Daniel L. Barton

AlGaN/InGaN/GaN blue light emitting diode degradation under pulsed current stress

This study focused on the performance of commercial AlGaN/InGaN/GaN blue light emitting diodes (LEDs) under high current pulse conditions. The results of deep level transient spectroscopy (DLTS), thermally stimulated capacitance, and admittance spectroscopy measurements performed on stressed devices, showed no evidence of any deep‐level defects that may have developed as a result of high current pulses. Physical analysis of stressed LEDs indicated a strong connection between the high intrinsic defect density in these devices and the resulting mode of degradation.

TIVA and SEI developments for enhanced front and backside interconnection failure analysis

Thermally-Induced Voltage Alteration (TIVA) and Seebeck Effect Imaging (SEI) are newly developed techniques for localizing shorted and open conductors from the front and backside of an IC. Recent improvements have greatly increased the sensitivity of the TIVA/SEI system, reduced the acquisition times by more than 20X, and localized previously unobserved defects. The system improvements, non-linear response of IC defects to heating, modeling of laser heating and examples using the improved system are presented.

Life tests and failure mechanisms of GaN/AlGaN/InGaN light emitting diodes

Our studies of device lifetime and the main degradation mechanisms in Nichia blue LEDs date back to Spring 1994. Following the initial studies of rapid failures under high current electrical pulses, where metal migration was identified as the cause of degradation, we have placed a number of Nichia NLPB-500 LEDs on a series of life tests. The first test ran for 1000 hours under normal operating conditions (20 mA at 23/spl deg/C). As no noticeable degradation was observed, the second room temperature test was performed with the same devices but with a range of currents between 20 and 70 mA. After 1600 hours, some degradation in output intensity was observed in devices driven at 60 and 70 mA, but it was still less than 20%. The subsequent tests included stepping up the temperature by 10/spl deg/C in 500 h intervals up to a final temperature of 85/spl deg/C using the same currents applied in the second test. This work reviews the failure analysis that was performed on the degraded devices and the degradation mechanisms that were identified.

FLIP-chip and “backside” techniques

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.).

Life tests and failure mechanisms of GaN/AlGaN/InGaN light-emitting diodes

Our studies of device lifetime and the main degradation mechanisms in Nichia blue LEDs date back to Spring 1994. Following the initial studies ofrapid failures under high current electrical pulses, where metal migration was identified as the cause of degradation, we have placed a number ofNichia NLPB-500 LEDs on a series oflife tests. The first test ran for 1000 hours under normal operating conditions (20 mA at 23 °C). As no noticeable degradation was observed, the second room temperature test was performed with the same devices but with a range of currents between 20 and 70 mA. After 1600 hours, some degradation in output intensity was observed in devices driven at 60 and 70 mA, but it was still less than 20%. The subsequent tests included stepping up the temperature by 10 °C in 500 h intervals up to a fmal temperature of 95 °C using the same currents applied in the second test. This work reviews the failure analysis that was performed on the degraded devices and the degradation mechanisms that were identified.

Degradation of blue AlGaN/InGaN/GaN LEDs subjected to high current pulses

Short-wavelength, visible-light emitting optoelectronic devices are needed for a wide range of commercial applications, including high-density optical data storage, full-color displays, and underwater communications. In 1994, high-brightness blue LEDs based on gallium nitride and related compounds (InGaN/AlGaN) were introduced by Nichia Chemical Industries. The Nichia diodes are 100 times brighter than the previously available SiC blue LEDs. Group-III nitrides combine a wide, direct bandgap with refractory properties and high physical strength. So far, no studies of degradation of GaN based LEDs have been reported. Our study, reported in this paper, focuses on the performance of GaN LEDs under high electrical stress conditions. Our observations indicate that, in spite of a high defect density, which normally would have be fatal to other III-V devices, defects in group-III nitrides are not mobile even under high electrical stress. Defect tubes, however, can offer a preferential path for contact metals to electromigrate towards the p-n junction, eventually resulting in a short. The proposed mechanism of GaN diode degradation raises concern for prospects of reliable lasers in the group-III nitrides grown on sapphire.

Degradation of single-quantum well InGaN green light emitting diodes under high electrical stress

We performed a degradation study of high-brightness Nichia single-quantum well AlGaN-InGaN-GaN green light-emitting diodes (LEDs). The devices were subjected to high current electrical stress with current pulse amplitudes between 1 A and 7 A and voltages between 10 V and 70 V with a pulse length of 100 ns and a 1 kHz repetition rate. The study showed that when the current amplitude was increased above 6 A, a fast (about 1 s) degradation occurred, with a visible discharge between the p- and n-type electrodes. Subsequent failure analysis revealed severe damage to the metal contacts which lead to the formation of shorts in the surface plane of the diode. For currents smaller than 6 A, a slow degradation was observed as a decrease in optical power and an increase in the reverse current leakage. After between 24 and 100 hours however, a rapid degradation occurred which was similar to the rapid degradation observed at higher currents. The failure analysis results indicate that the degradation process begins with carbonization of the plastic encapsulation material on the diode surface, which leads to the formation of a conductive path across the LED and subsequently to the destruction of the diode itself.

Room-Temperature Life Test of Nichia AlGaN/InGaN/GaN Blue Light Emitting Diodes

The authors report on the current status of room-temperature life testing of Nichia NLPB-500 blue light emitting diodes. So far, two tests have been completed. During the first 1,000-h test, a constant current of 20 mA was maintained in all devices. During the second 1,650 h test, groups of 3 or 4 devices were driven at currents ranging from 20 mA to 70 mA. Very little degradation has been observed in devices driven at normal conditions (20--30 mA), with a noticeable increase in degradation rate above 60 mA.

Life testing and failure analysis of GaN/AlGaN/InGaN light-emitting diodes

Our studies of device lifetime and the main degradation mechanisms in Nichia blue LEDs date back to Spring 1994. Following the initial studies of rapid failures under high current electrical pulses, where metal migration was identified as the cause of degradation, we have placed a number of Nichia NLPB-500 LEDs on a series of life tests. The first test ran for 1000 hours under normal operating conditions (20 mA at 23 degree(s)C). As no noticeable degradation was observed, the second room temperature test was performed with the same devices but with a range of currents between 20 and 70 mA. After 1600 hours, some degradation in output intensity was observed in devices driven at 60 and 70 mA, but it was still less than 20%. The subsequent tests included stepping up the temperature by 10 degree(s)C in 500 h intervals up to a final temperature of 85 degree(s)C using the same currents applied in the second test. This work reviews the failure analysis that was performed on the degraded devices and the degradation mechanisms that were identified.

Failure Site Isolation: Photon Emission Microscopy Optical/Electron Beam Techniques

Global failure analysis techniques are critical to keep pace with the increasing complexity of ICs. Global techniques provide methodologies for the isolation of failures without a detailed understanding of IC operation. Ideally, global analysis techniques should be easy to use, non-destructive, sensitive, and should provide high spatial resolution. In addition to the thermal methods described in the last chapter, other techniques generally fall into two categories: photon based and electron beam based. Photon probing of ICs has been and should continue to be a powerful approach to failure analysis. Because of silicon’s relative transparency to infrared light, photon probing is particularly useful in cases where backside analysis provides the easiest access.