8:30 – 9:00Research and Educational Objectives / Spanos 9:00 – 9:45 CMP / Doyle, Dornfeld, Talbot, Spanos 9:45 – 10:30 Plasma & Diffusion / Graves, Lieberman, Cheung, Haller 10:30 – 10:45 break 10:45 – 12:00 Poster Session / Education, CMP, Plasma, Diffusion 12:00 – 1:00 lunch 1:00 – 1:45 Lithography / Spanos, Neureuther, Bokor 1:45 – 2:30 Sensors & Controls / Aydil, Poolla, Smith, Dunn, Cheung, Spanos 2:30 – 2:45 Break 2:40 – 4:30 Poster Session / all subjects 3:30 – 4:30 Steering Committee Meeting in room 373 Soda 4:30 – 5:30 Feedback Session 3rd Annual SFR Workshop & Review, May 24, 2001

5/24/ Diffusion and Plasma UC-SMART Major Program Award E. Haller, N. Cheung, D. Graves, and M. Lieberman, University of California Third Annual Workshop & Review 5/24/2001

3 Fermi Level Dependent Diffusion in Silicon Eugene E. Haller University of California at Berkeley and Lawrence Berkeley National Laboratory Collaborators Ian D. Sharp, Undergraduate Student Research Assistant, Chem. Eng. & MSE, UC Berkeley Samuel P. Nicols, Graduate Student Research Assistant, MSE, UC Berkeley Dr. Hartmut A. Bracht, Research Associate, Physics Dept., University of Münster, Germany Dr. Steven Burden, ISONICS Corp., Golden, CO

5/24/ Motivation Downscaling of devices is, in part, limited by diffusion of dopants (see: Paul Packan, Intel Corp., MRS San Francisco, April 19, 2001, Symposium X3, “Materials issues related to dopant diffusion and activation to form shallow, low resistance profiles will be addressed.”). Advanced modeling and control of diffusion requires an improved basic understanding of diffusion processes. Quantitative knowledge of the properties of silicon interstitials, the major active native defect assisting diffusion, is extremely limited. What are its charge states? Where do the energy levels lie in the silicon bandgap? What are the formation and migration energies?

5/24/ Approach Use undoped and doped Si isotope multilayer structures to study self- and dopant diffusion. Determine simultaneously the diffusivities of dopants and silicon as a function of temperature and Fermi level position. Introduce dopants without disturbing the local equilibrium of native defect concentrations (i.e., avoid “interstitial wind” caused by oxidation, implantation or clustering of excess dopant concentrations. Such extra interstitials lead to transient diffusion behavior.) Use a low-temperature MBE-grown amorphous silicon cap layer, implanted at low energies as dopant diffusion source. Boron diffusion is our first target.

5/24/ Theory Boron diffusion mechanism: kickout: Participation of different charge states: The various charge states of the silicon interstitial are not known. )erstitialintneutral(hIBB )donor ionized(IBB 0 S 0 I S 0 I     B S  I  B I

5/24/ Theory (cont.) System of four coupled differential equations has to be solved numerically: k f,b = forward/backward rate constants xxt  

5/24/ Experimental Results: As-implanted isotope Si superlattice

5/24/ Major Results First Fermi level dependent Si self-diffusion experiments have been conducted. Si self-diffusion is enhanced by moving the Fermi level towards the valence band. The kick-out mechanism accurately describes the experimental results assuming: i.e., Boron interstitials are neutral, substitutional boron acceptors are negatively charged (ionized acceptors), Si interstitials are positively charged (ionized donors). B I 0  B S   I ,

5/24/ Future Work Milestone 2002: Identical studies with phosphorus and arsenic Milestone 2003: Identical studies with arsenic and perhaps antimony (diffuses vacancy assisted)

5/24/ Plasma Assisted Controllable Bonding Yonah Cho, Chang-Han Yun, and Nathan Cheung UC-Berkeley, CA 2001 Milestone: To establish plasma recipes and bonding data for Si, oxide, and metal surfaces.

