Exploring the limits of transistor scaling with electron microscopy

The smallest features on transistors used in computer circuits today have approached atomic dimensions: the SiO2 gate oxides are between 5 and 8 silicon atoms thick and the concentration of dopant atoms has increased to the point that electrically inactive dopant clusters as small as a few atoms are common enough to affect device performance. We have used atomic-resolution STEM with single atom sensitivity to identify the size, structure and distribution of clusters responsible for the saturation of charge carriers and address the question of how many atoms are needed before the gate oxide loses its bulk properties. This provides a challenge for the design of replacement gate dielectrics, many of which contain a few monolayers Of SiO2.