Optical monitoring of nonquarterwave film thicknesses using a turning point method

A method is presented for monitoring film thicknesses in fabricating multilayer structures where the thicknesses are not simply quarterwave multiples. This method is similar to the conventional turning point method, except that the monitor signal wavelength is allowed to vary from one layer to the next. No physical modifications to the conventional apparatus are required. Results are presented for an example of the use of this method.