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Modifications to Improve CVD Diamond Films. Patrice Allen & Twanaze Mitchell ELEC 6750 Y. Tzeng. Outline. Questions Review CVD Process Metallization of Diamond Films Ion Bombardment Electron Cyclotron Resonance (ECR) Oxygen Plasma Etching Reactive Ion Etching (RIE) of Diamond Films

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modifications to improve cvd diamond films

Modifications to ImproveCVD Diamond Films

Patrice Allen & Twanaze Mitchell

ELEC 6750

Y. Tzeng

outline
Outline
  • Questions
  • Review CVD Process
  • Metallization of Diamond Films
  • Ion Bombardment
  • Electron Cyclotron Resonance (ECR) Oxygen Plasma Etching
  • Reactive Ion Etching (RIE) of Diamond Films
  • Answers
questions
Questions
  • Describe two modifications to improve the usability of diamond films.
  • Why is metallization necessary?
cvd process
CVD Process
  • Two types of reactors

http://www.me.berkeley.edu/diamond/submissions/diam_review/review.htm

cvd process1
CVD Process
  • Procedure
    • Gases activated by plasma
    • Chemical bonds begin to break down
    • Carbon is left and deposited on substrate as a thin layer of diamond film.

www.p1diamond.com

cvd process2
Example:

Fabrication of this CVD diamond was carried out in a 2.45 GHz microwave plasma assisted system with max power at 700 W

These diamond films are a result of activate H2 and CH4 mixtures on substrates held at temperatures between 500 and 1100 C

CVD Process
  • A SEM image of a CVD film on Si

http://www-ibt.lbl.gov/PAG/DiamondFilms.htm

modifications
Modifications
  • Modifications are being researched to enhance the usability of diamond films for microelectronic applications
    • Metallization
    • Ion bombardment for sculpting purposes
    • ECR Oxygen Plasma etching for sculpting purposes
metallization of diamond films
Metallization of Diamond Films
  • Purpose of Metallization
    • Some difficulties are encountered during bonding due to the poor adhesion that exists between substrates and the diamond films that are deposited
    • These difficulties can be overcome by metallizing the diamond using carbide forming transition metals
    • Transition-metal carbide has to be formed at the metal/diamond interface

http://www.wiley-vch.de/berlin/journals/pss/rapid/contents/98-035/wong.html?jURL=http://<?php%20echo

metallization of diamond films1
Metallization of Diamond Films
  • Technique
    • Ion Beam Enhanced Deposition (IBED)
      • Substrate is bombarded with an ion beam to improve the quality of the substrate
      • Main ion beam can deliver power that can reach values from 5 to 60 keV, 0-20mA.
      • Low energy ion beam can deliver a power from 0 to 4 keV, 0-200mA (used to increase deposition rate) .

http://www.wiley-vch.de/berlin/journals/pss/rapid/contents/98-035/wong.html?jURL=http://<?php%20echo

metallization of diamond films2
Metallization of Diamond Films
  • TiC Carbide formed during Ti implementation
  • As a result, adherent Ti/Ni metal layer was obtained on CVD diamond substrates
  • Technique

http://www.wiley-vch.de/berlin/journals/pss/rapid/contents/98-035/wong.html?jURL=http://<?php%20echo

metallization of diamond films3
Metallization of Diamond Films

Metal lines after deposition

http://www.semiconfareast.com/metallization.htm

metallization of diamond films4
Metallization of Diamond Films
  • Experiment
    • Polished CVD diamond films of thickness 250 to 300 mm were used in a study. The deposition was conducted in an IBED system consisting of a metal ion implanter and an Ar ion sputtering system.
    • The diamond samples were initially cleaned by an Ar ion beam with an extracting voltage of 30 kV for 5 to 10 minutes, followed by Ti ion implantation with a dose of 5 × 10^16 ions/cm²

http://www.wiley-vch.de/berlin/journals/pss/rapid/contents/98-035/wong.html?jURL=http://<?php%20echo

metallization of diamond films5
Metallization of Diamond Films
  • Experiment (continued)
    • Ni film was deposited on the samples via simultaneous Ar ion sputtering and Ti ion implantation. The Ti ion was replaced by Ni ion when the thickness of Ni film was about 200 Å, and the whole process ended when the thickness of Ni film reached 1000 Å

http://www.wiley-vch.de/berlin/journals/pss/rapid/contents/98-035/wong.html?jURL=http://<?php%20echo

metallization of diamond films6
Metallization of Diamond Films
  • Results of Experiment
    • Ti ion beam enhanced Ni deposition on diamond results in the formation of TiC carbide in the metal/diamond interface, without the need of high temperatures. As a result, the deposited layer exhibits good adhesion to diamond substrate.

http://www.wiley-vch.de/berlin/journals/pss/rapid/contents/98-035/wong.html?jURL=http://<?php%20echo

ion bombardment
Ion Bombardment
  • Technique
    • Focused Ion Beam (FIB) Sputtering
      • currently used to modify microdevices and fabricate microtools.
      • FIB methods are attractive for machining at the microscale, since they can shape almost any solid including hard materials.
      • FIB is also beneficial because negligible force and heat are imposed on a target during fabrication.

