Applications of Nano Patterning Process 1. Patterned Media

Applications of Nano Patterning Process 1. Patterned Media

Contents Introduction Part. 1. Nanoimprinting on Glass Substrate for Patterned Media Part. 2. Nanoinjection Molding of Nanopillars for Patterned Media Part. 3. Preparation of Patterned Media with Magnetic Layer Summary

HDD Roadmap New techniques Patterned Media Source: Hitachi Global Storage Technologies

Why Patterned Media? Cost-advantage of magnetic media Price/MByte, Dollars 100 DRAM/Flash HDD DRAM Flash Paper/Film 10 1 0.1 0.01 0.001 Source : IBM 0.0001 1990 1995 2000 2005 2010 [ Average Price of Storage ] Limit of conventional HDD media Year Track Suggestion of patterned media Promising technology to achieve over 1 Tb/in 2 Continuous domain Soft under layer [ Concept of patterned media ] Thermal stability Separated single magnetic bit Less Medium Noise Single magnetic dot (One bit / dot) Track Zig-zag Jitter 80~100 grains in one bit Patterned media Recording head 8 nm Higher densities require smaller volume of grain < Superparamagnetic limit in continuous media> Magnetic dot Schematic of patterned media Single magnetic domain : 1 dot = 1 bit Overcome superparamagnetic limit

Fabrication Overview of Patterned Media Using Top-Down Nano Patterning Processes E-beam lithography and RIE 1) Nanoimprinting 2) Nanoinjection Si master molding Glass substrate Si mold UV curable resin 1. Polymer master by UV nanoimprinting Metallic stamp Polymer master 2. Metallic stamp by electroforming Polymeric pattern Nickel or Cobalt Metallic stamper 3. Nanoinjection molding Magnetic layer Polymeric pattern 4. Deposition of magnetic layer 1) Stephen Y. Chou et al, proceedings of the IEEE, Vol. 85, 1997 2) Hitachi Global Storage Technologies Nano probe Magnetic dot

Why Nano Replication for Patterned Media? Requirement technology for patterned media Low Cost & High Throughput Uniform Distribution of Nano Pattern Arrays (~10nm) Low cycle time fabrication method High uniform distribution in large area Nanoreplication technology is most proper for mass-production Nanoreplication Technology Patterned Media Mass-production Patterned Media Ref. IBM 1Tbits/in 2 Patterned Media

Nano Replication Processes for Patterned Media Design Nano Master/ Stamp Fabrication Nano Replication Application of Patterned Media Pattern design Focused ion beam E-beam lithography UV nanoimprinting Nanoinjection molding Deposition of Magnetic film Process design Etching process Nano electroforming Thermal nanoimprinting Soft lithography Patterned Media Modelling/ Simulation Transparent stamp Metallic stamp Material Technology for Nanoimprinting Measurement /Analysis Nano-releasing technology Photo-curable polymer MFM/AFM Self Assembled Monolayer Thermal-curable polymer MOKE

What are the Core Technologies for Nano Replication for Patterned Media? Nano Stamp Technology - EBL/RIE/FIB - Nano electroforming - Metallic/transparent stamp Nano-releasing Technology - Thiol based SAM - Silane based SAM Nano Replication Process - Nanoimprinting - Nanoinjection molding High Density Patterned Media Application of Patterned Media - Deposition of magnetic layer - Magnetic analysis

PART. 1 Nanoimprinting on Glass Substrate for Patterned Media Contents of PART. 1 Stamp Fabrication Technology Nano-releasing Technology Nanoimprinting of Nanopillar Arrays on Glass Substrate (UV nanoimprinting, Thermal nanoimprinting)

Fabrication of Si Nano Master by E-beam Lithography (EBL) Fabrication of Si nano master by EBL and RIE Photo resist E-beam Si sub. Si nano master [PR Resist spin coating] [E-beam exposure & Developing] [Si nano master by RIE] - Very fine nano patterning process : ~10 nm - High aspect ratio can be fabricated by additional deep RIE process. Fabrication results of Si nano master 100nm 50nm 50nm 15nm [Dia. 50 nm, pitch 100 nm] Si nano master for patterned media [Dia. 30nm, Pitch 50nm] [Spacing 15nm, Pitch 50nm] Si nano master with line pattern Si nano master with minimum 30 nm dia., 60nm depth was realized.

