Nondestructive interface state measurement by pulse photoconductivity method

Abstract

The interface states between Si substrate and the gate oxide (Si/SiO2) have significantly influences to device properties. The conventional measurement methods for interface states need a long turn around time evaluation period since test element group structure is necessary to be constructed. The in‐line measurement in the wafer process has been expected strongly to achieve the Quick TAT analysis to increase the throughput of the process. We have studied to present a new measurement method for observing the interface states under the nondestructive condition. The specimens of the oxide, SiO2, on the Si wafers are prepared by the thermal oxidation of representative wafers, which surface–crystal planes have various miller indices of (100), (110), and (111). An electrode is set close to the SiO2 surface, where the voltage and pulsed light are applied and irradiated at the same time. The photo‐carriers generated at the Si surface absorption are excited to the Si upper bands and surmount the SiO2 potential barrier. The carrier excitation could be selected by varying the wavelength of pulsed light to focus on the trapped and localized carriers' excitations from the Si forbidden band gap, excluding the Si interband transition. For the preliminary result, we demonstrate to detect the signals from the trapped carriers' excitations and their energy distribution, which is compared with the results on the distribution of the interface states density as reported in other research works. The measurement result at this time indicates the possibility toward the noncontact detection for Si/SiO2 interface states. Copyright © 2016 John Wiley & Sons, Ltd.