1. 8:30 – 9:00 Research and Educational Objectives / Spanos 9:00 – 9:50 Plasma, Diffusion / Graves, Lieberman, Cheung, Haller 9:00 – 9:50 Plasma, Diffusion / Graves, Lieberman, Cheung, Haller 9:50 – 10:10 break 10:10 – 11:00 Lithography / Spanos, Neureuther, Bokor 11:00 – 11:50 Sensors & Metrology / Aydil, Poolla, Smith, Dunn 12:00 – 1:00 lunch 1:00 – 1:50 CMP / Dornfeld, Talbot, Spanos 1:50 – 2:40 Integration and Control / Poolla, Spanos 2:40 – 4:30 Poster Session and Discussion, 411, 611, 651 Soda 3:30 – 4:30 Steering Committee Meeting in room 373 Soda 4:30 – 5:30 Feedback Session 3rd Annual SFR Workshop, November 8, 2000

2. 11/08/2000 2 UC SMART Major Program Award D. Graves, E. Haller, M. Lieberman, and N. Cheung SFR Workshop 11/8/00 Plasma and Diffusion Studies

3. 11/08/2000 3 Outline Plasma-Surface Interactions and Modeling (Graves) Diffusion in Isotopically Controlled Silicon (Haller) Plasma Sources for SFR (Lieberman) Plasma-Assisted Surface Modification: Low Temperature Bonding and Layer Transfer (Cheung)

4. 11/08/2000 4 Plasma-Surface Interactions and Plasma Modeling David Graves, Frank Greer, Dave Humbird, John Coburn, and Dave Fraser University of California Berkeley SFR Workshop November 8, 2000 Berkeley, CA

5. 11/08/2000 5 Radical Enhanced Atomic Layer Chemical Vapor Deposition (REALCVD) Frank Greer, John Coburn, David Fraser, David Graves SFR Workshop November 8, 2000

6. 11/08/2000 6 What is A.L.D.? Atomic Layer Deposition –A.K.A. – Sequential Deposition, Digital Deposition, … –Usually a two step process Chemisorption of a metallic precursor Reactive ligand stripping by reactive stable molecule –Distinguishing feature  Each step is self-limiting –Film thickness controlled by number of cycles M ~1 mL of M-L x ~1 mL of M-Y L L L L Y S S S S LS LS

7. 11/08/2000 7 Likely A.L.D. Applications High-k Gate Dielectrics –Highly uniform deposition –Atomic layer control of interface Nitride Diffusion Barriers –Highly conformal deposition Theoretically 100% step coverage

8. 11/08/2000 8 Barrier Layer Deposition by A.L.D. Key Issues: Barrier Properties Conductivity Conformality Thermal budget ** Current barrier/seed films deposited via i-PVD challenged by high aspect ratios Nitride diffusion barrier Low k ILD

9. 11/08/2000 9 Radical Enhanced Atomic Layer CVD (REAL CVD) 1 Uses a volatile precursor and a radical source to deposit a film Reactants introduced in separate steps to achieve atomic layer control Products are nitride film and HCl Radical flux instead of heated substrate catalyzes precursor decomposition –Potentially lower processing temperatures 1 A. Sherman U.S. Patent 1999. Wafer Heated (?) Pedestal Precursor/Radical Inlet Step 2: TiCl x (ab) + XH * (g) + N * (g)  TiN (s) + HCl (g) Step 1: TiCl 4 (g)

10. 11/08/2000 10 Surface Reaction Products Atom Source Schematic of the Beam Apparatus in Cross-section (Top View) Quadrupole Mass Spectrometer (QMS) Main Chamber Analysis Section Rotatable Carousel + Experimental Diagnostics 1.QCM - Measures mass change of film 2.QMS - Measures products formed on film - Characterize beams Silicon-coated Quartz Crystal Microbalance (QCM) Ion Source + Chopper X TiCl 4 Precursor Doser X = O, N, D Load Lock Future in- vacuo Auger Analysis

