A Simple And Calibratable Method For The Determination Of Optimal Focus

Achieving a proper focus setting in sub-micron optical lithography is extremely important. A technique has been developed for the determination of optimal focus setting on production lots. Using aerial image simulation the dimensions of the test structure studied have been optimized. With a simple optical microscope a judgement can be made about the focus setting. As the depth of focus becomes comparable to the resist thickness, it was observed that different methods of focus determination do not give the same results.