Small Feature Reproducibility A Focus on Plasma Etching

1. Small Feature ReproducibilityA Focus on Plasma Etching UC-SMART Major Program Award E. Aydil, N. Cheung, D. Graves, E. Haller, and M. Lieberman, Second Annual Workshop 11/8/99 SFR Workshop - Plasma

2. Agenda 8:30 – 9:00 Introductions, Overview / Spanos 9:00 – 10:15 Lithography / Spanos, Neureuther, Bokor 10:15 – 10:45 Break 10:45 – 12:00 Sensor Integration / Poolla, Smith, Solgaard, Dunn 12:00 – 1:00 lunch, poster session begins 1:00 – 2:15 Plasma, TED / Graves, Lieberman, Cheung, Aydil, Haller 2:15 – 2:45 CMP / Dornfeld 2:45 – 3:30 Education / Graves, King, Spanos 3:30 – 3:45 Break 3:45 – 5:30 Steering Committee Meeting in room 775A / Lozes 5:30 – 7:30 Reception, Dinner / Heynes rm, Men’s Faculty Club SFR Workshop - Plasma

3. Plasma Milestones, Year 1 • Develop spatially resolved Langmuir probe for measurements of electron and ion density, electron temperature, and plasma and floating potential. • Initiate measurements of plasma and process uniformity in LAPS using spatially resolved diagnostics. • Simulations of Cu+ and Ar+ on Co surfaces at 55 eV and 175 eV, at angles 0, 30, 45, 60, 75, 85 degrees. Collections of ion reflection and sputter product energy and angular distributions. • Using MD information, simulations of Cu seed layer deposition in high aspect ratio feature (5/1) under conditions relevant to ionized metal physical vapor deposition (IMPVD) tools. • Development of a working inter-atomic potential for the C-F-H system. • Test with trajectory simulations on carbon surfaces. • Refinement of low energy reactive ion source based on helicon technology. SFR Workshop - Plasma

4. Plasma Milestones, Year 2 • Experimental study of plasma and process uniformity using Langmuir probe, OES, and etch-rate metrology. • Design matching networks for real-time control of standing wave ratio on LAPS and conventional tools. • Measurements of H/F radical-surface reactivity at photoresist surfaces. • Measurement of photoresist etch kinetics with Ar+/F/H • Studies of the structure and kinetics of the mixed CxFyHz layer formed during fluorocarbon plasma etching. • First experimental determination of Si TED in isotope heterostructures. • Secondary Ion Mass Spectrometry (SIMS) study of the Si interstitial "wind" (has never been detected directly!) • Effects of n- and p-type doping on Si TED . • Control of TED of Si and dopants with carbon implantation. SFR Workshop - Plasma

5. Plasma Processing Effects SFR Workshop November 8, 1999 Nathan W. Cheung Research Students: Yonah Cho Adam Wengrow, Changhan Yun Website: www.plasmalab@vivante.eecs.berkeley.edu SFR Workshop - Plasma

6. Goals 1) Layer Transfer Using Plasma Processing for SMART-Wafer -New applications of plasma processing for system integration of photonics, MEMS, and electronics2) Modeling and experiments on surface charge accumulation during plasma processing-Multiple-species model developed to investigate effect of high density plasmas (HDP) on wafer charging SFR Workshop - Plasma

7. Plasma Assisted Materials Processing Lab • General purpose HPD tools for plasma research (charging studies, etching, implantation, materials modification) • Large selection of species available (BF3, O2, H2, Ar, N2, F, He, CO2, H2O, plus others). • Substrate bias 0-80kV DC, and 0-20 kV pulsed-AC. Large Area Plasma Source Plasma Immersion Ion Implanter Transformer Coupled Plasma Source SFR Workshop - Plasma

8. (1) Progress vs Milestones Year 1 • Single-crystal Si membrane on buried cavities with thickness good uniformity (<0.3%) and surface micro-roughness (<10nm) • Plasma surface-activated Si-Si direct bonding and anodic Si-Glass bonding demonstrated. Year 2 • Demonstrate GaN Blue-LED layer transfer • Integration of GaN LED array and c-Si resonator array in progress SFR Workshop - Plasma

