A wireless and passive wafer cleanliness monitoring unit via electromagnetic coupling for semicondutcor/MEMS manufacturing facilities

This paper presents a wireless and passive chemical sensing system, in situ real time, via electromagnetic (EM) coupling, capable of monitoring wafer cleanliness during rinsing process at semiconductor/MEMS manufacturing facilities. A MEMS chemical sensor is embedded in a wafer-form transponder to evaluate the rinsing process in situ by measuring the conductivity of rinsing water inside micro-features formed by two interdigitated electrodes. All necessary power for the transponder is supplied from an external interrogator via the on-wafer transponder antenna. The modulated conductivity data is then emitted back from the transponder to the external interrogator in wireless and battery-free manner. The wireless system has been implemented on a 4-inch glass wafer to maintain the wafer form factor, not disturbing hydrodynamics of the rinsing process. The working distance of the system was measured to be about 25 cm, primarily limited by the coupled power to the transponder. Real time and in situ characterization of system was performed with three different control solutions: hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and sodium hydroxide (NaOH). Detection uncertainty of the system was observed to be less than 2% (2 ppb for a 100 ppb solution).