Distortion compensation for accurate overlay in lithography of quasiperiodic patterns

In this paper, we address the problem of ensuring accurate overlay in lithography of patterned substrates with low-order distortions. This problem becomes more important in situations where warpage and thermally induced distortion of high-density quasi-periodic patterns in large flat panel displays (FPDs), or high-density memory cells demand appropriate compensation schemes. A recently developed signal processing technique is used to estimate and compensate for substrate distortion. While avoiding time-consuming (e.g. site-by-site) alignment procedures, the proposed technique permits the use of time-efficient alignment procedures (e.g. global alignment) without compromising overlay accuracy. The proposed technique first estimates the existing low-order distortion of the patterned substrate. After estimating the distortion, global alignment schemes can be used to align the image of next layer to the previous one in a few check points. In the final step, the estimated distortion function can be used for compensating the local misalignments.