Soft Lithography. Jin-Goo Park. Materials and Chemical Engineering Hanyang University, Ansan. Electronic Materials and Processing Lab.

Transcription

1 Hanyang University Soft Lithography Jin-Goo Park Materials and Chemical Engineering Hanyang University, Ansan Electronic Materials and Processing Lab. Introduction to Soft Lithography Research Micro- Electro- Mechanical System Micro- Reactors Micro- Electronics Microelectronics (low cost, < 100 nm) Micro- Analysis Bio- Technology Micro- Optics Micro- Sensors Present (Photolithography) Future (Photolithography and Non-photolithography Methods) 1

2 Photolithography vs. Imprinting Photo Lithography Rigid photomask High cost Optical diffraction - Not surmount 100nm barrier Not apply for nonplanr surface No control over chemistry -Chemical functionalities on surface 2-D structure Limited by photosensitive material Imprinting Elastomeric stamp or mold Non-photolithography Low cost, easy to use, 30 nm ~ 500 um Apply nonplaner surface 2-D, 3-D structure Use variety of materials Surface chemistry Photo Litho. vs. Imprinting To make metal lines Photolithography Imprinting PR Spin Coat Resist Spin Coat Soft Bake Bake Mask Alignment Alignment Exposure Heating and Pressing Develop Hard Bake RIE (Reactive Ion Etching) Deposition Deposition Lift Off Lift Off 2

3 Embossing Nano Imprint Lithography (NIL) Cold Embossing Embossing Step and Flash Imprint Lithography (SFIL) Hot Embossing Imprint Lithography Soft Embossing Soft Lithography Two Types of Embossing Many different names for the same process UV Light Heat and Pressure Cold Embossing Soft Embossing Soft Lithography Step and Flash Imprint Lithography (SFIL) Nano Imprint Lithography (NIL) Imprint Lithography Hot Embossing 3

4 Approaches to Nano Imprinting Temperature > Tg Contact Force ~2-40kN Vacuum Achieved Resolution : < 100 nm Room Temperature Contact Force ~ 1-100N UV Light ( nm) Achieved Resolution : < 15 nm Room Temperature Contact Force ~1-40N Inked stamp Achieved Resolution : < 50 nm Typical Equipment set EV520 Semi-Automated Bonder and Hot Embosser Automated Bonding process Hot Embossing and Nanoimprinting Support for All Bonding Processes Temp. 550C max. Voltage 2kV max. Pressure 8,000 lbf max. Up to 8 s & Substrates 4

5 Hot Embossing Chamber Cross Section Center Contact Pin (Ceramic or Teflon) Top and bottom side heater with independent temperature control Contact Force generated by external pneumatic cylinder Uniforce Compliant Membrane Small Chamber Hot Embossing Procedure Mold Align Heating Plate Molding Demolding 5

6 Silicon Master Nickel Master Embossing tool: Electroplated nickel from a silicon master after demolding step 6

7 Embossing Technique Embossing from Material : Ni 500 μm Embossed Microstructure Material: Polycarbonate Height : 50 μm Micro-Embossing Solutions for Polymer-Bio-Chips 7

8 Hanyang University PDMS Based Technique Electronic Materials and Processing Lab. Introduction to PDMS PDMS (Polydimethylsiloxane) has many unique properties and is therefore used in many various applications. PDMS stem from the nature of the siloxane bond The siloxane bond CH 3 CH 3..-(-Si-O-Si-O-) n -.. CH 3 CH 3 Curing Siloxane oligomer Siloxane cross-linker Property Value Color Clear Viscosity 3900 mpa s Specific gravity 1.08 Glass transition temperature 150 K Thermal conductivity 0.18 WmºK Shelf life 24 months Product specification Dow Corning Sylgard 184 Recommend curing conditions 24 hr at 23 C or 4 hr at 65 C or 1 hr at 100 C or 15 min at 150 C 8

