Nanofabrication of sharp conductive diamond tip probe chips and their application in reverse tip sample scanning probe microscopy

At a Glance

Metadata	Details
Publication Date	2025-07-01
Journal	Micro and Nano Engineering
Authors	Lennaert Wouters, Jaehee Cho, Suji Gim, Jonghee Yang, A. Kanniainen
Citations	1
Analysis	Full AI Review Included

Technical Analysis and Documentation: Conductive Diamond Tip Arrays for RTS SPM

6CCVD Material Science Analysis of Wouters et al. (2025)

Executive Summary

Novel Architecture: The research successfully developed a novel Hedgehog Full Diamond Tip (HFDT) array integrated into probe chips, specifically designed for high-throughput Reverse Tip Sample Scanning Probe Microscopy (RTS SPM).
Material Requirement: The core material is a highly Boron-Doped Diamond (BDD) microcrystalline film (~1 µm thick), chosen for its high electrical conductivity and superior mechanical robustness necessary to withstand gigapascal-scale contact pressures (~10 GPa).
Resolution Benchmark: The HFDT tips achieved exceptional spatial resolution, resolving critical features (e.g., 27 nm FinFET gate width) in Scanning Spreading Resistance Microscopy (SSRM), significantly outperforming conventional Coated Diamond Tips (CDTs).
Ultra-Sharp Apex: A self-patterned dry etching process was optimized to generate nanoscopic sharp tips, achieving minimum tip apex radii as low as 2.7 nm.
Scalable Fabrication: The process utilizes standard semiconductor techniques (KOH etching, HFCVD, electroplating, dry etching) on 4-inch Si wafers, demonstrating a path toward scalable production of high-density tip arrays (25 µm minimum spacing).
High Throughput: The RTS SPM configuration, enabled by the dense, robust HFDT array, allows for rapid and seamless tip switching, achieving up to fivefold higher throughput compared to conventional SPM setups.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Material Type	Highly Boron-Doped	N/A	Microcrystalline Diamond (BDD)
Diamond Film Thickness	~1	µm	Grown via Hot-Filament CVD (HFCVD)
Minimum Tip Apex Radius	2.7	nm	Achieved via self-patterned dry etching
Tip Apex Yield (2.7 nm)	~5	%	For preferred single sharp tip morphology
Minimum Inter-Tip Spacing	25	µm	Required for rapid, reliable tip switching
Tip Height Requirement	> 8	µm	To prevent cantilever collision
Contact Pressure Endurance	~10	GPa	Required for metallic β-Sn phase transition in Si
Resolved Feature Size	27	nm	FinFET gate width resolved by RTS SSRM
Wafer Substrate Used	4-inch	N/A	(100) Silicon
Metal Stack (Adhesion/Seed)	TiW/Cu/Ti	N/A	Stack deposited prior to Ni electroplating

Key Methodologies

The fabrication of the HFDT probe chips required critical modifications to standard FDT processes to enable high-density array integration and RTS compatibility.

Mold Etching: Arrays of 15 x 15 µm² squares were patterned into an SiO₂ hard mask on a 4-inch (100) Si wafer, followed by anisotropic KOH etching to create inverted pyramid molds.
Diamond Deposition: A highly Boron-Doped microcrystalline diamond film (~1 µm thick) was grown into the molds using Hot-Filament Chemical Vapor Deposition (HFCVD).
Diamond Patterning: An Aluminum (Al) hard mask was used in conjunction with O₂ plasma etching to selectively remove diamond between the pyramidal mold areas.
Metal Stack Deposition: A thin stack layer of Titanium-Tungsten (TiW, adhesion), Copper (Cu, seed layer), and Titanium (Ti, protection) was deposited via sputtering.
Membrane Formation: A several-micrometers-thick Nickel (Ni) layer was electroplated onto the Cu, forming the robust supporting membrane for the tip array.
Substrate Release: The diamond tip array and Ni membrane were released by localized underetching of the Si substrate in KOH, utilizing a four-anchor-point design with trapezium-shaped openings to ensure complete underetching while maintaining membrane flatness.
Tip Sharpening: A final self-patterned dry etching step was employed to convert the pyramidal Full Diamond Tips (FDTs) into the ultra-sharp, high-aspect-ratio Hedgehog Full Diamond Tips (HFDTs).

6CCVD Solutions & Capabilities

The successful replication and advancement of this high-resolution RTS SPM technology depend entirely on the quality, conductivity, and geometric control of the initial diamond material and subsequent processing steps. 6CCVD is uniquely positioned to supply the foundational materials and custom engineering services required for next-generation diamond probe chips.

Applicable Materials

To replicate the high conductivity and mechanical stability demonstrated by the HFDTs, 6CCVD recommends the following materials:

Heavy Boron-Doped Polycrystalline Diamond (BDD PCD): This material directly matches the paper’s requirement for a highly conductive, robust microcrystalline film. 6CCVD offers BDD PCD films with customizable doping levels to optimize electrical performance (minimizing parasitic resistance) while maintaining the mechanical integrity required for 10 GPa contact pressures.
PCD Film Thickness Control: The paper utilized a ~1 µm thick film. 6CCVD provides precise thickness control for PCD films ranging from 0.1 µm up to 500 µm, allowing researchers to tune the film thickness for optimal tip height (> 8 µm) and mechanical stiffness.

Customization Potential

6CCVD’s in-house capabilities directly address the complex dimensional and material requirements of the probe chip fabrication process:

Research Requirement	6CCVD Capability	Technical Advantage
Large-Scale Array Production	Custom PCD plates/wafers up to 125mm diameter.	Provides a scalable platform exceeding the 4-inch Si substrate used, enabling higher throughput and larger array integration.
Complex Metal Stacks	Internal metalization services: Au, Pt, Pd, Ti, W, Cu.	We can deposit the required TiW/Cu/Ti stack (or optimized alternatives like Ti/Pt/Au) directly onto the BDD diamond film, ensuring excellent adhesion and conductivity for subsequent electroplating steps.
Substrate Thickness	SCD/PCD substrates available up to 10mm thick.	Offers robust handling and mechanical stability for complex multi-step nanofabrication processes like KOH underetching and peel-off assembly.
Surface Quality	Polishing capability: Ra < 5nm for inch-size PCD.	Ensures the starting diamond surface is ultra-smooth, minimizing defects that could compromise the uniformity and yield of the subsequent pyramidal mold etching and tip sharpening steps.
Custom Geometry	Precision laser cutting and shaping services.	Allows for custom dicing and shaping of the final probe chip membrane or support substrate to fit specific RTS SPM system requirements.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers specializes in optimizing MPCVD diamond for advanced metrology applications. We offer comprehensive consultation services to assist researchers in selecting the ideal BDD doping concentration, film thickness, and metalization scheme necessary to replicate or extend this high-performance RTS SSRM project.

Call to Action: For custom specifications or material consultation regarding high-performance conductive diamond for Scanning Probe Microscopy (SPM) applications, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.mne.2025.100307

References

2017 - Dopant, composition and carrier profiling for 3D structures
2018 - Metrology for the next generation of semiconductor devices
1995 - Lateral and vertical dopant profiling in semiconductors by atomic force microscopy using conducting tips [Crossref]
2019 - Diamond probes technology
1997 - Fabrication of integrated diamond cantilevers with tips for SPM applications [Crossref]
1996 - Chemical vapor deposition diamond for tips in nanoprobe experiments [Crossref]
2000 - Highly conductive diamond probes for scanning spreading resistance microscopy [Crossref]
2009 - Conductive diamond tips with sub-nanometer electrical resolution for characterization of nanoelectronics device structures [Crossref]