Although much traditional FA depends on physical observation to localize failures, electrical techniques are also important, particularly with advances in design for testability (DFT) on modern ICs. DFT structures combined with automated test equipment and algorithmic fault diagnosis facilitate a test-based fault localization (TBFL) approach to identify defect locations on ICs based on scan test patterns. This article and a companion piece in the November 2001 issue of EDFA provide an overview these methods and show how they can reduce the number of potential defect sites on a chip and, in some cases, identify defects that would be missed by other techniques.

This is the second article in a two-part series on test-based failure analysis (TBFA). The first article, which appeared in the August 2001 issue of EDFA, discussed the need for automated diagnostics and the general concept of TBFA. This article discusses the steps involved in implementing a TBFA process and addresses the challenges that are likely to be encountered. It explains how to gather data required to link observed behavior to specific faults, how to set up and use fault dictionaries, and how to handle unmodeled as well as bridging faults. It also discusses the use of TBFA with conventional voltage and quiescent current (IDDQ) testing.

Scan-based diagnostics produce high-confidence target lists of suspected faults associated with electrical fail signatures. Physical coordinates extracted from these lists serve as a guide for physical failure analysis. When certain conditions are met for the design database and pattern sets, the extraction can be automated and the analysis completed within minutes. The logic mapping flow is a natural extension of scan-based diagnosis with the potential to reach new levels of electrical failure analysis without the extensive data collection and resources associated with signature analysis. This article describes the logic mapping concept and how to implement the flow. It also presents the results of actual cases in which logic mapping was used.

Unit level traceability (ULT) is a powerful tool that allows complete die histories to be accessed in the course of testing and analysis. It is especially useful for identifying the likely causes of microprocessor failures and in cases where failure analysis resources are limited. In the article, the author explains how he used ULT in the investigation of a 0.25-µm CMOS processor. Using the ULT of the die, he discovered a failure signature based on die location on the wafer. One root cause of failure was traced to cross-field variation in the lithography process due to marginal focus control. Another failure, observed after burn-in, was traced to the presence of residual titanium left after metal etch.

Failure analysis of dynamic random access memory follows a three-step process consisting of electrical test and diagnosis, localization, and physical defect analysis. The electrical test delivers pass-fail results that are graphically displayed in bitmaps, which are then used to localize defects based on layout data. This article describes each step of the process and compares and contrasts laser scanning techniques.

The analysis of scan-based ICs is essentially split between two domains: that of the designer and that of the device analyst. Designers tend to operate within the confines of fault characterization, looking for defects within logic blocks or structures based on test data. Device analysts, on the other hand, are more concerned with physical aspects of the defect such as location, composition, and morphology. These separate worlds are beginning to merge, however, as this case study shows, streamlining the entire failure analysis and resolution process.

Chip-scale packages (CSPs) make efficient use of space on PCBs, but their small size, multilevel stacking arrangements, and complex interconnects present serious challenges when it comes to testing and failure analysis. This article describes some of the problems encountered when dealing with various types of CSPs and provides practical solutions based on the tools and techniques available in most FA labs. It discusses the causes and effects of package and die related failures and walks readers through the steps involved in decapsulating plastic FBGA packages using conventional etching, polishing, and milling techniques. It also includes a case study involving a failure caused by improper laser marking.

Chip-scale packages (CSPs) make efficient use of space on PCBs, but their small size, multilevel stacking arrangements, and complex interconnects present serious challenges when it comes to testing and failure analysis. This article describes some of the problems encountered when dealing with various types of CSPs and provides practical solutions based on the tools and techniques available in most FA labs. It discusses the causes and effects of package and die related failures and walks readers through the steps involved in decapsulating plastic FBGA packages using conventional etching, polishing, and milling techniques.

Scan-logic diagnosis is used in industry for three main purposes: root-cause analysis, improving manufacturing processes, and improving designs. This article reviews the principles of scan-logic diagnosis and its applications in each of the three areas. It also discusses ongoing challenges and emerging approaches.

The ISTFA 2006 panel discussion focused on the integration of test and failure analysis, a topic that was originally addressed at ISTFA 2000. The goal of this year’s panel was to discuss the improvements made to the integration of test and failure analysis and to explore our capabilities for analyzing future technologies.

Semiconductor trends, as embodied in the International Technology Roadmap for Semiconductors (ITRS), provide a guide for the challenges facing the failure analysis community. This process is a risk assessment of key features forecast for the impact of future technologies on failure analysis. The technical challenges fall primarily into two categories: failure site isolation and physical analysis. The failure site isolation challenges are largely driven by the device complexity and reduced accessibility of circuit nets. Additional challenges arise due to the increase in device operating speed and pin count. The challenges in physical analysis are driven primarily by smaller device feature sizes and by the host of new materials being introduced. In addition to the technical challenges, infrastructure changes are also likely to occur. The industry paths for addressing these challenges are discussed.

Wafer-level failure analysis plays an important role in IC fabrication, both in process development and yield enhancement. This article outlines the general flow for wafer-level FA and explains how it differs for memory and logic products. It describes the tools and procedures used for failure mode verification, electrical analysis, fault localization, sample preparation, chemical analysis, and physical failure analysis. It also discusses the importance of implementing corrective actions and tracking the results.

This article provides a high-level review of the tools and techniques used for backside analysis. It discusses the use of laser scanning and conventional microscopy, liquid and solid immersion lenses, photon emission microscopy (PEM), and laser-based fault isolation methods with emphasis on light-induced voltage alteration (LIVA). It explains how laser voltage probing is used for backside waveform acquisition and describes backside sample preparation and deprocessing techniques including parallel polishing and milling, laser chemical etching, and FIB circuit edit and modification.

This article describes a yield-driven approach for characterizing IC logic failures at the wafer level and presents several case studies to demonstrate its versatility and assess its value.

Faster time-to-production of a new product is the common goal of design houses and foundries. This article demonstrates how foundries can contribute through post silicon validation, which allows design houses to focus on more complicated issues.

CMOS IC failure mechanisms are of three general types: bridge defects, open circuit defects, and parametric related failures. This article summarizes bridge and open-circuit defect properties and provides references for further self-study. Bridge defects are characterized based on location, their significance in terms of logic gates and transistors, and critical resistance for dc logic and timing failures. Open defects are more complex and diverse with six possible failure modes each of which are described in the article.

This article explains how the success rate of in-line scan chain logic macros can be nearly doubled for certain types of failures with the help of laser voltage imaging and laser voltage probing. The authors provide background information on LVI, LVP, and scan chain logic macros and show how they are used to diagnose skip test, clock-type, and soft single-latch failures.

This month’s guest columnist shares his thoughts on the effects of consolidation and automation in the semiconductor industry and the importance of training for failure analysts.

This article provides insights into the nature of IDDQ and timing defects and the challenges they present to failure analysts based on the findings of a Sematach study.

This article assesses the capabilities of failure analysis techniques in the context of 65 nm CMOS ICs. It demonstrates the use of OBIRCH, voltage contrast, Seebeck effect imaging, SEM and TEM techniques, and FIB cross-sectioning on failures such as dielectric breakdown, open and resistive vias, voids, shorts, delaminations, and gate oxide defects.