Nano-Machining and Nano-Patterning Using Near-field Optics :Nano-Machining and Nano-Patterning Using Near-field Optics Anargyros (Roger) Panayotopoulos Professors Greif and Grigoropoulos Graduate Students- David Hwang and Anant Chimmalgi Laser Thermal Laboratory University of California, Berkeley February 25, 2002


Why is Nano-Technology Important? :Why is Nano-Technology Important? Current Feature Size ~ 0.25 microns Applications Nano-Lithography (Photomask production and repair) Nano-Machining High density data storage Nanophotonic devices Fabrication of hybrid systems of molecular electronics Micro/nano surgery (Dentistry, Ophthalmology) Micro/nano biological technology


Methods to Reach Nanometer Resolutions :Methods to Reach Nanometer Resolutions Electron Beam Lithography X-ray Lithography Scanning Tunneling Microscopy (STM) Atomic Force Microscope (AFM) Scanning Near-field Optical Microscope (NSOM) Ultra-fast Laser Ablation (Multi-photon effects)


What Differentiates NSOM? :What Differentiates NSOM? Complicated Mask Dependence Preferential Etching Conductivity NSOM Mask-free deposition Reliable and controllable Metals, oxides, semi-conductors, insulators Chemical composition and morphology PCVD (Photo-Chemical Vapour Deposition) coupling


Far-field and Near-field Optics :Far-field and Near-field Optics Far-field Optics Geometric optics based on traditional optical element (Lens) Fails to perform adequately under certain circumstances Sub-wavelength apertures Deep UV radiation Wavelength independence Ultra-short pulses Near-field optics Form of lens-less optics with sub-wavelength resolution Independent of the wavelength of light being used


Far-field and Near-field Optical Schematics :Far-field and Near-field Optical Schematics


Critical Parameters Defining NSOM :Critical Parameters Defining NSOM Concentration of Light Energy Nano-metric Dimensions of Light Electromagnetic Interactions of Tip Enables Deposition of Various Materials Photo-decomposition of chemical gases. Optical Resolutions Beyond the Diffraction Limit Process Limitations


NSOM Combinational Techniques :NSOM Combinational Techniques NSOM Using Optical Fiber Tips NSOM/AFM Cantilevered Tips NSOM Using Micro-machined Apertures NFO-PCVD


Experimental Setup of NSOM System :Experimental Setup of NSOM System Fiber tip by Nanonics Inc. NSOM Schematic by DI Inc.


NSOM/AFM Cantilever Tip Focusing :NSOM/AFM Cantilever Tip Focusing SiO2 cantilevered tip (Mitsuoka et al. 2000) Waveguide tip (Takashi et al.1999)


Probe Tip and System Control of NSOM :Probe Tip and System Control of NSOM Probe Tips Receiving/Transmitting Antennas Tip Distance Control Beam Deflection Method Shear Force Measurement Piezo-Electric Tuning Fork Cantilever Normal Force Piezo-resistive micro cantilever (Muramatsu et al. 2000)


NSOM Using Optical Fiber Tips :NSOM Using Optical Fiber Tips Force Pulling Fabrication Method Foil-heater Schematic (above), Tips from one pulling step (left) (Gallacchi et al. 2000)


Optical Fiber Tips by Foil Heating :Optical Fiber Tips by Foil Heating Heat pulled fiber tips (Gallacchi et al. 2000)


Fabrication of Cantilevered Tips :Fabrication of Cantilevered Tips Etching/Micro-Machining E-beam lithography, LPCVD, DRIE Fabrication Steps Selective etching Sacrificial deposit and masking Metals core coating Apex removal Fabrication steps for SiO2 tip (Minh et al. 2000)


Etched Cantilever Tip Images :Etched Cantilever Tip Images Fabrication of Si3N4 cantilever tip (Jung et al. 2000) Topological image of tip radius (Jung et al. 2000)


SEM Micrographs of AFM Tip Profiles :SEM Micrographs of AFM Tip Profiles Tip radius (Jung et al. 2000)


