A comprehensive cross-layer overlay prediction method with reticle heating for enhanced process optimization

As semiconductor devices continue to scale down, innovative overlay control strategies have been integrated into lithography process controls. Before these strategies can be implemented in high-volume manufacturing, they must first be thoroughly evaluated and verified. To enhance the cost and time efficiency of this verification process, overlay prediction becomes essential. There are two primary methods for overlay predictions: - Single layer overlay prediction: This method predicts the overlay impact on the current layer, resulting in new wafer alignment and overlay strategies. - Cross-layer overlay prediction: This method predicts the overlay impact on the subsequent layer, based on the new wafer alignment and overlay strategies of the current layer. However, these methods are only applicable when the overlay fingerprint from the exposure side of scanners remains constant. During exposure, however, heating effects such as reticle heating can cause the overlay fingerprint to expand over time. Although scanner suppliers offer options to compensate for these heating-induced grid distortions through additional feedforward corrections during exposure, the effectiveness of these corrections on the overlay of both current and subsequent layers needs further examination. In our study, we aimed to determine whether the reticle heating correction is beneficial for overlay. Initially, we extracted the reticle heating correction data from the scanner and applied it to the current layer to recalculate the exposure grid. Subsequently, we employed the cross-layer overlay simulation method using the newly calculated grid to predict the overlay for the subsequent layer. Finally, we summarized the impact of reticle heating on both the current and subsequent layers.