27. Spektrometertagung 2017

Due to the high requirements regarding the purity of polymer parts used in the semiconductor industry, there has been a significant amount of effort dedicated to non-destructively detecting defects and thereby increasing the manufacturing yield rate [1,2]. Critical defects are air-filled cavities, burned parts of the polymer material, metallic enclosures, as well as other polymer materials. In a comprehensive study we investigated potential methods able to detect these kinds of defects: optical microscopy, mid infrared imaging spectroscopy (MIRS), Raman imaging spectroscopy (RS), optical coherence spectroscopy (OCT), THz imaging tomography, x-ray tomography as well as ultrasound imaging. We present the measurement results of each of the evaluated detection techniques and compare them mutually. As expected none of the investigated methods was able to solve the task completely as a stand-alone technique. Each procedure demonstrated different advantages and limitations. Both spectroscopic techniques, such as MIRS and RS are able to identify the material of the defect, if compared with a suitable database, but only close to the surface. X-ray transmission measurements allow the separation of metallic and non-metallic particles, but only expensive tomographic setups would be able to provide the defect position in depth. Optical microscopy is able to characterize size of surface defects excellently, but fails for deeper lying defects. OCT is able to detect all defects up to a depth of 2 mm, but is not able to identify the defect material. Thus a combined approach is required. We propose a prototype facilitating the combination of an optical microscope and an OCT probe that is capable of detecting the critical defects in a depth of up to 2 mm. The unique combination of optical microscopy with OCT provides the preferable detection capabilities at moderate system costs. The bright and dark field illumination of the microscopy enables the required surface scanning capability to identify near-surface defects rapidly. The OCT probe allows the detection and localization of deeper lying defects and thus complements the microscope forming a unique combination of two methods with complemental advantages. To the best of our knowledge, such a system has not been proposed so far elsewhere.