Cycle-Shift Scan Chain Failure Analysis Using Single Pulse Test Pattern

Conventional scan chain test pattern of "0011" repeating data is widely used to tackle scan chain failures such as stuck-at and transition failures using Laser Voltage Imaging's (LVI) fundamental and second harmonic frequency approaches. However, this "0011" scan chain test pattern when combined with LVI technique is ineffective in isolating cycle-shift scan chain failures even with the integration of a lock-in amplifier which is also known as phase LVI. This is because phase LVI isolation technique requires detailed understanding of the scan chain design and fault isolation for all types of cycle-shift scan chain failing signatures is not possible using this technique. In this paper, we propose a technique to effectively isolate the failing flop for an entire range of cycle-shift scan chain failures using a novel single pulse chain test pattern paired with Laser Voltage Probing (LVP) that overcomes the challenges faced by phase LVI.

Introduction

Scan chain fault isolation is a process of identifying one or more defective scan cells in a design-for-test (DFT) scan chain [1]. Among the most commonly used chain test patterns, all-0s and all-1s test patterns are restricted to detecting stuck-at-1 and stuck-at-0 scan chain failures, respectively. On the other hand, chain tests that consist of repetitive "0011" pattern has been proven robust for detecting stuck-at failures, and all types of transition failures including slow-to-fall, slow-to-rise, fast-tofall and fast-to-rise [2]-[4].