Material Simulation of Carbon Thin Film

1. Material Simulation of Carbon Thin Film Kwang-Ryeol Lee Korea Institute of Science and Technology Seminar @ Sandia National Lab. (2005. 4. 29)

2. People http://diamond.kist.re.kr/DLC

3. Present Simulation Topics • Novel diluted magnetic semiconductors : SiC, Diamond, GaN, GaAs, TiN, various Nanowires • Interfacial intermixing of metallic multilayers : Asymmetry of interfacial intermixing in Al-Co, Co-Cu, Au-Pt • Field emission simulation of doped CNTs : N and B doped CNT • Atomic scale analysis of amorphous carbon thin film : Stress control • Prototype TCAD for nano CMOS devices (just launched)

4. Search for DMS materials x = 0.03 (3%) • b-SiC:TM(Si1-xTMxC) • Si-substituted TM VASP with PAW potential

5. Deposition in Co-Al System Co on Al Al on Co

6. Asymmetric Intermixing Cu on Co (100) Al on Co Au on Pt (001) Co on Al Pt on Au (001) Co on Cu (100)

7. (5,5) Caped CNT, 250atoms Localized basis • Ab initio tight binding calc. To obtain self-consistent potential and initial wave function • Relaxation of the wave function • Basis set is changed to plane wave to emit the electrons • Time evolution • Evaluation of transition rate by time dependent Schrödinger equation Plane wave Field Emission from CNT : Calculation

8. Emission from N doped CNT B state D state C state A state πbond: Extended state Localized state π*+localized state Coupled states between localized and extended states contribute to the field emssion.

9. Nitrogen doped CNT Pure CNT Energy states (eV, E-EF) Energy states (eV, E-EF) Emitted current(μA) Emitted current(μA) Total current: 13.2mA Total current: 8.8mA Enhanced Field Emssion by Nitrogen Doping A B C D

10. Localized state - Undoped CNT - N-doped CNT EF Doped Nitrogen Position Nitrogen Effect The nitrogen has lower on-site energy than that of carbon atom. T. Yoshioka et al, J. Phys. Soc. Jpn., Vol. 72, No.10, 2656-2664 (2003). The lower energy of the localized state makes it possible for more electrons to be filled in the localized states.

11. Present Simulation Topics • Novel diluted magnetic semiconductors : SiC, Diamond, GaN, GaAs, TiN, Various Nanowires • Interfacial intermixing of metallic multilayers : Asymmetry of interfacial intermixing in Al-Co, Co-Cu, Au-Pt • Field emission simulation of doped CNTs : N and B doped CNT • Atomic scale analysis of amorphous carbon thin film : Stress control • Prototype TCAD for nano CMOS devices (just launched)

12. Bond Structure of Carbon Allotropes 1S2 2S22P2

13. Hard disk Heart valve Diamond-like Carbon • Amorphous Solid Carbon Film • Mixture of sp1, sp2 and sp3 Hybridized Bonds • High Content of Hydrogen (20-60%) • Synonyms • (Hydrogenated) amorphous carbon (a-C:H) • i-Carbon • Tetrahedral Amorphous Carbon

14. 2-D Analogy of Structure ta-C a-C:H

15. High Residual Compressive Stress Film Deposition

16. 2-D Analogy of the Structure Structure and Mechanical Properties • Hardness • 3-D interlink of the atomic bond network • Residual Stress • Distortion of bond angle and length • Both are dependent on the degree of 3-D interlinks.

17. Hardness Hardness and Residual Stress

18. Hardness Hardness and Residual Stress

19. Stress Reduction by Si Incorporation C.-S. Lee et al, Diam. Rel. Mater., 11 (2002) 198-203 S.-H. Lee et al, to be Submitted (2005)

20. Brenner force field for C-C bonds Tersoff force field for C-Si and Si-Si bonds Diamond substrate : 6a0 x 4.75a0 x 6a0 1,368 atoms with 72 atoms per layer Deposition Total 2,000 atoms Incident Kinetic Energy : 75 eV for both C and Si Si concentration : 0.5 % ~ 20 % Molecular Dynamics Simulation Deposited atoms created on this plane Fully Relaxed Layer Fixed Layer

