Skip to content
6CCVD Research

Structure Fabrication on Silicon at Atomic and Close-To-Atomic Scale Using Atomic Force Microscopy - Implications for Nanopatterning and Nanodevice Fabrication

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-03-26
JournalMicromachines
AuthorsPaven Thomas Mathew, Wei Han, Brian J. Rodriguez, Fengzhou Fang
InstitutionsTianjin University, Fudan University
Citations4
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research details the achievement of deterministic structure fabrication on Si(100) substrates at the atomic and close-to-atomic scale using Atomic Force Microscopy (AFM) based electrochemical and mechanical methods.

  • Atomic-Scale Removal Achieved: Direct material removal depth as small as 0.32 nm (3.2 Angstrom), equivalent to approximately three silicon atoms, was achieved using single-crystal diamond tips.
  • Mechanism Differentiation: Platinum-coated tips induce Local Anodic Oxidation (LAO), forming raised oxide deposits, while diamond tips enable direct, single-step material removal (etching).
  • Substrate Optimization: HF-treated silicon substrates yielded significantly smoother and more consistent material removal compared to bare silicon with native oxide layers.
  • Process Control: For LAO, relative humidity (RH) is highly influential, lowering the threshold voltage for oxide formation from 6-7 V (ambient) to 2 V (high RH).
  • Bias Independence (Etching): Material removal depth using diamond tips was found to be largely independent of the applied tip bias (0 V to 10 V), which is highly favorable for consistent manufacturing.
  • Nanodevice Implication: The ability to fabricate trenches approximately 1 nm deep provides a critical pathway for developing atomic-scale electrodes and channels required for molecular electronic components and transistors.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Minimum Removal Depth0.32 (3.2 A)nmAchieved using single-crystal diamond tip
Etched Trench Depth (Average)3.98AAverage depth of seven trenches (approx. 3 Si atoms)
Optimal LAO Tip Bias7VPt-coated tip, 0.1 ”N force, 1 ”m/s velocity
LAO Threshold Voltage (Ambient, 36% RH)6-7VVoltage required for clear oxide deposit formation
LAO Threshold Voltage (High RH, 75-90% RH)2VVoltage required for clear oxide deposit formation
PtIr5 Tip Spring Constant2.9N/mPPP-EFM probe (used for LAO)
Diamond Tip Spring Constant20.7N/mAD-40-AS probe (used for direct removal)
PtIr5 Nominal Tip Radius20nmUsed for LAO experiments
Diamond Nominal Tip Radius10nmUsed for direct removal experiments
High Relative Humidity (RH) Range75-90%Used for enhanced LAO consistency
Native Oxide Thickness (Bare Si)1.5 to 2nmThickness before HF treatment

Key Methodologies

Section titled “Key Methodologies”

The structure fabrication utilized a commercially available AFM system (MFP-3D) in contact mode, employing two distinct tip types and controlled environmental conditions.

  1. Substrate Preparation:

    • Bare Si(100) was cleaned by sonication in acetone and isopropanol (30 min at 25 °C), followed by a DI water rinse.
    • HF-treated Si(100) involved dipping the substrate in 10% aqueous HF solution for 10 s to remove the native oxide layer (experiments performed within 1 h of treatment).

  2. Humidity Control:

    • High relative humidity (RH 75-90%) was maintained by bubbling dry nitrogen gas over a 1M NaCl solution.
    • Ambient air conditions (RH 22-38%) were also tested for comparison.

  3. Local Anodic Oxidation (LAO) (Platinum Tips):

    • Tip: Conductive PtIr5-coated AFM probes (PPP-EFM).
    • Mechanism: Tip forms a water meniscus with the adsorbed water layer, facilitating the reaction: 2H2O + 2e- → H2 + 2OH-, followed by Si + 2OH- → SiO2 + 2H+ + 4e-.
    • Parameters: Optimal settings were 7 V tip bias, 0.1 ”N tip force (FT), and 1 ”m/s tip velocity (VT).

  4. Direct Material Removal (Diamond Tips):

    • Tip: Single-crystal diamond probes (AD-40-AS).
    • Mechanism: Mechanical shearing and extrusion dominate, resulting in direct material removal without oxide formation.
    • Parameters: Tip forces ranged from 2 ”N to 6 ”N. Tip bias (0 V to 10 V) showed negligible effect on removal depth.
    • Post-Processing: Formed debris was removed or displaced by subsequent contact mode scanning over the etched area.