9. Motivation: Layer Transfer for System Integration Membrane by Ion-cut GaN LED array by Laser Liftoff Si GaN 100mm 1mm Integration of Optics, MEMS, and Electronics Oxide Electronic LED/LASER Membrane Devices SFR Workshop - Plasma

10. Ion-Cut Layer Transfer Process H+ 1. H+ Plasma Implantation SiO2 Hydrogen peak Si donor Handle wafer Si donor Bonding interface 2 Plasma activated Wafer Bonding Handle wafer Si donor Hydrogen induced Si layer cleavage 3. Donor wafer cleavage with heat treatment Transferred Si overlayer Handle wafer SFR Workshop - Plasma

11. 29nm 0nm 2mm 2mm 1mm 1mm 0mm 0mm Results: SOI fabrication by Plasma Implantation V bias= -20kV, Dose = 1017 H/cm2, T cut = 550C Transferred silicon layer, 120nm Buried oxide, 200nm AFM scan over 2mm2mm area of transferred silicon layer surface RMS roughness ~ 4.1nm (as-cut) SFR Workshop - Plasma

12. Wafer Bonding with Plasma Surface Treatment Wafer direct bonding 1) Chemical (piranha, HF, RCA) cleaning 2) Plasma surface treatment to increase bond strength Bond Strength Measurement XPS Result before and after Plasma Treatment Wafer t 2y 5000 before Razor after L Counts (a.u.) Bond strength = 1000 Et3y2 3 SiO2 Si 0 8 L4 112 108 104 100 96 92 Binding Energy (eV) SFR Workshop - Plasma

13. Discussion * Membrane thickness uniformity across 100mm wafer is less than 0.3%. *AFM scan over membrane surface. The as-cut surface micro-roughness is 6nm. Excellent resonator Q-factor expected from uniform , smooth membranes SFR Workshop - Plasma

14. Results: Oxide Membrane Fabrication 1. H+ Implantation & Etching Cavity 2. Wafer Bonding at room temp. 3. Si Cleavage at ~500OC 4. XeF2 Etching of Si overlayer Si donor Oxide Membrane Silicon on Oxide H+ Etched Cavity Handle wafer 100mm 20 mm SEM Cross-section 1mm Optical micrographic top view SFR Workshop - Plasma

15. GaN GaN Si GaAs hn Laser Liffoff and Bonding Pd-In bond supporting substrate supporting substrate sapphire sapphire sapphire Approach: 1. Low-T In-Pd bond of GaN to Si or GaAs 2. Laser Liftoff and transfer of GaN Develop methodology for integration of GaN with Si and GaAs GaN successfully bonded and transferred from sapphire onto Si GaN Pd-In Next step Integration of GaN-based LEDs with Si-based ICs for emitter-detector arrays 1 mm Si 1mm SFR Workshop - Plasma

16. resonator Future Work (2000-2002) • Prototyping of integrated optical, micro-mechanical resonator and active IC devices on a SMART wafer for real-time processing diagnostics LED Thermal Sensor SFR Workshop - Plasma

17. (2) Progress vs. Milestones Year 1 • Develop an ion flux model for multiple-species plasma • Preliminary results demonstrating mass attenuation effect with different source apertures Year 2 • Work in progress to verify effective mass separation using mass attenuation concept • Verification of multiple-species charging model with various antenna ratios and thin dielectrics SFR Workshop - Plasma

18. Multiple-Species Effects on Charging • Plasma composition will effect charging flux (e.g. molecular gas sources CFx+, carrier gas ionization, and plasma instability) A SFR Workshop - Plasma

19. n ion density v electron velocity i e u ion Bohm velocity V plasma potential b p s sheath width k secondary electron constant M ion mass V applied voltage o V sheath voltage C sheath capacitance s s Single Ion Species Model Ion Current Sheath Diff. Eq. Electron Current Secondary Electrons Displacement SFR Workshop - Plasma

