Microsystems-enabled photovoltaics (MEPV) can potentially meet increasing demands for light-weight, portable, photovoltaic solutions with high power density and efficiency. The study in this report examines failure analysis techniques to perform defect localization and evaluate MEPV modules. CMOS failure analysis techniques, including electroluminescence, light-induced voltage alteration, thermally-induced voltage alteration, optical beam induced current, and Seabeck effect imaging were successfully adapted to characterize MEPV modules. The relative advantages of each approach are reported. In addition, the effects of exposure to reverse bias and light stress are explored. MEPV was found to have good resistance to both kinds of stressors. The results form a basis for further development of failure analysis techniques for MEPVs of different materials systems or multijunction MEPVs. The incorporation of additional stress factors could be used to develop a reliability model to generate lifetime predictions for MEPVs as well as uncover opportunities for future design improvements.
We present the results of a two-year early career LDRD that focused on defect localization in deep green and deep ultraviolet (UV) light-emitting diodes (LEDs). We describe the laser-based techniques (TIVA/LIVA) used to localize the defects and interpret data acquired. We also describe a defect screening method based on a quick electrical measurement to determine whether defects should be present in the LEDs. We then describe the stress conditions that caused the devices to fail and how the TIVA/LIVA techniques were used to monitor the defect signals as the devices degraded and failed. We also describe the correlation between the initial defects and final degraded or failed state of the devices. Finally we show characterization results of the devices in the failed conditions and present preliminary theories as to why the devices failed for both the InGaN (green) and AlGaN (UV) LEDs.
SEM and SOM techniques for IC analysis that take advantage of 'active injection' are reviewed. Active injection refers to techniques that alter the electrical characteristics of the device analyzed. All of these techniques can be performed on a standard SEM or SOM (using the proper laser wavelengths).
State-of-the-art techniques for failure localization and design modification through bulk silicon are essential for multi-level metallization and new, flip chip packaging methods. The tutorial reviews the transmission of light through silicon, sample preparation, and backside defect localization techniques that are both currently available and under development. The techniques covered include emission microscopy, scanning laser microscope based techniques (electrooptic techniques, LIVA and its derivatives), and other non-IR based tools (FIB, e-beam techniques, etc.).
The working of induced voltage alteration (IVA) techniques and its major developments in areas of hardware for analysis, electrical biasing, detection advances, resolution improvements, and future possibilities, is discussed. IVA technique uses either a scanning electron microscope's (SEM) electron beam or a scanning optical microscope's (SOM) laser beam as the external stimulus. The other IVA techniques were developed using different localized stimuli, with the same sensitive biasing approach. The IVA techniques takes advantage of the strong signal response of CMOS devices when operated as current-to-voltage converters. To improve the biasing approach, externally induced voltage alterations (XIVA) was introduced, in which an ac choke circuit acts as a constant-voltage source. Synchronization with device operation also allows specific vectors to be analyzed using local photocurrent and thermal stimulus.