5/24/ New Applications of Plasma Enhanced Bonding Systems Integration Metal polymer Enhanced Adhesion between low k /metal Metal Precleaned wafers stored as bonded pair Si Particle/contaminant free storage Debond SOI Technology

5/24/ Summary of Progress and Research Activities Established SCA technique to monitor surface charge time-dependence of plasma treated surface. Bipolar substrate bias demonstrated as a control variable for surface charging Si-Si full-strength bonding can be achieved at temperature at low as 100 o C with plasma treatment Transient and steady-state bonding kinetics studied (SEE POSTER FOR DETAILS).Polarizability of water moleculars proposed as major mechanism for plasma enhanced bonding. Work initiated for Si and oxide bonding to surfaces with patterned metal Industrial interaction Changhan Yun as 2000 summer intern at AMD for SOI characterization

5/24/ Surface Charge Control: e - Bombardment Vacuum V Capacitance + V- V0 accumulation inversion After e- bombardment plasma exposed Complete neutralization by e- bombardment PIII Chamber with ECR plasma source Ar V wafer = +50 V dc I wafer =.17 A Surface Charge Analyzer Data p-Si

5/24/ Proposed Bonding Model O H O O H H H Si O O O H O O H H H OO Hydrophilic Bonding Plasma Enhanced Bonding ++ -- ++ ++ Interaction between Partial charges (  + and  -) due to high  x (electronegativity): O-H: 1.2, N-H: 0.8, C-H:0.3 Ref: I.N. Levine, Physical Chemistry ++ -- ++ -- ++ -- ++ ++ -- ++ -- ++ -- ++ Enhanced interaction between surface charge and H 2 O

5/24/ Bonding Kinetics E a = 0.58 eV Plasma enhanced bonding E a >> HL bonding (E a ~ 0.05 eV) Arrehenius Plot HL bonding at RT Time Dependent Bonding Strength,  (t)

5/24/ and 2003 Milestones Demonstrate polymer/metal adhesion enhancement with bipolar plasma bias Demonstrate concomitant plasma treated deposition surfaces as effective diffusion barrier. Surface Layer Si Substrate Plasma treatment Deposition Modified Surface What are the control variables and physical mechanisms for plasma enhanced adhesion ?

5/24/ F. Greer, M. Nierode, M. Radtke, M. Kiehlbauch*, D. Fraser, J. Coburn and D. Graves Berkeley, CA * Graduating May 2001 Plasma-Assisted Processes for Small Feature Reproducibility

5/24/ Novel Technologies: Radical-Enhanced Atomic Layer Deposition Atomic layer deposition (ALD) has been proposed to deposit high conformality, very thin diffusion barriers for Cu interconnects Key issue for integration : low deposition temperature –Improve chemical stability of organic low-k films –Reduce mismatch of thermal expansion coefficients –Reduce copper migration Lower temperature deposition using radical activation promises easier process integration with low residual Cl content.

5/24/ Experimental Procedure: TiN from TiCl 4, D and N Conventional ALD-like sequence –Each step in process monitored in-situ with QCM –Many cycles used to grow a film –Resulting films removed for ex-situ XPS analysis Surface temp varied ( 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. Nitrogenation N ~1 mL of Ti-N x

5/24/ Precursor (TiCl 4 ) Dissociative Chemisorption: Near-Monolayer as TiCl 2 1 L = Molecules/cm 2 QCM TiCl 4 TiCl 2 Adsorption Cl 2 Cl 2 desorption

5/24/ Dechlorination: D Atoms Abstract Cl from Surface as DCl D Cl QCM Dechlorination Cl Atoms/cm 2 Cl loss due to abstraction by D atoms Cl Lost Upon Exposure to Deuterium D atom Exposure (L) DCl

5/24/ QCM D Cl Dechlorination Residual Chlorine vs. Relative D Exposure Cl Content (%) Relative D Atom/Cl Exposure 100 o C Results Overall Dechlorination Results After Film Deposition Key result: Low Cl content at only 100 o C. Conventional thermal ALD requires > 400 o C DCl

5/24/ Nitrogenation Results N D Uptake Upon Exposure to N atoms QCM Nitrogenation N Atoms/cm 2 Nitrogen Atom Exposure (L) 2002  Study effects of surface preparation, type and temperature on film properties  Apply method to patterned surfaces for barrier film application. Explore DRAM capacitor applications. Milestones 2002/2003 ND

5/24/ Modeling and Simulation Well-diagnosed plasma experimental station Model development: plasma + neutral chemistry Focus on etch products altering plasma and etch characteristics Si and new gate stack materials: high k and metal gate electrodes

5/24/ Experimental Apparatus

5/24/ Etch Chamber (side view)

5/24/ Example: Silicon etching with Cl 2 Neutral transport and redeposition plays a key role in etch performance. Redeposition of silicon from gas phase on wafer can lead to loss of CD control. Deposition of silicon onto reactor wall requires expensive cleans. Etch Products in Plasma: CD Effects Vahedi et.al., 1999 Dry Process Symposium, Tokyo Mask Redeposited sidewallfilm CD 0 Mask Silicon CD f

5/24/ sccm SiCl 2 Transport & Inlet Position Center Inlet Cl 2 Flux Showerhead Inlet Cl 2 Flux Key result: location of etch gas inlet greatly alters etch product flow

