A global node optimization (GNO) technique can generate a model for a planar multiple layer film stack structure, e.g. a binary grating structure. In this technique, after obtaining spectra and target thicknesses from one or more wafers, a continuous film approximation (CFA) and a grating factor (GF) set are identified. A model using the CFA and the GF set is optimized by simultaneously fitting a plurality of the spectra while minimizing error compared to the target thicknesses. After simultaneously fitting all of the spectra, a GNO stack is created. A GNO recipe is then created using the GNO stack. Notably, a tool implementing the GNO technique uses minimal modeling capabilities and computational resources.