In situ aberration measurement technique based on multi-illumination settings and principal component analysis of aerial images

The impact of lens aberrations becomes severe when the critical dimensions (CDs) shrink. The accurate measurement of both low- and high-order Zernike aberrations is important during a photolithographic process. Based on the multi-illumination settings and principal component analysis of aerial images, a novel in situ aberration measurement technique that can accurately measure all the Zernike aberrations, except for the sinusoidal 2-\theta and sinusoidal 4-\theta terms (under polar coordinates, and Z1 to Z4 are not considered) is proposed in this letter. The estimated maximum error of the Zernike aberrations ranges from 0.43 to 0.78 m\lambda when the amplitudes of the Zernike coefficients range from –20 to 20 m\lambda. The standard and root mean square errors are both in the range from 0.14 to 0.4 m\lambda.