A temperature- adjusted spectrometer includes a light source, a temperature sensor and a spectral analyzer. The light source is configured to direct light along a light path through a first lens toward a substrate position in the process chamber; the spectral analyzer is configured to receive light scattered from a material sample in sample area on a substrate located at the substrate position in the process chamber; and the temperature measurement device is configured to measure the temperature of a material sample on a substrate located at the substrate position in the process chamber. Further, the spectrum is corrected by means the measured temperature by a calibration module to provide a temperature - adjusted spectrum.
