Project conclusion

The most promising market for Nanoimprint Lithography (NIL) for high volume production (HVP) is the hard disk drive (HDD) industry. Targeted magnetic bit sizes of sub-20nm aim at storage densities exceeding 1 terabit per square inch. Significant penetration of NIL into the HDD market demands for imprint processes satisfying stringent total cost of ownership requirements. A promising technique to fulfill these requirements is soft UV-NIL. Elastomeric working stamps replicated from master stamps can be used for a multitude of imprints and a large number of working stamps can be replicated from a single master. The most cost intensive process step in UV-NIL is master stamp fabrication. The estimated price of a nanoimprint stamp for the fabrication of hard disks with 20nm dots and a patterned area of 50% on a 3.5inch disk is 200.000â?¬. This number is based on the template price for the 32nm node of the semiconductor industry. Fabrication techniques for such templates range from electron beam lithography to massively parallel ion beam writing techniques as proposed in the project NILdirectstamp.

 

The main objective of the project NILstampreplication was to develop reliable and reproducible nanoimprint processes to facilitate high volume production of next generation hard disks utilizing soft UV-NIL. For this purpose a process flow has been initially proposed which covers master stamp design, simulation of working stamp deformation, material evaluation, working stamp fabrication, single and double side nanoimprinting as well as pattern transfer into the HDD substrate by selective etching. In a first step, deformation of working stamps during imprinting has been simulated by utilizing a finite element method in order to determine working stamp design rules for bit patterns in the sub-20nm range. The master stamps have been fabricated by ion multi-beam exposure of HSQ films by the CHARPAN Tool within the project NILdirectstamp. This tool allows to write random patterns down to feature sizes of 20nm utilizing 10keV Hydrogen, when using up to 43-thousand programmable beams of 12.5nm beam size. Utilizing special exposure techniques with a stencil mask, providing 200-fold reduction, approx. 575-thousand 10keV Hydrogen ion beams of 8.3nm beam size enabled realization of dots, lines and grids in HSQ with 12.5nm half-pitch resolution. The clear focus within this project was to evaluate the resolution limits of working stamp replication by UV-NIL. Based on intense material evaluation working stamps have been successfully replicated from master stamps down to 12.5nm half-pitch patterns. The minimum replicated feature size was limited by the available feature sizes of available master stamps rather than by the working stamp and imprint material properties. The resulting elastomeric working stamps have been utilized for development and optimization of soft UV-NIL processes down to 12.5nm half-pitch patterns into commercially available imprint resists. Surface characterization of master stamps, working stamps and nanoimprints have been conducted by means of atomic force and scanning electron microscopy. For the process transfer onto industrial scale nanoimprint platforms an EVG IQ Aligner® has been designed and manufactured which features toolings tailored for bit patterned media applications for HDD substrate sizes up to 3.5 inch. Etching of the imprinted disks and characterization revealed a clear picture of the complex interplay of all individual process steps required for next generation harddisk manufacturing utilizing Nanoimprint Lithography.