Apparatus and method for interferometrically measuring the thickness of thin films using full aperture irradiation

An apparatus for measuring the thickness of a layer of material having front and rear surfaces, said layer being one of a possible plurality of layers each having front and rear surfaces and formed on a front surface of a substrate, said material having properties that will transmit light, said apparatus comprising:

• means for providing a beam of collimated light;
• means for inserting in said beam of collimated light a plurality of narrow band filters, each filter passing a single wavelength so that the beam of collimated light becomes monochromatic;
• means for expanding the beam of collimated light so as to irradiate the entire front surface of said layer, said light being reflected off the front and rear surfaces of the layer and the front and rear surfaces of the possible plurality of other layers and the front surface of the substrate, said reflected light interacting to form a fringe pattern the image of which is reflected;
• means for directing the image of the reflected fringe pattern onto an active surface of a charge coupled device camera, said camera providing an output corresponding to said fringe pattern;
• means for digitizing the output of the charge coupled device camera;
• and
• means for receiving the digitized output of the charged coupled device camera for comparing said output with a set of stored fringe pattern reference characteristics corresponding to known layer thicknesses and for providing an output corresponding to a thickness map of the layer thickness.

A method for measuring the thickness of a layer of material having front and rear surfaces, said material having the ability to transmit radiation, said method comprising the steps of:

• irradiating a full aperture area of the layer with radiation so that reflected radiation from said front and rear surfaces has characteristics corresponding to the thickness of the layer in the area;
• receiving the reflected radiation;
• detecting said characteristics of said received radiation;
• comparing the detected characteristics of the received radiation with a set of reference characteristics corresponding to known thickness;
• and
• providing an output corresponding to the thickness of the layer in the area based on the comparison of the detected characteristics with the set of reference characteristics.