A cassette lid opening device for use in a clean room apparatus configured for cooperation with a wafer cassette. The cassette lid opening device comprises a wall structure having a separation wall having a wall opening for transferring wafers therethrough, a cassette docking port, and a lid handler provided to the wall structure. The cassette docking port is arranged at a first side of the wall structure for docking a wafer cassette. The lid handler is movable relative to the wall opening and configured to engage a cassette lid of the wafer cassette docked in the cassette docking port. The cassette lid opening device further comprises a blower having an elongated, slit-like nozzle substantially spanning a height or a width of the wall opening and configured to blow a curtain-shaped jet stream of a purge gas into a cassette interior of the wafer cassette.