http://mfgshop.sandia.gov/1400_ext/DiamondFIBJVSTBpaper2003November.pdf

ion bombardment1
Ion Bombardment
  • Products
    • Diamond microtools

for ultra-precision

turning operations

This tool has cutting edge radii of curvature equal to 40 nm. Image on right shows intersection of three FIB sputtered surfaces at high magnification

http://mfgshop.sandia.gov/1400_ext/DiamondFIBJVSTBpaper2003November.pdf

ion bombardment2
Ion Bombardment
  • Experiment -Effect of H2O on Yield in Ion Bombardment of Diamond
    • Purpose of Experiment
      • Determine the effect of H2O in removal of carbon atoms through ion bombardment
    • Experiment Apparatus
      • Chamber Pressure = 1x10^-7 Torr
      • Beam = Gallium Ions
      • Fixed current = 2.8nA
      • Incident angle controlled by rotary attachment
      • Nozzle for gas assistant : inner diameter = 250µm

http://mfgshop.sandia.gov/1400_ext/DiamondFIBJVSTBpaper2003November.pdf

ion bombardment3
Ion Bombardment
  • Experiment (continued)
    • Focused Ion Beam is swept across desired area at different incident angles
    • Experiment is repeated using H20 administered through gas jet nozzle

http://mfgshop.sandia.gov/1400_ext/DiamondFIBJVSTBpaper2003November.pdf

ion bombardment4
Ion Bombardment
  • Experiment (continued)
    • Results
      • X-axis: distance of gas jet from surface
      • Y-axis: amount of carbon atoms removed per gallium ion
      • Dotted line is with no H2O

http://mfgshop.sandia.gov/1400_ext/DiamondFIBJVSTBpaper2003November.pdf

ion bombardment5
Ion Bombardment
  • Experiment (continued)
    • Results
      • X-axis: Incident angle in degrees
      • Y-Axis: Amount of carbon atoms removed per gallium ion

http://mfgshop.sandia.gov/1400_ext/DiamondFIBJVSTBpaper2003November.pdf

ion bombardment6
Ion Bombardment
  • Experiment (continued)
    • Conclusions
      • Best incident angle = 86°
      • All results were better with the gas-assisted bombardment using H2O

http://mfgshop.sandia.gov/1400_ext/DiamondFIBJVSTBpaper2003November.pdf

ecr oxygen plasma
ECR Oxygen Plasma
  • ECR - Electron Cyclotron Resonance
  • Purpose of research:
    • To overcome disadvantages of ion beam etching
      • Radiation damage
      • Low etch rate
      • Re-deposition
  • Basic technique: Etch CVD diamond with oxygen plasma

http://ej.iop.org/links/q98/YoQjT65nRp8yuiNvqEx7lw/Na9404.pdf

ecr oxygen plasma1
ECR Oxygen Plasma
  • Experiment Apparatus
    • Typical CVD conditions for fabrication of diamond films
    • Diamond films samples held 5 cm from plasma chamber outlet by a holder
    • Holder has a thermocouple electrode and a bias voltage electrode.

http://ej.iop.org/links/q98/YoQjT65nRp8yuiNvqEx7lw/Na9404.pdf

ecr oxygen plasma2
ECR Oxygen Plasma

Diagram of the plasma etching apparatus with an ECR-type oxygen source

http://ej.iop.org/links/q98/YoQjT65nRp8yuiNvqEx7lw/Na9404.pdf

ecr oxygen plasma3
ECR Oxygen Plasma
  • Experiment Results
    • Etch rate depends on microwave power, gas flow rate, and negative bias voltage.
    • Etch rate increases linearly with increased microwave power from 100 to 300 W

http://ej.iop.org/links/q98/YoQjT65nRp8yuiNvqEx7lw/Na9404.pdf

ecr oxygen plasma4
ECR Oxygen Plasma
  • Experiment Results

Dependence of the etching rate of CVD diamond films on the microwave power for different oxygen flow rates

Dependence of the etching rate of CVD diamond films on the gas flow rate for different microwave power

http://ej.iop.org/links/q98/YoQjT65nRp8yuiNvqEx7lw/Na9404.pdf

ecr oxygen plasma5
ECR Oxygen Plasma
  • Experiment Results

Dependence of the etching rate of CVD diamond film on the negative bias voltage

http://ej.iop.org/links/q98/YoQjT65nRp8yuiNvqEx7lw/Na9404.pdf

rie of diamond films
RIE of Diamond Films
  • RIE – Reactive Ion Etching
    • RIE in O2 Plasma is used for patterning diamond in a large area.
    • Has yielded good etching rates

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide29
RIE
  • Experiment
    • Narrow electrode gap
    • O2/CF4 mixture plasma
    • Measurements
      • Etch Rate
      • Electron Temperature
      • O and F atom densities

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide30
RIE

Diagram of the plasma chamber

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide31
RIE
  • Experiment
    • Chamber: 250 mm high, 160 mm in diameter
    • Electrodes: 70 mm in diameter
      • Distance between electrodes varied from 0.5 to 5.5 cm
    • RF Power – 13.56 MHz at a constant 100 W
    • Diamond films 14 µm in thickness

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide32
RIE
  • Experiment Results
    • Etch rate of diamond decreases as the electrode gap increases

Etching rate as a function of the distance between electrodes.

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide33
RIE
  • Experiment Results
    • Etch rate of diamond increases with CF4 concentrations, peaks around 20% CF4, then decreases

Etching rate as a function of the CF4

concentration in O2/CF4 plasma.

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide34
RIE
  • Experiment Results
    • Electron temperature is max at 20% CF4, the decreases

Electron temperature as a function of CF4

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide35
RIE
  • Experiment Results
    • O atom density reaches max at 20% CF4, then decreases
    • F atom density increases up to 80% CF4

O and F atom densities as a function of CF4 concentration

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

slide36
RIE
  • Conclusions
    • RIE of diamond films with 02/CF4 plasma was studied using narrow gap
    • Max etching rate was obtained with 02 / 20%CF4

http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

answers
Answers
  • Modifications:
    • Metallization
      • Formation of carbide at metal/diamond interface
    • Ion Bombardment
      • Inject ions to bombard surface to sculpt diamond surface for microtools
answers1
Answers
  • Metallization
    • To improve adhesion between diamond and metal so that diamond films bond completely.