Towards traceability in scatterometric-optical dimensional metrology for optical lithography

Currently, the application of scatterometry for dimensional metrology for optical lithography is limited to a relative measurements for process control and development. To establish scatterometry for traceable and absolute dimensional metrology an estimation of the measurement uncertainty is required. In scatterometry, the geometry of the object is deduced from measured light properties after interaction with the object under test. This indirect method requires the solution of an inverse diffraction problem e. g. by nonlinear optimisation. Different aspects have to be considered: Algorithms are required to propagate the uncertainties of the input parameters, the directly measured optical properties, to the output using covariance or Monte-Carlo methods. The model representation of the geometry of the object and inherent model assumptions of the used mathematical methods are essentially imperfect. We present an analysis of uncertainty contributions based on experimental data. To enable traceable scatterometry in semiconductor industry, we started to develop a wafer based scatterometry standard. Design, suitable materials and calibration procedures for this standard are discussed.