FLCC Feature-level Compensation & Control Plasma Technology April 5, 2006 A UC Discovery Project

Plasma Technology FLCC Workshop & Review April 5, 2006 Professors Jane P. Chang (UCLA), Michael A. Lieberman, David B. Graves (UCB) and Allan J. Lichtenberg, John P. Verboncoeur, Zhuwen Zhou, Sungjin Kim, Alan Wu, Emi Kawamura, Jon T. Gudmundsson, Chengche Hsu, Joe Vegh, Insook Lee (UCB), and John Hoang (UCLA) FLCC Workshop & Review April 5, 2006 FLCC - Plasma 04/05/2006

Dual/Triple Frequency Capacitive Discharge for Dielectric Etch Coordinated research involving three PI’s Michael A. Lieberman (UCB) - Theory and kinetic (PIC-MCC) simulations - Global model and experiment (supported by NSF & Lam Research) David 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 SiO2, porous dielectrics, high-k dielectrics - Feature scale simulations (DSMC) and experiments (SEM) FLCC - Plasma 04/05/2006

Relationships Among the Plasma Projects Lieberman (Theory, PIC-MCC) Reactor-scale experiments Graves (Fluid and MD) Reactor-scale experiments Surface-scale experiments Electron energy deposition Ion and neutral fluxes Ion energy distribution Dielectric etch molecular dynamics Chang (DSMC) Feature-scale experiments Feature level profile evolution and control FLCC - Plasma 04/05/2006

Plasma Sources for Feature Level Compensation and Control FLCC Workshop & Review April 5, 2006 Michael A. Lieberman, Allan J. Lichtenberg, John P. Verboncoeur, Zhu-wen Zhou, Sungjin Kim, Alan Wu, Emi Kawamura, Jon T. Gudmundsson UC Berkeley FLCC - Plasma 04/05/2006

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 FLCC - Plasma 04/05/2006

Voltage Ions See and Predicted IEDF (Alan Wu) Using the inverse slope of the voltage-time graph, predict the IEDF. Notice the peaks are around voltages where the slope of the previous graph is nearly flat. FLCC - Plasma 04/05/2006

Dual Frequency Sheath Model (Emi Kawamura) Normalized Stochastic Heating Upper Bound High f controls n and ion flux while low f controls : wh2/wl2 >>Vl/Vh>>1 Low f coupling enhances by widening sheath and transporting oscillating e- to lower sheath density and hence higher sheath velocity. Hl = a normalized low f bulk oscillation amplitude. PIC result for normalized stochastic heating agrees well with Kawamura et al (2006) which uses a “hard wall” model which subtracts out the bulk oscillation . FLCC - Plasma 04/05/2006

Comparison of global model with experimental results (Sungjin Kim) ( experimental data from T. Kimura at Nagoya Institute of Technology) By introducing effective volume of ionization and energy losses, simulated results shows good agreement with the experimental data. FLCC - Plasma 04/05/2006

Confined and unconfined discharge with instabilities at transition (Sungjin Kim) Main discharge only (150 W @100 mTorr) 80 W absorbed power@100mTorr High frequency (43.3 kHz) relaxation oscillation Main & peripheral discharge (280 W @100 mTorr) 202 W absorbed power@77mTorr Low frequency (4.21 Hz) relaxation oscillation FLCC - Plasma 04/05/2006

Future Milestones Perform particle-in-cell simulations with dual and/or triple frequency source power to determine ion energy distributions at substrate Complete experiments and theory on instabilities in dual frequency discharges FLCC - Plasma 04/05/2006

Plasma Sources for Feature Level Compensation and Control FLCC Workshop & Review April 5, 2006 David B. Graves, Chengche Hsu, Joe Vegh and Insook Lee UC Berkeley FLCC - Plasma 04/05/2006

