This month we feature part 3 of the “Optical lithography for Thin Film Head (TFH) manufacturing” series.

Part 3: Ultimate performance from state of the art TFH lithography systems

Today’s leading edge TFH manufacturers use advanced scanners, with TFH specific options, to manufacture the highest performance Thin Film Heads. These options push stitching, overlay, resolution and CD uniformity to the limit. However, advanced options can only deliver the specified imaging performance if they are in harmony with the TFH process. Furthermore, the optical lithography system specifications are based on flat surfaces, CMOS/Logic film stacks and associated metrology. Unfortunately, this is not the case in TFH processing, and subtle process differences have a significant impact on these parameters. For example, variations in surface flatness will generate alignment offsets, and will also reduce depth of focus which in turn impacts CD uniformity. These processing effects were recognized by ASML and lead to the generation of patent US20090237635 which further expands on these concepts.

What’s the solution? Well, the best solution would of course be to make the surface flat. However, in order to achieve this, one would need to be able to accurately characterize the wafer’s surface using a method such as the Benchmark PSFM reticle http://www.benchmarktech.com/PSFM.htm in conjunction with feedback from the lithography systems leveling device. The PSFM method is short range and the Lithography system’s leveling device is long range - the best performance will be when both the planes are parallel to each other.

For more information and discussion, please This e-mail address is being protected from spambots. You need JavaScript enabled to view it. at simaxlithography.com