Fabrication of Si Master by Focused Ion Beam (FIB) Fabrication of Si nano master by FIB Ion beam Si [Si substrate] Si nano master [Si nano master by FIB] - Very simple and time consuming process - Direct patterning can be carried out on various materials (silicon, metal, etc.). Fabrication results of Si nano master [FIB system (Yonsei Univ.)] 140 nm In our research, nano pattern arrays with 65 nm pitch was fabricated on silicon substrate by FIB. 0.6 µm [Dia. 70 nm, pitch 140 nm] [Dia. 30 nm, pitch 65 nm]

Fabrication of Metallic Stamp Fabrication of metallic stamp by nano electroforming Si nano master Metallic stamp polymer Glass Polymer master Polymer master [Replication of polymer master] [Deposition of Ni seed layer] [Nano electroformnig] 1. Expensive Si nano master can be saved : This method is cost-effective process for metallic stamp. 2. Metallic stamp with high quality nano patterns can be fabricated by this process. Advantages of metallic stamp 1. It has excellent mechanical property and durability under high pressure. 2. It has good thermal and chemical stability. Fabrication results of metallic stamp [Dia. 50 nm, pitch 100 nm] [Metallic stamp for nanoimprinting] 100 nm Core technologies of metallic stamp fabrication - Deposition of seed layer on the polymer master - Optimization of nano electroforming process

Fabrication of Transparent Stamp Fabrication process of transparent stamp Polymer material Transparent substrate Polymer master Polymer master Si master Si master Transparent stamp [ Material coating ] [ Fabrication of polymer master ] Advantages of transparent stamp 1. It has good replicating property by UV nanoimprinting. 2. It is an low cost and simple fabrication method for nano stamp. 3. It has a optically transparency for UV nanoimprinting. Fabrication results of transparent stamp [ Transparent stamp by photo curing of thermal curing ] Core technologies of transparent stamp fabrication - Replication technology of nano pattern in stamp - Releasing technology with polymer master Dia. 50nm/Pitch 100nm [ Transparent stamp ] - Adhesion property with transparent substrate

Issues in Nano-releasing Process In nanoimprinting process : Increase of Area/Volume in patterns Interfacial phenomena between stamp and imprinted polymer governs replication of nano patterns Interfacial phenomena : Adhesion, Diffusion, Wettability Sticking, Tear-off, Stretching etc. Surface quality of nano replica can be deteriorated by interfacial problem Nano Stamp Tear-off A nm B Sticking 140 120 100 80 60 40 20 0 0.0 0.5 1.0 1.5 2.0 0 500 1000 1500 2000 A B nm Tear-off in releasing process by sticking problem Sticking in nano replication process by excessive high temperature Modification of stamp surface or anti-adhesion layer is necessary to improve the surface quality of replica. Our solution for anti-adhesion layer in nanoimprinting is self-assembled monolayer.

Thiol Based Self-assembled Monolayer (SAM) on Metallic Stamp Thiol based SAM Material : n-dodecanethiol [CH 3 (CH 2 ) 11 SH] Function group : Methyl group( -CH 3 ) Hydrophobic properties and low surface energy S. Kang et al, Applied Physics Letters, Vol. 88, 2006 Comparison of water contact angle 106.92⁰ 68.24⁰ Thiol based SAM on nickel stamp Polymer molded part SAM Nickel nano stamper Bare nickel stamp Molding results by thermal nanoimprinting nm 100 80 60 40 20 SAM coated nickel stamp at 25ºC Ave. roughness : 24.1A 0 Function group Body group Reaction group Nickel Stamper CH 3 (CH 2 ) 11 SH n-dodecanethiol SAM -20 0 1 2 3 μm Molded part from the nickel stamp without SAM nm 100 80 60 40 20 0 Ave. roughness : 12.1A -20 0 1 2 3 μm Molded part from the nickel stamp with SAM

Silane Based SAM for Non-metallic Stamp : Glass, Polymeric Master Anti-adhesion on non-metallic stamp (Tridecafluro-1,1,2,2-tetrahydrooctyl) trichlorosilane (FOTS) : Water contact angle = 107 High internal bonding energy (covalent bonding) Comparison of water contact angle 115⁰ 70.37⁰ [Bare glass stamp] [Glass stamp with anti adhesion] Fabrication results by UV nanoimprinting Chemical reaction of FOTS-SAM F C F F F C F F C F C F F F C C F H F C H H C H H C H Si Cl Cl Cl O - Si - O- Si - O- Si - O- Si - O O O O O H + Cl HCl (Destroy polymer surface ) [Without anti-adhesion treatment] [With anti-adhesion treatment]

