Modifications to Improve CVD Diamond Films

1. Modifications to ImproveCVD Diamond Films Patrice Allen & Twanaze Mitchell ELEC 6750 Y. Tzeng

2. 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

3. Questions • Describe two modifications to improve the usability of diamond films. • Why is metallization necessary?

4. CVD Process • Two types of reactors http://www.me.berkeley.edu/diamond/submissions/diam_review/review.htm

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Metallization of Diamond Films Metal lines after deposition http://www.semiconfareast.com/metallization.htm

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. ECR Oxygen Plasma Diagram of the plasma etching apparatus with an ECR-type oxygen source http://ej.iop.org/links/q98/YoQjT65nRp8yuiNvqEx7lw/Na9404.pdf

25. 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

26. 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

27. 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

28. 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

29. 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

30. RIE Diagram of the plasma chamber http://www.icpig.uni-greifswald.de/proceedings/data/Misu-Arai_1

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. Answers • Modifications: • Metallization • Formation of carbide at metal/diamond interface • Ion Bombardment • Inject ions to bombard surface to sculpt diamond surface for microtools

38. Answers • Metallization • To improve adhesion between diamond and metal so that diamond films bond completely.

39. Questions??