New Overlay Metrology System Of Advanced Node Process

With the dimension of the integrated circuit shrinking,the overlay criteria of the advanced node manufacturing process became more rigorous.It is still a challenge to improve the accuracy of the overlay.The ambiguous measurement results can sabotage the overlay control system,directly disturb the process stability,even cause yield issue.To solve this problem,this paper developed new overlay metrology system for the advanced node manufacturing process.The development had been implemented on mass production,reduced almost 30% rework rate,and improved about 1% yield.The specific research progress is as follows:1.The root cause and the mechanism of overlay measurement inaccuracy had been investigated,and the overlay metrology optimization solutions of specific process layers were proposed.The chemical mechanical polishing,etching and such other processing could induce profile asymmetry of the measurement targets.Because the slightly process fluctuations is inevitable,the profile variation is not controllable.After the measurement targets segmentation,dummy features saturation and other solutions the stability of targets were significantly improved through the manufacturing process flow.2.Diffraction-based overlay metrology was evaluated and implemented successfully.Diffraction-based overlay used a scatterometry to obtain the positive and negative first-order diffracted light and calculated the overlay with the light intensity.Due to high sensitivity,it is compulsive to design measurement targets and recipe according to the specific manufacturing process conditions.3.Based on the concept of design for control,the best combination of overlay measurement targets and recipe with premier stability were screened out among multiple designs.The measurement results were able to be predicted by simulations,the different combinations were ranked by the key performance index.It is more efficient and beneficial to develop the metrology system with the simulation rather than the experiment on Si wafers.4.The metrology systems screened out by simulation were further verified with the Si wafer-based experiments,the mass production also achieved good performance with the new overlay metrology.The new metrology system measurement result of the critical process layers was better than ordinary image-based overlay metrology on total measurement uncertainty,tool induced shift and precision.New metrology system can reduce the lithography process rework rate significantly and benefit the productivity and yield.The innovation of this thesis is that based on the investigation of the process flow effect on overlay metrology,the measurement target optimization solution were proposed,new metrology system was developed with simulation instead of Si wafer experiment,and eventually the diffraction-based overlay were implemented successfully.