Study of advanced mask inspection optics with super-resolution method for next-generation mask fabrication

Abstract

The lithography potential of an ArF (193nm) laser exposure tool with high numerical aperture (NA) will expand its lithography potential to 45nm node production and even beyond. Consequently, a mask inspection system with a wavelength nearly equal to 193nm is required so as to detect defects of the masks using resolution enhancement technology (RET). A novel high-resolution mask inspection platform using DUV wavelength has been developed, which works at 199nm. The wavelength is close to the wavelength of ArF exposure tool. In order to adapt 199nm optics for hp2x nm node and beyond defect detection on next generation mask with appropriate condition, further development such as the illumination condition modification technique has been studied. The illumination optics has the advantageous feature that super-resolution method is applied by adding the optics. To evaluate the super-resolution effect of illumination condition control optics, the interaction of light with mask features is calculated rigorously using RCWA (Rigorous Coupled-Wave Analysis) method.In this paper, image contrast enhancement effect using newly designed super-resolution optics which is applied to transmitted and reflected light image acquisition system are presented with simulation and experiment.

Improvement of a DUV mask inspection tool to hand over the baton for next-generation tool smoothly

“…[1]- [3] We have also proved the inspection sensitivity characteristics of C-pol, Ppol, and S-pol illuminations with the proof machine NT-7000α in joint research with Selete [4] . Based on these results, the optical system in NPI-7000 is equipped with a reflection C polarized inspection mode, a reflection P polarized inspection mode, and a reflection-reflection P/S concurrent inspection mode.…”

“…It is also known that phase defects in EUV blanks can be detected by the variance in reflection intensity of the 199nm wavelength light source, and we have previously demonstrated that these detection signals can be enhanced by using focus offsets [4] [5] .Our NPI-7000 incorporates two different sensors that can be used in de-focus mode to simultaneously obtain the reflection images to inspect the EUV mask blanks. Figure 4 shows the outline of the optics system.…”