NFO Using Ultra-fast Laser Ablation :NFO Using Ultra-fast Laser Ablation Extremely Fast Energy Deposition Femto/Pico second time scales Resulting in Subsequent Material Ablation Without thermal heat shocks or mechanical damaging (ie. Melting, burr formation, cracks)


Ablation- Rapid Absorption Process :Ablation- Rapid Absorption Process Ablation Related to direct transmission from solid to gaseous state without liquid phase Laser energy absorbed (excitation and ionization of material) inside electronic subsystem (lattice) by free electrons by inverse Bremsstrahlung Bremsstrahlung- Energy lost by electrons that appears as energy radiating away from site Collision momentum transfer to atom, electron KE losses


NFO-PCVD Patterning Method :NFO-PCVD Patterning Method Utilizes NFO in vacuum Photo-dissociation NFO-PCVD Schematic (Polonski et al.1999)


NFO-PCVD Pattern Processing :NFO-PCVD Pattern Processing 2 Step Process a) Pre-nucleation b) Film Growth NFO-PCVD Process (Polonski et al.1999)


NFO-PCVD Pattern Processing :NFO-PCVD Pattern Processing NFO-PCVD Absorption/Decomposition Mechanism (Ohtsu et al. 2000) Near-field/Far-field Exposure


NFO-PCVD Patterned Resolutions :NFO-PCVD Patterned Resolutions Shear-force image (Polonski et al.1999)


NSOM Transmission Efficiency :NSOM Transmission Efficiency Efficiency (Transmission Throughput) Scattered light power from the aperture/ input light power Function of aperture diameter, distance, polarization Key Considerations for Higher Efficiencies Tip reproducibility Reliable distance control and probe handling Large refractive index Leads to short effective wavelength inside the probe material resulting in high transmission effect


NSOM Transmission Efficiency of Fiber Tips :NSOM Transmission Efficiency of Fiber Tips Fiber Material- Glass constant optical properties, thus good for infrared spectroscopy Intensity strongly dependent on dielectric properties of tip Typical Transmissions ~10^-4 to 10^-6 Possible Solutions to Decrease Propagation Loss Multiple tapered probes Metal coatings


Multi-Tapered Optical Fibers :Multi-Tapered Optical Fibers Probe configuration ~ Intensity Enhancement Electric field of tapered fiber tip (left), Intensity Plots (right) (Nakamura et al. 2000)


Transmission Efficiencies of Cantilevered Tips to Fiber Tips :Transmission Efficiencies of Cantilevered Tips to Fiber Tips Excellent optical efficiency/throughput Transmission efficiencies ~ 10^-2 to 10^-4 Large NA objectives provide high optical throughput, but also means shorter working distance and disturbs optical path Tip-to-sample Regulation Normal force deflections of the cantilever Better control, and easier than other techniques Flexible and metal coated apertures not damaged after scanning


Probe-to-Probe Intensity Measurement :Probe-to-Probe Intensity Measurement Probe-to-Probe configuration (Ohtsu et al. 2000) Constant Height Mode Soft/hard substrate ~ rough estimate


NSOM Intensity Distribution :NSOM Intensity Distribution Elliptical Profile Distributions NFO properties of tip aperture Asymmetry of the tip Vibrational effects Polarization effect Intensity Distribution (Lu et al. 2001) NFO Intensity (Minh et al. 2000)


Photo-Chemical Intensity Measurement :Photo-Chemical Intensity Measurement Analyzing Oxidation Region 2-D Intensity Distribution ~ Photo-Oxidized Region N(x,y) ~ SS I(u,v)O(x-u,y-v) dudv O(x,y)~ I(x,y) >> N(x,y) ~ SS I(u,v)I(x-u,y-v)dudv Contour plot of photo-oxidation region (right), Cross-sectional plots of intensity regions (above) (Wei et al. 1996)


Polarization Effects on Intensity Transmission :Polarization Effects on Intensity Transmission Polarization Effects (Kawashima et al. 2000) Transmission Effect (Kawashima et al. 2000)


Current Research Goals :Current Research Goals Determine Intensity Correlations of Photosensitive Polymers Designs for Optimal Tip Configurations Parametric Studies of Material Responses Studies due to Various Lasers Femto/pico second laser, Excimer