11. 11/08/2000 11 Experimental Procedure Conventional ALD-like sequence –Each step in process monitored in-situ with QCM –Cycle used multiple times to grow a film Surface temp varied (32, 80, 135 o C) TiCl 4 ~1 mL of TiCl x 1. Adsorption 2. Pump down D ~1 mL of Ti-D x 3. Dechlorination 4. Pump down 5. Nitridation N ~1 mL of Ti-N x

12. 11/08/2000 12 Precursor Adsorption QCM Results Two distinct uptake regimes –Initial rapid ads. followed by significantly slower ads. Adsorption may not be confined to a single monolayer Data fairly well represented by assuming precursor adsorbs two monolayers of TiCl 2 * Model fit allows estimation of: –Sticking probabilities –Active site (*) densities * TiCl x * * Suntola, T. et al. 1996 Uptake Upon Exposure to TiCl 4 TiCl 2 Molecules/cm 2 TiCl 4 Exposure (L) TiCl 4 Adsorption 1 L = 10 15 Molecules

13. 11/08/2000 13 Adsorption Model Results initial sticking ~ 100x self sticking –contributes to uniformity self sticking decreases with inc. T –coverage is more monolayer-like at higher temperatures TiCl 4 5x10 14 6x10 -5 8x10 -3 135 5x10 14 9x10 -5 8x10 -3 80 5x10 14 1x10 -4 8x10 -3 32 Site Density (#/cm 2 ) s(TiCl x ) self sticking s(TiN) initial sticking Temperature ( o C)

14. 11/08/2000 14 Dechlorination Results Cl loss due to abstraction by D atoms ex-situ XPS analysis shows ave. Cl conc. = 2.2% (0.6%- 3.8%) * D Cl Cl Lost Upon Exposure to Deuterium QCM Dechlorination Exponential decay in Cl/cm 2 fit assuming replacement of Cl with D k D+Cl  DCl = 3x10 -4 Fairly insensitive to T Calculated removed Cl density within a few% of ads. assumptions Suggests TiCl 2 is appropriate surface species Cl Atoms/cm 2 D atom Exposure (L) * Process not optimized for chlorine removal

15. 11/08/2000 15 Nitrogenation Results N D Uptake Upon Exposure to N atoms QCM Nitrogenation N Atoms/cm 2 Nitrogen Atom Exposure (L) Nitrogen uptake does not saturate! ex-situ XPS shows N/Ti > 3 Initial uptake of nitrogen fit to linear model s N = 8x10 -3 fairly insensitive to T uptake slows over time suggesting diffusional limitations into the film

16. 11/08/2000 16 Summary and Implications 1. TiCl 4 has two adsorption regimes at these temperatures: Initial rapid uptake (s 1 =8x10 -3 ) Slower continuing uptake (s 2 ~8x10 -5 ) Change likely coincides with 1 st monolayer coverage 2.D atoms remove Cl from surface:  = 3 x10 -4 ex-situ XPS shows not all Cl removed from surface Summary of Results Cl content of films –TiCl 4 overexposure –Insufficient D exposure

17. 11/08/2000 17 Summary and Implications 3. N atoms react with surface Initial Reaction Probability: s = 8x10 -3 Rate slows over time, but does not stop Likely becomes diffusion limited Summary of Results H N Low rxn. probabilities for all species Correct comparison for processing is rate of transport of radicals to feature bottom with rate of reaction on feature sides Transport rate > Reaction rate for aspect ratio ~ 5 –uniform rxn. rates throughout features As aspect ratio increases, transport rate will slow –could lead to non-uniform deposition

18. 11/08/2000 18 Milestones 2001 –Design and test precursor doser, conduct preliminary film deposition studies –Test self-limiting film formation kinetics 2002 –study effects of surface type, preparation and temperature on film properties –measure radical-surface kinetics 2003 –apply method for patterned barrier film application –Explore DRAM capacitor applications

19. 11/08/2000 19 Damage Profiles of Low-Energy Ion Bombardment: Application to Ion Milling Dave Humbird, David Graves SFR Workshop November 8, 2000 Berkeley, CA

20. 11/08/2000 20 Motivation Theory suggests that ion energy deposition is closely related to surface roughening and rippling: possible LER impact MD studies show energy deposited by low-energy (eg. 200 eV) ion impact is localized to a very narrow region near the surface Motivates question: how small a feature can be etched or milled by very tightly focused ion beam?

