The sensing method of the alien substance of the back side and the sensing apparatus of the alien substance of the back side and coating apparatus

This invention aims to accurately and certainly detect harmful alien substances of the back side which could possibly cause a slit nozzle to scratch the upper surface of the substrate and thereby harm the slit nozzle during a floating type spinless coating process. A spinless coating apparatus, by providing with a back side alien substance detection apparatus 50, can certainly detect harmful alien substances Q of the back side (namely, alien substances that may a slit nozzle 14 to scratch the upper surface of a substrate G and thereby harm the slit nozzle) on the upstream side of the slit nozzle 14 in the substrate conveyance direction (X direction). Further, in response to an alarm signal WS generated when the back side alien substance detection apparatus 50 detects such harmful alien substances Q of the back side, a main control section 50 makes the slit nozzle 14 move upwards immediately via a nozzle lifting mechanism 36 so that the slit nozzle 14 may fend off the raised portion GQ of the substrate G (avoi