Scientists have discovered the bull’s-eye answer to the semiconductor industry’s search for more precise way to measure the relative positions of smaller tools squeezed by the millions onto silicon chips. They are likewise not expensive.
The industry  still continue to depend  on the use of the high-throughput optical equipment   to align level after level of complicated circuitry patterns even as the size of individual devices drops well below 50 nanometers (nm). This is hoped to spare chip makers of the challenge and extra cost of changing to a more complex technology for   overlay measurements.

In the process of chip production, instruments are used to calculate the distances between selected lines on one target on one chip layer, as well as corresponding lines on another target on the layer immediately above. The measurements are utilized to find out the size of the offset between levels. A modern microprocessor chip could have 28 levels.  The comparative position of any two targets must be known with a precision of approximately a nanometer or two. Since the measurements of chip features are already dwarfed by the wavelength of visible light, many scientists suspect that the industry’s bag of technological tricks for extending conventional optical measurement methods will be exhausted within the next few rounds of miniaturization.
The scientists may use alternative tools such as the high power atomic-force microscopes which would supply the required resolution.  However, they are known to be slower and are not likely to be as cost effective as compared to the rapid, non-destructive optical techniques already utilized for overlay measurements.  Scientists have looked at better designs for the targets, or benchmark reference patterns, which are used to verify the precision and accuracy of overlay measurement device.

Scientists have investigated the target patterns   in the modeling studies which are considered as the nanotechnology equivalent of slightly overlapping picket fences. As monitored under the high power microscope, together, the two sets of densely arranged nanoscale lines as well as the grooves create a hybrid target that solidly reflects light.  This created an image that is measurable with a conventional optical microscope. It was also observed that the individual sets of lines are so thick that no individual optical image of the lines occurs.   However, the combined superstructure results in the new unique optical pattern which can be best observed with the use of the high power microscope.  Likewise it was noted that the intensity patterns of the reflected light are rare to the combination.  The patterns are easily analyzed to find out the relative position of the lines that make up the pattern. In the modeling studies, feature sizes ranging from 10 nm to 50 nm were positioned as close as 100 nm apart which is beyond the theorized limits of resolution.
The scientists noted that the combined pattern greatly magnifies better than forty times the size of the overlay offset between layers. An article was published in the Optic Letters, which described the pattern design and modeling results.  Scientists are working closely with the semiconductor industry to fabricate prototype targets with the new geometry.Read more