Absolute coordinate system adjustment and calibration by using standalone alignment metrology system

摘要

We propose a construction and calibration method of an absolute coordinate system for lithography tools. In the conventional overlay control system, subsequent layers are overlaid on the 1st layer that could have unknown wafer distortion. This method is insufficient because the distortion of the 1st layer may be large. A higher level of overlay control can be achieved using an absolute coordinate system by correcting the 1st layer to zero distortion. This can be possible using an absolute alignment metrology system. In order to demonstrate and prove our theory, we report experimental results of the improvement of alignment accuracy by using absolute grid and the stability of its coordinate system.