Advancing overlay metrology using digital holographic microscopy

In semiconductor industry, integrated circuits are manufactured on wafers, built up layer-by-layer, resulting in a complex multilayer stack. In order for a chip to work properly after manufacturing, each layer should be positioned with sub-nanometer accuracy relative to the previous layer. This positioning is called overlay, which is the lateral misalignment of a newly patterned layer with respect to the previous layer in a multilayer stacked wafer. With the continued shrink of device feature sizes and more complex devices being developed, there has been a relentless push for semiconductor overlay metrology improvements for accurate, precise, and fast overlay measurements. In this thesis, the potential of dark-field digital holographic microscopy as an overlay metrology tool is explored. Digital holographic microscopy enables the reconstruction of complex fields, allowing for computational corrections of imperfections in the imaging system. In this study, six key challenges are addressed. The questions explore the major difficulties of digital holographic microscopy, its practical implementation, and its potential to meet the demanding requirements of advanced semiconductor metrology.