Oblique Angle Artifact Reduction using Wavelet-Based Filtering in Off-centered Circular Geometry of Cone Beam Computed Tomography

A tomographic methodology for inspection of TSV (Through Silicon Via) process wafers is developed by utilizing an X-ray source. In conventional X-ray computed tomography (CT), the scanning axis of X-ray source and detector is approximately parallel to the long axis of the phantom and perpendicular to the plane of X-ray source. However, because TSV projection data are captured by angling the phantom bed relative to the plane of X-ray beam, the conventional CT geometry can not produce the visible projection images and results in a poorer resolution in TSV phantom. In such cases, an off-centered circular trajectory geometry of cone beam computed tomography (CBCT) is more effective. However, each projection is transversely truncated, bringing errors and artifacts in reconstruction. In this paper, the wavelet-based filtering as the adaptive denoising filter of compressed sensing (CS) enhancement is proposed for the off-centered circular trajectory scanning geometry. In the experiment, TSV imaging of nanofocus CT (nCT) is used to evaluate the accuracy and practicability of the proposed method, which is equipped with an off-centered flat panel detector. Results show that artifact enhancement is acceptable for practical use, and the image quality appears sufficient for specific diagnostic requirements. It provides a novel solution for wafer inspection CBCT system, in order to reduce the effect of oblique angle artifact.