Front and back side SIMS analysis of boron-doped delta-layer in diamond

At a Glance

Metadata	Details
Publication Date	2017-03-19
Journal	Applied Surface Science
Authors	M.A. Pinault-Thaury, François Jomard, C. Mer‐Calfati, N. Tranchant, M. Pomorski
Institutions	Centre National de la Recherche Scientifique, CEA LIST
Citations	8
Analysis	Full AI Review Included

Analysis of Boron Delta-Layer Control in MPCVD Diamond for Advanced Devices

This documentation analyzes the research paper “Front and back side SIMS analysis of boron-doped delta-layer in diamond,” focusing on the fabrication, characterization, and implications of ultra-sharp boron doping interfaces in Chemical Vapor Deposition (CVD) diamond, directly relating findings to 6CCVD’s capabilities in high-quality diamond engineering.

Executive Summary

Ultra-Sharp Interface Control: The study confirms precise control over nanometric boron-doped ($\text{P}^{+}$) delta-layers in diamond, achieving extremely sharp interfaces crucial for advanced quantum and electronic devices.
High Doping Achievement: MPCVD successfully generated highly boron-doped layers, reaching concentrations up to 2x10²⁰ at/cm³, essential for high-power electronics and p-type semiconductor applications.
Nanoscale Thickness: The critical $\text{P}^{+}$ delta-layer thickness was demonstrated to be $\le 7$ nm, proving feasibility for quantum well and superlattice structures in diamond.
Interface Quality Quantified: Front-side Secondary Ion Mass Spectrometry (SIMS) measured an interface sharpness ($\Lambda_{\text{up}}$) as low as 2.5 nm/decade (nm/dec), indicating highly efficient stopping of boron incorporation during growth.
Methodological Innovation: A complex five-step process, including ion implantation, bulk growth, lift-off, and precise etching, was developed to enable comparative front-side and back-side SIMS analysis, validating the material quality by overcoming instrumental limits (ion mixing).
Strategic Applications: Controlled boron delta-layers position diamond as a superior alternative to silicon for electronics, photonics, and spintronics applications that require extreme operating conditions (high temperature/voltage).

Technical Specifications

The following parameters define the structure and characterization results of the Boron-Doped P-/P+/P- Multilayer Diamond:

Parameter	Value	Unit	Context
Substrate Type	HPHT Type Ib (100)	N/A	Initial substrate for epitaxy
Substrate Dimensions	3 x 3 x 0.5	mm³	Initial sample size
Growth Method	Microwave Plasma CVD	N/A	Used for all epitaxial layers
Growth Temperature	850	°C	Fixed process temperature
Growth Pressure	120	mbar	Fixed process pressure
Microwave Power	600	W	Fixed power input
P- Layer Boron Conc. ([B])	3x10¹⁶	at/cm³	Low Boron Doping (Bkgd)
P+ Delta-Layer Boron Conc. ([B])	2x10²⁰	at/cm³	Heavy Boron Doping (BDD)
P+ Delta-Layer Thickness	$\le 7$	nm	Nanometric functional layer
P- Layer Thickness (Total)	320 + 350	nm	Epilayer thickness for profiling
SIMS Primary Ion Energy	10	keV	$\text{Cs}^{+}$ source primary beam
SIMS Interaction Energy	14.5	keV	Primary ions interaction with sample (biased to -4500 V)
SIMS Primary Beam Current	40	nA	Set to optimize sensitivity
SIMS Sputtering Rate	0.2	nm/s	Achieved rate during analysis
Ion Mixing Depth (Artifact)	$\approx 10$	nm	Instrumental limit of standard SIMS analysis
Front Side Roughness (RMS)	1.5	nm	Measured on 5x5 $\mu\text{m}^{2}$ area
Back Side Roughness (RMS)	2.0	nm	Measured on 5x5 $\mu\text{m}^{2}$ area
Interface Sharpness ($\Lambda_{\text{up}}$) - Best	2.5	nm/dec	Front side analysis, P+/Second P- interface
Interface Sharpness ($\Lambda_{\text{down}}$) - Front	7.3	nm/dec	Front side analysis, First P-/P+ interface

Key Methodologies

The experiment combined precise MPCVD synthesis of the P-/P+/P- multilayer structure with an extensive, multi-step preparation process to enable artifact-free SIMS characterization.

I. MPCVD Growth Recipe (Delta-Layer Structure)

P- Layer Growth:
- Gases: $\text{CH}{4}/\text{H}{2}$ ratio of 1%; $\text{O}{2}/\text{H}{2}$ ratio of 0.25%.
- Doping Precursor: Residual TMB (Trimethylboron).
- Goal: Achieve low boron background concentration (3x10¹⁶ at/cm³).
P+ Delta-Layer Growth:
- Gases: $\text{CH}{4}/\text{H}{2}$ ratio of 0.6%. No $\text{O}_{2}$.
- Doping Precursor: $\text{B}/\text{C}$ gas ratio of 21,400 ppm (using TMB via specialized injection system).
- Goal: Achieve ultra-high boron content (2x10²⁰ at/cm³) and sharp interfaces.

