Shuji Kishimoto

HSQ process development for a superior resolution and a reasonable sensitivity for an EB master-mold for nanoimprint lithography

Half-pitch (hp) 11 to 7.5nm will be resolution requirement for 3 to 5 years later in lithography technology. In specific, hp16nm in 2015 and hp11nm in 2019 for flash memory, bit pitch (bp) 18nm in 2015, bp15nm in 2018 for HDD patterned media, such extremely fine patterning capability is expected. We have been studying a positive resist ZEP520A particularly on its developers and process for the last 5 years. And, its resolution limit is hp16nm in lines and spaces pattern and bp22nm bit patterns for patterned media, in a large and practical patterning area (Figure 1). ZE520A is an option to pursue the resolution limit for the future. However, since it is a positive-tone resist, dark erosion is significant between holes particularly on bp25nm and below, even when the highest resolution developer of an alcohol and a fluoro-carbon mixture is used. ZEP holes in the nearest were not isolated but connected due to excess dark erosion, which seemed to be caused by EB back-scattering and fogging. If a negative-tone resist is employed, it would cause residue instead between pillars. However, the residue can be eliminated by etching back to the bottom, and the pillars can be remained without defects (Figure 2).

Challenges for quality 15nm groove patterning with ZEP520A for a master fabrication for track pitch 50nm full-surface DTR-Media

Discrete Track Recording Media (DTR-Media) requires 50nm track pitch patterns and a mold as the start for 1 Tb/inch2 areal density, which is a quality 15nm groove (trench) and beyond. Last year, 14nm groove was achieved with a newly designed solvent developer for ZEP520A, we reported in PMJ 2009. But, we still need to pursue extreme high resolution such as 10nm groove or 12.5nm dot array for bit patterns with ZEP520A since no alternative was found so far. To improve ZEP520 resolution, we just keep trying to find a new developer with a lower development speed for ZEP520 than the previous one. Then, a Fluoro-Carbon was selected from various candidates. It was proved that ZEP520 and the Fluoro-Carbon developer provided 11nm groove resolution at an exposure dose of 1800μC/cm2. Furthermore, the mixture of the Fluoro-Carbon and Solvent B provided the same 11nm groove resolution at a higher sensitive, i.e. less exposure dose than the Fluoro-Carbon and even the Solvent B.

Nanohole and dot patterning processes on quartz substrate by R–θ electron beam lithography and nanoimprinting

Fine hole and dot patterns with bit pitches (bps) of less than 40 nm were fabricated in the circular band area of a quartz substrate by R–θ electron beam lithography (EBL), reactive ion etching (RIE), and nanoimprinting. These patterning processes were studied to obtain minimum pitch sizes of hole and dot patterns without pattern collapse. The patterning on the circular band was aimed to apply these patterning processes to future high-density bit-patterned media (BPM) for hard disk drive (HDD) and permanent memory for the long life archiving of digital data. In hole patterning, a minimum-22-nm-bp and 8.2-nm-diameter pattern (1.3 Tbit/in.2) was obtained on a quartz substrate by optimizing the R–θ EBL and RIE processes. Dot patterns were replicated on another quartz substrate by nanoimprinting using a hole-patterned quartz substrate as a master mold followed by RIE. In dot patterning, a minimum-30-nm-bp and 18.5-nm-diameter pattern (0.7 Tbit/in.2) was obtained by introducing new descum conditions. It was observed that the minimum bp of successful patterning increased as the fabrication process proceeded, i.e., from 20 nm bp in the first EBL process to 30 nm bp in the last quartz dot patterning process. From the measured diameters of the patterns, it was revealed that pattern collapse was apt to occur when the value of average diameter plus 3 sigma of diameter was close to the bp. It was suggested that multiple fabrication processes caused the degradation of pattern quality; therefore, hole patterning is more suitable than dot patterning for future applications owing to the lower quality degradation by its simple fabrication process.

A single-nanometer nanoimprint-mask fabrication by EB lithography followed by nanoimprinting and self-aligned double-patterning

As a new scheme of a master-mold (imprint-mask) fabrication, half pitch (hp) 12nm lines and spaces (L/S) pattern was fabricated from hp 24nm L/S resist mandrels, which was prepared by EB writing as well as nanoimprinting, and followed by self-aligned double-pattering (SADP) technique. It was observed that line width roughness (LWR, 3 sigma value) was reduced and improved by a single and multiple nanoimprinting to make hp24nm resist mandrels in the new scheme. We have studied the phenomena and then revealed that the resist patterns of nanoimprinting had more sharp and smooth shoulders as well as bottom edges than EB resist patterns. Those seemed to be reflected to better LWR and LWR reduction by nanoimprinting. The new scheme has advantages of resolution enhancement and better pattern quality of LWR on a mold (mask) for nanoimprint lithography, with comparing to a conventional and single EB lithography.

A master-mold fabrication by electron beam lithography followed by nanoimprinting and self-aligned double patterning

As a new scheme of master-mold fabrication, a half pitch (hp) 12 nm line and space (L/S) pattern was fabricated from hp 24 nm L/S resist mandrels, which were prepared by electron beam (EB) writing as well as nanoimprinting, followed by the self-aligned double-patterning (SADP) technique. It was observed that the line width roughness (LWR) was reduced and improved by single and multiple nanoimprintings in the new scheme of the master-mold fabrication to make hp 24 nm resist mandrels. We have studied the phenomena and revealed that the resist pattern of nanoimprinting had sharper and smoother shoulders and bottom edges in cross section than those of the EB resist. These shoulder shapes of nanoimprinting seemed to be reflected in its LWR improvement. The new scheme has advantages of resolution enhancement and better pattern quality of LWR on a master mold for nanoimprint lithography, in comparison with conventional optical and EB lithography technologies.

25nm pitch master and replica mold fabrication for nanoimprinting lithography for 1Tbit/inch 2 bit patterned media

Nanoimprint Lithography and a mold, mold replication from an EB master mold as well, those are essential for a large-scale production of bit patterned media. 1Tbit/inch2 (bit pitch 25nm) areal density on a 2.5inch HDD media, it is feasibility demonstration target all the media makers and the HDD makers are aiming at. This paper describes difficulties we faced, and solutions we established by designing and optimizing materials and process, to fabricate 25nm pitch master mold by EBL as well as working replica mold by NIL.

Master mold and working replica fabrication for nano-imprinting lithography for 1Tbit/inch2 and 25nm pitch bit patterned media

Bit Patterned Media (BPM) is essential of HDD media areal density increase, which will be combined with heatassisted magnetic recording (HAMR) eventually for thermal diffusion prevention. 1Tbit/inch2 areal density is the first demonstration target, which is 25nm pitch hole array, for the BPM development. Nano-Imprinting Lithography (NIL) is indispensable too, so molds as well, for the BPM large-scale production for throughput. At the beginning, 52nm pitch and below was successfully made on quartz master-mold. However, by our comprehensive development and improvement in material and process, we successfully fabricate 25nm pitch master-mold by EB Lithography, 25nm pitch working-replica by Nano-Imprinting Lithography as well.