Design, Fabrication and Evaluation of Diamond Tip Chips for Reverse Tip Sample Scanning Probe Microscope Applications
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-02-27 |
| Journal | Korean Journal of Materials Research |
| Authors | Sugil Gim, Thomas Hantschel, Jin Hyeok Kim |
| Institutions | IMEC, Chonnam National University |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Diamond Tips for Reverse Tip Sample Scanning Probe Microscopy (RTS-SPM)
Section titled âTechnical Documentation & Analysis: Diamond Tips for Reverse Tip Sample Scanning Probe Microscopy (RTS-SPM)âThis document analyzes the research paper âDesign, Fabrication and Evaluation of Diamond Tip Chips for Reverse Tip Sample Scanning Probe Microscope Applicationsâ to highlight the critical role of high-quality MPCVD diamond in advanced metrology and to position 6CCVDâs capabilities as the ideal solution provider.
Executive Summary
Section titled âExecutive SummaryâThe research successfully developed an optimized, high-performance diamond tip-chip for Reverse Tip Sample (RTS) Scanning Probe Microscopy (SPM) combined with Scanning Spreading Resistance Microscopy (SSRM).
- Application Focus: High-resolution, quantitative 3D dopant profiling of advanced semiconductor devices (e.g., FinFETs, GaAs nanoridges) using RTS-SSRM.
- Material Requirement: Highly conductive, mechanically robust diamond tips capable of withstanding 8-12 GPa contact pressure.
- Process Optimization: The fabrication process was streamlined by reducing the number of mask layers and optimizing etching, cutting manufacturing time by over 50% (from 2+ weeks to 1 week).
- Performance Enhancement: Implementation of a sharpening process (Hedgehog FDT, HFDT) reduced the tip apex radius from hundreds of nanometers (nm) to tens or single nm.
- Metrology Achievement: Sharpened tips enabled clear SSRM imaging at a low set-point voltage (0.3 V), significantly reducing the required contact force and minimizing sample damage compared to typical 1 V operation.
- Structural Design: The final product is a 2D array of hundreds of Boron-Doped Diamond (BDD) tips, grown to a thickness of approximately 800 ”m via Hot-Filament Chemical Vapor Deposition (HFCVD).
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research detailing the material and performance requirements for the RTS-SSRM diamond tips.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Required Tip Hardness | 8-12 | GPa | Necessary mechanical stability for SSRM contact |
| Diamond Film Thickness (Grown) | ~800 | ”m | Thickness of the Boron-Doped Diamond (BDD) film |
| Nickel Electroplating Thickness | ~5.5 | ”m | Used to form the cantilever/membrane structure |
| KOH Etching Time (Release) | 6 | hours | Required for complete tip-chip separation from Si mold |
| Fabrication Time Reduction | < 1 | week | Optimized time for tip-chip fabrication (down from 2+ weeks) |
| Tip Apex Radius (Sharpened) | Tens to Single | nm | Achieved via the sharpening (HFDT) process |
| SSRM Set-Point Voltage (Sharpened) | 0.3 | V | Low force required for high-resolution imaging |
| SSRM Bias Voltage (FinFET) | +500 | mV | Applied during FinFET SSRM measurement |
| SSRM Scan Size (FinFET) | 700 | nm2 | High-resolution imaging area |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication of the optimized RTS diamond tip-chip relied on precise microfabrication techniques combined with advanced diamond growth.
- Mold Preparation: Silicon (Si) wafers were prepared with a hard mask (SiO2) layer.
- Pyramid Formation: Anisotropic wet etching using Potassium Hydroxide (KOH) was performed to create reverse pyramid molds (15 ”m x 15 ”m) in the Si substrate.
- Diamond Deposition: Boron-doped diamond (BDD) film, approximately 800 ”m thick, was grown onto the Si molds using Hot-Filament Chemical Vapor Deposition (HFCVD).
- Metalization Layering: A multi-layer metal stack was sputtered and patterned: Titanium-Tungsten (TiW) for adhesion, Copper (Cu) as a seed layer, and Titanium (Ti) as a protective layer.
- Structural Electroplating: Nickel (Ni) was electroplated to a thickness of approximately 5.5 ”m to form the rigid cantilever and membrane structure supporting the diamond tips.
