|M.Sc Thesis||Department of Quality Assurance and Reliability|
|Supervisor:||Dr. Singher Liviu|
|Full Thesis text|
The semi-conductor industry is progressing rapidly and smaller nano-structures are being designed and built in order to meet performance and capacity requirements. It is not clear how well current optical measurement tools will operate as the nano-structures reach critical dimensions.
Finite difference time domain (FDTD) technique is used in this work for simulating characteristic structures of modern day semi-conductor industry wafers with the purpose of investigating the limitations of the current optical systems to correctly identify and detect these structures and defects in these structures.
Successful adaptation of the FDTD tool is shown. Reflectance from silicon is successfully compared to theoretical values as well as reflectance from a thin film of oxide at various configurations.
Silicon with trenches is simulated in a 2D simulation using an array of trenches and using a single periodic cell. From the simulation results a method of predicting the trench pitch from the reflectance values is given and its accuracy is determined. In addition, the capability of the optical system of recognizing a missing trench is found. The spectral response of silicon with trenches is considered and a robust method of predicting the trench pitch from the entire spectral response is given.
Real reflectance measurement data of a shallow trench isolation (STI) structure on a wafer are compared to results achieved through FDTD simulations and a good correlation is shown to exist. A method of successfully predicting the height of the STI structure from the FDTD simulation data is also shown.
Transmission of a nano-sphere of water and gold of various diameters are simulated and the results are presented for several wavelengths. Transmission of evenly and randomly distributed suspended nano-spheres of water and gold are simulated and the results are presented for several wavelengths.
The conclusion from the results is that the FDTD tool is suitable for simulating structures of nanometer scale typical of the semi-conductor industry. In addition the limitations of the optical system are given in relation to defect identification and structure property prediction. The FDTD tool simulation results are also compared to real measurements showing that the FDTD tool is a practical solution. Calculated light scattering results from nano-spherical particles are also provided.