Process for monitoring the thickness of layers in a microelectronic device

A process for manufacturing a silicon integrated circuit product that includes a crystalline silicon substrate, a thin epitaxial silicon layer, and a thin silicon interface layer therebetween, comprising:

• a. constructing a depth profile of a target structure including:
• i a silicon substrate having a certain thickness, a known index of refraction and extinction coefficient;
• ii a silicon interface layer overlaying the silicon substrate, having an empirical depth, index of refraction and extinction coefficient;
• and
• iii an epitaxial silicon layer overlaying the interface layer, having a desired thickness and the known index of refraction and extinction coefficient;
• b. generating a first set of model behavior curves of the target structure, based on the depth profile, including:
• i an intensity change curve, also known as a tangent curve, also known as psi curve;
• and
• ii a phase change curve, also known as a cosine curve, also known as delta curve;
• c. forming a thin silicon epitaxial layer having the known index of refraction and extinction coefficient over the product substrate, the forming also including the forming of some interface layer;
• d. emitting light signals of certain wavelengths from an ellipsometer on the surface of the epitaxial layer at certain angles with respect to the surface of the epitaxial layer;
• e. generating reflected light signals from the surface of the epitaxial layer and the interface layer;
• f. collecting the reflected light signals with the ellipsometer;
• g. generating a second set of behavior curves from the reflected light signals collected by the ellipsometer including:
• i an intensity change curve, also known as a tangent curve, also known as psi curve;
• and
• ii a phase change curve, also known as a cosine curve, also known as delta curve;
• and
• h. ascertaining the thickness of the formed epitaxial layer by comparing the first set and the second set of the behavior curves and calculating the difference, if any, between the target thickness and the formed thickness.