Microbeam Analysis Techniques for ICs

The ion microprobe mass analyzer was used for a general chemical characterization of actual integrated circuits. The analysis technique was designed to determine impurities at the surface, in the deposited oxide, in the thermal oxide, in the metallization, and at the various interfaces between these layers. The identification of the intentional dopants in the silicon was performed where concentrations were above the detection limit. In-depth concentration profiles of intentional dopants such as phosphorus were obtained by monitoring the dopant ion signal as a function of sputter time. A quantitative estimate of some of the common dopants and/or impurities was accomplished using an emperical calibration. Depths were determined by emperically calibrating the sputter rates as a function of area, total primary ion current, and primary ion species. Interface regions were identified by sputter time analysis of layers where successive layers have an elemental matrix change. The interfaces between layers of similar matrix elements, such as deposited oxide - thermal oxide were assumed to have the same sputter time as dissimilar matrices, i.e., deposited oxide over metal has the same thickness and sputter characteristics as over thermal oxide. Negative or positive oxygen was used as the primary sputtering ion for data collection. Positive argon was used as the primary sputtering ion for data collection. Positive argon was used to rapidly sputter through layers for interfacial analysis.