Overlay control solution for high aspect ratio etch process induced overlay error

Abstract

In the semiconductor manufacturing process, especially in the high aspect ratio etch process of 3D NAND, overlay remains a constraint in an increasing device yield. With the increase in 3D layers, the etch process shows extreme inconsistency for different lots with different etch chambers, which makes it difficult to control within the budget. This article gives a systematic analysis on how the overlay feedback model reduces the overlay and which method should be used to reduce the etch-induced overlay residue. The linear and nonlinear inter- and intrafield models are used, and the overlay reduction performance is limited. Then, a correction per exposure (CPE) method is used, which shows the minimum residue. The feedforward overlay method together with the linear and nonlinear CPE method shows the best performance with only 20%–30% overlay residue. Two methods are recommended during the CPE model applied to control overfitting. One is to choose the best CPE order by judging the mark number of each exposure field, and the other is to define the fitting parameter range in a suitable range. Different CPE models are used and compared, and the verification results demonstrate that the suggested method has a great overlay fitting performance and overlay residue even if some parameters are excluded. That is, the study shows a method to balance the process variation, machine performance, feedback model, and metrology data.