Applications of Nano Patterning Process 1. Patterned Media

1Micro/Nano fabrication process 2009-02 Nano-fabrication& Microoptics Laboratory Yonsei University
Micro/Nano fabrication process 2009-02
Summary
80~100 grains in one bit
8 nm
Zig-zag Jitter
Thermal stability Separated single magnetic bit Less Medium Noise
Promising technology to achieve over 1 Tb/in2
Schematic of patterned media
Soft under layer
[ Average Price of Storage ] Year 1990 1995 2000 2005 2010
0.001
0.01
0.1
1
10
100
• Overcome super- paramagnetic limit
Nano-fabrication& Microoptics Laboratory Yonsei University
Fabrication Overview of Patterned Media Using Top-Down Nano Patterning Processes
Nickel or Cobalt
1) Stephen Y. Chou et al, proceedings of the IEEE, Vol. 85, 1997
2) Hitachi Global Storage Technologies
Si master
Si moldGlass substrate
3. Nanoinjection molding
Metallic stamp
UV curable resin
Magnetic dot Nano probe
1Tbits/in2 Patterned Media
Patterned Media Mass-production
Nanoreplication technology is most proper for mass-production
Patterned Media
Ref. IBM
Low cycle time fabrication method High uniform distribution in large area
Low Cost & High Throughput
Nanoreplication Technology
Nano Master/ Stamp Fabrication
Application of Patterned Media
Media
What are the Core Technologies for Nano Replication for Patterned Media?
- EBL/RIE/FIB - Nano electroforming - Metallic/transparent stamp
Nano Stamp Technology
Nano Replication Process
- Nanoimprinting - Nanoinjection molding
(UV nanoimprinting, Thermal nanoimprinting)
Contents of PART. 1
Fabrication results of Si nano master
[PR Resist spin coating] [E-beam exposure & Developing]
Photo resist
[Dia. 50 nm, pitch 100 nm]
E-beam
100nm
- Very fine nano patterning process : ~10 nm - High aspect ratio can be fabricated by additional deep RIE process.
[Dia. 30nm, Pitch 50nm] [Spacing 15nm, Pitch 50nm]
50nm 50nm 15nm
Si nano master for patterned media
Si nano master with minimum 30 nm dia., 60nm depth was realized.
Si nano master with line pattern
Si nano master
140 nm
Si
Ion beam
Fabrication of Si Master by Focused Ion Beam (FIB)
- Very simple and time consuming process
- Direct patterning can be carried out on various materials (silicon, metal, etc.).
[FIB system (Yonsei Univ.)]
In our research, nano pattern arrays with 65 nm pitch was fabricated on silicon substrate by FIB.
[Dia. 30 nm, pitch 65 nm]
- Optimization of nano electroforming process
Fabrication of Metallic Stamp
Fabrication of metallic stamp by nano electroforming Si nano master
Polymer master
Glass polymer
[Metallic stamp for nanoimprinting] [Dia. 50 nm, pitch 100 nm]
100 nm
Advantages of metallic stamp 1. It has excellent mechanical property and durability under high pressure. 2. It has good thermal and chemical stability.
Core technologies of metallic stamp fabrication
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.
Fabrication of Transparent Stamp
Si master
Polymer material
Si master
Transparent substrate
Polymer master
Transparent stamp
Dia. 50nm/Pitch 100nm [ Transparent stamp ]
Fabrication results 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.
- Replication technology of nano pattern in stamp
- Releasing technology with polymer master
- Adhesion property with transparent substrate
Core technologies of transparent stamp fabrication
patterns
A
B
nm
20 40 60 80
Sticking
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.
Tear-off
Issues in Nano-releasing Process
Surface quality of nano replica can be deteriorated by interfacial problem
Interfacial phenomena : Adhesion, Diffusion, Wettability Sticking, Tear-off, Stretching etc.
0 1 2 3 -20
0
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60
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100
nm
Ave. roughness : 24.1
0 1 2 3 -20
0
20
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100
nm
S. Kang et al, Applied Physics Letters, Vol. 88, 2006
Nickel Stamper
Reaction group
Body group
Function group
Bare nickel stamp SAM coated nickel stamp at 25ºC
106.9268.24
Comparison of water contact angle
Fabrication results by UV nanoimprinting
[With anti-adhesion treatment]
[Bare glass stamp]
115
• High internal bonding energy (covalent bonding)
Chemical reaction of FOTS-SAM
C C C
O O O OO
• Useful for fabrication of nano pattern with high aspect ratio
• Simple and cost-effective process
Photopolymer Dispensation Stamp Covering
UV-exposure with applying pressure
Pillar arrays on glass substrate
Replication of Nano Patterned Substrate for Patterned Media by UV nanoimprinting
UV-light
S. Kang et al, JMM, Vol. 49, 2005 S. Kang et al, J. Phys. D, Vol. 36, 2003
Nano stamp
Fabrication results of nano stamp (Dia.: 50 nm, Pitch: 100 nm )
Fabrication Result of Nano Pillar Arrays on Glass Substrate by UV Nanoimprinting
Nanoimprinting results of polymer pattern on glass substrate (Dia.: 50 nm, Pitch: 100 nm )
100 nm
0
350 nm
nm nm
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
Heating of Substrate and Stamp
to above Tg
to below Tg
Fabrication of nano master Deposition of seed-layer Electroforming for metallic
stamp
• Useful for the replication of nano patterns
Uniform nanopillar arrays with good surface quality was fabricated by thermal nanoimprinting. Molded nanopillars can be used for patterned media.
Nanoinjection Molding Process with Passive Heating System
Nanoinjection Molding Process with Active Heating System
PART. 2 Nanoinjection molding of Nanopillars for Patterned Media
Contents of PART. 2
2. Si nano master by RIE
E-beam resist
Si moldGlass substrate
5. Nanoinjection molding
Polymer master
Polymeric pattern
By controlling stamper surface temperature, the growth of solidified layer can be retarded.
Deterioration of Replication Quality in Replicating Polymer Nanopatterns Due to Solidified Layer
Solidified layer
- 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.
S. Kang et al, Microsystem Technologies, Vol. 11, 2005
Effect of solidified layer on pattern replication
Solidified layer
Solidified layer
Solidified layer
[ Micro patterns ]
[ Nano patterns ]
[ Nano patterns ]
Polymer melt

