Smart implant-layer overlay metrology to enable fab cycle time reduction

Overlay is one of the most critical design parameters in integrated circuit manufacturing. Maintaining good overlay performance during manufacturing is therefore essential in order to obtain high yield and to ensure that the performance and reliability of the eventual semiconductor device is according to specifications. For that reason, optical metrology is nowadays extensively used in any production facility for overlay monitoring and process control. Overlay metrology is typically required after each lithography step for (nearly) every lot. The number of process and lithograpy steps have increased significantly with advancing technology nodes and consequently there is an increased demand for overlay metrology. Although the benefits of overlay metrology are obvious, the use of metrology should be kept at acceptable levels as it adds cost and increases fab cycle time. Virtual overlay metrology, the replacement of some real overlay measurements with predicted values, is an effective solution for keeping the need for overlay metrology under control.