February_EDFA_Digital

edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 23 NO. 1 4 EDFAAO (2021) 1:4-10 1537-0755/$19.00 ©ASM International ® ENABLING TRUE ROOT CAUSE FAILURE ANALYSIS USING AN ATMOSPHERIC OXYGEN-ONLY PLASMA FOR DECAPSULATION OF ADVANCED PACKAGES Lea Heusinger-Jonda, Jiaqi Tang, and Kees Beenakker Jiaco Instruments, Delft, the Netherlands lea@jiaco-instruments.com INTRODUCTION Semiconductor devices are subject to increasingly higher quality and reliability standards. Manufacturers of these devices must take extensive measures to ensure these standards are met, while at the same time adopt- ing new highly integrated, complex packaging solutions including a variety of new materials and structures to achieve the economic and performance advantages that were previously met with silicon scaling. These factors imply the use of highly advanced tools to analyze potential failures, which often require physical access to the die. It is therefore essential that the decapsulation process does not affect the original state of the die, bond wires, and bond pads, and that consequently, original failure sites are preserved. It is the aim of this article to discuss a recently devel- oped decapsulation method using the effluent of an atmospheric oxygen-onlyplasma and its use for root cause failure analysis of complex semiconductor structures. ARTIFACT-FREE ATMOSPHERIC PRESSURE MICROWAVE-INDUCED PLASMA DECAPSULATION Decapsulation is conventionally carried out using acids or low-pressure reactive ion etching (RIE). While successfully used in routine analysis, these decapsula- tion methods have reached their limits with increas- ingly complex packages, and the use of a wide variety of materials. Acid etching causes corrosion damage on exposed metallization and bond wires, specifically if these are copper or silver. Conventional plasma decapsulation causes over-etching damage on the passivation and die due to the use of CF 4 gaswhile at the same time the plasma ion bombardment affects the electrical performance of the device under study. Both acid and CF 4 based plasma etching can cause damage to the silver-plating layer on the lead frame or the copper stitch bond. The fully automatedatmospheric pressuremicrowave- induced plasma (MIP) machine uses only oxygen and patent-pending hydrogen-based recipes to expose and preserve components and original failure sites inside of a package. The MIP effluent beam is scanned across the device surface, and the high-density of oxygen radicals and molecular oxygen metastable selectively remove the epoxy in the mold compound or underfill material. Following the oxygen MIP etching, the SiO 2 filler particles present in the mold compound or underfill material remain on the surface as a white layer, and the sample is subsequently submerged in an ultrasonic bath containing deionized water to remove the fillers. The sample is then dried and the etch-clean-dry cycle is repeated until the area of interest has been fully exposed. Due to the high selectivityof theprocess the functional components inside the package are fully preserved during this layer-by-layer etch process. CASE STUDY EXAMPLES Several case studies have been carried out and docu- mented over the past few years that illustrate the critical importance of preserving root causes of failures bymeans of artifact-free decapsulation. CASE STUDY I: CHLORINE CONTAMINATION [1] Todeterminewhether the evidence of a contamination can be preserved in its original state, during investigation a NaCl contamination was deliberately introduced into a QFN stacked-die sample. The sample was first partly decapsulated by laser and acid to expose the bond shelf on the middle layer die, then a 2% saline solution con- tamination was introduced and allowed to dry, and lastly the package was refilled using a refill epoxy. The sample