Impact of angle ranges on thickness resolution in thin film reflectometry

Thin film reflectometry is a common way to monitor film thicknesses in numerous processes. Semiconductor and optics producing industries, e.g., require film thickness observation. Spectral reflectometry interrogation is one of several methods, which can be assessed by various algorithms depending on resolution and measuring range demands. Incident angle is a crucial parameter to these interrogation methods. Light, under different incident angles, produces different spectral reflectivity functions. These are integrated by a detector, in this case a spectrograph. Therefore, one needs to minimize the range of incident angles onto the measured object in order to increase the resolution of film thickness. Lateral resolution may also be a crucial parameter in some processes. Lateral resolution is a function of the range of incident angle, it increases with increasing angle range. These two crucial facts result in an estimate of measuring error introduced by the angle range under a given maximal lateral resolution. A measuring setup for a range of incident angle measurements is presented, as well as an example interrogation of a thin film under different incident angles.