Stress Adjustment and Bonding of H-Implanted 2 in. Freestanding GaN Wafer: The Concept of Double-Sided Splitting

Abstract

Heterointegration of thin layers obtained from freestanding GaN wafers by the Smart-Cut process faces major challenges due to strong wafer bowing. The post-implantation bow was found to range between ϳ40 and 60 m for 2 in. wafers, prohibiting any bonding of H-implanted GaN. Here, we demonstrate that stress engineering by back-side implantation is an effective strategy to manipulate the bow to meet the criterion of long-range flatness. Based on our approach, high-quality bonding of a 2 in. freestanding GaN wafer onto sapphire was achieved. An efficient method to transfer thin layers from freestanding GaN is proposed.Light-emitting diode ͑LED͒ solid-state lighting is one of the strategies toward achieving the reduction of greenhouse gas emissions and energy consumption. GaN and related material heterostructures have been the building blocks of LED-based devices. 1 These heterostructures also provide a wide spectrum of applications in data communications, sensing, optoelectronics, and biophotonics. However, the potential of these devices is still limited by the quality of the grown materials. Presently, GaN used in device fabrication is epitaxially grown on sapphire despite its poor lattice and thermal match to GaN. The densities of misfit and threading dislocations in GaN layers deposited on sapphire range typically from 10 8 to 10 10 cm −2 , whereby the efficiency of GaN devices is limited. High-quality GaN bulk substrates can be produced by hydride vapor-phase epitaxy growth of thick GaN layers on foreign materials 2 and subsequent separation from the substrate. The current cost of these freestanding ͑fs-͒GaN wafers is still so high that the concept of transfer of several layers from one fs-GaN wafer to appropriate host substrates by the ion-cut process 3 is technologically and economically highly attractive. The most critical step in this process has to do with wafer bonding. Several surface imperfections and flatness deviations of the fs-GaN wafer ͑so-called device wafer in general͒ can limit the bonding to small areas or even forbid the direct and spontaneous wafer-bonding process and can negatively affect the thin-layer splitting process. 4 One of the major problems faced in direct bonding of 2 in. fs-GaN wafers is the strong enhancement of the bow due to H implantation. 5 In this work, we present an approach to manipulate the implantation-induced bowing phenomenon. By strain engineering at the back side of the H-implanted fs-GaN wafer, we reduced the post-implantation bow to meet the bonding criterion of long-range flatness. Consequently, high-quality wafer bonding of the H-implanted 2 in. fs-GaN wafers to sapphire handle wafers was achieved. Based on our approach, we present an efficient and cost-effective process for fs-GaN bonding and, ultimately, layer transfer. This article focuses specifically on different issues related to the bonding process. The optimization of postbonding steps and characterization of the transferred layers will be addressed elsewhere.Experimental ϳ300 m thick 2 in. double-side pol...

Bulk GaN Ion Cleaving

“…Recently, we demonstrated that double-sided implantation (under the same conditions) is an effective approach to obtain relatively flat H-implanted fs-GaN wafers. 4 Moreover, we found that the final bow can be reduced High resolution x-ray diffraction (HRXRD) spectra of (0002) GaN before and after H implantation with a fluence of 2.6 9 10 17 cm À2 at an ion energy of 50 keV. Fig.…”

“…8). 4 Since the main motivation behind the use of the ion-cut process is to reduce the cost of bulk quality GaN layers, the second implantation needed to adjust the bow is an additional step which can increase the cost of the ion-cut process. Here, we believe that it could be possible to take advantage of the second implantation.…”

“…In principle, this can be achieved by the use of the ion-cut process, commercially known as Smart-Cutä. [3][4][5] The different steps of this process are illustrated in Fig. 1.…”

The Phenomenology of Ion Implantation-Induced Blistering and Thin-Layer Splitting in Compound Semiconductors

“…FTIR data showed H-defect vibrational spectrum peaks at 3141 cm À1 , attributed to V Ga -H 4 . A large fraction of H was found to be trapped in higher-frequency modes, which we tentatively associate to N-H stretch modes in the 65 Using this method they could reduce the wafer bow to a few lm (Fig. 14).…”

Heterointegration of Compound Semiconductors by Ultrathin Layer Splitting

“…In the section insights into the physics of the ion-cut are elaborated with emphasis on the mechanisms of H-induced fs-GaN splitting. Engineering issues in the application of the ion-cut to transfer thin layers from 2 inch bulk GaN are described elsewhere (49,50). From a thermodynamics viewpoint, the limited solubility of the implanted species in ECS Transactions, 33 (13) 177-187 (2010) most materials provokes their segregation into cavities that grow and coalesce at high temperatures (51,52).…”