21. 11/08/2000 21 Molecular Dynamics (MD) Simulation Interatomic PotentialInteratomic Forces typical MD time step: initial configuration update positions update velocities evaluate forces Simulation is non- equilibrium! Kinetic + potential energy is always conserved

22. 11/08/2000 22 Ion-Induced Displacement Simulations Simulation cell size is 20 x 20 x 20 ų (512 atoms) Introduce energetic Ar with velocity normal to surface Follow motion of all Si atoms until collision cascade subsides Repeat x 2000 for statistics Formulate a distribution (in r and z, relative to the point of impact) of atoms’ displacements 1 Expense: 100 impacts = 40 min (PIII-700) 1 in the spirit of Winterbon, Sigmund, and Sanders, Mat. Fys. Medd. Dan. Vid. Selsk. 37 (14) (1970)

23. 11/08/2000 23 Ion Energy Deposition (Displacement) Profile Atomic Displacement Distribution 200 eV Ar Impacts, Normal Incidence Si atoms are displaced from their origins by a distance proportional to the color temperature. (red → ~6 Å, blue → 0 Å) ion trajectory Relative coordinate system: 20Å

24. 11/08/2000 24 Ion “Milling” Simulation Simulation cell is substantially larger (60 x 60 x 40 ų, 9200 atoms) Introduce energetic Ar ion above surface, confined to a “beam” of radius 12 Å about the center Follow collision cascade Delete sputtered Si atoms Cool cell to room temperature Accumulate impacts on the same cell Expense: 100 impacts = 20 hours (PIII-700)

25. 11/08/2000 25 Feature Evolution Representations of the surface after 330 impacts (200 eV Ar, normal incidence) Stereograph top view Tissue-paper plot side view, +y direction 25 Å

26. 11/08/2000 26 Milestones 2001 Milestone Write and test MD code to study energy deposition profiles. Conduct preliminary sputtering studies. Compare to phenomenological theory. 2002 Milestone Write and test code to study ion-induced surface diffusion. Compare results to phenomenological theory and experiment. 2003 Milestone Simulate energy deposition and surface diffusion and compare to LER experiments.

27. 11/08/2000 27 Diffusion in Isotopically Controlled Silicon Eugene E. Haller University of California at Berkeley and Lawrence Berkeley National Laboratory SFR-UCB SMART, November 8, 2000

28. 11/08/2000 28 Collaborators C. B. Nelson, GSRA in MSE Dept., UCB Dr. H. Bracht, Univ. of Münster, Germany Dr. S. Burden, ISONICS Corp., Golden, CO

29. 11/08/2000 29 Diffusion, Native Defects and Impurities – Major experimental observation: Substitutional impurities diffuse assisted by native defects – The major native defects are vacancies and self- interstitials in monatomic crystals – Many native defects exist in more than one charge state: Fermi level effects

30. 11/08/2000 30

31. 11/08/2000 31 Dopant and Self-Diffusion in Crystalline Solids interstitialcy-vacancy -Exchange (ring) mechanism IV

32. 11/08/2000 32 Self-Diffusion in Crystalline Solids Self-diffusion studied with radioactive isotopes: –often limited by low activity and short half-life of the radiotracer (e.g. T 1/2 of 31 Si is 2.6 hrs) –deposition alters the near-surface crystal quality of the material under study –special safety requirements Self-diffusion studied with stable isotopes: –at least two stable isotopes must exist ( 28 Si, 29 Si, 30 Si) –growth of epitaxial layers by VPE or MBE –self-diffusion can be observed at several buried interfaces

