A lithography apparatus includes an extreme ultraviolet (EUV) scanner, an EUV source coupled to the EUV scanner, a quartz crystal microbalance and a feedback controller. The quartz crystal microbalance is disposed on an internal surface of at least one of the EUV source and the EUV scanner. The feedback controller is coupled to the quartz crystal microbalance and one or more of a radiation source, a droplet generator, and optical guide elements controlling the trajectory of the radiation source associated with the EUV source.