Wafer level inspection for determination of yield of surface-micromachined pressure sensors

Development of a surface micromachining process for commercial scale production of absolute pressure sensors necessitates the definition of inspection tests at each stage of the process and for the completed packaged product. The yield measurement described in this paper is for a Field Effect Transistor pressure sensor integrated into a CMOS process. This measurement can be divided into verification of the electrical and mechanical properties of the pressure device. This paper describes the development of a simple method for mechanical yield determination. The method is based on a visual inspection procedure where the interference rings observed under a conventional 5X/20X inspection microscope, are correlated with white light interferometry (wafer level and packaged devices) and Atomic Force Microscopy (AFM) (wafer level) measurements. The application of these two profiling methods is also compared in the paper. Based on this work a simple, low cost, automatic system for yield determination using standard equipment can be developed. Initial results from a software system for inspection automation are presented.