Vector Magnetic Current Imaging of an 8 nm Process Node Chip and 3D Current Distributions Using the Quantum Diamond Microscope

At a Glance

Metadata	Details
Publication Date	2021-10-28
Journal	Proceedings - International Symposium for Testing and Failure Analysis
Authors	Sean M. Oliver, Dmitro Martynowych, Matthew J. Turner, David A. Hopper, Ronald L. Walsworth
Institutions	University of Maryland, College Park, Mitre (United States)
Citations	9
Analysis	Full AI Review Included

6CCVD Technical Analysis: Quantum Diamond Microscopy for 3D Microelectronics Failure Analysis

This document analyzes the requirements and achievements detailed in the research paper, “Vector Magnetic Current Imaging of an 8 nm Process Node Chip and 3D Current Distributions Using the Quantum Diamond Microscope,” and correlates them with 6CCVD’s advanced MPCVD diamond capabilities.

Executive Summary

The research successfully demonstrates the utility of the Quantum Diamond Microscope (QDM), leveraging Nitrogen-Vacancy (NV) centers in diamond, for non-destructive failure analysis in complex 3D microelectronics.

Core Achievement: Simultaneous vector magnetic field imaging (B_x, B_y, B_z) of current distributions in an 8 nm process node flip chip IC and a custom multi-layer PCB under ambient conditions.
Material Requirement: The QDM relies on a high-purity, isotopically enriched Single Crystal Diamond (SCD) chip featuring a precisely controlled, thin (1.7 µm) NV ensemble layer.
High Resolution: Achieved high lateral spatial resolution (~1 µm) due to the minimal sensor standoff distance (average 0.85 µm) enabled by placing the diamond directly on the Device Under Test (DUT).
IC Fault Detection: Successfully resolved adjacent current traces (11 µm width, 8 µm separation) in the NVIDIA GA106 GPU, demonstrating potential for detecting shorts and leakages.
3D Localization: Demonstrated the ability to detect vertically oriented current paths (vias) using B_x and B_y components, and confirmed vertical layer separation (~155 µm) in the PCB structure.
Future Protocol: Established a protocol utilizing Maxwell’s linearity for layer-by-layer magnetic field subtraction, paving the way for 3D current density mapping using neural networks.

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Diamond Sensor Size	4 x 4	mm²	Field-of-view
Diamond Substrate Thickness	0.5	mm	Total chip thickness
NV Layer Thickness	1.7	µm	Uniform sensing layer
Isotopic Purity ([¹²C])	~99.995	%	Required for high coherence
Nitrogen Concentration ([¹⁵N])	~17	ppm	Required for NV creation
NV Concentration ([NV^-])	~2	ppm	Active sensor density
Lateral Spatial Resolution	~1	µm	Achieved resolution for current mapping
Minimum Standoff Distance	0.85	µm	Average distance from DUT surface
IC Trace Width (NVIDIA GPU)	11	µm	Current path width resolved
IC Trace Separation (Minimum)	8	µm	Minimum separation resolved
PCB Layer Separation (Measured)	~155	µm	Depth difference between Layer 1 and Layer 3
Magnetic Field Magnitude (Resolved)	~1	µT	Signal from TRST_N trace
Excitation Laser Wavelength	532	nm	CW illumination

Key Methodologies

The QDM relies on precise material engineering and controlled experimental parameters to achieve high-resolution vector magnetic field imaging:

Sensor Fabrication: A 4x4x0.5 mm³ Single Crystal Diamond (SCD) chip was used, featuring a 1.7 µm thick surface layer of NV centers created via controlled [¹⁵N] doping (17 ppm) in an isotopically pure [¹²C] substrate.
Standoff Minimization: The diamond sensor was placed directly on the Device Under Test (DUT) to achieve a minimal standoff distance (average 0.85 µm), critical for maximizing spatial resolution against the inverse square law decay of magnetic fields.
Optical Excitation: A 532 nm continuous wave (CW) laser delivered 1.5 W of power, shaped into a top-hat profile, to excite the NV centers across the 4x4 mm² area.
Magnetic Resonance: A 7 mm diameter microwave (MW) loop antenna delivered 1 W of MW power to drive the NV electron spin transitions.
Vector Field Measurement: Optically Detected Magnetic Resonance (ODMR) spectroscopy was performed. The frequency separation of the fluorescence dips (Δf) was measured, allowing simultaneous calculation of all three vector components (B_x, B_y, B_z) based on the four possible orientations of the NV axis.
Thermal Control: A thermistor and PID controller were employed to maintain a constant sample temperature, stabilizing the magnetic properties of the Ni under-bump metallization (C4 bumps) and isolating the current signals of interest.
Data Analysis: Magnetic field images were processed by subtracting the unbiased (0 V) magnetic field reference image to remove background gradients from C4 bumps. Current density maps were generated using the 2D magnetic inverse problem solved via the Fourier Filter formalism.