In replicating the high density optical disc substrates, transcribability is deteriorated by solidified layer. 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 transcribability. This effect is more critical in replicating the high density optical disc substrate as depicted in this figure. Stamper surface temperature, polymer melt temperature, velocity of polymer melt and viscosity have effect on the growth of solidified layer. This implies that the growth of solidified layer can be retarded by controlling stamper surface temperature.
Passive heating system
Retardation of heat transfer from polymer melt to stamper surface
Control of stamper surface temperature with thickness of insulation layer
Insulation layer
Delay of the development of the solidified layer
Micro heater MEMS RTD sensor
Stamper
Increase the stamper surface temperature to above the glass transition
temperature during the filling stage
Prevention of the development of the solidified layer
Governing equations
• For temperature field in the polymer melt ( ), stamper ( ), insulation layer ( ),
and mold block ( ) m st ins
mb
• For flow analysis in the cavity ( )mfm ∂+
01 =
r
lii

−
− +−=
−
S. Kang et al, J. Phys. D, Vol. 37, No.9, 2004
15 20 25 30 35 40 45
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
Th ick
ne ss
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
Th ick
ne ss
Radius (mm)
With insulation layer thickness of 75 μm Without insulation layer [ Advancement of solidified front with respect to time]
86mm
Analysis conditions - Polymer material: Polycarbonate (PC) - Initial polymer melt temperature: 300 - Initial mold temperature: 100 - Stamper: Nickel, 295 - Insulation layer: Polyimide, 75
Analysis results
Replication results of Nanoinjection Molding with Passive Heating
[ Diameter: 50 nm, pitch: 100 nm, height: 35 nm ] Without passive heating system With passive heating system
[ Nanoinjection molded nanopillar array ]
5
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Polymeric master Injection molded with passive heating Injection molded with bare stamper
[ Comparison of surface profiles between polymeric master and nanoinjection molded nanopillar pattern
with and without passive heating ]
For flow analysis in the cavity ( ) : Axisymmetric radial flow, Hele-Shaw approximation
01 =

∂ ∂
∂ ∂
=

∂ ∂
+ ∂ ∂
For thermal analysis in mold with micro heater - Stamper( ), 1st insulation layer ( ), micro heater ( ), 2nd insulation layer ( ),
and mold block ( ) st 1ins
mb
Micro heater
Metallic stamper

