An acoustic sensor for monitoring microelectronics packaging manufacturing processes

Since microelectronics fabrication processes require numerous steps, cost and yield are critical concerns. In-situ monitoring is vital for process control. However, this goal is restricted by the shortage of available sensors capable of performing in this manner. This paper proposes a silicon acoustic sensor to be used for in-situ monitoring of electrochemical or plasma deposition processes. The sensor was fabricated using common integrated circuit (IC) and micromachining techniques. Such techniques enable the creation of extremely thin beams and membranes, thus enabling devices to be highly sensitive to a measurand such as pressure. The sensing element of the microphone is a deflectable thin diaphragm composed of silicon and a piezoelectric material, zinc oxide (ZnO). The transduction operation is based on the piezoelectric effect, where a mechanical pressure applied to a polarized ZnO crystal results in a mechanical deformation. This resulting strain induces an electrical charge on the ZnO surface. To collect these surface charges on the sensor optimally, we implement segmented electrodes in the regions of greatest bending stress. The measured sensitivity of this sensor is 195 μV/μbar.