II. Sample Preparation for Back-Side Analysis (Lift-Off Procedure)

Implantation (Substrate Graphitization): HPHT (100) substrate was implanted with Oxygen ions (3 MeV, 10¹⁷ ions/cm² dose) to create a graphitized layer 2 $\mu\text{m}$ below the surface, facilitating subsequent lift-off.
Delta-Layer Structure Growth: P-/P+/P- layers grown via MPCVD. (Front side SIMS analysis performed here).
Bulk Thickening: A $30$ $\mu\text{m}$ undoped diamond layer was grown on top of the $\text{P}^{-}$ layer for handling stability during subsequent thinning steps.
Lift-Off: Substrate was removed using bipolar electrochemical etching (Marchywka effect) in ultra-pure water, applying 700V - 1000V for 42 hours, releasing the epilayers at the graphitized zone.
Back-Side Etching (Precision Thinning): The 2 $\mu\text{m}$ residual diamond layer (original substrate material) was removed using $\text{Ar}/\text{O}_{2}$ plasma in a PVD magnetron sputtering system.
- Parameters: Ar/$\text{O}_{2}$ flow: 32 sccm; Pressure: 11.2 mbar; RF Power: 200 W; DC Bias: 1200 V.
- Rate: $\approx 1$ $\mu\text{m}/\text{h}$.
- Procedure: Two subsequent etchings were performed, stopping precisely within the P- layers to position the delta-layer closer to the new surface for back-side SIMS.

III. SIMS Characterization

Equipment: CAMECA IMS4f, optimized for high sensitivity (vacuum $\approx 10^{-8}$ mbar).
Configuration: $\text{Cs}^{+}/\text{M}^{-}$ configuration (positive primary ions, detection of negative secondary ions) to maximize sensitivity for B and H detection in diamond.
Analysis Area: Sputtering crater 150x150 $\mu\text{m}^{2}$; analyzed zone restricted to 33 $\mu\text{m}$ diameter to limit edge effects.

6CCVD Solutions & Capabilities

The complexity and precision required for manufacturing and processing these advanced diamond structures align perfectly with 6CCVD’s expertise in custom MPCVD growth and post-processing engineering. We deliver the foundational materials and specialized services necessary to replicate and advance this research into commercial applications.

Applicable Materials

To achieve the ultra-sharp, heavily doped $\text{P}^{+}/\text{P}^{-}$ interfaces required for delta-doping structures, 6CCVD recommends:

Boron-Doped Diamond (BDD) Wafers:
- We offer heavily B-doped $\text{P}^{+}$ layers (matching the required 10²⁰ at/cm³ range) and low-doped $\text{P}^{-}$ layers (matching the 10¹⁶ at/cm³ range) via precise MPCVD gas control, suitable for multilayer epitaxy.
- Our ability to produce layers down to $0.1$ $\mu\text{m}$ ensures that ultra-thin structures (like the $\le 7$ nm delta-layer) can be integrated reliably within the multilayer stack.
Single Crystal Diamond (SCD) Substrates:
- The research utilized (100) HPHT substrates. 6CCVD supplies high-quality SCD substrates, critical for defect-free homoepitaxial growth and achieving the low surface roughness (RMS $\lt 2.0$ nm) required for nanoscale interface fidelity.

Customization Potential

The experimental procedure involved precise dimensional control, thinning, and complex layer removal. 6CCVD provides in-house engineering services to support similar high-precision projects:

Required Process/Feature	6CCVD Capability	Research Link & Application
Complex Substrate Preparation	Laser Cutting & Shaping Services	The initial $3\text{x}3\text{x}0.5$ $\text{mm}^{3}$ square was reduced to a $\approx 2$ mm isosceles triangle. We offer custom dimensions up to $125$ $\text{mm}$ and precise laser cutting for post-processing shapes.
Ultra-Smooth Surfaces	Polishing Ra $\lt 1$ nm (SCD)	Achieving low RMS (1.5 nm front, 2.0 nm back) is critical for minimizing SIMS artifacts. We guarantee SCD surfaces with Ra $\lt 1$ nm.
Multilayer Stacks	Custom Thickness Control	We offer SCD/PCD layer thicknesses from $0.1$ $\mu\text{m}$ to $500$ $\mu\text{m}$, ensuring precise growth of the P-/P+/P- stack on various substrate types.
Integrated Contacts	Custom Metalization Services	While not used here, advanced electronic devices derived from this research (e.g., MESFETs) require custom ohmic and Schottky contacts. We offer in-house deposition of Au, Pt, Pd, Ti, W, and Cu layers.

Engineering Support

The successful demonstration of controlled boron delta-layers opens doors to next-generation diamond devices for photonics, spintronics, and high-power electronics. Our in-house $\text{PhD}$ team specializes in addressing challenges related to defect engineering (e.g., NV centers or other color centers) and high-carrier mobility doping profiles. We can assist researchers in selecting optimal gas recipes ($\text{CH}{4}/\text{H}{2}$ ratios, TMB flow, $\text{O}_{2}$ introduction) and post-growth processing steps (like precise etching and surface activation) to maximize device performance derived from these sharp BDD interfaces.

Global Supply Chain: 6CCVD offers reliable global shipping (DDU default, DDP available) for sensitive research materials worldwide, ensuring material continuity for demanding, multi-step experimental projects like this one.

> Call to Action: For custom specifications or material consultation on high-purity SCD, advanced BDD multilayers, or complex processing requirements, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.apsusc.2017.03.118

References

2012 - Engineering shallow spins in diamond with nitrogen delta-doping [Crossref]
2012 - Growth and electrical characterisation of δ-doped boron layers on (111) diamond surfaces [Crossref]
2012 - In situ etching-back processes for a sharper top interface in boron delta-doped diamond structures [Crossref]
2012 - Optical and spin coherence properties of nitrogen-vacancy centers placed in a 100nm thick isotopically purified diamond layer [Crossref]
2012 - High temperature application of diamond power device [Crossref]
2014 - Doping and interface of homoepitaxial diamond for electronic applications [Crossref]
2008 - Unlocking diamond’s potential as an electronic material [Crossref]
2005 - Diamond power devices. Concepts and limits [Crossref]
2010 - Simulations of carrier confinement in boron δ-doped diamond devices [Crossref]
2014 - Electronic and physico-chemical properties of nanometric boron delta-doped diamond structures [Crossref]