Resolution Target Description
The central structure is a radial grating with radial pitch of 4o, having the smallest feature of 1 um in the center. Small interruptions are placed where the radial sectors widths are of 2, 3, 4 … 7 um, while the maximum width at the outermost end is 7.85 um. The center of the radial grating is shown by a structure with corner-to-corner configuration. The target is flanked on all sides by variable pitch rulers. The lines widths start at 0.5 um and increase by 0.1 um up to 9.1 um. Each line is followed by a space of the same width. Each integer value width line is shortened and a number is placed asside, showing its width in um.
The corners of the target contain corner-to-corner lithography tests with groups of lines and spaces of 1, 2, 3, 4, 6, 8, and 10 um, respectively.
The target also contains 4 “USAF 1951” resolution targets (MIL-STD-150A format) with 4 groups (6, 7, 8, and 9) and two “layers.” This resolution target has spatial frequencies as expressed in Table 1 and line/space widths as given in Table 2, below. A useful description of these targets can be found at http://en.wikipedia.org/wiki/1951_USAF_resolution_test_chart.
The resolution target contains also rectangular fields with grating structures in two perpendicular directions. The line/space widths of the gratings are given in um by the numbers placed nearby.
The membranes are made of 300-nm-thick low stress silicon nitride. The target structures are made of 2 - 2.5-um-thick gold (specified more exactly upon request). Fields of the sub-micrometer structures can occasionally be missing or be distorted. The line/space filling ratio is targeted upon 1:1, but may differ slightly for the smallest structures. However, the pitch is accurate better than 5% for all structures. Small, unimportant variations of the presence, placement, and accuracy of particular structures are possible.