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Synchrotron X-ray section topographs and etch-pit micrographs of the wafers processed in a CMOS fab, are analyzed and correlated against the measured process-control monitoring data and the device yield obtained from the wafers. The etch-pit micrographs detail precipitates, dislocations, and stacking faults, whereas the X-ray topographs additionally show the strain gradient-caused by lattice bending and misfit. Specifically written image-processing software extracts features from the digitized topographs and micrographs after making computational adjustments. These extracted feature parameters are correlated against the electrically and optically obtained process-control monitoring data, collected from the wafer-processing results, and against the yield obtained from the wafer-probing stage. Several image features extracted from the synchrotron X-ray topographs exhibit a strong correlation to certain measured process parameters, e.g., PMOS transistor threshold voltage, polysilicon sheet resistance, and N-sheet contact chain resistance, rather than with others, like NMOS breakdown voltage, which correlated poorly. As a new result, positive correlation between good device yield and a strong near-surface strain gradient is found by synchrotron X-ray topography. Unexpectedly, computed from the etch-pit micrographs, the yield correlates very poorly to the defect-free zone depth of the wafer surface. The results suggests that strain has more impact on the operation of the electronic device than precipitates solely would have.

The white beam Synchrotron X-Ray Topography (SXRT) technique was used to assess the quality of sapphire wafers grown by the Heat-Exchanger Method (HEM) and the Modified Czochralski Method (MCM). Sapphire is a potential new material for X-ray crystal optics, especially for use as Bragg backscattering mirrors for X-rays and Mössbauer radiation. The dislocation distribution, dislocation density and Burgers vector of selected dislocations and stacking faults in the sapphire wafers were studied. A correlation between the sapphire quality and its performance as an X-ray backscattering mirror was established in this paper. The results reveal the high quality of the inspected HEM sapphire wafers and their subsequently improved performance as Bragg backscattering mirrors.

Section transmission white beam X-ray topography was applied to the evaluation of the growth of GaN on sapphire using the epitaxial lateral overgrowth (ELO) technique. Using openings in 100 nm thick SiO2 windows, a new GaN growth took place, which resulted in nominal overgrowth thicknesses of 6.8 μm. Measurements of the recorded Laue section topographs revealed misorientation between the epilayer and the substrate. Neglecting the misorientation contribution due to the 30° rotation of the epilayer with respect to the substrate, the misorientation mechanism was found to be a consequence of lattice rotation and dilatation. In the case of the ELO sample, these parameters varied with the stripe/window dimensions. The quality of the ELO epilayer is improved when compared to the non-ELO sample, though some local deviations from lattice coherence were observed. These results were complemented by observations made using X-ray diffraction and transmission electron microscopy.

Failure analysis of ultra-bright LED arrays under varying degrees of electrical stress was performed. Green (565 nm), red (660 nm) and infrared (890 nm) LEDs were subjected to currents between 0 and 1 A and voltages between 0 and 7 V. Using white beam synchrotron X-ray topography (SXRT) in back reflection large-area and section modes, the failure modes of the devices were observed. As the power to each device was increased, a reduction in the definition of device lattice structure due to increased thermal stressing was observed. An increase in strain is witnessed in the devices as they are stressed to the point of near failure. It was noted that at or near failure, the strain fields in the ball-bonded regions of the device become anomalously large (0.08% for the red LED, 0.19% for the green LED and 0.27% for the infrared LED), as observed via orientational contrast on the topographs. This is most likely due to thermally induced damage. The onset of failure took place when the power supplied to each individual LED exceeded 600 mW in the case of the green LEDs, 500 mW for the red LEDs and 745 mW for the infrared LEDs. Surprisingly, this is approximately 25 times greater than the nominal recommended supply for each LED array. This was confirmed by studying the I –V characteristics of the devices in conjunction with their emission spectra. As the power supplied to the devices was increased a narrowing of the radiative bandgap was witnessed in the red and green LEDs; whereas a broadening occurred in the infrared LED. When complete failure occurred in the samples, it was observed that large lattice deformations of the original device structure took place. Optical micrographs indicated that the structure of the devices remains spatially unaltered although the gold bond wire became detached. This confirmed that the distortion observed in the X-ray topographs is mainly due to severe thermally induced lattice distortion. The induced lattice distortion is greatest for the red LEDs; the sample appears to possess distinct and completely misorientated sub-grains.

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