L. Cisotto | TU Delft Repository

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

Doctoral thesis (2018) - Luca Cisotto

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… ...

Analytical calculation on the determination of steep side wall angles from far field measurements

Journal article (2018) - Luca Cisotto, Silvania F. Pereira, H. Paul Urbach

In the semiconductor industry, the performance and capabilities of the lithographic process are evaluated by measuring specific structures. These structures are often gratings of which the shape is described by a few parameters such as period, middle critical dimension, height, and side wall angle (SWA). Upon direct measurement or retrieval of these parameters, the determination of the SWA suffers from considerable inaccuracies. Although the scattering effects that steep SWAs have on the illumination can be obtained with rigorous numerical simulations, analytical models constitute a very useful tool to get insights into the problem we are treating. In this paper, we develop an approach based on analytical calculations to describe the scattering of a cliff and a ridge with steep SWAs. We also propose a detection system to determine the SWAs of the structures. ...

Amplitude and phase beam shaping for highest sensitivity in sidewall angle detection

Journal article (2017) - Luca Cisotto, H. Paul Urbach

In integrated circuits manufacturing, specific structures are used as tools to evaluate the quality of the lithographic process, and the shape of these structures is often described by a few parameters, of which in particular the sidewall angle suffers from considerable inaccuracies. Using scalar diffraction theory, we investigate whether a properly shaped cylindrically focused probing beam could increase the ability to detect tiny changes in this angle in the case of a cliff-like structure, modeled as a phase object. This paper describes the theoretical formulation used to calculate the optimized beam and compares its performance with the case of a focused plane wave. ...

Determination of the full scattering matrix using coherent Fourier scatterometry

Journal article (2016) - Nitish Kumar, Luca Cisotto, Sarathi Roy, GKP Ramanandan, Silvania F. Pereira, H. Paul Urbach

We demonstrate a method to obtain within an arbitrary numerical aperture (NA) the entire scattering matrix of a scatterer by using focused beam coherent Fourier scatterometry. The far-field intensities of all scattered angles within the NA of the optical system are obtained in one shot. The corresponding phases of the field are obtained by an interferometric configuration. This method enables the retrieval of the maximum available information about the scatterer from scattered far-field data contained in the given NA of the system. ...