Replication of Nano Patterned Substrate for Patterned Media by UV nanoimprinting UV nanoimprinting S. Kang et al, JMM, Vol. 49, 2005 S. Kang et al, J. Phys. D, Vol. 36, 2003 Material : UV-curable photopolymer Good stability (heat, humidity, etc.), no fluidity problem Useful for fabrication of nano pattern with high aspect ratio Simple and cost-effective process Procedures Photopolymer Glass Photopolymer Dispensation Glass Glass Nano stamp Stamp Covering Pillar pattern [ Image of UV nanoimprinting system ] Pressure UV-light Glass Nano stamp UV-exposure with applying pressure Nano stamp Stamp releasing Polymer Glass Pillar arrays on glass substrate

Fabrication Result of Nano Pillar Arrays on Glass Substrate by UV Nanoimprinting Fabrication results of nano stamp (Dia.: 50 nm, Pitch: 100 nm ) 100 nm nm 700 700 350 nm 0 350 nm [Metallic stamp] [Transparent stamp] Nanoimprinting results of polymer pattern on glass substrate (Dia.: 50 nm, Pitch: 100 nm ) [UV-nanoimprinting with metallic stamp] [ UV-nanoimprinting with transparent stamp] Uniform nanopillar arrays with good surface quality was fabricated by UV nanoimprinting. Molded nanopillars can be used for patterned media.

Replication of Nano Pillar Arrays on Glass Substrate by Thermal Nanoimprinting Thermal nanoimprinting process Material : Thermal-curable polymer Good replication quality for high aspect ratio patterns Useful for the replication of nano patterns Heating of Substrate and Stamp to above T g Application of Molding Pressure Cooling of Substrate and Stamp to below T g Demolding Thermal nanoimprinting process with metallic stamp Fabrication of nano master Deposition of seed-layer Electroforming for metallic stamp Replication of the nano-patterned substrate Uniform nanopillar arrays with good surface quality was fabricated by thermal nanoimprinting. Molded nanopillars can be used for patterned media.

PART. 2 Nanoinjection molding of Nanopillars for Patterned Media Contents of PART. 2 Modeling of Passive/Active Heating System Nanoinjection Molding Process with Passive Heating System Nanoinjection Molding Process with Active Heating System

Proposed Nanoinjection Molding Processes of High Density Patterned Media E-beam resist Metallic stamp Si 1. E-beam patterning Polymer master 4. Metallic stamp by electroforming Si nano master 2. Si nano master by RIE Polymeric pattern Metallic stamp 5. Nanoinjection molding Glass Si substrate mold UV curable resin 3. Polymer master by UV nanoimprinting Si nano master Polymeric pattern 6. Deposition of magnetic material

Deterioration of Replication Quality in Replicating Polymer Nanopatterns Due to Solidified Layer S. Kang et al, Microsystem Technologies, Vol. 11, 2005 Solidified layer Effect of solidified layer on pattern replication Pressure Polymer melt Solidified layer Stamper [ Micro patterns ] Pressure [ Nano patterns ] Pressure Polymer melt Solidified layer Stamper Polymer melt [ Nano patterns ] - During the filling stage, the polymer melt in the vicinity of the stamper solidifies rapidly when the hot polymer melt front contacts the cold surface of stamper. - Solidified layer generated during the polymer filling worsens replication quality. By controlling stamper surface temperature, the growth of solidified layer can be retarded. Solidified layer Stamper

Nanoinjection Molding with Heating System S. Kang et al, Microsystem Technologies, Vol. 11, 2005 Passive heating system Active heating system Insulation layer Micro heater MEMS RTD sensor Stamper Control of stamper surface temperature with thickness of insulation layer Increase the stamper surface temperature to above the glass transition temperature during the filling stage Retardation of heat transfer from polymer melt to stamper surface Delay of the development of the solidified layer Prevention of the development of the solidified layer