9 Characteristics of PDMS Properties Elastic characteristic Low interfacial free energy (~ 21.6 dynes/cm) Chemically inert - do not adhere to, react with Not hydroscopic - not swell with humidity Easy to pass gases Good thermal stability (~ 186 in air) Transparent down to ~300 nm Durable elastomer ( over 50 time) Technical problems Thermal expansion - difficult to get high accuracy Sagging / pairing - deform or distort and generate defects in the pattern - relief structure can t withstand - aspect ratio must be 0.2~2 Shrinking - shrinks by ~1% upon curing - readily swelled by non-polar organic solvents Techniques of Soft Lithography μcp (Microcontact Printing) REM (Replica Molding) μtm (MicroTransfer Molding) MIMIC (Micromolding in Capillaries) SAMIM (Solvent-Assisted Micromolding) 9

10 Microcontact Printing Transfer of SAM precursor with elastomeric stamp onto substrat master generation by photolithography and similar techniques stamp is obtained by casting of elastomer (PDMS, e.g.) over master Pattern generation by stamping of SAM precursor onto substrate Microcontact Printing Stamped SAM pattern can be further processed by etching or deposition: µcp technique can also be applied to curved surfaces of stamp or substrate Quality of µcp SAMs is comparable to films obtained by adsorption from solution 10

11 Replica Molding -Mold prepolymer -Cure -Peel off Use elastic polymer as master for molding of prepolymer Elasticity and low surface energy of stamp make release of mold easy Allows duplication of three-dimensional topologis in a single step Faithful duplication of complex structure in the master Nanometer resolution (~10nm) UV curable prepolymers : shrinkage of less than 3% on curing (no solvent) Replica Molding (a) (b) (a) Cr nano-structures on a master (b) Polyurethane nano-structures by replication against PDMS mold Heights : Cr lines ~13nm, PU lines ~8nm (C) (d) (c) Au structures on a master (d) Polyurethane nano-structures by replication against PDMS mold Feature size: Au ~50 nm, Pu ~ 30 nm The relief structures are re-configured by mechanical deformation and then replicated No damage to the master after repeated times (10 times) to form PDMS stamps No change in the quality of these nano-structures on the PU replicas Simplicity and low cost of this procedure : manufacturing of nanometer-sized structures 11

12 Microtransfer Molding Procedures 1. A drop of liquid prepolymer is applied to patterned surface of a PDMS mold 2. The excess liquid removed by scraping with PDMS block or by blowing off with N 2 3. The filled mold is placed in contact with a substrate and heated 4. After curing the mold is peeled away 5. Thin films must be removed using O 2 RIE Convenient method for fabrication of microstructures Nonplanr substrates and 3D structures layer by layer Generating both interconnected and isolated microstructures Variety materials other than organic polymers: glassy carbon, sol-gels, ceramics Microtransfer Molding Polymeric microstructures fabricated using microtransfer molding (a) Arrays of 3-cm long wave guides of PU fabricated on Si/SiO2. - different lateral dimensions and are separated by different spacing (b) An SEM image of the ends of the wave guides ( ~3um 2 ) (c) An SEM image of an array of isolated micro-cylinders of epoxy on 5-um lines of epoxy, supported on a glass slide. (d ) An SEM image of a three-layer structure on a glass slide made from a thermally curable epoxy. 12

13 Micromolding in Capillaries Procedures 1. PDMS is placed on a substrate ( network of empty channels) 2. Low-viscosity liquid prepolymer is placed at the end of channels 3. Spontaneous filling by capillary action into the network of channels 4. After curing, mold is removed and network of Material remains 3D microstructure formation by filling of micro-capillaries with liquid precursor Low viscosity prepolymer Capillary filling is rapid and complete over short distance( ~ 1cm) Rate of filling decreases as the cross-sectional dimensions of the capillary decrease Micromolding in Capillaries System without solvents Systems with solvents A,C polyacyate B,D polyurethane A,B polymer beads C,D polyaniline Emeraldine A shrinkage of less than 3% after curing Solvent are evaporated after filling Solvent does not swell PDMS 13