20. Multiple Ion Species Model and Results • Effective mass concept: • Effective ion Bohm velocity concept: BF3 Plasma Results SFR Workshop - Plasma

21. Plasma Mass Attenuator Set-up Processing Chamber Wafer Bias Plasma Sheath ECR Plasma Source Microwave & Gas Input Magnetic Coils Biased Ion Shutter Mass/Energy Spectrometer 3/2 " diameter 3/4 " diameter 3/8 " diameter SFR Workshop - Plasma

22. Small Diameter Shutter (3/8”) • 300W m-wave power • 5 sccm of both Ar and H • Multi-cusp magnet mode (240Amps, plasma confined) • No wafer bias • 300W m-wave power • 10 sccm of Oxygen • Multi-cusp magnet mode (220Amps, plasma not confined) • No wafer bias SFR Workshop - Plasma

23. Future Work for 2000-2002 • Development and verification of a unified model to predict particle flux and charge flux related to HDP processing. SFR Workshop - Plasma

24. Plasma-Surface Interactions: Vacuum Beam Experiments and Molecular Dynamics Simulations David Graves, Frank Greer, and Cam Abrams University of California Berkeley Department of Chemical Engineering Workshop on SFR Nov. 8, 1999 Berkeley, CA SFR Workshop - Plasma

25. Motivation • Plasma-surface interactions key to controlling plasma effects at feature scale • Most poorly understood part of plasma processing • Complex coupled processes: physical and chemical processes • Events often take place over small length scale and short time scales (e.g. ion-surface) • Surface chemistry affects feature scale and tool scale phenomena • How to model feature scale and tool scale processes? • Development of surface process rate expressions • How does PR etch rate depend on ion energy and neutral flux? • How to model processes with simultaneous etch and deposition? SFR Workshop - Plasma

26. Inlet Gas Flow Bulk Plasma Reactive/Etching/ Depositing Species Reactor Scale Wall Interactions Reactive neutral and ionic species Etch and other reaction product species Feature scale Atomic scale Plasma-Surface Chemistry in Plasma Etch Tools SFR Workshop - Plasma

27. Schematic of the Beam Apparatus in Cross-Section Facing Quadrupole Mass Spectrometer Quadrupole Mass Spectrometer Microwave Atom Source F ICP Atom Source Surface Reaction Products H Rotatable Carousel Analysis Section + High Energy Ion Source + + Main Chamber SFR Workshop - Plasma

28. Etch Yield Results for Olin i-line Resist SFR Workshop - Plasma

29. Effect of Hydrogen Atoms at Surface • Etch Yield Effects • Does adding flux of H atoms to photoresist surface reduce the Ar+/F atom etch yield? • Abstraction Chemical Kinetics • What are the abstraction probabilities for the following? • Incident F abstracting adsorbed H from the photoresist • Incident H abstracting adsorbed F from the photoresist SFR Workshop - Plasma

30. Effect of Large Hydrogen Fluxes During Etching GD = 0 GD ~ GF SFR Workshop - Plasma

31. Effect of Other Species on Photoresist Ion-Assisted Etching SFR Workshop - Plasma

32. 3. 5. F D QMS QMS 1. D F D D F D D F D D F QCM QCM 2. 4. 6. D D D F F Abstraction Kinetics Experiments 1. Expose virgin PR to F atoms 4. Pump out deuterium from system 2. Pump out fluorine from system 5. Expose PR to F atoms 3. Expose PR to D atoms 6. Return to step 2 SFR Workshop - Plasma

33. F abstracts D and replaces it on surface • DF signal declines as D is depleted from surface • gFD = 0.06 • D does not abstract F to form DF • gDF ~ 0 Plasma on DF QMS Signal Plasma on D2 only F and F2 D and D2 F2 only Time Time • Surface gains mass as D is replaced by F • F does not etch PR, so mass gain saturates • Mass loss due to slow PR etching from D atoms SFR Workshop - Plasma

