2023-4-27

Advanced high voltage e-beam system combined with an enhanced D2DB for on-device overlay measurement

ABSTRACT

Because high voltage scanning electron microscopy (HV-SEM) based on-device overlay metrology measures the overlay between 3 layers at least, metrology tool-induced error can significantly impact the mask or process correction, which is based on overlay measurement. In general, CD-SEM or e-beam inspection (EBI) tool-based on-device overlay measurement is prone to be biased by specific metrology tool errors such as image distortion and beam perpendicularity. Therefore, the capability of extremely low distortion and beam perpendicularity to minimize the metrology tool error is an essential requirement for HV-SEM overlay metrology use on state-of-the-art DRAM, 3D NAND, and Logic devices from the chip manufacturing industry. Additionally, a suitable algorithm and versatile platform for multi-layer-based overlay measurement are necessary due to the increase in complexity of the target measurement layer and region of interest (ROI). With this background, we developed the high voltage e-beam inspection (HV-EBI) tool that fills the requirement abovementioned. The developed HV-EBI tool has the capability of variable acceleration voltage in the range of 30kV to 50kV and wide field of view (FOV) imaging up to a maximum of 50μm with extremely low first-order distortion in the level of ＜ 0.01% and 0.1mrad and uniform beams perpendicularity. In this paper, we demonstrate the performance of the on-device overlay measurement of the HV-EBI tool combined with an enhanced die-to-database (D2DB) algorithm.
For evaluation purposes, we utilize IMEC logic wafer stacked as multiple layers in the step of the back end of the line (BEOL). Firstly, we optimized the beam condition regarding acceleration voltage and maximum FOV size. Under optimized beam conditions, all the data processing of alignment (SEM image – CAD layout) and measurement was conducted for all three target layers in parallel to image acquisition using an enhanced D2DB algorithm. Finally, correlation work validates the proposed system's reliability compared to optical overlay metrology and electrical test result. Based on the impact of this work, we expect that the proposed HV-EBI system can be used for accurate and efficient on-device overlay monitoring of both R&D and HVM steps.

Key words: High voltage, EBI, SEM, D2DB, CD, EPE, Overlay