Mechanism of mechanical nanolithography using self-excitation microcantilever
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-03-04 |
| Journal | Nonlinear Dynamics |
| Authors | Linjun An, I. Ogura, Kiwamu ASHIDA, Hiroshi Yabuno |
| Institutions | National Institute of Advanced Industrial Science and Technology, University of Tsukuba |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates and validates the mechanism of mechanical nanolithography (MNL) using a self-excited microcantilever in an Atomic Force Microscope (AFM), focusing on enhancing efficiency and depth control for nanoscale fabrication.
- Core Innovation: Utilized self-excited oscillations, generated via phase modulation in a feedback loop, to drive a redesigned trapezoidal microcantilever equipped with a diamond abrasive grain tip.
- Machining Modes Identified: Two distinct modes were verified based on the applied pressing load:
- Tapping Mode (Low Load, < 250 ”N): Groove formation achieved by periodic impacts of the tip.
- Indentation Mode (High Load, > 375 ”N): Groove formation achieved by continuous, sustained pressing and rubbing action.
- Mode Verification: The transition between modes was confirmed by observing the vibrational profiles of the tool using a Laser Doppler Velocimeter, noting changes in displacement symmetry and tip contact state.
- Depth Control Mechanism: Machining depth was successfully controlled in both modes by manipulating the oscillation amplitude (deflection or deflection angle) via the variable resistor (R0) in the phase modulation circuit.
- Performance: Demonstrated a strong positive correlation between increased oscillation amplitude and increased machined groove depth, aligning with theoretical predictions. Maximum depths reached approximately 400 nm in tapping mode.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Machining Tool Material (E) | 1.93 x 1011 | Pa | Youngâs Modulus |
| Machining Tool Density (Ï) | 7.93 x 103 | kg/m3 | Density |
| Microcantilever Length (lm) | 9.2 x 10-4 | m | Redesigned trapezoidal beam |
| Base Length (lb) | 1.7 x 10-3 | m | Stepped beam design |
| Microcantilever Width (am) | 5.0 x 10-4 | m | At cantilever section |
| Base Width (ab) | 2.0 x 10-3 | m | At base section |
| Deflection Angle Stiffness (kΞ) | 3.5 x 10-3 | N/° | Calculated stiffness constant |
| Deflection Displacement Stiffness (kw) | 2.5 x 102 | N/m | Calculated stiffness constant |
| Tapping Mode Load Range | 125 to 250 | ”N | Low pressing load regime |
| Indentation Mode Load Threshold | > 375 | ”N | High pressing load regime |
| Tapping Mode Frequency | 13.5 | kHz | First-order self-excited oscillation (250 ”N) |
| Indentation Mode Frequency | 13.7 | kHz | First-order self-excited oscillation (375 ”N) |
| Optical Lever Sensitivity | 14.25 | V/° | Deflection angle detection |
| Phase Shift Control (R0) | 100 to 175 | Ω | Variable resistor used for amplitude modulation |
| Maximum Machined Depth | ~400 | nm | Achieved in tapping mode |
| Sample Material | Silicon (Si) | N/A | Substrate for nanolithography |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure focused on redesigning the machining tool, generating stable self-excited oscillations, and verifying the resulting machining modes.
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Tool Redesign and Preparation:
- A microcantilever was redesigned into a trapezoidal shape (stepped beam) to increase stiffness and achieve larger self-excited oscillation amplitudes compared to conventional designs.
- The tip was equipped with a diamond abrasive grain, formed into a triangular pyramid shape using Focused Ion Beam (FIB) technology, to reduce tool wear and enhance accuracy.
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Self-Excited Oscillation Generation:
- A linear feedback loop, incorporating a filter, phase shifter (variable resistor R0), and amplifiers, was used to generate steady-state self-excited oscillations in the fundamental mode.
- Amplitude control was achieved by manipulating the phase difference in the feedback loop via the variable resistor R0.
-
Vibrational Profile Observation:
- A Laser Doppler Velocimeter (Polytec MSA-500) was used to scan 17 equidistant measurement points along the machining tool.
- Velocity signals were integrated into displacement signals to approximate the vibrational profile shape during the steady state of oscillation.
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Machining Mode Determination:
- Pressing loads were incrementally applied to the tip (calculated using beam deflection equations).
- Tapping Mode: Confirmed at low loads (< 250 ”N) by observing asymmetric displacement waveforms and periodic tip impacts.
- Indentation Mode: Confirmed at high loads (> 375 ”N) by observing symmetric displacement waveforms and continuous tip contact with the sample surface.
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Nanolithography and Depth Control:
- Nanolithography was performed on a silicon sample using an AFM device (Seiko SPA300HA).
- Experiments were conducted at 250 ”N (Tapping) and 375 ”N (Indentation).
- The phase shift (R0) was varied (100 Ω to 175 Ω) to modulate the oscillation amplitude (deflection or deflection angle).
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Groove Measurement:
- Machined grooves were analyzed using AFM imaging (12 ”m x 12 ”m area).
- Machining depth was quantified by measuring the difference between the average sample surface height and the deepest point in the groove across four cross-sectional directions.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a flexible, high-resolution, and low-cost alternative to traditional lithography methods (like FIB or EBL) for nanoscale manufacturing.
- Nanodevice Manufacturing: Fabrication of high-accuracy components for next-generation products, including:
- Nanofluidic devices (e.g., controlled DNA transport and separation).
- Nanosenors (e.g., point-of-care monitoring).
- Scanning Probe Lithography (SPL): Enhancing the capabilities of commercial AFM/SPM systems for subtractive manufacturing, offering better efficiency and reduced tip wear compared to static plowing.
- Advanced Materials Processing: Applicable to a broader range of materials than methods limited by oxidation (Oxidation SPL) or thermal sensitivity (Thermal SPL), as it relies purely on mechanical removal.
- Micro/Nanoelectromechanical Systems (MEMS/NEMS): Precision patterning and etching of silicon and other substrates required for complex mechanical structures at the micro- and nanoscale.
- Maskless Lithography: Provides a flexible, direct-write patterning method that does not require a mold, unlike Nanoimprinting Lithography (NIL).