Reduction of x-ray irradiation-induced pattern displacement of SiN membranes using H⁺ ion implantation technique

We have developed a technique for improving X-ray irradiation stability of silicon nitride (SiN) X-ray mask membrane using H⁺ implantation. This technique can realize the reduction of X-ray irradiation-induced pattern displacement to less than 20 nm after X-ray absorption with a dose of 30 MJ/cm³ by optimizing the implantation dose to 4 × 10¹⁵/cm² at 150 keV. It is found that the mechanism of the reduction of the displacement is that the stress change after X-ray absorption in the implanted layer (top to 1.1 μm in depth) of SiN film compensates the stress change in the unimplanted layer (1.1 to 2.0 μm (bottom) in depth).