Summary of Research (Graves) Develop fluid simulation models of multiple frequency capacitive discharge and inductive tools for dielectric etch and deposition Coupling neutral and plasma in the reactor-scale modeling for DPS tools. Focus on chemical composition and plasma-surface interactions FLCC - Plasma 04/05/2006

Reactor Scale Model Experimental Validation Experimental System Diagnostic ICP Multiple Diagnostics Fits 6-in wafer Well-defined boundaries Stainless steel walls and dielectric top plate Axisymmetric Model 2D, Fluid Model Ar/O2 ICP as the preliminary test FemlabTM and MatlabTM Coupled neutral and plasma model Easy to share / access Easy to extend to different chemistries/systems FLCC - Plasma 04/05/2006

Equation System Iteration Scheme Plasma Model Details Iteration scheme Able to handle over 9 neutral species, and 8 charged species (22 equations) with PC (~1GB memory). 6 neutral ,4 ions species and 15 equations in Ar/O2 model. Convergence: one iteration < 20min. Need < 10 iterations. Robust, and easy to converge. Model assumptions: Ambipolar, quasineutral, isothermal ions, and Maxwellian electrons Model solves for: Neutrals: overall continuity equation, mass balance equation for each species, momentum balance and energy balance Plasma: ion continuity and electron energy. EM field: Helmholtz Wave Equation FLCC - Plasma 04/05/2006

Modeling DPS Tools (Chengche Hsu) 500W, Ar/O2:20/20sccm, 40mT. Neutral velocity field ne plot: peak ne=2.3*1011 cm-3 FLCC - Plasma 04/05/2006

Neutral Flow Configuration: Top-fed and Side-fed (Chengche Hsu) Gas feeding system directly impact the process. Investigate the significance of neutral flow pattern and how it influences the chemistry and the plasma characteristics. Preliminary work for extending the current model to Dual flow/Duel power DPS II system. FLCC - Plasma 04/05/2006

Neutral Flow Configuration: Top-fed and Side-fed (Chengche Hsu) 500W, Ar/O2:20/20sccm, 40mT. O radial mass fraction plots. Side-fed Top-fed Chemistry strongly affected by the feed gas configuration. FLCC - Plasma 04/05/2006

MD Results (Joe Vegh) FC SiC SiF Bulk Si Sideviews of Si layers etched with CxFy/F/Ar+; demonstrates FC film thickness fluctuations at surface FLCC - Plasma 04/05/2006

MD Results (Joe Vegh) For all FC/F/Ar+ ratios examined, a significant fraction of the C leaving the surface does so in clusters of 6 or more C: implications for FC etch plasma chemistry models at tool and feature scales FLCC - Plasma 04/05/2006

MD Results (Joe Vegh) On a relative carbon weighted basis, the products show similar distribution across all simulations. FLCC - Plasma 04/05/2006

Future Milestones Coupling the fluid model with multi-frequency driven plasmas, including EM effects. Modeling DPS II tools: capture the characteristics of dual flow and dual power system. Use surface simulations to improve reactor scale and feature scale models FLCC - Plasma 04/05/2006

Plasma Sources for Feature Level Compensation and Control Feature Profile Evolution during Shallow Trench Isolation (STI) Etch in Chlorine-based Plasmas FLCC Workshop & Review April 5, 2006 Jane P. Chang and John Hoang UCLA FLCC - Plasma 04/05/2006

Summary of Research (Chang) Feature Scale Modeling Combine accurate descriptions of plasma fluxes to quantitatively predict the feature profile evolution during etching/deposition processes Enable process development by shortening experimental time and cost Feature scale model can be coupled to tool scale (e.g. Prof. Graves, UCB) Feature scale model can be coupled with PIC/MC model (Prof. Lieberman, UCB) Shallow Trench Isolation (STI) An enabling technology over local oxidation of Si (LOCOS) since the 0.18 µm node A lower temperature process avoiding annealing used for thermal oxidation A promising technology for even smaller dimensions with properly developed lithography, etch, and gap-fill technology FLCC - Plasma 04/05/2006

