Patent ID: 7339382

Claim:
A method of determining thickness of a film on a substrate, comprising: directing primary microwave energy from a microwave transmitter toward a film of unknown thickness of a substrate located at a distance from the transmitter; receiving reflected microwave energy returned from the substrate as affected by the film; separating the reflected microwave energy from the primary microwave energy; measuring components of the reflected microwave energy; and determining from the effect of the film on the reflected microwave energy while eliminating the effect of the distance between the microwave transmitter and the substrate on the reflected microwave energy, a thickness value of the film from the components, or functions of the components, of the reflected microwave energy using a stored relationship between the properties of reflected microwave energy and thicknesses of films, the stored relationship being obtained from previous measurements of calibration films of known thicknesses, in which directing microwave energy toward a film on a substrate includes moving a microwave transmitter parallel to the surface of the substrate as part of a robotic or automatic coating application system, the method including measuring a thickness of a wet film overlaying a dry film by employing two sensors—one microwave sensor over the wet film atop the dry film, and another sensor over the dry film—and determining the difference in measurements of the two sensors the wet film thickness.