Classical approaches to PSG and BPSG dopants have yielded acceptable results in some cases, but considerable difficulties are associated with predicting the concentration of boron and phosphorus over large ranges. These difficulties arise as a result of the changes in spectroscopic features associated with changing dopant levels. 

Significant improvement in determining unknown film concentrations is possible using the Partial Least Squares (PLS) algorithm, making it possible for a single test instrument to analyze film thickness, and boron and phosphorus concentration, in a single measurement.