Ionic Contamination and Transport of Mobile Ions in MOS Structures

A fast, simple and very sensitive technique has been developed to determine the extent of ionic contamination of oxides in MOS capacitors. The method is capable of detecting better than 109 mobile ions/cm2 and is based on the measurement of the displacement current response to a slow linear ramp voltage at elevated temperatures. This yields an ionic displacement current peak whose area is proportional to the total mobile ionic space charge. The method is expected to be very useful for routine process and quality control applications. This technique has been used to study positive mobile charge behavior in silicon dioxide. The voltage dependence of the ionic displacement current indicates that trapping of ions occurs at the metal‐oxide interface and that ionic transport from the metal to the silicon interface is controlled by trap emission. Ion transport from the silicon to the metal interface is characterized by a single, bulk‐limited transport mechanism below 300°C with an activation energy that appears concentration dependent. Above 300°C an additional transport mechanism is observed which is slow in comparison to the primary transport mechanism.