| Popis: |
Recently, technologies of ArF laser exposure tools and alternating phase shifting masks (Alt-PSM) are expected to be used in actual production. To utilize such newly developed technologies, it is inevitable to develop a mask inspection technology to check them properly. But it is currently difficult to check them precisely because sufficient image contrast is hard to obtain with any conventional mask inspection tools. It is not well understood whether we can get sufficient sensitivity with conventional optical setups and wavelength with the assistance of some kind of resolution enhancement techniques (RET), or we should move toward inspection using revolutionary new optics or shorter inspection wavelength. To study precisely the sensitivity of inspection optics for common types of defects, we have made a captured image simulator based on the RCWA (Rigorous Coupled Wave Analysis) method with which we can take into account the effect of the three-dimensional structure of a mask. We tried to calculate captured images for some mask structures at two different wavelengths, namely 199 nm and 257 nm. We made certain that no significant differences were observed for larger scale defects, but that a considerable difference of image contrast was observed for small scale defects around 50 nm in size. Thus we confirmed that this simulator is effective for evaluating and designing optical systems of mask inspectors, in order to achieve a high sensitivity for the detection of small defects in Alt-PSMs. |
