Passive Wireless Monitoring of Wafer Cleanliness During Rinsing of Semiconductor Wafers

Semiconductor facilities consume large amounts of water, most of which is used for rinsing of wafers during cleaning steps. To optimize water use, real-time and
in situ
monitoring of wafer cleanliness during rinsing is necessary. Yet no prior art is real-time and
in situ
. In this paper, we present a passive wireless sensing system capable of measuring the residual contamination on the wafers in real-time and
in situ
. The wireless system consists of a micromachined Electro-Chemical Residue Sensor (ECRS) and wireless transponder circuitry based on RFID technology. The ECRS measures the impurities concentration of the water inside micro-features during the rinsing processes. The sensor reading is converted to a frequency by the on-wafer transponder and remotely logged through a wireless link between two coupled inductors, while the transponder captures power from the remote RF signal: a battery-free system. A prototype system was fabricated and its frequency output was characterized by using sodium chloride solution ranging from 190 ppb to 6 ppm. The measured wireless chemical sensor system has a relative uncertainty of less than 1% in the concentration range.