1 Feature-level Compensation & Control Plasma Technology September 15, 2005 A UC Discovery Project 9/15/05 - Plasma Technology
2 Plasma Technology Professors Jane P. Chang (UCLA), Michael A. Lieberman, David B. Graves (UCB) and Allan J. Lichtenberg, John P. Verboncoeur, Sangsup Jeong, Zhu-wen Zhou, Sungjin Kim, Alan Wu, Emi Kawamura, Insook Lee, Joe Vegh (UCB), and John Hoang (UCLA) Workshop & Review September 15, 2005 9/15/05 - Plasma Technology
Coordinated research involving three PI s Michael A. Lieberman (UCB) - Physics of dual/triple frequency capacitive discharge - Theory and kinetic (PIC-MCC) simulations 9/15/05 - Plasma Technology 3 Dual Frequency Capacitive Discharge for Dielectric Etch David B. Graves (UCB) - Chemistry, plasma and neutral transport, and transient effects - Fluid simulations (FEMLAB) and molecular dynamics simulations of fluorocarbon chemistries Jane P. Chang (UCLA) - Profile evolution in SiO 2, porous dielectrics, high-k dielectrics - Feature scale simulations (DSMC) and experiments (SEM)
4 Relationships Among the Plasma Projects Lieberman (Theory, PIC-MCC) Reactor-scale experiments Electron energy deposition Graves (Fluid and MD) Reactor-scale experiments Surface-scale experiments Ion energy distribution Ion and neutral fluxes Chang (DSMC) Feature-scale experiments Dielectric etch molecular dynamics Feature level profile evolution and control 9/15/05 - Plasma Technology
5 Plasma Sources for Feature Level Compensation and Control Workshop & Review September 15, 2005 Michael A. Lieberman, Allan J. Lichtenberg, John P. Verboncoeur, Sangsup Jeong, Zhu-wen Zhou, Sungjin Kim, Alan Wu, Emi Kawamura UC Berkeley 9/15/05 - Plasma Technology
6 Summary of Research (Lieberman) Develop kinetic simulation models of multiple frequency capacitive discharge tools for dielectric etch and deposition Focus on electron energy depositions and ion energy distributions 9/15/05 - Plasma Technology
7 1e+16 Full PIC Simulation with Mobile Ions Full PIC Density(x) for p = 30mT, f=27.12 MHz 2 J = 30A/m, s = 5.38 mm rf m (Emi Kawamura) 2 F(v x) at x = 0.9s m for full PIC model (v < 0 is towards sheath) x Density(x) (m-3) 8e+15 6e+15 4e+15 F(v ) x 1.5 1 t = 0 t = T/8 t = T/4 t = 3T/8 t = T/2 t = 5T/8 t = 3T/4 t = 7T/8 2e+15 s m. n = n (s ) 0 i m 0.5 0 0 0.01 0.02 0.03 0.04 0.05 X (m) 0-3e+06-2e+06-1e+06 0 1e+06 2e+06 3e+06 v (m/s) x Good agreement between PIC and analytical models 9/15/05 - Plasma Technology
8 Ion Energy Distribution (V 64 = 400V, V 8 + V 2 = 800V) (Allan Wu) 0.02 0.015 0.01 IEDF 400-sum(800) 400-800-000 400-600-200 400-400-400 400-200-600 400-000-800 0.005 0 0 200 400 600 800 1000 Energy (ev) 9/15/05 - Plasma Technology
9/15/05 - Plasma Technology 9 Time-average flux ratio of O neutrals to positive ions (Γ O /Γ + ) vs. pulse periods Γ Ο / Γ+ 15 14 13 12 11 10 9 Global Model with Spatial Variations (Sungjin Kim) Aspect ratio = 1 Aspect ratio = 1/6 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 Pulse period (sec) Duty 50% Duty 25% CW Reducing the aspect ratio to 1/6 results in ~56% of Γ O /Γ + reduction. 25% duty ratio pulse leads to ~27% of Γ O /Γ + reduction at the pulse period of minimum neutral density. Γ Ο / Γ+ 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 Duty 50% Duty 25% CW 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 Pulse period (sec)
10 Ignition of peripheral breakdown and the hysteresis behavior Main discharge only (150 W @100 mtorr) (Sungjin Kim) RF voltage vs. peripheral breakdown 100mTorr, Ar = 40sccm, 1/4 inch gap, 27.12MHz Breakdown of periphery Breakdown Main & peripheral discharge (280 W @100 mtorr) Confined 0 50 100 150 200 250 9/15/05 - Plasma Technology Vrf (Volt) When decreasing the rf voltage (V rf ), the maintenance of the peripheral plasma occurs at a lower voltage than that required to create the peripheral discharge