STI Process AMAT DPSII Reactor Cl2 N2 O2 Ws Wbias Coil Power Substrate Bias Iouter Iinner Pressure Shallow trench isolation (STI) replaced LOCOS since the 0.18 μm node Rounded bottom corners to minimize stress and allow void-free trench fill Positive trench tapering of 75° to 89° to avoid a sharp corner in active silicon Parameters examined for STI etch Chamber Pressure (mTorr) Source Power (Ws) Wafer bias (Wbias) DC ratio = Iouter/Iinner Cl2 flowrate (sccm) N2 flowrate (sccm) O2 flowrate (sccm) FLCC - Plasma 04/05/2006

Correlation between Process and Simulation Parameters Process Parameters Simulation Parameters Chamber Pressure (mTorr) Ion Angle Distribution (IAD) Source Power (Ws) Ion Energy Distribution (IED) Wafer bias (Wbias) Mean Ion Energy DC ratio = Iouter/Iinner Cl Neutral to Ion Ratio Cl2 flowrate (sccm) N to Ion Ratio (in development) N2 flowrate (sccm) O to Ion Ratio (in development) O2 flowrate (sccm) E-Field lines (future plans?) Other simulation parameters defined by elemental assignment of initial profile Additional simulation parameters defined by different plasma compositions FLCC - Plasma 04/05/2006

Monte Carlo Simulation with Elemental Balance in Cells Source plane + n Periodic boundary conditions Si N Mask (SiNx) O Cl Silicon Si provides available sites Etchant such as Cl leads to the formation of volatile products Reactant such as O leads to the oxidation thus changing the etching characteristics Deposition of SiCl2 and Si will add sites FLCC - Plasma 04/05/2006

Fractional Factorial DOE for Si Etch Pressure (mT) Ws (W) Wb (W) DC ratio Cl2 (sccm) N2 (sccm) O2 (sccm) Mechanisms considered in simulation Chlorination: Sorption of Chlorine ion: Ion-enhanced etching: SiCl2 Deposition: Oxygenation: Sputtering: Sorption of sputtered Si: Recombination of chlorine: 7 factors, 2 levels, and 16 experiments Pressure (plasma density) and DC ratio had statistically significant effects Need to quantify the effect of oxygen addition Cho, H.S. et al. Mat. Sci. in Semi. Process. 8 (2005) 239 Ulal, S.J et al. J. Vac. Sci. Technol. A 20(2) 2002 FLCC - Plasma 04/05/2006

Comparison of Simulation with Experiments Similar plasma densities Substrate bias governs the etch depth High density versus low density plasmas Plasma composition controls profile evolution Simulation on-going (significantly different sidewall slope could be due to a change in plasma composition) FLCC - Plasma 04/05/2006

Refined Surface Normal Determination Previous Approach Current Approach - 82 218 348 Mask Silicon 5 cells included in normal computation Number of cells included increase as long as R2 approaches unity The discrete nature of cell surface representation results in artificial changes in surface normal at a sloped surface and requires a refined approach “bumps” in sloped side walls removed FLCC - Plasma 04/05/2006

Outcome of Design of Experiments Low density plasma High density plasma, with O2 in Cl2 With O2 in Cl2 Without O2 in Cl2 Low DC ratio High DC ratio Without oxygen, microtrenching formation and less tapering More hard mask erosion, resulting in slight bowing High density plasma High density plasma, with O2 in Cl2, low DC ratio With O2 in Cl2 Without O2 in Cl2 Low substrate bias High substrate bias Without oxygen, much less tapering Higher etch rate, more hard mask erosion, resulting in slight bowing FLCC - Plasma 04/05/2006

Future Milestones Quantify the effect of O2 addition to the etch profile evolution during STI etch Predict feature profile evolution during STI etch and confirm simulation with experimental measurements Special Acknowledgements: Helena Stadniychuk and Andrey Zagrebelny at Cypress FLCC - Plasma 04/05/2006