Optimisation of Coherent Fourier Scatterometry for Side Wall Angle Estimation of Printed Structures

Abstract

The electronic industry strives continuously to increase the performance of electronic components by adding new functionality, by making them more energy efficient or by increasing their absolute performance. This last possibility is mainly achieved by a higher density of electrical components. In a photo-lithographic process, this is associated with the ability of printing finer and finer details on a wafer, without impacting the speed and the accuracy of the overall process. In industry, this concept is expressed with a single word: yield. The higher the yield, the more profits for the chip producer. One of the often chosen procedures to improve the yield is through a tight control of key quantities related to the chip making process such as dose, focus, overlay and other relevant parameters in order to ensure the creation of a defect free device. In other words, through metrology. The root of this word is derived from the ancient Greek and it stands for the science of measuring. In the description of a target, it is often convenient to parametrize it with few geometrical quantities that are chosen as representative of dimensions or specific features. In the field of metrology applied to the semiconductor industry, one of the most used test targets are periodic gratings. These objects are usually described in terms of four quantities: height h, middle critical dimension MidCD, period (often named pitch) p and the side wall angle SWA; this last quantity represents the angle between the edge of a trench and the bottom of a line. Particularly, we focus our efforts on improving the estimation of the side-wall angle. Improving the quality of printed target relying on metrology techniques is the underlying motivation of this dissertation and the ultimate goal behind it…