A study on device robustness with integrated effects from low parts-per-billion level of metallic elements in wafer cleaning process chemicals

The existence of metallic elements in incoming chemicals is one of the great concerns in fab processing, degrading the fabricated device properties. In particular, with the unknown handling activity and environment influence caused by different means of transportation on the incoming chemicals stored typically in drum packaging, tight specifications in terms of various metallic species need to be enforced. These metallic impurities, if not controlled, are then introduced to the device during wafer fabrication especially during wafer cleaning process steps, with the contaminated incoming chemicals. Even trace amounts in metal concentration may alter the device electrical properties at their operating condition or even cause significant degradation over time. The impacts are especially critical on dielectric (gate oxide) quality. Correlation of such impact on device with respect to the metallic concentration level can help in setting references for reasonable specification limits, while not jeopardizing the device characteristics as well as its reliability. In this experiment, contamination levels of 0.1, 0.4, 0.7 and 1.0 parts-per-billion (ppb) are simulated and the impacts are then assessed at device level. Under evaluation are the 10 most common elements encountered namely Al, Ca, Cr, Cu, Fe, Na, Ni, Zn, Co, Mg.