Ultrasound Hardware Setup For CMP Pad Characterization

Chemical Mechanical Polishing, (CMP), pads made of polyurethane material are utilized in the Integrated Circuit, (IC), industry to planarize wafers between successive process steps. The properties of such pads and their behavior must be known in order to determine under what conditions and for how long they can be used efficiently. This research involved the development of a system to study the properties of such pads. The system developed during this research enabled the pads to be tested under varying physical conditions. The setup used a combination of several instruments to provide excitation to the pad and acquire a measure its response. A central computer controlled the instrumentation system employed. In this research the determination of the physical properties of CMP pads was accomplished through the use of Ultra Sound testing. Ultra sound methods offer a non-destructive method of characterizing pads to be used in the production of IC wafers. Ultra sound characterization is currently one of the most widely used techniques utilized for non-destructive inspection. This report provides a detailed account of the hardware instruments involved and the method of integration of those instruments into a system that could easily, rapidly and accurately characterize CMP pads. The pad response was measured in terms of the signal voltage transmitted through the pad to the ultrasound sensor. The software stored these readings for every set of testing conditions. Changing the temperature, humidity and depth from the pad\u27s surface where measurements are made changed the test conditions. These data were analyzed statistically to determine the behavior of the pad. This research was part of a larger research effort that provided the statistical tool required to determine the uniformity of a CMP pad