New simple method of extending the limit of rim phase-shift mask

Even though rim PSM, unlike Levenson Phase Shift Mask, has no design restriction that neighboring patterns should be altered, its benefit is modest in both resolution and DOF enhancement, which masks it difficult to be applied to high resolution patterns. In order to improve the performance of rim PSM, we propose a new simple method called rim+ATOM, which combines rim PSM with ATOM (Advanced Tilted illumination On Mask). By combining rim PSM with ATOM, we could obtain resolution improvement by 20% compared to that of rim PSM with i-line stepper (5X, NA equals 0.45). And rim+ATOM showed less pattern degradation than ATOM for 45 degree patterns.