14 Solvent-Assisted Micromolding procedure 1. Wet a PDMS mold with the solvent 2. Bring it into contact with the surface of the substrate 3. Solvent dissolves (or swells) a thin layer of the substrate, 4. Fluid or gel is molded against the relief structures in the mold. 5. The solvent dissipates and evaporates, 6. Fluid solidifies and forms a patterned SAMIM uses a solvent instead of temperature to soften the material Solvent have high vapor pressure and a moderately high surface tension - rapid evaporation of the excess solvent and minimal swelling of the PDMS Hydrophilic elastomers or surface modification of PDMS is required - partially wet Solvent-Assisted Micromolding (a) SEM images of structures in photoresist (1.6um) spin-coated on Si/SiO2, (b) Polystyrene ( 2.0 um thick) (c) ABS ( 0.85 um thick) (d )AFM image of nanostructures in a thin (0.4 mm thick) film of Microposit Common characteristic of structure are joined by a thin, underlying film of the polymer Film can be removed by O 2 RIE Polymeric structures can be used as masks in the etching of underying substrates 14

15 Summary in PDMS Based Pattern Generation Advantage Non-Photolithographic technics Patterning on scales < 100nm Patterning : solid materials liquid materials surface functionalities large areas Three dimensional microstructures No diffraction limit (30nm) Optical transparency of the mask Good control over surface chemistry Convenient, inexpensive Minimize waste of materials Disadvantage Patterns, mold may distorted, deformed ( pairing, sagging,swelling, shrinking ) Difficult to achieve accurate registration with elastomers (<1um) Defects higher than photolithography Micro contact printing works well only a limited range of surfaces Micro molding in capillaries is slow REM, utm, SAMIM leave a thin film -- must be removed by O 2 RIE The soft-lithography model system Microcontact printing of alkanethiols on gold was the first representative of soft-lithography processes Master Elastomer Stamp Resist-forming ink Inking methods Printing Wet etching Based on contact and pattern replication Silicon, SOI : Photolithography, e-beam PDMS(dimenthylsiloxane) : curing hours Thermal and chemical shrinking : To consider the design of the master To self-assemble monolayer on noble metal Wettability, adhesion, chemical reactivity electrical conduction Wet inking or contact inking Printing time dependent Self-assembled monolayer as resist 15

16 Micro-Contact Printing Micro-Contact Printed of Thiols SEM image // Scheme Feature of the stamps ; 0.6 μm Ⅹ 3.0 μm Scheme showing diffusion paths of molecular ink during printing ; The diffusion of ink molecules ; Zone of contact is dominant ; Printing & reaction time ; reactant contcentration ; Pattern width 16

17 The Factor of Defect Wet inking-print-etch Contact inking-print-etch DDT : Dodecanethiol -No contrast HDT : Hexadecanethiol - >500nm ink diffusion ECT : Eicosanethiol - 100nm ink diffusion SEM Image of Gold Patterns Contact inking printing - etching The formation of this pattern is difficult using immersion inking Simultaneous printing of large areas and small Printing of small features using a diffusive and volatile ink Accurate printing of small voids Formation of 100 nm Au line 17

18 The Effect of Stamp Hardness The SEM images were acquired after coating molded PDMS stamps with a thin layer of gold Sylgard 184 with a Young s modulus of 3MPa Material with a Young s modulus of 9.7MPa Examples of Layered Hybrid Stamps 18

19 Directed Processing of a Substrate with Fluids These are several approaches for the selective placement of single or multiple chemicals with inherent alignment Printing of Biological Molecules (I) Direct printing 19

20 Printing of Biological Molecules (II) Localized inking and offset printing Printing of Biological Molecules (III) Subtractive offset printing 20

21 Printing of Catalysts The capability of printing to transfer chemical reagents from an elastomeric stamp to a substrate can be used to direct the electroless deposition(eld) 21