Spectral Sensitivity Analysis of OCD Tool for Sub 40 Nm Process

Since the measurement precision of OCD (Optical Critical Dimension) technology highly depends on the optical hardware configuration, spectra types, and inherently interactions between the incidence of light and various materials with various geometrical structures, here a method is introduced for seeking the most sensitive measurement configuration to enhance the metrology precision and to reduce the noise impact to the greatest extent. In seeking the best mode and spectrum type for data collection, system noise of tools were estimated based on hardware precision. All spectrum types (e.g. SE, SR, Mueller matrix) were normalized for comparability. The sensitivity of different normalized spectra modes with several hardware configurations of incidence angles and azimuth angles were investigated. The optimal hardware measurement configuration and spectrum parameter can be identified. The minimum parameter tolerance of a given model can be retrieved by theoretical simulations. Poly-silicon (P2-ET) models of 28 nm nodes were constructed to validate the algorithms. The best measurement mode was selected. This method can provide guidance to the measurement precision before measuring actual device CDs.