L 9/15/05 - Plasma Technology 11 Comparison of theoretical maintenance curve with experimental results g w peri w w I rf V rf I rf V rf V d (V) 10 4 10 3 10 2 10 1 (Sungjin Kim) ( L = 2.54cm, g = 0.635cm, w = 3.8cm, w peri =5.1cm) Slot with ignited periphery Periphery with ignited plasma in slot Periphery with no plasma in slot Slot with no ignited periphery 75mTorr 100mTorr 10 0 10 0 10 1 10 2 10 3 p (mtorr) Periphery with 1cm diffusion plasma in slot Periphery ignites Confinement restored
12 Year 3 Milestones Year 3: January 27, 2006 ~ January 26, 2007 Perform particle-in-cell simulations with dual and/or triple frequency source power to determine ion energy distributions at substrate 9/15/05 - Plasma Technology
13 Plasma Sources for Feature Level Compensation and Control Workshop & Review September 15, 2005 David B. Graves, Mark Nierode, Joe Vegh, and Insook Lee UC Berkeley 9/15/05 - Plasma Technology
14 Relationships Among the Plasma Projects Lieberman (Theory, PIC-MCC) Reactor-scale experiments Electron energy deposition Graves (Fluid and MD) Reactor-scale experiments Surface-scale experiments Ion energy distribution Ion and neutral fluxes Chang (DSMC) Feature-scale experiments Dielectric etch molecular dynamics Feature level profile evolution and control 9/15/05 - Plasma Technology
15 Summary of Research (Graves) Develop fluid simulation models of multiple frequency capacitive discharge tools for dielectric etch and deposition Focus on chemical composition and plasma-surface interactions 9/15/05 - Plasma Technology
16 One Dimensional Dual Frequency Fluid Model Results Vs. PIC Results Argon, p = 300 mtorr, 800 V rf @ 27 MHz,, 800 V rf @ 2 MHz applied at left electrode 27 MHz 2 MHz 0.02 m PIC results from Alan Wu, XPDP1; fluid results from Mark Nierode (graduated 7/05) 9/15/05 - Plasma Technology
17 Dual Frequency Results: PIC-Fluid Comparison Argon, p = 300 mtorr, 800 V rf @ 27 MHz,, 800 V rf @ 2 MHz applied at left electrode 9/15/05 - Plasma Technology
18 Dual Frequency Results: PIC-Fluid Comparison Argon, p = 300 mtorr, 800 V rf @ 27 MHz,, 800 V rf @ 2 MHz applied at left electrode 9/15/05 - Plasma Technology
19 Neutral Flow Configuration (Mark Nierode) Commercial tools typically feature dual flow configurations to allow for greater process control (e.g. balance fluorocarbon deposition and etching) Investigate the transport of the tuning gas and its effect on reactor chemistry Pressure ~ 30 mtorr 400/20/9 sccm Ar/c-C 4 F 8 /O 2 0-100 sccm O 2 9/15/05 - Plasma Technology
20 Effects of Altering O 2 Tuning Gas Flow (Mark Nierode) Propose CF/F as model deposition/etch ratio index Varying the outer O 2 flow (Qtune) the ratio of CF to F can be modified radially although the overall ratio of CF to F changes too 9/15/05 - Plasma Technology
21 MD Results (Joe Vegh) Sideviews of Si layers etched with C x F y /F/Ar + ; demonstrates FC film thickness fluctuations at surface 9/15/05 - Plasma Technology
22 MD Results (Joe Vegh) Typical clusters emitted from FC surface during etch: implications for FC etch plasma chemistry models at tool and feature scales 9/15/05 - Plasma Technology
23 Year 3 Milestones Year 3: January 27, 2006 ~ January 26, 2007 Perform fluid simulations to determine effects on neutral species concentration with dual and/or triple frequency source power Use surface simulations to improve reactor scale and feature scale models 9/15/05 - Plasma Technology
24 Plasma Sources for Feature Level Compensation and Control Workshop & Review September 15, 2005 Jane P. Chang, John Hoang UCLA 9/15/05 - Plasma Technology
25 Relationships Among the Plasma Projects Lieberman (Theory, PIC-MCC) Reactor-scale experiments Electron energy deposition Graves (Fluid and MD) Reactor-scale experiments Surface-scale experiments Ion energy distribution Ion and neutral fluxes Chang (DSMC) Feature-scale experiments Dielectric etch molecular dynamics Feature level profile evolution and control 9/15/05 - Plasma Technology