34. SFR Workshop - Plasma

35. Molecular, Reactive Ion-Surface Interactions: CFx+ on Si SixCyFz CFx+ Many plasma etching applications include molecular ions that can fragment on impact and that can both deposit and etch. SixCyFz mixed layer Si Mixed layer structure especially complicated with depositing species present in the ion (e.g. C or Si). What is thickness, composition, profile within layer? What controls etch rate? What determines transition between etching and deposition? Can we develop and apply a site balance model of the mixed layer? SFR Workshop - Plasma

36. Molecular Dynamics (MD) Simulation • Simulates the motion of a collection of several hundred to several thousand coupled atoms • Interatomic potential energy function (PEF) governs the forces atoms exert on each other • Numerical integration of the atomic equations of motion until steady state is reached • For C-F: Tersoff/Brenner/Tanaka PEF; accounts for neighboring atom influence on bonding • Added Si for a Si-C-F PEF (Abrams) SFR Workshop - Plasma

37. Introduce ion above surface Integrate using MD Desorb weakly bound clusters, cool to Ts Repeat x2000 Molecular Dynamics Simulations of CFx+/Si InteratomicPotential(Tersoff/Brenner Formalism) Simulation Scheme j i SFR Workshop - Plasma

38. Steady-State Si Etching Througha Fluorocarbon Overlayer: 100 eV CF3+ SFR Workshop - Plasma

39. C,F Si,C,F SixCyFz Si Mass Balance Model MD SiCF Model z 0 q 1.0 SFR Workshop - Plasma

40. Mass Balance Model, continued  = Sites/cm3; L = depth; J+ = ions/(A•cm2) SFR Workshop - Plasma

41. Mass Balance Model, continued Comparison of Model to MD Simulation Basis: J+ = 5 mA/cm2 SFR Workshop - Plasma

42. Second Year Plans • Measure effects of surface temperature and surface type on photoresist etch/abstraction chemistry in beam experiments • Add neutral radical (F, CFx) impact to MD simulations • Further development of phenomenological models for fluorocarbon chemistry SFR Workshop - Plasma

43. TRANSIENT ENHANCED DIFFUSION (TED) IN ISOTOPICALLY ENGINEERED SILICON Hartmut A. Bracht, Cynthia B. Nelson and Eugene E. Haller University of California at Berkeley and Lawrence Berkeley National Laboratory SFR-UCB SMART, Nov. 8, 1999 SFR Workshop - Plasma

44. • Motivation • Transient Enhanced Diffusion (TED) in Silicon • Semiconductor Isotope Heterostructures • Future Work SFR Workshop - Plasma

45. COLLABORATORS • Joel W. Ager III, LBNL • Steven Burden, ISONICS Corp., Golden, CO • Manuel Cardona, MPI Stuttgart, Germany • Nick Cowern, Phillips Eindhoven, Holland • Hans Gossmann, Bell Labs, Lucent Techn., Murray Hill, NJ • William Hansen, LBNL SFR Workshop - Plasma

46. MOTIVATION • Shrinking device dimensions: the SIA roadmap • Doping techniques: ion implantation, diffusion • A new tool: isotopically enriched Si SFR Workshop - Plasma

47. 6515 J. Appl. Phys., Vol. 81, No. 10, 15 May 1997 Appl. Phys. Rev.: Chason et al. • The in-plane dimension reductions (e.g. gate length) demand equivalently shallower implantation and diffusion depths. SFR Workshop - Plasma

48. Dominant Diffusion Mechanisms in Silicon - Interstitial assisted diffusion (kick-out mechanism) AS + I <=> AI - Vacancy assisted diffusion (Frank-Turnbull or dissociative mechanism) AS <=> AI + V (A = Si or impurity)  Self-diffusion coefficient DSD: SFR Workshop - Plasma

49. SELF-DIFFUSION IN SILICON Native point defects: self-interstitials (I) and vacancies (V) Si-tracer self-diffusion coefficient: SFR Workshop - Plasma

50. TRANSIENT ENHANCED DIFFUSION (TED) • The origin of TED: Si interstitial “wind” • Boron clustering • The “+1” rule • The effect of carbon SFR Workshop - Plasma