Modeling of Passive Heating System Governing equations For temperature field in the polymer melt ( ), stamper ( ), insulation layer ( ), and mold block ( ) m Ω st Ω ins Ω Ω mb = z T k z t T ρc p - Heat conduction equation: For flow analysis in the cavity ( ) m Ω mf Ω + 0 1 = + r ru r t ρ ρ - Continuity equation: 2 ηγ ρ + = + z T k z r T u t T C p - Energy equation: 0 z u z r p = + η - Momentum equation: 0 z w z z p = + η [ Schematic view of Multi-layer structure for numerical analysis ] r z Solidified layer Z=0 Z=h D s Ω st Ω ins (Ω mb ) Z=H (Ω st ) Ω mb Flow direction To predict the development of solidified layer - p-v-t equation of state: { } z h T T T T z D l i i g i i s + = S. Kang et al, J. Phys. D, Vol. 37, No.9, 2004

Analysis of Development of Solidified Layer 0.014 Analysis conditions 86mm [ Mold cavity for simulation ] Analysis results 1.2mm - Polymer material: Polycarbonate (PC) - Initial polymer melt temperature: 300 - Initial mold temperature: 100 - Stamper: Nickel, 295μm - Insulation layer: Polyimide, 75μm 0.014 Thickness of solidified layer, D s (mm) 0.012 0.010 0.008 0.006 0.004 0.002 0.000 0.622s 0.702s 0.782s 0.862s 0.942s 1.022s Thickness of solidified layer, D s (mm) 0.012 0.010 0.008 0.006 0.004 0.002 0.000 0.622s 0.702s 0.782s 0.862s 0.942s 1.022s 15 20 25 30 35 40 45 15 20 25 30 35 40 45 Radius (mm) Radius (mm) Without insulation layer With insulation layer thickness of 75 μm [ Advancement of solidified front with respect to time]

Replication results of Nanoinjection Molding with Passive Heating 40 Polymeric master Injection molded with passive heating Injection molded with bare stamper 35 30 Height (nm) 25 20 15 10 5 [ Nanoinjection molded nanopillar array ] 0 0 50 100 150 200 Distance (nm) [ Comparison of surface profiles between polymeric master and nanoinjection molded nanopillar pattern with and without passive heating ] Without passive heating system With passive heating system [ Diameter: 50 nm, pitch: 100 nm, height: 35 nm ]

Modeling of Active Heating System For flow analysis in the cavity ( - Continuity equation ρ 1 ρru + = 0 t r r (1) - Momentum equation p u + η = 0 r z z - Energy equation T T T ρc p + u = k t r z z ) : Axisymmetric radial flow, Hele-Shaw approximation + For thermal analysis in mold with micro heater - Stamper( ), 1 st insulation layer ( ), micro heater ( ), 2 nd insulation layer ( ), Ω Ω st ins 1 and mold block ( ) Ω mb Ω m p z η γ u + η = 0 z z 2 (3) (2) Ω Ω h ins 2 - Heat conduction equation T T ρc p = k + S t z z where, S W V W = dv : power density : volume (4) Metallic stamper Micro heater [Multi-layer structure for numerical simulation]

Simulation Results Decrease of viscosity due to increase of stamper surface temperature Viscosity Viscosity [Pa-s] 10 12 10 10 10 8 10 6 10 4 10 2 without micro heater with micro heater Z R Fluidity 10 0 0.00 0.05 0.10 0.15 0.20 1E-6 Z [mm] Center line Stamper surface Fluidity [m 3 /Pa-sx10-14 ] 1E-8 1E-10 1E-12 1E-14 1E-16 without micro heater with micro heater Increase of fluidity due to increase of stamper surface temperature 1E-18 0.00 0.05 0.10 0.15 0.20 Z [mm] Center line Stamper surface

Control Scheme for Active Heating System u in PLANT: Injection mold with micro heater T s Controlled replication process Injection molding system RTD MEMS sensor T s Determination of Input power density (linear quadratic gaussian regulator ) T T ( e Qe u Ru) J = + dt 0 e - T s Desired reference stamper surface temperature + T opt Kalman filter Controller Temperature Time 1 cycle e = T s T opt T s : Stamper surface temperature T s : Filtered stamper surface temperature

Experiments: Control Result by Active Heating System Control results in the injection molding process using active heating system [ Applied voltage ] [ Temperature of nickel stamper surface] - The cycle time: 5 sec., Heating duration: 1 sec. - The temperature of nickel stamper surface is maintained at 200 C for 1 sec.

