Study of scanner stage vibration by using scatterometry

The stage synchronization (vibration) performance highly impacts image quality, especially for ArF immersion tool due to high NA and high scan speed is used. But it is very difficult to judge scanner stage vibration effect by measuring CD impact since different factors such as energy, focus, PEB temperature may cause CD variation and cannot be decoupled. This problem can be solved by using a focus-energy regression model based Scatterometry CD measurement. Exposed wafers by ArF immersion scanner with different scan speed are measured by Scatterometry with 12X13 intra field measurement points. Then the data is regressed by the focus-energy model to separate the factors of energy, focus (z direction), and fitting error (other factors include x, y direction). Based on the regression result, stripes can be clearly seen in the focus and fitting error map which indicates the vibration distribution. By reducing the stage scan speed, the fitting error can be significantly reduced.