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.

Multiple techniques including electrical resistance measurement plus calculation, cross-sectional view of passive voltage contrast (XPVC) sequential searching, planar and cross-section STEM are successfully used to isolate a nanoscale defect, single metallic stringer in a snakecomb test structure. The defect could not be found by traditional failure analysis methods or procedures. The unique approach presented here, expands failure analysis capabilities to the detection of nanometer-scale defects and the identification of their root causes. With continuous shrinking feature sizes, the need of such techniques becomes more vital to failure analysis and root cause identification, and therefore yield enhancement in fabrication.

This paper presents two cases utilizing high KeV Passive Voltage Contrast (PVC) for defect localization that is impossible with other techniques. The first case is thin layer resistor of CrSi. De-processing or polishing to expose the defective layer may damage it. High KeV PVC combined with FIB etch allows for a clear top view and x-section image. The second case involves a beam sensitive via chain. In order to avoid ion-beam-caused-damage, carbon paste was used to ground the sample. A high KeV electron beam was used to localize the defective via. This paper also discusses the way to avoid beam caused sample damage and how to apply it for further grounding and FIB cross sectioning to reveal the defect.

This article describes a novel way to prepare TEM samples from existing FIB lift out samples for third dimensional observation. An in situ needle in a FIB column is applied to handle the sample and a special sample holder is used that tilts the sample rapidly to 90º in the FIB column. The application of this technique is also discussed.

A technique to “graft” a FIB lift-out TEM sample onto a scrapped wedge polished sample was introduced. In this way, the sample can be ion milled with lower accelerating voltage to avoid FIB caused problems. This technique does not require special attachment for the FIB. Improved imaging quality and potential applications are discussed.

This paper describes the FA technique to identify very tiny defects that cause gate oxide damage. These defects as examples include crystal originated pits, gate oxide pinhole and residual. The defects may have the same electrical signature; the same kind of holes in gate oxide will be seen when the sample is simply deprocessed with wet chemical and observed with SEM; but they are distinctly different mechanisms. Electrical test, emission microscope, FIB and SEM were used to localize the defect and TEM for the final analysis. The application of planeview, cross-sectional and three-dimensional TEM is discussed.

This paper introduces a technique to reveal a small feature defect of an SRAM cell via utilizing a 200kV dedicated field emission STEM on a FIB prepared sample. The initial TEM sample contains the entire defective cell; one side of the sample has n-type transistors and the other p-type. Both sides of the sample were observed using STEM bright field and dark field (HAADF) detectors (transmitted beam – inner information) and SEM mode (surface and sub-surface information). With deep beam penetration of STEM, one contact was found to be very close to the poly gate. Further FIB cuts were performed to remove the rest of the bulk away from the defect, thinning down to the area of interest. When the sample was thinned to a final thickness of less than ~100nm, a final image was taken of the exposed defect. The failing root cause was that the upper corner of the poly had touched the adjacent contact. Such an approach offers many unique advantages for site specific failure analysis over conventional SEM and/or TEM techniques.

To find defects and their root cause in semiconductor devices has become more and more difficult as chip size dramatically drops. A novel method combining FIB sequential cross-sectioning and TEM is described in this paper. This combination has provided a powerful tool for defect mechanism analysis. FIB slicing through a failed cell can be controlled to a precision of 0.1 micron. Passive voltage contrast imaging with FIB enhances defect detection. After a defect is found, in-situ TEM sample is prepared with FIB milling. By putting together the series FIB images along side with the TEM images and its associated high resolution EDS data, the detailed defect formation mechanism was discovered and feedback to process engineering for process improvement.