This paper demonstrates a new de-process flow for MEMS motion sensor failure analysis, using layer by layer deprocessing to locate defect points. Analysis tools used in this new process flow include IR optical microscopy, thermal system, SEM and a cutting system to de-process of MEMS motion sensor and successful observation defect points.

This paper discussed on how the importance of failure analysis to identify the root cause and mechanism that resulted in the MEMS failure. The defect seen was either directly on the MEMS caps or the CMOS integrated chip in wafer fabrication. Two case studies were highlighted in the discussion to demonstrate how the FA procedures that the analysts had adopted in order to narrow down to the defect site successfully on MEMS cap as well as on CMOS chip on MEMS package units. Besides the use of electrical fault isolation tool/technique such as TIVA for defect localization, a new physical deprocessing approach based on the cutting method was performed on the MEMS package unit in order to separate the MEMS from the Si Cap. This approach would definitely help to prevent the introduction of particles and artifacts during the PFA that could mislead the FA analyst into wrong data interpretation. Other FA tool such as SEM inspection to observe the physical defect and Auger analysis to identify the elements in the defect during the course of analysis were also documented in this paper.

MEMS samples, with their relatively large size and weight, present a unique challenge to the failure analyst as they also included thin films and microstructures used in conventional integrated circuits. This paper describes how to accommodate the large MEMS structures without skimping on the microanalyses needed to get to the root cause. Investigations of tuning folk gyroscopes were used to demonstrate these new techniques.

Adhesion is important to the yield and performance of MEMS (Micro-Electro-Mechanical Systems) and NEMS (Nano- Electro-Mechanical Systems). Measuring the work of adhesion, with an AFM (Atomic-Force Microscope), allows one to study surface interactions from an energy perspective as opposed to an adhesion (force) perspective. The works of adhesion were measured with different AFM tip radii on multiple types of samples. Two sample variables were examined: four die attach conditions (no attachment, silicone, polyimide silicone, and silver glass), and two surface conditions (native oxide with and without a few angstroms of vapor-deposited diphenyl siloxane). For a normal silicon cantilever, the work of adhesion seems to be slightly less for the treated surfaces than the untreated, except for the silverglass die attach material. There were at least three orders of magnitude difference in the works of adhesion for the different AFM tip radii. Presumably, the trend is due to some combination of material properties, interfacial roughness, and torque on the AFM cantilever.

The debugging-time for polycrystalline MEMS structural layers is the aim of this paper. A description of the fatigue phenomenon for elementary structure in the case of microactuators is presented. It is obtained by combining elementary in situ test benches of varying dimensions and cyclic actuation; in the same way, the debugging-time is determined according to the design and the structural material. Test benches have been developed allowing performance of bending fatigue tests of polycrystalline structural layers, describing the fatigue phenomenon and obtaining a constant debugging-time for a same polycrystalline layer, whatever the excitation frequency and the beams length.

An ellipsometry based measurement protocol was developed to evaluate changes to MEMS sensor surfaces which may occur during packaging using unpatterned test samples. This package-level technique has been used to measure the 0-20 Angstrom thin films that can form or deposit on die during the packaging process for a variety of packaging processing conditions. Correlations with device performance shows this to be a useful tool for packaged MEMS device and process characterization.

Freescale Semiconductor is employing a new, multi-layer integrated seal (IS) on its next generation accelerometers. The IS, which encloses the moveable sensing element, consists of alternating layers of poly-Si and PSG. A technique needed to be developed to remove the integrated seal in order to permit failure analysis. Mechanical methods were attempted first, but these resulted in severe damage to the sensing element. Chemical deprocessing was considered, but eventually abandoned because there seemed to be no way to protect the sensing elements from the wet etchants that would be used on the IS. Eventually, Reactive Ion Etching (RIE) with an Inductively Coupled Plasma (ICP) source proved to be a successful means for removing the IS without impacting the sensing element. As the design of the integrated seal underwent multiple redesigns, the removal process was successfully modified multiple times to comply with these changes. By using the right gases in the correct order, a high level of selectivity was maintained, allowing for removal of successive layers of different materials (poly-Si, PSG) without harming the sensing element. After removal of some IS designs, a wispy residue was observed on the sensing element and remaining IS support pillars. Chemical analysis identified this material as a by-product of the RIE process, and methods were devised to eliminate it.