First, we analyzed the effect of increase of stamper surface temperature due to MEMS heater. This slide shows mathematical model. For flow analysis in the cavity, continuity equation, momentum equation and energy equation were used. And For thermal analyis in the mold with MEMS hetaer, we used transient heat conduction equation like this. S is heat source term by MEMS heater. This figure shows the multi-layer structure for numerical analysis.
1E-16
1E-14
1E-12
1E-10
1E-8
1E-6
ui di
ty [m
Increase of fluidity due to increase of stamper surface temperature
0.00 0.05 0.10 0.15 0.20 100
102
104
106
108
1010
1012
Vi sc
os ity
[P a-
Decrease of viscosity due to increase of stamper surface temperature
Simulation Results

This slide shows the simulation results for growth of solidified layer. This line presents a profile of solidified layer in case of replication process without MEMS heater at end of filling. And this is in case of with MEMS heater. As you see, by MEMS heater, the growth of solidified layer was delayed. And it implies that transcribability to sub-micron patterns on the stamper is improved.
(linear quadratic gaussian regulator )
+ -
e = Ts’ – Topt Ts: Stamper surface temperature Ts’ : Filtered stamper surface temperature
Injection molding system
Control results in the injection molding process using active heating system
- The cycle time: 5 sec., Heating duration: 1 sec.
- The temperature of nickel stamper surface is maintained at 200°C for 1 sec.
[ Applied voltage ] [ Temperature of nickel stamper surface]
Experiments: Control Result by Active Heating System
10 15 20 80
Mold temp.
Cycle time = 5 sec.
- The cycle time 5 sec, heating duration: 1 sec.
- The temperature of nickel stamper surface is maintained at 200°C for 1 sec.
Filling stage. = 1 sec
Active heating system with a micro heater is a feasible method to increase the temperature of nickel stamper surface to above Tg in nanoinjection molding process.
Experiments: Control Result by Active Heating System
Analysis of Magnetic Force Microscopy (MFM)
PART. 3 Preparation of Patterned Media with Magnetic Layer
Contents of PART. 3
(1) Diameter 200 nm, pitch 500 nm (2) Diameter 100 nm, pitch 250 nm MFM measurement results
0 0.4 0.8 1.2 0 0.4 0.8 1.2
M
• Deposition materials
- Underlayer : Cr 100 - Magnetic layer : Co 200 - Longitudinal magnetic recording
0 0.4 0.8 1.2 0 0.4 0.8 1.2
S. Kang et al, Nanotechnology, Vol.15 (8), 2004
Deposition of Magnetic Layer on Pillar Array for Longitudinal Magnetic Recording Patterned Media
[Deposition of magnetic layer on polymer pattern ] Polymer pattern by nanoimprinting
Glass Polymer
• Single magnetic domain states were successfully observed on the nano-patterned substrate.
Perpendicular magnetic anisotropy control
Co-Cr-Pt alloy (HCP structure)
[ MOKE (magneto-optic Kerr effect) result ]
[ MOKE (magneto-optic Kerr effect) result ]
Coercive force (Hc): 1800 Oersted
Coercive force (Hc): 3400 Oersted High enough for patterned media
-15000 -10000 -5000 0 5000 10000 15000 -15
-10
-5
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-15
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Deposition of Magnetic Layer on Pillar Array for Perpendicular Magnetic Recording Patterned Media
Effect of MFM tip on measurement result
[ AFM topagraphy] [High resolution MFM tip] [Conventional MFM tip]
Requirement of measurement technology for sub 50nm magnetic patterns
[Conventional MFM tip] [High resolution MFM tip]
- Single side coated MFM tip - MFM tip radius : ~23nm
High Resolution MFM Tip
Saturation at 15,000 Oe and 30nm thickness of magnetic layer (1) Without saturation (2) With saturation
Dia. : 50 nm, pitch: 100 nm
[ Magnetization (perpendicular magnetic recording) ]
Analysis of magnetic force microscopy (MFM) for Perpendicular Magnetic Recording Patterned Media

, . UHV , 100 , 200 . , , MFM . 200 nm , 100 nm . .
Summary
Issues on high density patterned media (1 Tbits/inch2, 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
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Applications of Nano Patterning Process 1. Patterned Media