FIB with EDX analysis use for thin film contamination layer inspection

Abstract

In current backend assembly house, there is yet standard inspection method available to confirm the incoming bond pad quality. The different severity oxidation level of the bond pad may highly influence the wire bonding process integrity. Due to this variation, there is a need to have an efficient monitoring method to confirm the quality of incoming wafer. As referring to the defect or problem occur due to bond pad condition, EDX has been identified as a potential solution method to combat the issues. Common SEM or FESEM tool has been mainly used for imaging purpose. This tool is normally equipped with EDX detector for further elemental analysis. For conventional use, Energy-dispersive X-ray spectroscopy (EDX) is an analytical tool used for the elemental analysis or chemical characterization of a sample. It relies on the X-ray source excited from bulk sample for elemental inspection. The basic Principle of the X-ray generated mainly occurs due to bombardment of high speed electron on metal target. The X-ray generated is based on the unique atomic structure which allows unique set of peaks in its X-ray spectrum. The energy dispersive X-ray (EDX) tool is generally applied for contamination elemental analysis on sample substrate surface. However, the capability of the EDX detector in detecting the thin film contamination layer which has a thickness layer less than 100nm is weak. This is mainly correlated to the natural working principle of the X-ray signal being generated. EDX detector is based on the emission of x-ray signal from the bulk sample substrate activated by primary electron to differentiate the elemental species. The higher the energy of primary electron being applied, the deeper the X-ray activation volume activated from the bulk substrate will be. Due to huge amount of bulk substrate X-ray volume been activated, this indirectly will suppress the X-ray signal generated from the thin film contamination layer. In other words, the gap of the x-ray ratio on the sample surface versus bulk sample will get bigger when the primary electron energy increases proportionally. To efficiently test the contamination layer which has a thickness less than 100nm, FIB complementary with EDX functionality had been successfully applied for thin layer contamination analysis.