Paiboon Tangyunyong

The effect of frequency on the lifetime of a surface micromachined microengine driving a load

Experiments have been performed on surface micromachined microengines driving load gears to determine the effect of the rotation frequency on median cycles to failure. We did observe a frequency dependence and have developed a model based on fundamental wear mechanisms and forces exhibited in resonant mechanical systems. Stressing loaded microengines caused observable wear in the rotating joints and, in a few instances, led to fracture of the pin joint in the drive gear.

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.

Electrostatic discharge/electrical overstress susceptibility in MEMS: a new failure mode

Electrostatic discharge (ESD) and electrical overstress (EOS) damage of Micro-Electrical-Mechanical Systems (MEMS) has been identified as a new failure mode. This failure mode has not been previously recognized or addressed primarily due to the mechanical nature and functionality of these systems, as well as the physical failure signature that resembles stiction. Because many MEMS devices function by electrostatic actuation, the possibility of these devices not only being susceptible to ESD or EOS damage but also having a high probability of suffering catastrophic failure doe to ESD or EOS is very real. Results from previous experiments have shown stationary comb fingers adhered to the ground plane on MEMS devices tested in shock, vibration, and benign environments [1,2]. Using Sandia polysilicon microengines, we have conducted tests to establish and explain the EDS/EOS failure mechanism of MEMS devices. These devices were electronically and optically inspected prior to and after ESD and EOS testing. This paper will address the issues surrounding MEMS susceptibility to ESD and EOS damage as well as describe the experimental method and results found from EDS and EOS testing. The tests were conducting using conventional IC failure analysis and reliability assessment characterization tools. In this paper we will also present a thermal model to accurately depict the heat exchange between an electrostatic comb finger and the ground plane during an ESD event.

Frequency dependence of the lifetime of a surface micromachined microengine driving a load

Abstract Experiments have been performed on surface micromachined microengines driving load gears to determine the rotational frequency dependence on median cycles to failure. A sample of 272 microengines, each driving a load, was stressed at eight different frequencies. Frequency dependence was observed and a model was developed based on fundamental wear mechanisms and forces exhibited in resonant mechanical systems. Stressing loaded microengines caused observable wear in the rotating joints and in a few instances led to fracture of the pin joint in the drive gear.

Failure analysis of surface-micromachined microengines

Microelectronic failure analysis (FA) has been an integral part of the development of state-of-the-art integrated circuits. FA of MicroElectroMechanical Systems (MEMS) is moving from its infancy to assume an important role in the successful design, fabrication, performance and reliability analysis for this new technology. In previous work, we focused on the application of several techniques developed for integrated circuit analysis to an earlier version of a surface micromachined microengine fabricated at Sandia. Recently, we have identified important new failure modes in binary counters that incorporate a newer design of the microengine, using a subset of integrated circuit failure analysis techniques including optical microscopy, focused ion beam (FIB) techniques, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The primary failure mode we have identified is directly related to visible wear on bearing surfaces. In this paper, we describe in detail the characteristics of the failure modes in binary counters. We also compare the failure characteristics with those of an earlier version of the microengine.

Identification of radiation-induced parasitic leakage paths using light emission microscopy

Eliminating radiation-induced parasitic leakage paths in integrated circuits (ICs) is key to improving their total dose hardness. Semiconductor manufacturers can use a combination of design and/or process techniques to eliminate known radiation-induced parasitic leakage paths. However, unknown or critical radiation-induced parasitic leakage may still exist on fully processed ICs and it is extremely difficult (if not impossible) to identify these leakage paths based on radiation induced parametric degradation. We show that light emission microscopy can be used to identify the location of radiation-induced parasitic leakage paths in ICs. This is illustrated by using light emission microscopy to find radiation-induced parasitic leakage paths in partially-depleted silicon on insulator static random-access memories (SRAMs). Once leakage paths were identified, modifications were made to the SRAM design to improve the total dose radiation hardness of the SRAMs. Light emission microscopy should prove to be an important tool for the development of future radiation hardened technologies and devices.

Failure Analysis Techniques for Microsystems-Enabled Photovoltaics

Microsystems-enabled photovoltaics (MEPV) has great potential to meet the increasing demands for light-weight, photovoltaic solutions with high power density and efficiency. This paper describes effective failure analysis techniques to localize and characterize nonfunctional or underperforming MEPV cells. The defect localization methods such as electroluminescence under forward and reverse bias, as well as optical beam induced current using wavelengths above and below the device band gap, are presented. The current results also show that the MEPV has good resilience against degradation caused by reverse bias stresses.

Thermal modeling of localized laser heating in multi-level interconnects

Abstract Thermal modeling was used to simulate thermal profiles from localized laser heating on two multi-level interconnect structures with metallization complexity comparable to those used in advanced interconnect systems. The modeling focused on addressing issues with regard to the effectiveness of laser-based techniques in defect localization in state-of-the-art metallization schemes. Modeling results indicate that indirect heating from the laser does not propagate effectively through adjacent metal layers from both the front side and the back side. Poor heat conduction and its associated thermal spreading during laser heating make defect detection difficult beyond three levels of metal. Thermal distribution and spreading were found to be more affected by interconnect geometries than by variations in laser spot size. Smaller temperature rises during laser heating were observed in the newer interconnect structures consisting of copper and low-k dielectric materials than in those with conventional aluminum, tungsten, and silicon dioxide. The smaller temperature rise leads to weaker signal strength at the defect sites and makes it more difficult to detect defects in the newer-material structures. Metallization density also affects heat conduction in advanced interconnect systems but the temperature rise during laser heating varies slowly as a function of metallization density.

Fault localization and failure modes in microsystems-enabled photovoltaic devices

Microsystems-enabled photovoltaic (MEPV) technology is a promising approach to lower the cost of solar energy to competitive levels. This paper describes current development efforts to leverage existing silicon integrated circuit (IC) failure analysis (FA) techniques to study MEPV devices. Various FA techniques such as light emission microscopy and laser-based fault localization were used to identify and characterize primary failure modes after fabrication and packaging. The FA results provide crucial information used in provide corrective actions and improve existing MEPV fabrication techniques.

Thermal modeling of a polysilicon-metal test structure used for thermally induced voltage alteration characterization

Thermal modeling and simulations were used to analyze the thermal profiles of a polysilicon-metal test structure generated by localized heating with an infrared laser. Localized laser heating is the basis of a new failure analysis technique, thermally induced voltage alteration (TIVA), that can identify shorted interconnects in integrated circuits. The modeling results show that variations in thermal profiles of the test structure measured by the TIVA technique are due mainly to preferential laser absorption in various locations in the test structure. Differences in oxide thickness also affect the local heat conduction and temperature distribution. Modeling results also show that local variation in heat conduction is less important than the absorbed laser power in determining the local temperatures since our test structure has feature sizes that are small compared to the length over which the heat spreads.