This paper is about a sample preparation technique that is based on a previous research publication1. The technique was initially used for the investigation of salicide formation for CMOS process development. The initial results were very good and proved to be helpful with root cause failure analysis. Once the technique proved to be a viable failure analysis (FA) tool, a research team was formed to continue the development. This paper is written in conjunction with this team. The team is presently focused on developing a repeatable and reliable methodology of deprocessing CMOS devices from the backside. The team is also developing a methodology for post deprocessing analysis once the backside silicon is removed. The research that is presented here focuses on packaged as well as unpackaged devices. Etch rates and selectivity of tetramethylammoniumhydroxide (TMAH) is investigated along with temperature dependencies. Package material and chemical interference issues were discovered and remedied with special preparation techniques. Post deprocessing analysis is considered and many ideas are proposed as part of future research.

A new tool (Schlumberger IDS 2000) has become available for acquiring waveforms from C4 (also known as flip chip) packaged IC’s. The waveform acquisition technique is based on electro-optic sampling through the backside of silicon. After explaining the physics of electro-optic sampling, the technique is demonstrated through the backside of Si on a simple diode test structure and a flip chip microprocessor. Also, many of the issues and challenges with this tool are discussed.