- Tip Release: Reactive Ion Etching (RIE) was used to remove residual metal and mask layers. A final, timed KOH wet etching (6 hours) was performed to undercut the Si and release the 2D array diamond tip-chip.
- Apex Sharpening: A final dry etching process was applied to the released tips to create the Hedgehog FDT (HFDT) structure, achieving the necessary sharp apex for sub-nm resolution SSRM.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the high-specification diamond materials and custom fabrication services required to replicate and advance this critical RTS-SSRM research.
Applicable Materials
Section titled âApplicable MaterialsâThe core requirement of this research is a thick, highly conductive, and mechanically stable diamond film. 6CCVD specializes in producing these exact specifications using Microwave Plasma Chemical Vapor Deposition (MPCVD).
| Research Requirement | 6CCVD Material Solution | Specification Match |
|---|---|---|
| Boron-Doped Diamond (BDD) | Heavy Boron-Doped Polycrystalline Diamond (PCD) | Provides high conductivity (essential for SSRM) and extreme hardness (8-12 GPa). |
| Thick Film Growth (~800 ”m) | Thick PCD Substrates | 6CCVD routinely supplies PCD wafers up to 500 ”m thick, and custom substrates up to 10 mm, easily accommodating the required thickness for robust tip structures. |
| High Mechanical Stability | Optical Grade SCD or High-Quality PCD | Our MPCVD process ensures low defect density, maximizing the mechanical integrity required to withstand high contact forces during scanning. |
Customization Potential
Section titled âCustomization PotentialâThe fabrication process detailed in the paper requires precise control over film thickness, doping, and metal integration. 6CCVD offers comprehensive in-house services to meet these needs:
- Custom Dimensions: While the paper focused on small tip arrays, 6CCVD can provide large-area PCD wafers up to 125 mm in diameter, allowing for high-volume production of tip-chips.
- Advanced Metalization: The paper utilized TiW/Cu/Ti and Ni electroplating. 6CCVD offers internal metalization capabilities, including:
- Adhesion/Barrier Layers: Ti, W, TiW.
- Seed/Contact Layers: Cu, Pt, Pd, Au.
- We can apply these custom stacks directly to the diamond surface, ensuring optimal electrical contact and adhesion for subsequent microfabrication steps (e.g., electroplating).
- Surface Finish: Although the tips are etched, the base diamond material quality is crucial. 6CCVD provides ultra-smooth polishing: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring a pristine starting surface for lithography and etching.
- Laser Cutting & Shaping: 6CCVD offers precision laser cutting services to define the final chip geometry, simplifying the post-growth processing steps.
Engineering Support
Section titled âEngineering SupportâThe successful implementation of RTS-SSRM relies on optimizing the diamond material properties (doping concentration, crystal orientation, surface termination) for specific electrical and mechanical performance.
6CCVDâs in-house PhD engineering team specializes in material selection and process optimization for advanced electro-mechanical applications like Scanning Spreading Resistance Microscopy (SSRM) and other SPM techniques. We provide consultation on:
- Doping Optimization: Tuning Boron concentration to achieve the ideal balance between conductivity and mechanical hardness for specific SSRM voltage requirements.
- Surface Preparation: Advising on optimal surface termination (e.g., hydrogen or oxygen termination) to minimize friction and maximize electrical signal stability.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Scanning probe microscopy (SPM) has become an indispensable tool in efforts to develop the next generation of nanoelectronic devices, given its achievable nanometer spatial resolution and highly versatile ability to measure a variety of properties. Recently a new scanning probe microscope was developed to overcome the tip degradation problem of the classic SPM. The main advantage of this new method, called Reverse tip sample (RTS) SPM, is that a single tip can be replaced by a chip containing hundreds to thousands of tips. Generally for use in RTS SPM, pyramid-shaped diamond tips are made by molding on a silicon substrate. Combining RTS SPM with Scanning spreading resistance microscopy (SSRM) using the diamond tip offers the potential to perform 3D profiling of semiconductor materials. However, damage frequently occurs to the completed tips because of the complex manufacturing process. In this work, we design, fabricate, and evaluate an RTS tip chip prototype to simplify the complex manufacturing process, prevent tip damage, and shorten manufacturing time.