33. 11/08/2000 33 Isotope Heterostructures The Isotope Superlattice

34. 11/08/2000 34 Undoped Silicon Isotope Heterostructure

35. 11/08/2000 35 Self-Diffusion in Pure Silicon Profiles: H. Bracht, E. E. Haller, and R. Clark-Phelps, Phys. Rev. Lett 81 (1998) 393 as-grown

36. 11/08/2000 36 Self-Diffusion in Pure Silicon Temperature dependence: H. Bracht, E. E. Haller, and R. Clark-Phelps, Phys. Rev. Lett 81 (1998) 393

37. 11/08/2000 37 Thermodynamic Properties I-related data consistent with theoretical results reliable data for V are still lacking (controversy: low T  high T) Results: Transport coefficients:

38. 11/08/2000 38 Boron and Si Self-Diffusion Boron diffusion mechanism Considering charge states: and

39. 11/08/2000 39 Boron and Si Self-Diffusion Boron and Si self-diffusion are coupled via the Si interstitial population System of four coupled differential equations has to be solved numerically k f,b = forward/backward rate constants

40. 11/08/2000 40 Boron and Si Self-Diffusion Modification of the Si self-diffusion coefficient through the presence of B Extraction of as function of the temperature and E F Determination of donor level position of I 0/+ In case C I ~ C boron, compensation of boron acceptors will accrue, allowing the determination of C I

41. 11/08/2000 41 Boron and Si Self-Diffusion

42. 11/08/2000 42 Conclusions and Outlook Boron doped Si isotope heterostructures hold promise for the first determination of the interstitial transport coefficient C I V I as a function of E F and temperature. In case C I ~ C B, we can determine C I Accurate knowledge of C I V I is crucial for modeling B diffusion Analogous experiments will be conducted with P. High P concentrations will induce the formation of vacancies

43. 11/08/2000 43 SFR Workshop November 8, 2000 Berkeley, CA M. A. Lieberman, A. J. Lichtenberg, A. M. Marakhtanov, K. Takechi, and P. Chabert Berkeley, CA Plasma Sources for Small Feature Reproducibility

44. 11/08/2000 44 Milestones September 30, 2001 - Etch resist in LAPS to examine uniformity. - Characterize instability using OES/actinometry and planar probe. - Install the Z-scan sensor and explore the spectral RF signature of plasma instabilities. September 30, 2002 - Characterize plasma instability using V-I-phase probe. - Model for reduced electron temperature and density. September 30, 2003 - Develop and test instabilities control. Reduce electron temperature and density in discharges.

45. 11/08/2000 Experimental LAPS Setup A Xm (0.5uH) X1X1 X2X2 Rs Vrf Plasma 900 pF (fixed) 12- 1000 pF 12- 500 pF Bm 1 Voltage sensor D C B Bm 2 Antenna coil embedded in the plasma Eight quartz tubes threaded by copper antenna tubes 36.0 cm x 46.5 cm processing area New series-parallel system configuration

46. 11/08/2000 46 Oxygen Discharge Model r1r1 r2r2 r8r8 ….. Substrate holder metal Side metal Calculation area R Quartz -5 5 -15 15 (cm) B.C. V n=0 Chamber geometry used in the model (Center of the chamber) (cm) Particle balance : Power balance :

47. 11/08/2000 47 Ion flux profiles at substrate surface for various gas pressures (simulation results)

48. 11/08/2000 48 Photoresist Etch Model E.R. : Etch rate j i : Ion current density at substrate surface p O : O-atom pressure at substrate surface k ref : Ion-induced desorption rate constant at V bias = 0 V Plots of etch rate vs. pressure for various rf powers. The fits are from the above equation with simulation results.