5/24/ Modeling/Testbed Milestones 2002/2003 Convert plasma/neutral code to FEMLAB/MATLAB platform for ease of use and code transferability. Include self-consistent electron kinetics in model. Compare plasma/neutral model to test-bed experimental system: role of etch products in etching. Experimental studies of plasma-wall interactions (e.g. Si/O/Cl for gate/trench etch) Studies of new high-K and gate stack etching (e.g. etch precursors, by-products, selectivity)

5/24/ M. A. Lieberman, A. J. Lichtenberg, A. M. Marakhtanov, K. Takechi, and P. Chabert Berkeley, CA Plasma Sources for Small Feature Reproducibility

5/24/ Milestones September 30, Etch resist in LAPS to examine uniformity (completed). - Characterize instability using OES/actinometry and planar probe (completed). - Install the Z-scan sensor and explore the spectral RF signature of plasma instabilities (in progress). September 30, Characterize plasma instability using V-I-phase probe. - Model for reduced electron temperature and density. September 30, Develop and test instabilities control. Reduce electron temperature and density in discharges.

5/24/ Experimental LAPS Setup A Xm (0.5uH) X1X1 X2X2 Rs Vrf Plasma 900 pF (fixed) pF 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

5/24/ Effect of Argon Addition to Oxygen Plasma on Photoresist Etch Rate Etch Rate (nm/min) Total Gas Pressure (mTorr) Rf power:1000 W ■ :Pure O 2, V bias =0 V ● :Pure O 2, V bias = 80 V □ :O 2 /Ar=1:1, V bias = 0 V ○ :O 2 /Ar=1:1, V bias = 80 V Experimental Data Ar* + O 2  Ar + 2O

5/24/ Effect of Argon Addition to Oxygen Plasma on Photoresist Etch Rate (Simulation vs. Experiment) Etch Rate (nm/min) Total Gas Pressure (mTorr) Data: O 2 /Ar, V bias =0 V Data: O 2 /Ar, V bias = 80 V Fit: O 2 /Ar, V bias = 0 V Fit: O 2 /Ar,V bias =80V Rf power:1000 W E – etch rate Y i – etch product desorbed/ion  0 – flux of O-atoms  i – flux of ions

5/24/ Experimental TCP Setup Mass Spectrometer Plasma Inductive Coil Langmuir Probe OES (PMT) 30 cm 19 cm Planar Probe Monochromator

5/24/ Upgraded TCP Coil and Matching Network Rogowski coil (RF current measurement, fast time response) Z-scan sensor (V-I measurements) 3-turn water cooled coil (high power)

5/24/ Instability Windows Capacitive Inductive Capacitive Inductive Instability linked to average attachment rate Old TCP system Upgraded TCP system Ar/SF 6 (1:1) SF 6

5/24/ 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

5/24/ Global Model Equations Negative ion balance Electron balance Electron energy balance Charge neutrality at the walls Quasineutrality (slow time variation) (medium) (fast) (n - not lost to walls) (highly electronegative)

5/24/ Example of Phase Plane Motion Integrate DE’s for n -, n e, and T e for a given initial condition in the unstable regime Theory Ar/SF 6, 5 mTorr Experiment

5/24/ Future Work Characterize plasma instability using V-I-phase probe. Continue experiments and modeling of instability. Develop model for reduced electron temperature and density. Development of particle-in-cell (PIC) code for compassionate plasmas (in progress). Publications 1.K. Takechi and M.A. Lieberman, Effect of Ion Energy of Photoresist Etching in an Inductively Coupled, Traveling Wave Driven, Large Area Plasma Source (to appear in J. Appl. Phys.) 2. K. Takechi and M.A. Lieberman, Effect of Ar Addition to an O 2 Plasma in an Inductively Coupled, Traveling Wave Driven, Large Area Plasma Source: O 2 /Ar Mixture Plasma Modeling and Photoresist Etching (to appear in J. Appl. Phys.) 3.K. Takechi and M.A. Lieberman, Photoresist Etching in an Inductively Coupled, Traveling Wave Driven, Large Area Plasma Source, J. Appl. Phys. 89, 869 (2001) 4.M.A. Lieberman, A.J. Lichtenberg, and M.A. Marakhtanov, Instabilities in Low-pressure Inductive Discharges with Attaching Gases, Appl. Phys. Lett. 75, 3617 (1999) 5.P. Chabert, A.J. Lichtenberg, M.A. Lieberman, and A.M. Marakhtanov, Instabilities in Low-pressure Electronegative Inductive Discharges (to appear in Plasma Sources Sci. Technol.)