Ellipsometry And Its Application To Testing Integrated Circuits

Ellipsometric measurement instrument is an important tool for research andmeasurement of the optical properties of film and materials. Its principle is: a beam ofpolarized light is incident on the surface of the sample, and the beam will interact withthe sample, such as reflection, transmission, scattering; these interactions will lead tothe changes of polarization of beam depending on the sample’s own properties. Bymodeling the interaction between the polarized light and the sample, the thickness andthe optical parameters and other information of the sample can be determined from thecurve-fitting.The precision of ellipsometer can be achieved down to0.1, and its accuracyprimarily was guaranteed through the calibration of physical information of the system.Therefore, the system calibration method determines the accuracy of ellipsometer. Onthe other hand, especially in the industrial production environment, its physical andcalibration parameters will have variations with the time and environment change.Repetitive correction and calibration are required to keep the ellipsometer in a validstate for daily use. Therefore, a fast, simple, and accurate calibration method forellipsometry is critical for maintaining ellipsometer working efficiently and properly. Inthis thesis, a novel calibration method based on standard measurement reference system(standard samples) was revealed, and the method of calibration is simple and fast. Theprinciple is: if the relevant information of the samples (refractive index n, absorptioncoefficient k, thickness d) is given prior to the measurements (by more accuratemeasurement system or golden calibrated measurement system), the system calibratingparameters (angel of polarizer P, offset angle of compensator Cs,angel of analyzer A,phase shift of compensatorδ, and angel of incidenceθ0) can be deduced from thecomparison of the measured and calculated Fourier coefficients, with nonlinearregression and least square methods. These parameters will be used for systemcalibration and the system can be used to measure unknown samples.In this thesis, based on a single wavelength ellipsometer, the calibration method isanalyzed by simulation and verified by experiment. In detail, the calibration processrequires2to6standard samples, and the feasibility of the method is demonstrated and analyzed. The sensitivity of the angle of incidence and the numerical issue of multiplesolutions are analyzed systematically. Samples are measured by the calibrated systemand the maximum error is2.6. As to spectroscopic ellipsometry, the experimentalverification of the film measurement was carried on to illustrate the advantages of thenovel calibration method, including the combination of RCWA algorithm andmeasurement of the three-dimensional structure of the integrated circuit.In this thesis study, a novel calibration method is developed, which is fast, simpleand good for application in on-line integrated circuit metrology equipment compared tothe conventional method, and is more sensitive and accurate. Through the measurementof the integrated circuits film samples and CD samples, the validity of the innovativecalibration method in metrology of integrated circuit technology is demonstrated.