A method for exfoliating AlGaN films from sapphire substrates using heated and pressurized water

Abstract

Thin films of AlN, AlGaN, and AlGaN-based device structures of approximately 1 cm2 formed on a sapphire substrate were successfully exfoliated from the substrate by immersion in heated (115°C) and pressurized (170 kPa) water. These thin films were crystalline grown on periodically formed AlN nanopillars. The water was permeated through intentional voids formed in the AlGaN or AlN crystalline layers by using periodic AlN nanopillars. The exfoliated AlGaN exhibited clear X-ray diffraction peaks from its (0002) plane diffraction. Transmission electron microscopy confirmed that exfoliation introduced few additional dislocations and that the device structure was maintained.

Exfoliation mechanism of AlGaN-based thin films using heated-pressurized water

“…We reported a method for exfoliating AlGaN with a wafer size of 1 cm 2 fabricated on a sapphire substrate using deionized water under heated-pressurized saturated vapor pressure of 170 kPa and 115 °C using an autoclave apparatus. 19) This method involves exfoliating AlGaN templates formed on periodic AlN nanopillars via nanoimprinting and ICP etching with Cl 2 gas. These AlGaN templates are used as an underlying layer for UV-B LDs.…”

“…[20][21][22] Previously, it has been reported that AlOOH, Al(OH) 3 , and Al 2 O 3 are formed by reaction with water for AlN powders and polycrystalline substrates. [23][24][25][26] In the report, 19) an alteration layer is formed by heating and pressurizing water, and the alteration layer is identified as AlOOH using the X-ray diffraction method. 27) Nevertheless, the details of the exfoliation mechanism of the AlGaN film using heated-pressurized water have not yet been clarified.…”

“…Furthermore, a 5 μm thick −c-plane AlN sample was obtained by exfoliating AlN from the sapphire substrate using the heated-pressurized water method described in Ref. 19 and by chemically mechanical polishing the exfoliated surface. The exfoliated AlN was fixed onto the sapphire support substrate using resin (NAMICS Corp., SUF1575-9).…”

“…Thus, it was deduced that the main mechanism of this exfoliation is the etching of the aand m-plane due to the penetration of water under saturated vapor pressure into the AlN nanopillar area. 19) Moreover, the etching rate is relatively fast even for AlGaN with an AlN mole fraction of 0.62, suggesting that this method applies to AlGaN with various AlN mole fractions and is highly versatile. Furthermore, it is suggested that the proposed method applies to large-diameter AlGaN wafers if saturated vapor pressure water is allowed to penetrate the infiltrating AlN pillars.…”

Fabrication of vertical AlGaN-based ultraviolet-B laser diodes using a laser lift-off method

“…Among these methods, laser lift-off (LLO), [25][26][27][28][29][30][31][32] electrochemical etching, 33) grinding and polishing, 34) and heatedpressurized water 35,36) have been reported to exfoliate sapphire substrates. We focus on achieving LLO-based exfoliation at the 1 cm 2 square wafer level using AlGaN templates grown on periodic AlN nanopillars formed through inductively coupled plasma (ICP) etching and nanoimprinting on sapphire substrates.…”