SRAM is often chosen to be the process qualification vehicle during technology development or yield learning vehicle during product manufacturing, and consequently failure analysis of SRAM is the main feedback for process improvement and yield learning. The most common SRAM failure is single bit cell failure. Although its location can be precisely localized by functional test and the defect causing the failure is within the failing bit cell, its failure analysis becomes more and more challenging in advanced technology nodes. As semiconductor technology continuously scales down, SRAM bit cell size and power supply voltage decrease, resulting in increased transistor strength variation and mismatch. SRAM single bit cell soft failures have become more and more common. For such a failure, its defect is usually subtle or even there is not physical defect at most cases. The soft failure is just due to transistor parameter variation. To evaluate the single bit cell soft failure and identify its root cause, electrical nano-probing is an indispensable measure. In this paper, we will first describe the operation of a 6-Transistor (6-T) SRAM single bit cell and three different types of single bit cell soft failures, then discuss the two electrical nano-probing methods for the SRAM single bit cell soft failure.

Failure analysis plays a very important role in semiconductor industry. Photon Emission Microscopy (PEM) has been extensively used in localization of fails in microelectronic devices. However, PEM emission site is not necessarily at the location of the defect. Thus, it has limitation for the success rate of the follow-up physical failure analysis focusing on the emission site. As semiconductor technology advanced in the 3D FinFET realm and feature size further shrank down, the invisible defects during SEM inspection are tremendously increased. It leads to the success rate further decreasing. To maintain good success rate of failure analysis for advanced 3D FinFET technology, electrical probing is necessary to be incorporated into the failure analysis flow. In this paper, first, the statistic results of PEM emission sites versus real defect locations from 102 modules of microprocessors manufactured by 14nm 3D FinFET technology was present. Then, we will present how to wisely design electrical probing plan after PEM analysis. The electrical probing plans are tailored to different scan chain and ATPG failures of microprocessors for improving failure analysis success rate without increasing too much turn-around time. Finally, two case studies have been described to demonstrate how the electrical probing results guide the follow-up physical failure analysis to find the defect.

This paper describes novel concepts in equipment and measurement techniques that integrate optical electrical microscopy and scanning probe microscopy (SPM) capabilities into a single tool under the umbrella of optical nanoprobe electrical (ONE) microscopy. Optical imaging ONE microscopy permits non-destructive measurement capability that was lost more than a decade ago, when the early metal levels became electrically inaccessible to microprobers. SPM imaging techniques do not have sensitivity to many types of defects, and nanoprobing all of the transistors in an area pinpointed by optical electrical microscopy is often impractical. Thus, in many cases, ONE microscopy capability will permit analytical success instead of failure.

Contrary to known art, we have discovered that lubricated tin-silver connectors have better electrical performance and are more reliable than lubricated silver-silver connectors under high-current and high-vibration conditions. The antifretting lubricant, that enhances the performance and reliability of the tin-silver connectors, is a grease consisting of a hydrocarbon oil in a nano-sized silica-particle base. Focused ion beam and scanning electron microscopy were used to understand the contact degradation mechanism. The superior electrical performance and reliability of the lubricated tin-silver connectors is due to a mechanism that replaces the tin plating from the contact surface with a coating of silver. The removal of the tin plating may be due to wear and the replacement by the silver coating may be due to an electrochemical displacement reaction.