Study of the influence of the shape of projection lens focal plane on the focus control of advanced lithography

Abstract The high-precision focus control technology becomes more and more important, as the effective depth of focus (DOF) shortens dramatically in advanced lithography. In conventional focus control technology, the focal plane of projection lens is assumed as an ideal plane, but in fact it is a curved surface. The difference between the ideal plane assumed and its real shape results in partial defocus of wafer exposure field, thereby affecting the exposure quality. In our current work, the real shape of projection lens focal plane is brought into consideration for the focus control, and the simulation shows that this method can effectively improve the accuracy of focus control by 26%.

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