Failure Analysis in Semiconductors

Introduction

Approximately all modern electronic devices consist of semiconductors, from mobile phones, computers, automobiles to industrial control systems. Hence, these devices must be highly reliable since semiconductors become more complex and miniaturized. Semiconductor failure not only results in product recalls but also in economic losses and system-level malfunctioning. Thus, failure analysis is very important in the diagnosis of the problem, improvement in the product development, and help in corrective action. Knowing the semiconductor failure mechanisms will help the manufacturers to avoid similar problems in the future production batches.

Principle and Methodology

The general principles of semiconductor failure analysis must isolate, analyze, and characterize any defect or anomaly that can be observed to cause device malfunction. While the first step of the analysis usually constitutes a functional test to verify the failure mode, the next steps would involve a systematic localization of the defect through electric, thermal, and optical means. After locating the fault, destructive analysis would take place to detect whether the defect is due to electrical overstress (EOS), electrostatic discharge (ESD), metallization defect, or silicon die-cracks. Failure analysis follows a sequential pattern: first, nondestructive tests are performed (such as X-ray or infrared imaging), then fault isolation (via emission microscopy), and finally, destructive physical analysis (examination including cross-sectioning or chemical etching to identify root cause).

Instrumentation

Advanced instrumentation now serves to visualize and characterize defects at the micro or atomic level in failure analysis. Scanning Electron Microscopes (SEM) and Focused Ion Beam (FIB) systems are widely employed in the field of imaging and device cross-sectioning. High-resolution internal imaging of defects is offered by Transmission Electron Microscopy (TEM). Emission microscopes and thermal imaging tools detect hot spots and current leaks. Time-Domain Reflectometry (TDR) and Curve Tracers are for the electrical isolation of faults. Energy Dispersive X-ray Spectroscopy (EDS) is considered for the study of defect sites in order to characterize the material compositions. All these together create a good multidimensional view to pinpoint failures.

Strength and Limitations

The most important power of semiconductor failure analysis, however, is providing very interesting insight into the problems, both material- and design-related, within the product. It serves to promote continuous improvement, customer satisfaction, or compliance with quality standards and identifies systemic problems back to the invention, packaging, or assembly processes. Yet, it is limited. Analysis takes time and money, often a huge expenditure for very complex or exceptionally deeply embedded faults. Destructive techniques have a property of creating irreversible damage to the sample that limits the chances of repeated analysis. Further, the interpretation of results requires very high technical expertise; furthermore, some failure modes may remain elusive with advanced or rare equipment, and variance in the environmental exposures of testing could also influence results.