Improved failure analysis in scanning acoustic microscopy via advanced signal processing techniques

Abstract

With the upcoming semiconductor devices, becoming more and more complex, also the failure analysis becomes more challenging. Advanced signal processing methods can improve the abilities of scanning acoustic microscopy significantly. On the one hand, they can reduce the measurement effort, on the other hand, they can improve detection capabilities.In contrast to conventional imaging, which requires each layer needs to be scanned separately, this paper proposes the application of synthetic aperture focusing technique to the scan data. By superposing the signals of several scan positions a virtual, much larger aperture is generated. This allows a reconstruction of the full volume and provides information about structures in any depths. Reconstruction is done in time domain and frequency domain. The method is applied on a reference sample and real microelectronic samples are examined.Especially for structures with a huge number of interfaces and a periodic structure the signal to noise ratio is very low for the deeper interfaces. Wavelet transform using fast Mexican hat and its coefficient selection filtering techniques are used for improving the SNR and by this enhancing defect detection. The method is demonstrated on a reference sample and on high bandwidth memory modules consist of a stack of small memory dies.