49. 11/08/2000 49 Etch rate profiles at a gas pressure of 5 mTorr at V bias = 0 V and V bias = -80 V Applying a V bias leads to increase in both etch rate and uniformity over the processing area. Effect of applying a substrate bias on etch rate and uniformity

50. 11/08/2000 Experimental TCP Setup Mass Spectrometer Plasma Inductive Coil Langmuir Probe OES (PMT) 30 cm 19 cm Planar Probe Monochromator

51. 11/08/2000 51 Instability Windows Unstable in most of discharge conditions used in etching Instability linked to average attachment rate Capacitive Inductive

52. 11/08/2000 52 Effect of Matching Network In Ar/SF 6 discharges the frequency depends on the settings of the matching network Ar / SF 6 (1:1) p = 5 mTorr P rf = 500 W f 1 = 1.0 kHz f 2 = 8.5 kHz SETTING 1 (LOW FREQ.)SETTING 2 (HIGH FREQ.)

53. 11/08/2000 53 Determination of time varying densities from planar and cylindrical probes currents The negative ion fraction a can be deduced from the saturation current ratio: time (ms), where Ar / SF 6 (1:1) p = 5 mTorr P rf = 550 W f = 0.8 kHz

54. 11/08/2000 54 Results in (1:1) Ar/SF 6 discharge Ar / SF 6 (1:1) p = 5 mTorr P rf = 500 W f = 0.8 kHz The electron density changes by a factor of 20 with fast rise and decay times Positive and negative ion densities decay at the same rate

55. 11/08/2000 55 Results in pure SF 6 discharge SF 6 p = 5 mTorr P rf = 500 W f = 12.9 kHz   5   400 The electron density exhibit sharp peaks; the ion density is slightly modulated The discharge spends a long time in low-density regime with   400

56. 11/08/2000 56 Future Work Modeling silane deposition processes in LAPS Modeling reduced electron temperature and density processing plasmas in LAPS or TCP Upgrading TCP with higher power, Z-scan, and new matching network Instability measurements in upgraded TCP

57. 11/08/2000 57 Plasma Assisted Surface Modification: Low Temperature Bonding SFR Workshop November 8, 2000 Yonah Cho, Adam Wengrow, Changhan Yun, Nathan Cheung UC-Berkeley, CA 2001 GOAL: Establish plasma recipes and bonding data for Si, oxide and metal surfaces

58. 11/08/2000 58 Motivation : Heterogeneous Integration by Bonding SiO 2 SOI Si SOI Photonics on Si Silicon-On-Insulators Microfludic Transport 200  m Dual Gate MOS

59. 11/08/2000 59 Bonding Methods & Temperature Dependence Anodic Bonding Anodic Bonding Direct Bonding Direct Bonding Metal Bonding Metal Bonding Adhesive Bonding Adhesive Bonding Choice of bonding method depends on thermal budget & materials systems Hydrophobic Si Hydrophilic Si 3000 2500 2000 1500 1000 500 0 100 200 300 400 500600 700 800900 Bonding Energy (mJ/m 2 ) Annealing Temperature ( o C) Bonding Energy vs. Temperature

60. 11/08/2000 60 *Plasma Treatment* Gases Used: O 2, He, N 2, Ar Pressure 200mTorr Power 50W-300W Time 15-30 seconds + O2O2 Thermal Annealing Room Temp Bonding Chemical Cleaning: Piranha + RCA - Plasma Assisted Bonding

61. 11/08/2000 61 Bonding Kinetics 2.02.53.03.5 10 100 1000 Bonding Energy (mJ/m 2 ) Temperature ( o C) 50 100 200 1000/Temperature (K) Si-Si O 2 Plasma-treated Si-Si Chemically cleaned Si-Si Chemically cleaned SiO 2 -SiO 2 E a ~ 0.07 eV E a ~ 0.2 eV E a > 0. 7 eV Plasma treated Si surfaces achieve covalent bonding as low as 105 o C O 2 Plasma-treated Si-SiO 2

62. 11/08/2000 62 Surface Chemistry: XPS 115 Binding energy (eV) SiO 2 Si Hydrophobic Si Hydrophilic Si O 2 plasma treated Si Thermal SiO 2 SiO 2 Si

63. 11/08/2000 63 Plasma Effect Over Time

64. 11/08/2000 64 Surface Morphology Chemically cleaned Si O 2 plasma 150W-300W 30 seconds No Change in Surface Roughness RMS < 0.5 nm

65. 11/08/2000 65 Surface Modification by Concomitant/Sequential Plasma Treatment Mechanical and chemical properties of surface can be effected. Modified surface layer can be from substrate or grown / deposited / transferred layer. Physical and/or chemical changes of surface possible by altering chemical composition of plasma and ion energies. Surface Layer Si Substrate Plasma Treatment Modified Surface *By simply varying the potential of the PIII reactor, it can serve as surface modifier to implanter.

