Novel strong resolution enhancement technology with phase-shifting mask for logic gate pattern fabrication

We propose the new phase-shifting mask named the centerline phase-shifting mask (CL-PSM; generically named "Mask Enhancer"). The minute phase-shifting aperture is disposed at the center of the opaque rim pattern on the mask to enhance the aerial image. The CL-PSM is able to maximize the aerial image contrast of the line patterns with any line width and any pitch by controlling the size of the phase-shifting aperture. We investigated the fundamental characteristics of the CL-PSM in KrF lithography. 70 rim line patterns with any pitch above 250 rim were successfully fabricated with a DOF of more than 300 rim. We studied the influence of various kinds of mask errors on the CD error, and we clarified that the influence of mask error is sufficiently small for practical use of the CL-PSM. The mask error enhancement factor is practically small for the opaque rim and phase-shifting aperture. A phase error of +/- 5 degrees does not reduce the process margin, and induces no CD variation. Furthermore, we demonstrated that the CL-PSM achieves a 65-nm random line pattern like a logic gate pattern in ArF lithography. The pattern fabrication by CL-PSM attains the required DOF of 300 rim for 65-nm node device fabrication. We confirmed that the "Mask Enhancer" has a resolution potential of 45-nm corresponding to a 1/4 wavelength.