Chapter 12: Reliability and Failure Analysis Homework solutions

Gate-oxide integrity [1] The gate oxide of an MOS device is one of the most important MOS device parameters. It is very sensitive to damage and can easily degrade. The degradation manifests as an increase in gate, or leakage, current and can lead to breakdown, a rapid increase in gate current. [1]

Negative Bias Temperature Instability Occurs in p-channel MOS devices stressed with negative gate voltages at elevated temperatures, manifests itself as absolute drain current and transconductance decrease, and absolute threshold voltage increase. The cause of NBTI is believed to be interface traps and fixed oxide charges. Similar to the NBTI effect is the bias stress observed in TFTs with n-type metal-oxide semiconductors, such as zinc-oxide (ZnO), where the drain current drops and threshold voltage shifts towards more positive values under positive gate voltage stress as shown in Figure 2.[2] [3]

Stress Induced Leakage Current (SILC) It is defined as the increase of oxide leakage current after high-field stress, compared to before stress. It is typically observed at low to moderate oxide electric fields and increases markedly as oxide thicknesses decrease but decreases for thickness below 5 nm. SILC degrades data retention of non-volatile memories that store charge on floating gates and it is usually not detected by time-zero or time-dependent breakdown measurements. Reliance on these latter characterization techniques may lead to overestimation of oxide integrity and reliability. [1]

Electrostatic Discharge (ESD) Electrostatic discharge is the transient discharge of static charge due to human handling or contact with equipment. A contact by a charged human body with an IC pin can result in a discharge for about 100 ns with peak currents in the ampere range, leading to failure in electronic devices.

Quiescent Drain Current (IDDQ) In quiescent drain current (or IDDQ), an integrated circuit is subjected to a steady state current with the circuit in off- mode (no operation, only biased circuit). Faulty circuit containing shorts show current increases through gate- oxide shorts, shorted interconnects, shorts from drain/source to gate between drain and source [1]

Fluorescent Microthermography (FMT) thin film of europium thenoyl trifluoroacetonaten dissolved in acetone is deposited onto the surface and illuminated with 340–380 nm ultraviolet light, stimulating fluorescence whose intensity is temperature dependent. Spatial resolution 0,5 um. Lifetime about 200 us.

Liquid Crystals Polarization of crystals change above a certain temperature. Can be used to find hot spots. [1]

Infrared Thermography Body above the absolute temperature emits radiation and in IR detection of radiations intensity gives the temperature measurement in non-contact form [4]

Voltage contrast local electric fields of the circuit components cause a local contrast difference on the signal detected by the secondary electron detector. Transient behavior (switching of the circuit state) can be detected with stroboscopic techniques [1]

Laser Voltage probe (LVP) An infrared laser probes the electric field and the free carrier induced absorption modulation in a reverse biased pn junction without requiring a vacuum. The absorption modulation is directly dependent on the voltage across the junction, allowing measurements of the voltages in the junctions. Si is transparent, doped Si less so, in IR region also metalized structures can be inspected from the backside of the wafer. In this way, e.g. CMOS chips can be inspected from the backside. [1]

Optical Beam Induced Resistance Change (OBIRCH) The obirch technique is based on resistivity changes due to temperature variations. A laser probe is scanned over e.g. an IC and the heating effects of the laser on the IC is observed. The IC is kept under either constant voltage (CV) or constant current (CC). Heat transmission is impeded over defect areas and appear as bright spots [1]

Noise Noise can be measured in all devices and typically noise amplitude increases during some device degradation. Noise manifests in different forms, such as thermal noise, shot noise, generation-recombination (G-R) noise and low-frequency or flicker (or more commonly noted as 1/f) noise.

references 1.M. Ohring, Reliability and Failure of Electronic Materials and Devices, Academic Press, San Diego, High-mobility polymer gate dielectric pentacene thin film transistors Hagen Klauk, Marcus Halik, Ute Zschieschang, Günter Schmid, Wolfgang Radlik et al. J. Appl. Phys. 92 (6), Trap States of a-ZnO Thin Film Transistors Jin Tae Yuh and Byung Seong Bae Electronic Materials Letters 6 (4),