A system for detecting liquid flow from a nozzle in a semiconductor processing device includes a first fiber optic sensor, a second fiber optic sensor, and an amp. The first fiber optic sensor and second fiber optic sensor are located on opposite sides of at least one nozzle. The first fiber optic sensor transmits light, and the second fiber optic sensor receives more of the light when the nozzle is not dispensing liquid than when the nozzle is dispensing liquid. The amp is coupled to the first fiber optic sensor and second fiber optic sensor. The amp indicates whether the nozzle is dispensing liquid according to an amount of the light received at the second fiber optic sensor.