Alignment accuracy evaluation of the x-ray stepper SS-1 for processed wafers

Abstract The alignment accuracy of the X-ray stepper SS-1 for synchrotron radiation (SR) lithography was evaluated. The mark state changes whenever the process layer is deposited. The alignment mark can be classified into four types based on the mark composition of all the process layers in LSI manufacturing. The alignment accuracy was evaluated by these four typical process marks. For a silicon mark, alignment repeatability of 25 nm (3σ) was obtained. For the renewal mark composed of SiO 2 or metal layer, alignment repeatability of 60 nm (3σ) or less was obtained. In all the process layers used in the experiment, alignment repeatability of 80 nm (3σ) or less was obtained. The signal level can be improved by optimizing the step depth of the alignment mark and by optimizing the process layer thickness. The same alignment accuracy as that of a silicon mark is possible by optimizing the mark step depth and the process layer thickness.