SUBSTRATE PROCESSING METHOD AND SUBSTRATE PROCESSING APPARATUS

In a first measuring process, P-polarized infrared light is emitted onto a substrate at a first incident angle at which an interference signal becomes smaller than a change by light absorption by the substrate, and light transmitted through or reflected from the substrate is measured. In a substrate processing process, substrate processing is performed on the substrate after the first measuring process. In a second measuring process, after substrate processing, P-polarized infrared light is emitted onto the substrate at a second incident angle at which an interference signal becomes smaller than a change caused by light absorption by the substrate, and light transmitted through or reflected from the substrate is measured. In an extraction process, a difference spectrum between the spectrum of the transmitted light or reflected light measured in the first measuring process and the transmitted light or reflected light measured in the second measuring process is extracted.