Observations of interfaces in direct wafer-bonded InP-GaAs structures

摘要

Direct wafer-bonded InP-GaAs structures were studied by cross-sectional observations using a field-emission scanning-electron microscope (FESEM) and by infrared-absorbance spectra using a Fourier-transform infrared spectroscopy. FESEM observations demonstrate that the interfaces of 560 and 580℃ bonded InP-GaAs structures are smooth and uninterrupted, while interfacial gaps appear for the samples bonded at 620 and 680℃. However, large dimensional areas of bonding interfaces cannot be observed by FESEM because its inspection size is limited to microregions. Experimental results show that infrared-absorbance measurements can be an effective method for quality examination of bonded InP-GaAs structures. By soaking wax into poorly bonded interfaces and using its absorption characteristics at 3.383, 3.426, and 3.509 μm, interfacial gaps are indirectly measured by infrared spectra. Absorbance-intensity mappings at absorption peaks were used to image poorly bonded areas. Thus the interface quality of the whole wafer-bonded sample can be seen clearly. Nonuniform pressure applied over the sample during annealing step accounts for poorly bonded interfaces. Using the improved fixture, uniformly bonded InP-GaAs structures that do not have interfacial gaps were obtained.