UC Riverside

In this dissertation thesis, I will discuss the fundamental basic technology necessary for continuing the prosperity status of 21st century electronic devices; Lithography. I will give an overview of the concepts of scanning electron microscopy (SEM) and development of direct electron beam lithography (D-EBL) for magnetic bit patterned media (BPM), capable of achieving magnetic recording areal densities above 1 terabit/in2. Furthermore, I will present the peripheral equipment mainly used for developing innovative processes.

One of the main challenges in developing direct electron beam lithography technique for fabricating magnetic bit patterned media, which I was faced with was not only to reduce the minimum feature size below 10 nm but also to ensure an adequately small pitch size of less than 26 nm. The latter is the critical value for the side of a square pattern period (assuming a 1:1 bit-aspect ratio (BAR)) necessary to achieve over 1 terabit/in2 density in hard disk industry. The main concern was to overcome the technical limitations associated with a relatively wide electron beam tail. For instance, according to Gaussian distribution, even a "5-nm" electron beam spot size can have a "tail" of over 50 nm because of beam scattering and secondary effect. Another limitation in the spatial resolution of EBL resulted from the interaction of the electron beam with stray magnetic fields emanating from the transitions in the BPM film under study. Throughout my research I comparatively studied a number of EBL processes, the results from which led me into selecting a lift-off based EBL process on films spin-coated with a hydrogen silsesquioxane (HSQ) negative-tone e-beam resist. Using this process, we successfully transferred large-scale square periodic arrays of nano-"dots" with a sub-13-nm diameter and a sub-26-nm pitch, as required for densities above 1 terabit-per-square-inch, into continuous magnetic films made of exchange-coupled Co/Pd perpendicular multi-layers. Furthermore, I used the same EBL process to transfer ultra-high-density patterns not only in conventional single-layer recording media but also into potentially next-generation 3-D structures consisting of several independent magnetic layers. Meanwhile, I fabricated Magnetic Force Microscopy probes for analyzing magnetic properties of nanometer size patterns. This process requires high sensitivity of the resolution and high coercivity at same time. Finally, I will discuss the results from a special magnetic force microscopy (MFM), scanning electron microscopy (SEM), Atomic Force Microscopy (AFM), focused magneto-optical Kerr Effect (F-MOKE) measurements developed to study the EBL-fabricated ultra-high-density BPM media.