Challenges in 1 Teradot∕in.2 dot patterning using electron beam lithography for bit-patterned media

Abstract

Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots∕in.2) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist ZEP520 and 12 nm for a negative-tone resist silsesquioxane, corresponding to the areal density of ∼2.0 and ∼4.5 Tdots∕in.2, respectively. Using the ZEP520 resist process, a Cr dot array with a pitch of 21 nm (∼1.5 Tdots∕in.2) for template fabrication is demonstrated. High-quality scanning electron microscopy and atomic force microscopy images were used as primary metrology for both the dot size uniformity and the placement accuracy analysis.

Understanding of hydrogen silsesquioxane electron resist for sub-5-nm-half-pitch lithography

“…Impressive high-resolution patterning of sub-20-nm pitch structures have been demonstrated using these methods. 6,10 As the resolution of HSQ-based EBL is currently thought to be limited in part by the resist performance, 11 better understanding of HSQ should enable further improvements in the resolution.…”

“…2 This patterning capability has enabled several technologies such as the fabrication of high-resolution nanoimprint molds, 3 narrow and densely packed suspended strained Si nanowires, 4 and guiding structures for templating the self-assembly of block copolymers. 5 Several other development techniques, such as hot development [6][7][8][9] and KOH development, 10 have been used to increase the contrast of HSQ with the premise that a higher contrast would result in a higher patterning resolution. Impressive high-resolution patterning of sub-20-nm pitch structures have been demonstrated using these methods.…”

Fabrication of bit patterned media using templated two-phase growth

“…The base pressure during sputtering was <2 10 7 Torr. Using nanoimprint lithography 10,27 and an oxygen plasma in a Plasma Therm 790 reactive ion etching system, a well-ordered hexagonal array of pillars was patterned into a 20 nm amorphous carbon thin film, as observed in the scanning electron micrograph collected using a FEI Sirion 600 scanning electron microscope shown in Figure 2(a). The center-to-center spacing between the pillars was 27 nm (1 Tdpsi dot density).…”

“…6 The previously explored approaches for BPM fabrication 7 subtractive or additive. In the case of the subtractive ("top-down") approach, 8,9 the magnetic media film is first deposited as a sheet film and subsequently patterned into pillars using ion-milling or methanol etching, using etch masks defined using e-beam, 10 nanoparticle 11 or nanoimprint lithography, directed block copolymer self-assembly, [12][13][14] or combinations of these. 15 However, subtractive patterning of magnetic films typically leads to beam damage of the outer pillar surface; a phenomenon that gets exacerbated while scaling to higher bit densities due to the higher damaged surface/undamaged volume of the magnetic pillars.…”

Electron Beam Lithography for Fine Dot Arrays with Nanometer-Sized Dot and Pitch

“…There are some papers to improve them using HSQ negative resist. X. Yang et al have reported 12 nm x 12 nm or 15 nm x 15 nm pitch fine resist dot arrays using 100 keV EB drawing with hot developer of TMAH at 40 o C [6]. In addition, J. K. Yang et al have reported 12 nm or 14 nm pitch resist line and space pattern EB-drawn using 100 keV EB drawing with salty development [27].…”