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Impedance study of undoped, polycrystalline diamond layers obtained by HF CVD

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2017-04-01
JournalApplied Physics A
AuthorsK. Paprocki, K. Fabisiak, Anna Dychalska, MirosƂaw Szybowicz, Alina Dudkowiak
InstitutionsMahambet Otemiusly West Kazakhstan University, Kazimierz Wielki University in Bydgoszcz
Citations4
AnalysisFull AI Review Included

Technical Documentation & Analysis: Impedance Study of Polycrystalline Diamond

Section titled “Technical Documentation & Analysis: Impedance Study of Polycrystalline Diamond”

This document analyzes the research paper “Impedance study of undoped, polycrystalline diamond layers obtained by HF CVD” (Appl. Phys. A (2017) 123:300) to provide technical specifications and demonstrate how 6CCVD’s advanced Microwave Plasma Chemical Vapor Deposition (MPCVD) capabilities offer superior material solutions for electronic and optoelectronic applications.

Executive Summary

Section titled “Executive Summary”

The research investigates the electrical conduction mechanisms in undoped Polycrystalline Diamond (PCD) films grown via Hot Filament CVD (HF CVD) using impedance spectroscopy.

  • Core Achievement: Successful application of Cole-Cole plots and equivalent circuit modeling (double resistor-capacitor parallel circuit) to separate grain interior ($R_{gi}$) and grain boundary ($R_{gb}$) contributions to electrical conduction.
  • Key Finding: Electrical conduction in the 167 K to 300 K range is dominated by thermally activated grain interior resistance ($R_{gi}$), while grain boundary effects are weakly temperature dependent.
  • Material Quality: The HF CVD method resulted in high concentrations of sp2-hybridized carbon (up to 24.22% sp2/sp3 ratio) and broad luminescence backgrounds, indicating high hydrogen content and structural defects.
  • Limitation Identified: The high concentration of sp2 carbon phase and associated defects limit the electronic performance of the PCD layers.
  • 6CCVD Advantage: 6CCVD utilizes state-of-the-art MPCVD, which yields PCD films with significantly lower sp2 content, higher purity, and superior structural quality (lower FWHM), directly addressing the performance limitations observed in this HF CVD study.
  • Application Relevance: This work is foundational for developing PCD films as gate dielectrics, intermetal dielectrics, and passivation layers in microelectronics.

Technical Specifications

Section titled “Technical Specifications”

The following hard data points were extracted from the study, detailing the material properties and measurement conditions.

ParameterValueUnitContext
Growth MethodHF CVDN/AHot Filament Chemical Vapor Deposition
Substraten-Si (Monocrystalline)N/A10 x 10 mm, 0.2 mm thickness
Deposition Pressure80mbarTotal pressure during growth
Growth Temperature~750°CEstimated substrate temperature
Growth Rate0.2”m/hRate of film deposition
Film Thickness (DPK25)11.50”mSample deposited at 3.00% CH3OH/H2
Film Thickness (DPK26)10.02”mSample deposited at 2.30% CH3OH/H2
sp2/sp3 Ratio (DPK25)24.22%High sp2 content indicates low quality
sp2/sp3 Ratio (DPK26)9.43%Lower sp2 content, better quality
Average Grain Size (DPK26)0.73”mLarger grain size correlates with lower GB phase
Raman Peak Position1331.6cm⁻ÂčClose to ideal diamond monocrystal value (1332.5 cm⁻Âč)
Impedance Frequency Range42 Hz to 5 MHzN/AMeasurement range
Impedance Temperature Range167 to 300KMeasurement range (N₂ atmosphere)
Grain Boundary Resistance (Rgb)400 (DPK25), 1450 (DPK26)ΩAverage values, weakly temperature dependent
Grain Interior Capacitance (Cgi)1.5 x 10⁻âč (DPK25), 1.6 x 10⁻Âč⁰ (DPK26)FCapacitance values, temperature independent

Key Methodologies

Section titled “Key Methodologies”

The undoped polycrystalline diamond films were synthesized using Hot Filament CVD (HF CVD) and characterized using a suite of structural and electrical techniques.

  1. Substrate Preparation: Monocrystalline n-Si wafers (10x10 mm, 0.2 mm thickness) were ultrasonically cleaned and seeded with 1 ”m diamond powder in an ultrasonic bath.
  2. HF CVD Deposition:
    • A water-cooled stainless-steel chamber was used.
    • Total gas flow rate fixed at 100 sccm.
    • Carbon source: Methane (CH4) diluted in H2.
    • Methane concentration varied between 2.3 vol% (DPK26) and 3.0 vol% (DPK25).
    • Total pressure maintained at 80 mbar.
    • Growth temperature estimated at ~750 °C.
  3. Structural Characterization:
    • Morphology: Scanning Electron Microscopy (SEM).
    • Crystallinity/Purity: Raman Spectroscopy (488 nm Ar ion laser, 1000-2000 cm⁻Âč spectral range) to determine sp2/sp3 ratio and hydrogen content (via luminescence background slope).
    • Crystalline Orientation: X-Ray Diffraction (XRD, Cu Kα source) to determine texture coefficients (TC(hkl)) and average grain size (Debye-Scherrer equation).
  4. Electrical Characterization (Impedance Spectroscopy):
    • Electrode Configuration: Au/Diamond/n-Si structure (Fig. 1).
    • Equipment: HIOKI 3532-50 LCR HiTester.
    • Conditions: Measurements performed in N₂ atmosphere across a temperature range of 167 K to 300 K and a frequency range of 42 Hz to 5 MHz.
    • Analysis: Results were plotted as Cole-Cole plots and simulated using a double resistor-capacitor parallel circuit model (RgiCgi in series with RgbCgb) to isolate grain interior and grain boundary contributions.

