Laser Lift-off Process

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Process flow for bonding and transfer 71 Experimental results Delaminated 3 μm thick 2” GaN film (not structured) wafer-bonded onto GaAs (left) and the corresponding GaN-free sapphire substrate (right) The transferred GaN film is essentially defect free, except for some peeledoff areas at the wafer rim. 72 28
Summary and conclusions The present state-of-the-art concerning the laser-induced lift-off of both thin and thick GaN films and heterostructures from sapphire substrates has been reviewed. The physical background of the laserinduced thermal decomposition of GaN by short intense pulses of KrF excimer lasers and the third harmonic of Nd:YAG lasers is discussed, and potential applications for rapid etching of GaN have been outlined. Of particular interest for future applications is the possibility to produce freestanding GaN films by laser lift-off of heteroepitaxial layers from transparent sapphire substrates. Specific applications include the production of freestanding GaN pseudosubstrates starting from thick HVPE grown epilayers, as well as the delamination of thin GaN device heterostructures for the purpose of wafer bonding onto foreign substrates or for flip-chip bonding in device technology. 73 Summary and conclusions Using optimized processes, the defect free lift-off of entire 2” wafers can be achieved for GaN film thicknesses ranging from 3 to 300 μm. Separation of thin device heterostructures from their sapphire substrates opens up new possibilities for the formation of electrical contacts, the extraction of photons, and for thermal management. Thick GaN films grown by HVPE can be removed from their sapphire substrates to obtain freestanding GaN pseudosubstrates for the homoepitaxial growth of high quality epilayers. The required processing steps, including surface preparation after laser lift-off, have been described and the structural and optoelectronic properties of homoepitaxial GaN layers deposited on freestanding pseudosubstrates have been investigated. All results suggest that the laser lift-off method may become a major technique in future III-nitride device technology. 74 29
Page 1 and 2: 7. An introduction to Laser Lift-O
Page 3 and 4: Bonding and transfer process 5 X-ra
Page 5 and 6: [William S. Wong, Michael Kneissl,
Page 7 and 8: A simulated temperature profile as
Page 9 and 10: Approach to integration 17 Free-sta
Page 11 and 12: LLO integration process 21 Cleaved
Page 13 and 14: CW laser diodes on diamond 25 Impro
Page 15 and 16: Laser lift-off (LLO) technique Ther
Page 17 and 18: - 0.5 mm Start 0.5 mm 0.5 mm Laser
Page 19 and 20: 46 47 19
Page 21 and 22: 50 53 21
Page 23 and 24: Thermally induced decomposition of
Page 25 and 26: Comparison between the maximal etch
Page 27: Experimental results Image of a HVP
Page 31 and 32: 77 78 31
Page 33 and 34: 81 Process flow for bonding and tra
Page 35 and 36: Room-temperature dc I -V characteri
Page 37 and 38: Forward I-V curves and Room tempera
Page 39: I-V characteristics of chemically l

Laser Lift-off Process

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