Micro X-ray fluorescence device based on monocapillary ellipsoidal lens for thin film thickness measurement

Abstract

X-ray fluorescence (XRF) is a crucial non-destructive technique for determining the thickness of thin films or coating materials to ensure their optimal performance. In order to further expand the application of XRF in thin film thickness analysis, we have developed an inner-wall coated elliptical monocapillary X-ray lens (EMXRL), which has a larger acceptance angle and higher utilization efficiency for light sources compared to traditional inner-wall uncoated EMXRL. In addition, we have built a laboratory micro-X-ray fluorescence (Micro-XRF) thickness measurement device based on coated EMXRL. Compared to common XRF devices, it has a smaller X-ray spot size and higher intensity gain, resulting in smaller spatial resolution and higher detection efficiency in XRF thickness measurement applications. We established a standard curve in the range from 0.85μm to 56.5μm for measuring the thickness of Cu coating on silicon using this Micro-XRF device. The experimental results show that the micro-area thickness measurement device, based on the standard curve method, can measure the thickness of Cu coatings from 0.85μm to about 30.00μm with a relative deviation of about 3%. Within the thickness range from about 30.0μm to 56.5μm, the relative deviation of the measured thickness increased and was larger than 5%. This larger relative deviation mainly resulted from the greater absorption from the thicker coating. Furthermore, We used the device to perform mapping scans on scratched areas of Cu-plated circuit board to verify its usefulness. The results show that the device has the advantages of simplicity and speed, and has potential applications in fields such as semiconductors.