6CCVD Solutions & Capabilities

Section titled “6CCVD Solutions & Capabilities”

This research highlights the inherent quality limitations of HF CVD diamond, specifically high sp2 content and structural defects, which restrict electronic performance. 6CCVD specializes in high-purity MPCVD diamond, offering materials and customization capabilities necessary to advance this research into high-performance electronic devices.

Applicable Materials for Advanced Impedance Studies

Section titled “Applicable Materials for Advanced Impedance Studies”

To replicate or extend this research with materials exhibiting superior electronic properties (e.g., lower leakage current, higher breakdown voltage), 6CCVD recommends transitioning from HF CVD PCD to high-purity MPCVD materials.

6CCVD MaterialDescription & AdvantageRelevance to Paper
Electronic Grade PCDHigh-quality Polycrystalline Diamond grown via MPCVD. Features significantly lower sp2 content (< 1% typical) and reduced hydrogen incorporation compared to HF CVD.Ideal for minimizing grain boundary effects and isolating intrinsic diamond conduction mechanisms, leading to clearer impedance spectra and higher activation energy.
Optical Grade SCDSingle Crystal Diamond (SCD) with ultra-low defect density (N < 5 ppb).Perfect for fundamental studies where grain boundaries must be eliminated entirely, allowing researchers to study only the intrinsic grain interior ($R_{gi}$) conduction path.
Heavy Boron Doped PCD (BDD)Highly conductive PCD films (metallic or semiconducting).Necessary for extending the research into electrochemical or high-current applications, where the intrinsic resistance must be intentionally lowered and controlled.

Customization Potential for Electronic Device Fabrication

Section titled “Customization Potential for Electronic Device Fabrication”

The paper utilized specific dimensions and a basic Au electrode system. 6CCVD offers comprehensive customization services to meet the precise requirements of advanced microelectronic research.

  • Custom Dimensions & Thickness: The paper used 10x10 mm samples (10-12 ”m thick). 6CCVD routinely supplies PCD wafers up to 125 mm in diameter and offers precise thickness control for both SCD and PCD from 0.1 ”m up to 500 ”m, enabling scalable device fabrication.
  • Surface Finish: The quality of the diamond surface significantly impacts interface capacitance ($C_{gi}$). 6CCVD provides ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD) to ensure optimal interface quality for gate dielectric applications.
  • Advanced Metalization: The Au/Diamond/n-Si structure used in the paper can be optimized. 6CCVD offers in-house, multi-layer metalization capabilities, including:
    • Ti/Pt/Au stacks for robust ohmic contacts.
    • W or Cu for high-temperature or high-power applications.
    • Custom patterning and laser cutting services for specific electrode geometries.

Engineering Support

Section titled “Engineering Support”

The observed dependence of activation energy on hydrogen content (indicated by the Raman slope $m$) requires precise control over deposition chemistry. 6CCVD’s in-house PhD team specializes in tailoring MPCVD recipes to control defect incorporation (e.g., nitrogen, hydrogen) and crystalline orientation (texture coefficients $TC_{(hkl)}$).

  • Defect Control: We can assist researchers in designing experiments to systematically vary gas composition (e.g., CH4/H2 ratio) and pressure to minimize sp2 content and achieve specific preferred orientations, directly addressing the structural differences observed between DPK25 and DPK26.
  • Global Logistics: 6CCVD ensures reliable, global shipping (DDU default, DDP available) of sensitive diamond materials, supporting international research collaborations.

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

View Original Abstract

In this paper, we report results of impedance measurements in polycrystalline diamond films deposited on n-Si using HF CVD method. The temperature was changed from 170 K up to RT and the scan frequency from 42 Hz to 5 MHz. The results of impedance measurement of the real and imaginary parts were presented in the form of a Cole-Cole plot in the complex plane. In the temperatures below RT, the observed impedance response of polycrystalline diamond was in the form of a single semicircular form. In order to interpret the observed response, a double resistor-capacitor parallel circuit model was used which allow for interpretation physical mechanisms responsible for such behavior. The impedance results were correlated with Raman spectroscopy measurements.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1994 - Synthesis diamond: emerging CVD science and technology
  2. 2005 - Progress in Chemometrics Research

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