Nanometers and Picometers: Roadmap to Success with 20 Terabit/in² Patterned Media

Production of patterned magnetic media requires nanometer control of track pitch and feature size variation. Nanometer control implies picometer accuracy and precision. This can be done without significant capital investment in new measurement tools. High-quality, general purpose SEMs and AFMs already in wide use in the HDD industry are capable of providing metrology at this level. In a typical measurement run, one makes images of an appropriate magnification calibration specimen along with the test samples. The resulting images are then analyzed offline with purpose-built calibration and measurement software. When these procedures were applied to measure individual pitch values of the calibration specimens themselves, the relative pitch variation (standard deviation/average pitch) was <0.5% for 7 different specimens whose pitch values cover 3 orders of magnitude (from 2000 down to 35 nm). The method is not only precise, it is also accurate. A 144-nm pitch 2D grating was measured by optical diffraction at PTB, the national standards lab of Germany, and by AFM in our lab. The average pitch values agreed within 0.023%. We present a metrology roadmap that applies the SEM and AFM methods to measure patterns down to 5 nm pitch, meeting the metrology requirements for patterned media up to densities of 20 Tb/in2. Since announcing this plan in 2008, we have made significant progress, having produced a commercial standard with 70 nm pitch. The relative standard deviation is <0.3% and our certificate of traceable calibration for this standard shows an expanded uncertainty of +-0.4 nm for single pitch measurements. The 70 nm standard is better than the roadmap requires.