Practical Methodologies in Restoring Initial Failure Mode and Backside Focused Ion Beam Cross-Section for Defect Visualization

Complementary Metal-Oxide Semiconductor (CMOS) Image Sensors are gaining popularity most especially in Automotive Safety and Advanced Driver-Assistance Systems (ADAS) applications. Customer application modules involve oftentimes a third party supplier. When failures involve interaction between an image sensor die and the customer's module, the Failure Analyst has to know the exact failure mechanism to pinpoint whether root cause is in the die fabrication (fab) or packaging assembly (third party supplier). Challenges can befall the analyst: failure modes can recover which renders the unit functional and laboratories most often do not have complete sophisticated analytical laboratory equipment for electrical testing, fault isolation and sample preparation. In this paper, a case study of a CMOS Image Sensor is presented wherein the failure mode recovered which was restored and how the structural limitations were overcome for fault isolation on both front- and back-side. A modified process flow was performed to visualize the defect through backside Focused Ion Beam (FIB) cross-section.