  5. Directional Analysis:

    • Concentric squares were etched to analyze the influence of crystal orientation and tip geometry.
    • Material removal was more prominent in the horizontal direction (0° to scan angle) than the vertical direction (90° to scan angle).

Commercial Applications

Section titled “Commercial Applications”

This atomic-scale manufacturing technique is foundational for the next generation of miniaturized electronics and high-precision fabrication processes, aligning with the concept of Manufacturing III.

  • Molecular Electronics and Transistors:

    • Enables the precise fabrication of atomic-scale electrodes and channels (1 nm depth) required for integrating single molecules into electronic circuits.
    • Supports the design of molecular transistors where the AFM tip and Si substrate act as electrodes and the molecule acts as the channel.

  • Advanced Integrated Circuit (IC) Components:

    • Provides a method for deterministic, atomic-layer control necessary for the mass production of ultra-miniaturized IC components, pushing device scaling limits.

  • Nanopatterning and Lithography:

    • Offers a highly controlled method for creating reference patterns (via LAO) and functional channels (via direct etching) on silicon surfaces for validating electronic transmission and conductivity in nanodevices.

  • High-Precision Tooling and Metrology:

    • The use of durable single-crystal diamond tips, which showed no observable damage after prolonged use, is ideal for reliable, long-term atomic-scale manufacturing operations.

  • Materials Science Research:

    • The established methodology is directly applicable to other advanced materials critical for future electronics, including highly oriented pyrolytic graphite (HOPG), silicon carbide (SiC), and transition metal dichalcogenides (TMDs).
View Original Abstract

In this paper, the atomic-scale structure fabrication on Si (100) substrate using atomic force microscopy (AFM) with the aid of electrochemical and mechanical processes in a humid environment and under ambient conditions is studied. The local oxidation patterns are formed using platinum-coated tips with the aid of bias applied to the tip-substrate junction, and direct removal has been achieved using single crystal diamond tips, enabling the structure fabrication at the atomic and close-to-atomic scale. The depth and height of the etched trenches reached about 1 nm, which provides an approach for the fabrication of atomic-scale electrodes for molecular device development. Furthermore, material removal close to about three silicon atoms (~3.2 Å) has been achieved. This is important in molecular device fabrication. A detailed comparison among the nanopatterns and the material removal over bare and hydrofluoric acid (HF) treated silicon substrates is provided. This comparison is useful for the application of fabricating atomic-scale electrodes needed for the molecular electronic components. A deep understanding of atomic-scale material removal can be pushed to fabricate a single atomic protrusion by removing the neighbouring atoms so that the molecule can be attached to a single atom, thereby the AFM tip and Si substrate could act as the electrodes and the molecule between them as the channel, providing basic transistor actions in a molecular transistor design. In this paper, platinum-coated and single-crystal diamond tips are used to explain the oxide formations and direct material removal, respectively.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1997 - Atomic Force Microscope Tip-Induced Local Oxidation of Silicon: Kinetics, Mechanism, and Nanofabrication [Crossref]
  2. 2002 - Nanopatterning of Si/SiGe Electrical Devices by Atomic Force Microscopy Oxidation [Crossref]
  3. 1998 - AFM-Tip-Induced and Current-Induced Local Oxidation of Silicon and Metals [Crossref]
  4. 2009 - Large Area Nanoscale Patterning of Silicon Surfaces by Parallel Local Oxidation [Crossref]
  5. 2001 - Fabrication of Silicon Utilizing Mechanochemical Local Oxidation by Diamond Tip Sliding [Crossref]
  6. 2001 - Nano-Oxidation of Silicon Surfaces: Comparison of Noncontact and Contact Atomic-Force Microscopy Methods [Crossref]
  7. 2020 - Atomic and Close-to-Atomic Scale Manufacturing: A Review on Atomic Layer Removal Methods Using Atomic Force Microscopy [Crossref]
  8. 2017 - Localized Etching of Silicon in Water Using a Catalytically Active Platinum-Coated Atomic Force Microscopy Probe [Crossref]
  9. 2013 - Electron Beam-Assisted Healing of Nanopores in Magnesium Alloys [Crossref]

Reads Similar to This

On the Role of the Cathode for the Electro-Oxidation of Perfluorooctanoic Acid Research On Structural Design and Performance Optimization of Diamond Transistors An Electrochemical Procedure to Form Metal Powders from Recycled Hard Particle Embedded Composite Cutting Tools