad isolation trench where it is thought to support the fragile epitaxial structure

Summary

Introduction

Light emitting diode (LED) based on GaN has been intensively studied for longer period, as a result of which, visible LEDs based on GaN have higher light extraction efficiency [1]. The fabrication technology for visible LEDs has reached to the point of maturity. Technology development of the ultraviolet light emitting diode (UVLED) based on GaN has been slower [2]. The extraction efficiency of the 365-nm UV-LEDs based on GaN is very low compare to the visible LEDs and the reasons are GaN self-absorption property and low epitaxial quality. GaN has the energy bandgap of 3.4 eV and the absorption edge coincide with the wavelength of 365-nm, majority of the light originated from the active region is absorbed by the n-type GaN epilayer and undoped-GaN [8–14].

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Results

Conclusion