66. 11/08/2000 66 2002 and 2003 Goals Demonstrate concomitant plasma treated deposition layer as effective diffusion layer. Demonstrate polymer surface modification with plasma implantation

67. 11/08/2000 67 Layer Transfer for System Integration SFR Workshop November 8, 2000 Adam Wengrow,Changhan Yun,, Yonah Cho, and Nathan Cheung Berkeley, CA 2001 GOAL: Establish new layer transfer methods for integration of photonics,IC, and MEMS

68. 11/08/2000 68 Motivation CPU UV-Blue laser Micro mirrors 1m1m Micro pump 100  m 200  m Micro-fluidic channels x-y Detector Arrays LED display Paste-and-Cut Approach for Integration of Si IC, Photonics, and MEMS

69. 11/08/2000 69 Substrate A Processing A Substrate A Material Growth A Substrate A Cut Receptor Wafer Substrate B Processing B Substrate B Material Growth B Substrate B Cut Paste Paste-and-Cut for Materials Integration * Bypass material compatibility limitations * Flexible process flow for integration

70. 11/08/2000 70 Mechanical Transfer of Pattern-Implanted Si Implantation Masks Si donor wafer Si handle wafer H + SiO 2 Device Region Hydrogen peak Transferred Si Layer   1. H + Implantation through mask pattern 2. Wafer Bonding at low temperature 3. Mechanical pulling for layer transfer Localized  can exceed the fracture strength of silicon, overcoming the limitation of the thermal cut method

71. 11/08/2000 71 Thermal-cut versus Mechanical-cut 020365075100 10 0 1 2 3 4 5 FIA(%) t(sec) No layer transfer >1day 550  C 600  C 650  C 700  C FIA = Total area Implanted area Hydrogen implantation: 5  10 16 H + /cm 2 at 150keV No thermal-cut for FIA  20% 1m1m Mechanical-cut shown possible for FIA~20%

72. 11/08/2000 72 Poly-Silicon Layer Transfer Using Ion-cut H+H+ Si donor Handle wafer Bonding interface Hydrogen peak SiO 2 Transferred poly-Si layer Poly-Si Poly dep. & H + implant Low-temperature wafer bonding Thermal or mechanical layer cleavage Si donor Oxygen plasma Si donor Handle wafer CMP poly-Si Handle wafer Plasma surface activation for bonding Rough surface for CVD Si. Smooth after CMP

73. 11/08/2000 73 Poly-Silicon CMP for Direct Bonding 2m2m 2m2m 0nm 76nm 0m0m 0m0m 2m2m 7.6nm 0m0m 0m0m 2m2m 0nm As-deposited: RMS roughness ~10.2nm NOT BONDABLE After CMP: RMS roughness ~0.93nm BONDABLE 10 times smoother after CMP!

74. 11/08/2000 74 Poly-Si Layer Transfer Time vs. Temperature 1314151617181920 -8 -7 -6 -5 -4 -3 -2 ln[1/t(sec)] 1/kT(eV -1 ) E a ~1.3eV E a ~0.17eV 400500600300 5 sec. 10 sec. 20 sec. 1 min. 2 min. 5 min. 10 min. 20 min. 50 min. T(  C) t Poly-Si c-Si Poly-Si has 10 times smaller E a than single-crystal Si ! RMS roughness of cut surface ~ 4.2nm, same as single-crystal cleavage

75. 11/08/2000 75 2002 and 2003 Goals Demonstrate integration vehicle with microfluidic flows, photonic source and photonic detection Establish low-temperature layer transfer methodologies for Si-based, III-V based, and polymer- based thin-film devices