Micro-crack defects detection of semiconductor Si-wafers based on Barker code laser infrared thermography

Micro-crack defects are easy to form in the semiconductor Si-wafer surface during the production process, which finally effect the quality of silicon based microelectronic products. In order to ensure the quality and performance of products, it is important and necessary to carry out nondestructive testing (NDT) for Si-wafers. This paper experimentally investigates the performance of the Barker code laser infrared thermography (BCLIT) technique for the semiconductor Si-wafer defect detection, using an optical infrared thermography set-up in transmission method. The thermal wave signal response of the laser to the Barker code modulation waveform is collected by an infrared camera, which was stored as image sequences. Then the detectability was studied according to processed results via the Total Harmonic Distortion (THD) algorithm from obtained image sequence. In addition, linear frequency modulation thermal wave imaging (LFMTWI) technique was used to compare and analyze the performance of BCLIT. Experiments performed on the Si-wafer under the low power density condition indicate that the higher of the excitation power and the wider of the crack width, the better the detection effect. Furthermore, the performance of BCLIT is better than the traditional LFMTWI with all cases in evaluation index result of signal-to-noise ratio (SNR). The research results show that the BCLIT technique significantly improve SNR and defect detectability, and it can be used for the semiconductor Si-wafers micro-crack defects detection even under low power density excitation.