21. Snapshots after Deposition 0.0 % 3.0 % 0.5 % 5.0 % 1.0 % 10.0 % 2.0 % 20.0 %

22. Residual Compressive Stress Experiment : C.-S. Lee et al, Diam. Rel. Mater., 11, 198 (2002).

23. Atomic Bond Structure Raman G-peak Position MD Simulation Experiment : C.-S. Lee et al, Diam. Rel. Mater., 11 (2002) 198-203

24. 2.54 Å 1.54 Å Radial Distribution of Pure a-C and Diamond

25. Radial Distribution Function

26. 2.185 A 2.184 A 93.1° 94.2° Carbon for Satellite Peak

27. Bond Angle Distribution 120.0° 109.5°

28. W-DLC by Hybrid Ion Beam Deposition Wn+ H+, Cm+  Sputter gun: Third elements addition to DLC (W, Ti, Si …); Ion gun: Easy controlling the ion bombardment energy with high ion flux. A.-Y. Wang et al, Appl. Phys. Lett., 86, 111902 (2005).

29. Stress & Mechanical Properties 170±15 GPa 21±3 GPa

30. -W2C (101) 3.6 1.9 4 nm 4 nm 4 nm -W2C(101) 2.8 8.6 -W2C(102) 4 nm TEM Microstructures Nano-crystalline -W2C phases evolve. W atoms are dissolved in a-C:H matrix. Amorphous to crystalline WC1-x transition occurs. -W2C

31. Ip/Is = 0.550.1 Raman & EELS Spectra

32. -W2C (101) 3.6 1.9 4 nm 4 nm 4 nm -W2C(101) 2.8 8.6 -W2C(102) 4 nm TEM Microstructures Nano-crystalline -W2C phases evolve. W atoms are dissolved in a-C:H matrix. Amorphous to crystalline WC1-x transition occurs. -W2C

33. H H C C W C Role of W atoms- ab initio calculation

34. Conclusions • Various properties of a-C films generated by MD simulation agrees well with those of experimentally obtained a-C films. • Brenner force field for C-C bond • Tersoff force field for Si-Si and Si-C bond • Stress reduction mechanism based on the atomic scale structure analysis • Small amount of Si incorporation in a-C network effectively relaxes the distorted bonds. • W atoms dissolved in a-C matrix play a role of pivot site where the atomic bond distortion can occur without inducing a significant increase in elastic energy.

35. Newly Launched Project @ KIST • Massive MD/MC simulation technology to understand atomic scale phenomena of 100 million atoms system. • Electron transport analysis technology to characterize nano-device. Next Generation Prototype TCAD for nano CMOS FET simulation Effect of atomic scale interfacial structure on the performance of nano-scale CMOS device

36. Technology Oriented CAD (TCAD) • using computer simulations to develop and optimize semiconductor processing technologies and devices • Process CAD + Device CAD Process CAD Device Structure Device CAD Device Properties

37. Process CAD Next Generation TCAD for Nano-devices • Atomic scale description of the devices • Electron transport in subatomic scale and via non-continuum media Device CAD Device Structure Device Properties

38. 0.13 m <10 nm CMOS FET : Scale down issue 1~3nm • Atomic scale oxide-channel structure simulation • Device characterization for various interface structures

39. Research Flow KIAS KIST Device Simulation Based on TB Theory and Electron Drift Theory Process Simulation Based on Massice MD/MC simulation 3 Tflop Cluster Supercomputing Environment (KIST)

40. KIST Supercomputer : grand.kist.re.kr 512 Computing Nodes Myrinet Storage Node • Calculation Nodes : 512 nodes • Intel Xeon 2.4GHz Dual • RedHat7.3 Kernel 2.4.20 SMP • Myrinet PCI-X D/Cisco Gigabit SW • 2G PC2100 ECC SDRAM • IDE 80GB HDD Head Node Public Network 3.07 TFlops

41. What we have to do • Have a massive MD/MC code with wide range of applicability, which can cover various processes such as deposition, oxidation, diffusion, implantation and other nano-scale processes. • Obtain oxide potentials for Si-O and Hf-O and integrate into the massive MD code. • Visualize the 100 million atoms assembly and characterize the atomic scale structures (bulk and interface).