Apparatus for optical measurements of nitrogen concentration in thin films

A method for evaluating the nitrogen content in a thin film layer formed on a sample comprising the steps of:

• directing an intensity modulated pump laser beam to a spot on the surface of the sample for periodically exciting the sample;
• directing a probe laser beam to a spot on the surface of the sample within a region that has been periodically excited and is reflected therefrom;
• monitoring the reflected probe beam to determine the effects of the periodic excitation on the sample and generating output signals in response thereto;
• and
• filtering the output signals to provide a measure of the magnitude or phase of the modulated changes in the sample and using the result to evaluate the nitrogen content in the thin film layer.

A method for evaluating the nitrogen content in a thin film layer formed on a sample comprising the steps of:

• directing an intensity modulated pump laser beam to a spot on the surface of the sample for periodically exciting the sample;
• directing a probe laser beam to a spot on the surface of the sample within a region that has been periodically excited and is reflected therefrom;
• monitoring the power of the reflected probe beam to determine the effects of the periodic excitation on the sample and generating output signals in response thereto;
• filtering the output signals to provide a measure of the magnitude or phase of the modulated optical reflectivity of the sample;
• and
• comparing the filtered output signals to a predetermined value to determine whether the expected concentration of nitrogen is present.

A method of evaluating the annealing of a wafer having a thin oxide film formed thereon, said thin film having a nitrogen concentration comprising the steps of:

• periodically exciting a region of the surface of the sample;
• monitoring the effects of the periodic excitation with an optical probe and generating output signals in response thereto;
• and
• evaluating the extent of the annealing of the wafer based on the output signals.

A method of fabricating a wafer comprising the steps of:

• forming a thin oxide layer over a substrate;
• adding nitrogen to the oxide layer;
• annealing the wafer;
• periodically exciting a region of the wafer;
• monitoring the effects of the periodic excitation with an optical probe and generating output signals in response thereto;
• and
• evaluating the extent of the annealing of the wafer based on the output signals.