6CCVD Solutions & Capabilities

The success of the QDM technique hinges entirely on the quality and precise engineering of the NV-diamond sensor. 6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate and extend this critical failure analysis research.

Applicable Materials & Services	Research Requirement	6CCVD Capability & Advantage
Optical Grade SCD Substrates	High isotopic purity ([¹²C] > 99.995 %) and low strain required for optimal NV coherence and sensitivity.	6CCVD specializes in high-quality Single Crystal Diamond (SCD) growth, providing substrates with superior purity and minimal lattice defects, essential for maximizing T₂* and T₁ times in NV ensembles.
Custom NV Layer Engineering	Precise control over NV layer thickness (1.7 µm) and nitrogen concentration (17 ppm [¹⁵N]) is necessary to tune sensor performance.	We offer Custom SCD Doping via MPCVD, allowing precise control of nitrogen concentration (e.g., [¹⁵N] or [¹⁴N]) and layer thickness from 0.1 µm up to 500 µm, tailored for specific QDM standoff requirements.
Custom Dimensions & Thickness	The experiment used a 4 x 4 mm² chip, 0.5 mm thick. Future systems may require larger wafers for wider field-of-view.	6CCVD provides Custom Dimensions for SCD and PCD plates, including wafers up to 125 mm (PCD). We can deliver SCD chips pre-cut and polished to exact specifications (e.g., 4x4 mm² or larger).
Ultra-Smooth Surface Finish	Minimizing standoff distance (0.85 µm) requires exceptional surface quality to ensure direct contact with the DUT.	Our advanced polishing services achieve Ra < 1 nm for SCD, guaranteeing the ultra-smooth surfaces necessary to minimize the sensor-to-DUT gap and maximize spatial resolution for 8 nm node analysis.
Integrated Sensor Solutions	QDM systems require integrated components like MW antennas and contact pads.	6CCVD offers In-House Metalization services, including deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to receive fully functional, metalized diamond sensors ready for QDM integration.

Engineering Support

The complexity of 3D magnetic inverse problems and the need for precise material tuning (doping, thickness, purity) necessitate expert consultation. 6CCVD’s in-house PhD team can assist with material selection and specification optimization for similar Quantum Diamond Microscopy (QDM) and IC Failure Analysis projects, ensuring the diamond sensor meets the rigorous demands of next-generation microelectronics testing.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Abstract The adoption of 3D packaging technology necessitates the development of new approaches to failure electronic device analysis. To that end, our team is developing a tool called the quantum diamond microscope (QDM) that leverages an ensemble of nitrogen vacancy (NV) centers in diamond, achieving vector magnetic imaging with a wide field-of-view and high spatial resolution under ambient conditions. Here, we present the QDM measurement of 2D current distributions in an 8-nm flip chip IC and 3D current distributions in a multi-layer PCB. Magnetic field emanations from the C4 bumps in the flip chip dominate the QDM measurements, but these prove to be useful for image registration and can be subtracted to resolve adjacent current traces in the die at the micron scale. Vias in 3D ICs display only Bx and By magnetic fields due to their vertical orientation and are difficult to detect with magnetometers that only measure the Bz component (orthogonal to the IC surface). Using the multi-layer PCB, we show that the QDM’s ability to simultaneously measure Bx, By, and Bz is advantageous for resolving magnetic fields from vias as current passes between layers. We also show how spacing between conducting layers is determined by magnetic field images and how it agrees with the design specifications of the PCB. In our initial efforts to provide further z-depth information for current sources in complex 3D circuits, we show how magnetic field images of individual layers can be subtracted from the magnetic field image of the total structure. This allows for isolation of signal layers and can be used to map embedded current paths via solution of the 2D magnetic inverse. In addition, the paper also discusses the use of neural networks to identify 2D current distributions and its potential for analyzing 3D structures.

Tech Support

Original Source

DOI: https://doi.org/10.31399/asm.cp.istfa2021p0096