Experiments: Control Result by Active Heating System Max. heating temp. by micro heater Mold temp. Temperature [ É] 220 200 180 160 140 120 100 80 Cycle time = 5 sec. 10 15 20 Time (sec) - The cycle time 5 sec, heating duration: 1 sec. Reference stamper surface temperature Measured Ni stamper surface temperature Filling stage. = 1 sec T g of Polycarbonate - The temperature of nickel stamper surface is maintained at 200 C for 1 sec. Active heating system with a micro heater is a feasible method to increase the temperature of nickel stamper surface to above T g in nanoinjection molding process.

PART. 3 Preparation of Patterned Media with Magnetic Layer Contents of PART. 3 Preparation of Patterned Media with Magnetic Layer Analysis of Magnetic Force Microscopy (MFM)

Deposition of Magnetic Layer on Pillar Array for Longitudinal Magnetic Recording Patterned Media S. Kang et al, Nanotechnology, Vol.15 (8), 2004 Deposition of magnetic layer for longitudinal recording patterned media Pillar pattern Magnetic layer Deposition materials - Underlayer : Cr 100 A - Magnetic layer : Co 200 A - Longitudinal magnetic recording MFM measurement results Polymer Glass Polymer pattern by nanoimprinting [Deposition of magnetic layer on polymer pattern ] (1) Diameter 200 nm, pitch 500 nm (2) Diameter 100 nm, pitch 250 nm Deposition of magnetic layer M M 0 0.4 0.8 1.2 0 0.4 0.8 1.2 μm 0 0.4 0.8 1.2 0 0.4 0.8 1.2 μm AFM MFM AFM MFM Single magnetic domain states were successfully observed on the nano-patterned substrate.

Deposition of Magnetic Layer on Pillar Array for Perpendicular Magnetic Recording Patterned Media 23nm thickness deposition of magnetic layer CCP (10 nm) Ruthenium (10 nm) Tantalum (3 nm) Co-Cr-Pt alloy (HCP structure) Perpendicular magnetic anisotropy control Adhesion layer Coercive force (Hc): 1800 Oersted Kerr rotation angle (mdeg.) 20 15 10 5 0-5 -10-15 -20-15000 -10000-5000 0 5000 10000 15000 H (Oe) [ MOKE (magneto-optic Kerr effect) result ] 30nm thickness deposition of magnetic layer CCP (12 nm) Ruthenium (10 nm) Ruthenium (5 nm) Tantalum (3 nm) Coercive force (Hc): 3400 Oersted High enough for patterned media Kerr rotation angle (mdeg.) 15 10 5 0-5 -10-15 -15000-10000 -5000 0 5000 10000 15000 H (Oe) [ MOKE (magneto-optic Kerr effect) result ]

Measurement Technology of Magnetic Domain Requirement of measurement technology for sub 50nm magnetic patterns High Resolution MFM Tip - Single side coated MFM tip - MFM tip radius : ~23nm [Conventional MFM tip] [High resolution MFM tip] Proper to analysis of sub 50 nm magnetic pattern Effect of MFM tip on measurement result 2um 2um 1um 1um 0 0 [ AFM topagraphy] [Conventional MFM tip] [High resolution MFM tip]

Analysis of magnetic force microscopy (MFM) for Perpendicular Magnetic Recording Patterned Media Saturation at 15,000 Oe and 30nm thickness of magnetic layer (1) Without saturation (2) With saturation Downward Direction Spin Upward Direction Spin 500 nm Single Magnetic Domain 500 nm Magnetic Saturation 250 nm [ MFM image ] 250 nm Dia. : 50 nm, pitch: 100 nm [ SEM image ] 0 [ MFM image ] 0 N S [ Magnetization (perpendicular magnetic recording) ]

Summary Issues on high density patterned media (1 Tbits/inch 2, pattern pitch: 25 nm) (1) Master and stamp fabrication (2) Replication of nanopatterns (Passive/Active heating) (3) Releasing (SAM Anti-adhesion) (4) Measurement of topology and magnetic properties Other applications of nano patterning process (1) Nano-photonics (2) Sub-wavelength optical elements (3) Nano-bio applications (4) Digital display applications (5) High density optical data storage system and media