Zernike model for overlay control and tool monitor for lithography and etch process

In advanced lithography and etch processes, the after-etch overlay is rendered unequal to the after-development overlay, and an etch process–induced overlay plays an extremely important role in determining the total overlay. This makes it difficult to achieve feedback control and also throws the overlay residue out of the control specifications. As the layer number of three dimensional integrated circuits increases or the overlay residue is only several nanometers in extreme ultraviolet technology, differentiations in etch tools lead to lot-to-lot overlay differences. Tool difference should be considered to compensate the overlay, irrespective of which method, interfield, intrafield, or correction per exposure (CPE), is used. However, it is not recommended to compensate the overlay for every lot as it will increase the cost of metrology. One of the widely used methods is to separate the lots by groups. In this paper, we propose a Zernike-CPE method to conduct a systematic study on how to reduce the overlay residue during the process of providing CPE feedback and to monitor tool performance. The research results demonstrate that the proposed method has potential roles to play in achieving overlay control and is highly suitable for advanced technology process monitoring.