Estimating Method for Electron Beam Accelerating Voltage Used in Energy‐Dispersive X‐Ray Microanalysis: Application in Failure Analysis of Wafer Fabrication

Abstract

Energy‐dispersive x‐ray microanalysis (EDX) techniques have been widely used for elemental analysis of thin film layers in wafer fabrication. However, during EDX analysis of thin film samples, sometimes it is difficult for us to identify elemental information of the surface layer from the underneath layers. Therefore, it is necessary for us to estimate the electron beam accelerating voltage used, and the penetration depth of the electron beam under this accelerating voltage before performing EDX analysis. In this particle, we will introduce a simple method/formula (V i = k E i, where the value of k is a constant, the unit of V i is in kV, and E i is in keV) to estimate the electron beam accelerating voltage, which should be used for determining the element of interest, and discuss the penetration depth of the electron beam under different beam accelerating voltages. The actual beam accelerating voltage used for a characteristic x‐ray line in EDX should be more than the theoretical value. In general, it is about 1.5–2.0 times that of the theoretical critical excitation energy. In this study, we have determined the over‐voltages of the characterization x‐ray lines of Al Ka, Si Ka, Ti Ka, W Ma, and W La, using TiN and TiW thin films and microchip Al bondpad (with Al/TiW/Ti metallization) samples. We have determined an experimental value of the over‐voltage constant, k, which was about 1.42, and it is near to the low side of 1.5–2.0 times. Moreover, we will also discuss an application case in failure analysis of wafer fabrication on nonstick bondpads.