The MEMS structure has its particular character like hollow areas inside, and “floating” structures. Traditional TEM sample preparation method usually leads to distortion and dissociation defects of the floating structure. This paper introduces two innovative practical methods of TEM sample preparation using focused ion beam (FIB) for MEMS floating structure analysis. Method 1 used glass needle to lift out the separated film onto glue coated blank wafer; method 2 used in situ pick up system to lift out L- or C-shaped cut film onto TEM half-grid. And then the sample can be applied to normal TEM membrane preparation procedure.

Metal-insulator-metal (MIM) capacitors with single TiO2 and a TiO2/Y2O3 stack are used as insulator films in MIM and MEMS, respectively, are explored. It is found that, under electron injection from bottom electrode, the TiO2 MIM capacitors demonstrate resistive switching with a magnitude of leakage currents not usable for MEMS application. The deposition of a stacked TiO2/Y2O3 dielectric film improves the MEMS performance without compromising the low dielectric charging of TiO2 single layer.

Currently gaps in non-destructive 2D and 3D imaging in PFA for advanced packages and MEMS exist due to lack of resolution to resolve sub-micron defects and the lack of contrast to image defects within the low Z materials. These low Z defects in advanced packages include sidewall delamination between Si die and underfill, bulk cracks in the underfill, in organic substrates, Redistribution Layer, RDL; Si die cracks; voids within the underfill and in the epoxy. Similarly, failure modes in MEMS are often within low Z materials, such as Si and polymers. Many of these are a result of mechanical shock resulting in cracks in structures, packaging fractures, die adhesion issues or particles movements into critical locations. Most of these categories of defects cannot be detected non-destructively by existing techniques such as C-SAM or microCT (micro x-ray computed tomography) and XRM (X-ray microscope). We describe a novel lab-based X-ray Phase contrast and Dark-field/Scattering Contrast system with the potential to resolve these types of defects. This novel X-ray microscopy has spatial resolution of 0.5 um in absorption contrast and with the added capability of Talbot interferometry to resolve failure issues which are related to defects within organic and low Z components.

Electrical shorting in micro-electro-mechanical systems (MEMS) is a significant production and manufacturing concern. We present a new approach to localizing shorted MEMS devices using Thermally-Induced Voltage Alteration (TIVA) [1]. In TIVA, the shorted, thermally isolated MEMS device is very sensitive to thermal stimulus. The site of the MEMS short will respond as a thermocouple when heated. By monitoring the potential across the shorted MEMS device as a laser scans across the sample, an image showing the location of the thermocouple (short site) can be generated. The TIVA signal for thermally isolated MEMS devices is much higher than that observed for conventional IC interconnections. This results from the larger temperature gradients generated during laser scanning due to little or no substrate heat sinking. The capability to quickly localize shorted MEMS structures is demonstrated by several examples. Thermal modeling of heat distributions is presented and is consistent with the experimental results.

Optical Micro-Electro-Mechanical Systems (Optical MEMS, or MOEMS) comprise a disruptive technology whose application to telecommunications networks is transforming the horizon for lightwave systems. The influences of materials systems, processing subtleties, and reliability requirements on design flexibility, functionality and commercialization of MOEMS are complex. A tight inter-dependent feedback loop between Component/ Subsystem/ System Design, Fabrication, Packaging, Manufacturing and Reliability is described as a strategy for building reliability into emerging MOEMS products while accelerating their development into commercial offerings.

The purposes of failure analysis are to localize the failure site, to establish the type of failure and to understand the failure mechanism. Some MEMS, such as Analog Device's accelerometer ADXL501, are confronted with stiction problems. Either we get around the problem by creating designs which are not subject to this type of failure, or we try to understand its mechanism. The residual stresses have an important role in the stiction because according to the configurations of the structures, they can stiffen beams and so oppose this failure, or amplify it by bending it towards underlying mechanical elements. That’s why we carry an interest in the residual constraints to understand and counteract this type of failure. Besides, the residual stresses have also repercussion on properties such as fatigue, fracture, friction... which are at the origin of other types of failure. In this article, we attempt to set up a method to qualify and quantify the residual stresses in the different layers of the MUMPs process.

