Abstract: A photomask may include a patterned layer, a phase-shift layer adjacent the patterned layer, a first aperture, a second aperture, and a light-absorbing layer. The first aperture may allow light to pass through the patterned layer and the phase-shift layer and provide a first phase shift. The second aperture may allow light to pass through the patterned layer and the phase-shift layer and provide a second phase shift different than the first phase-shift. The light-absorbing layer may be disposed adjacent the first aperture and may include a light-absorbing material that reduces the intensity of light passing through the first aperture such that the intensity of light passing through the first aperture is substantially equal to the intensity of light passing through the second aperture.

Abstract: A method for conveying information about a photomask substrate is disclosed. The method includes heating an area of a photomask substrate located between a top surface and a bottom surface of the photomask substrate with a laser. The heat applied to the area of the substrate forms a mark inside the substrate that stores information identifying the photomask substrate.

Abstract: An unconstrained removable protective cover for optical disks. With this apparatus a transparent protective cover can be mounted to an optical information recording disk wherein the different thermal expansion coefficients of the disk and the protective cover will not result in read write errors due to warping of the protective cover. An inner spacer ring is fixedly bonded to the inner diameter of the disk substrate and the protective cover. However, on the outer perimeter of the disk, a U-shaped spacer ring is fitted thereon and fixedly mounted to the outer perimeter of the transparent protective cover. This allows the transparent protective cover to expand and contract relative to the disk substrate by lateral movement of the spacer ring relative to the disk, without warping of the protective covering. A plurality of methods of mounting the outer spacer ring to the protective covering are disclosed.