26 Summary of Research (Chang) Develop a Monte Carlo based profile simulator to predict the feature evolution during shallow trench isolation (STI) Focus on the effect of ion energy, neutralto-ion ratios, and surface scattering 9/15/05 - Plasma Technology
27 Definition of Desired STI Profile ITRS dictates stringent conditions for optimal trench isolation as minimum feature size decreases Positive trench tapering angles desired to avoid sharp recesses leading to poly wrap-around Smooth sidewalls needed for less physical and electrical damage Round bottom corners to minimize stress and avoid voids in gapfill Nag, S. and Chatterjee, A. Solid State Technology. 40 (9), p129. Sept. 1997. PR nitride oxide Silicon Isolation stack Pattern nitride and strip PR Trench etch SEM Measured Parameters D 1 Nitride SWA Sidewall oxidation and deposit trench oxide CMP planarization Strip nitride and remove pad oxide tx 1 (nitride) D 2 Desired Properties: tx 2 (top Si) tx 3 (bot Si) D 3 Total Si Depth D 4 > D 2 /2 θ nitride = 90º arctan[(d 1 -D 2 )/2/tx 1 ] θ top Si = 90º arctan[(d 2 -D 3 )/2/tx 2 ] D 4 top Si SWA θ bot Si = 90º arctan[(d 3 -D 4 )/2/tx 3 ] bot Si SWA Recess < 0.1 D 2 SWA: sidewall angle Adapted from ITRS 2003 Thermal Films Supplemental 9/15/05 - Plasma Technology Curvature: r Nitride top = r Si bottom = 0.1 D 2
28 AMAT DP SII Reactor Setup (John Hoang) I outer I inner Coil Power W s Parameters examined for STI etch W s Chamber Pressure (mtorr) Source Power (W s ) Cl 2 N 2 O 2 Pressure Wafer bias (W bias ) DC ratio = I outer /I inner Cl 2 flowrate (sccm) N 2 flowrate (sccm) Substrate Bias W bias O 2 flowrate (sccm) (Courtesy of Helena Stadniychuk at Cypress) 9/15/05 - Plasma Technology
29 Major Enhancements in the Simulator Implemented ion etching yield dependence as a function of ion energy Implemented ion energy distribution and scattering function (to be enhanced with real experimental or plasma simulation results -Collaboration with Graves and Lieberman ) Gas cell (John Hoang) Etching Yield (Si/Cl+) number of ions 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 50 100 150 200 250 300 350 400 500 400 300 200 100 Flux Ratio (Cl/Cl + ) 0 0 50 100 150 200 250 300 350 Ion energy (ev) 235eV Cl + 195eV Cl + 155eV Cl + 115eV Cl + 75eV Cl + 55eV Cl + 35eV Cl + Solid interface cell Implemented sloped sidewalls Solid noninterface cell Least squares method normals 9/15/05 - Plasma Technology Determined surface normals using least squares regression fit to center of cells considered effective rounding of corners
30 Simulation Details (John Hoang) Parameters affecting profile evolution: plasma chemistry (Cl 2, HBr, O 2, ) plasma composition (Cl, Cl 2+, Cl +, O, ) electron temperature and distribution (T e and EEDF n i, n n, ) substrate bias (W s E ion ) substrate temperature (T sub ) Baseline Conditions: initial aspect ratio: 0.55 ion angular distribution (IAD) FWHM: 5.3º ion energy distribution (IED) FWHM: 23.5 ev ion energy: 200 ev neutral to ion ratio: 100 selectivity of nitride to Si: 33.3 9/15/05 - Plasma Technology
31 Comparison of Simulation with Experiments DOE 205-06 DOE 205-07 pressure (mtorr) 45 25 Ws (W) 500 350 Wb (W) 150 250 DC ratio 30 30 Cl2 (sccm) 140 140 N2 (sccm) 30 30 O2 (sccm) 25 25 Similar plasma densities Substrate bias governs the etch depth (John Hoang) DOE 205-10 DOE 205-14 pressure (mtorr) 45 25 Ws (W) 350 500 Wb (W) 150 250 DC ratio 11 11 Cl2 (sccm) 140 140 N2 (sccm) 60 60 O2 (sccm) 25 25 High density versus low density plasmas Plasma composition controls profile evolution Simulation on-going 9/15/05 - Plasma Technology (significantly different sidewall slope could be due to a change in plasma composition)
32 Year 3 Milestones Year 3: January 27, 2006 ~ January 26, 2007 Validate the profile simulation results with additional experiments planned based on analysis of the design of experiments Incorporate experimentally determined ion energy distribution Extend the simulation capability to study dielectric etch 9/15/05 - Plasma Technology