To investigate the mechanical behavior and failure modes of micro-electromechanical systems (MEMS), a high resolution optical tool capable of imaging both fast and slow movements in three dimensions on a microscopic scale is almost mandatory. We report the first experiments with a new tool, which provides the necessary speed and resolution. First, some common failure modes in MEMS are discussed, as are the possibilities of optical inspection methods to deal with them. We show that the system we describe may be used to monitor the resonances and small but fast movements of a MEMS device, to image erratic behavior, stuck parts, and so on. Furthermore, slow deformations, for example of expansion due to temperature changes, can be monitored with high resolution, and give information on deformation or delamination of layers.

Fluid ejection systems fabricated using MEMS (microelectromechanical systems) technology have a wide variety of applications ranging from ink jet thermal printing [1] to drug delivery for medical applications [2]. Microfluidic MEMS drop ejectors accurately control the volume and velocity of fluid dispensed. For the electrostatic drop ejector to function properly, the fluid must be contamination free, inert to the MEMS components and inert to materials and epoxies used for packaging. This paper will discuss the failure mechanisms and analysis techniques used to diagnose root cause(s) of failure in as-fabricated (unreleased) drop ejectors, and released, packaged drop ejectors tested in both air and water. Corrective actions implemented to mitigate the failure mechanisms and improve performance and reliability at both the wafer/die level and packaged level will be discussed.

The work presented in this paper concerns the characterization of MEMS structures, industrially manufactured using front-side bulk micromachining post-process techniques on CMOS dies. The systematic characterization of mechanical parameters, such as stiffness or mass, on a set of 100 cantilever devices provide us with basic knowledge concerning process parameter variations.

In this paper we discuss reliability and failure analysis issues of RF-MEMS capacitive switches. We describe specific instrumentation and methods that can be used for testing and examination of these switches. These include SEM, AFM, SAM, static and dynamic optical investigation and electrical lifetime testing. Processing as well as testing and packaging issues are discussed.

A new imaging technique called Wavefront Coding allows real-time imaging of three-dimensional structures over a very large depth. Wavefront Coding systems combine aspheric optics and signal processing to achieve depth of fields ten or more times greater than that possible with traditional imaging systems. Understanding the relationships between traditional and modern imaging system design through Wavefront Coding is very challenging. In high performance imaging systems nearly all aspects of the system that could reduce image quality are carefully controlled. Modifying the optics and using signal processing can increase the amount of image information that can be recorded by microscopes. For a number of applications this increase in information can allow a single image to be used where a number of images taken at different object planes had been used before. Having very large depth of field and real-time imaging capability means that very deep structures such as surface micromachined MEMS can be clearly imaged with one image, greatly simplifying defect and failure analysis.

This paper describes an acoustic phonon-based characterization technique as a novel tool for the characterization of dynamic microelectromechanical (MEMS) devices such as resonators, switches, micromirrors, accelerometers and gyroscopes. The technique intrinsically features non-invasive characterization due to the favorable transmission properties of acoustic phonons through device packaging and high throughput due to universal detectability from a single detection point, which facilitates high volume wafer and package level testing. The dependence of phonon generation on material properties yields information not obtained in existing electrical, optical and electron beam testing techniques such as contact tribology, energy dissipation, non-linear device behavior and device resonance modes. Preliminary case study results show that phonon-based characterization not only provides efficient, non-destructive testing (NDT) of MEMS functionality, but also insights into MEMS device lifecycle behavior.

This paper reports on a setup and a method that enables automated analysis of mechanical stress impact on microelectromechanical systems (MEMS). In this setup both electrical and optical inspection are available. Reliability testing is possible on a single chip as well as on the wafer level. Mechanical stress is applied to the tested structure with programmable static forces up to 3.6 N and dynamic loads at frequencies up to 20 Hz. The applications of the presented system include the postmanufacturing test, characterization and stress screens as well as reliability studies. We report preliminary results of long-term reliability testing obtained for a CMOS-based stress sensor.