Feature-level Compensation & Control

Feature-level Compensation & Control

2 Plasma Eray Aydil, UCSB, Mike Lieberman, UCB and David Graves UCB Workshop November 19, 2003 Berkeley, CA

3 Feature Profile Evolution Simulation Eray S. Aydil University of California Santa Barbara Workshop November 19, 2003 Berkeley, CA

4 Profile Evolution Simulation for Plasma Etching Tool-Scale Models Species fluxes & energy distributions Profile Simulator Tools: Centura TM and/or dual frequency capacitive plasma Experiments Year I Milestone: Development of a 2-D profile simulator for low-k dielectric etching. A flexible Kinetic Monte Carlo (KMC) based profile simulator for low-k dielectric and/or Si deep trench etching For interpretation of etching experiments and guiding process development

5 Goals To Develop of a 2-D profile simulator for low-k dielectric etching Understand and quantify kinetics of low-k dielectric etching semi-empirically Capture the balance between etching and sidewall passivation Identify key plasma properties that affect profile evolution Linking of the profile simulator with tool-scale models (with Graves) Testing and calibration of the simulator in an etching tool (Centura TM ) Obtain information about the kinetics and etching mechanisms by matching simulated profiles with those experimentally observed Eray & Joshua Ron Bessems

6 Proof of Concept from our related work in collaboration with Lam Research: SF 6 /O 2 etching of Si pure SF 6 increasing O flux SF 6 /O 2 In this work a continuum based (not KMC) simulator is used to model Si etching. KMC is ideally suited for complex surface chemistry and etching of low-k dielectric films with nanostructure. Predictive model is arrived at through the framework depicted in the first slide. Goal is to develop a similar tool for low-k dielectric etching.

7 Towards a predictive profile simulator 25 mtorr, 800 W rf power, -120 V rf bias, 80 sccm total flow SEMs of etched features Simulated features 45:35 40:40 35:45 30:50 SF 6 :O 2 SF 6 :O 2 SF 6 :O 2 SF 6 :O 2 decreasing F-to-O ratio

8 Future Work: Year II-IV Milestones Profile simulator development and refinement is ongoing continuously. The goal is to have the first version of the KMC based simulator at the end of the first year. Year II: Procure patterned wafers and etch them to make comparisons between the experimental SEM data and the profile simulations. Year II: Make adjustments to the profile simulations using the feedback from the experiments, MD simulations and reactor scale simulations. Year III: Couple reactor scale simulations with profile scale simulations. Year IV: Incorporate effects of feature charging in coupled reactor scale and feature profile simulation. Year IV: Compare profile simulations with experimentally obtained profiles in Centura and/or dual frequency capacitive coupled plasma.

9 Plasma Sources for Feature Level Compensation and Control Workshop November 19, 2003 Berkeley, CA Michael A. Lieberman, Allan J. Lichtenberg, John P. Verboncoeur, Sungjin Kim, Alan Wu UC Berkeley

10 Milestones Year 1: September 3, 2003 ~ August 31, 2004 Develop one-dimensional asymmetric particle-in-cell simulation of dual frequency capacitive discharge. Develop global discharge model for multiple rare gas mixtures.

11 Motivation and Highlights Kinetic Simulation of Dual Frequency Capacitive Discharges Alan Wu, A.J. Lichtenberg, M.A. Lieberman, J.P.Verboncoeur Single frequency standard for etching Major drawback Cannot independently vary ion flux and ion bombarding energy Dual frequency discharge High frequency controls plasma density (ion flux) Low frequency controls ion bombarding energy Ideal case Completely independent

12 2003 Objectives Investigate physics issues to incorporate into global model Particularly power deposition Investigate kinetic effects Investigate numerical simulation issues

13 Heating Mechanisms

14 Simulation Codes XPDC1 and XPDP1 PIC-MCC codes (cylindrical and planar) 1-D bounded electrostatic code Solves Poisson s equation Has external circuit (used for blocking capacitor) Ions and electrons are both collisional using MCC

15 Time Avg. T(x) (ev) Planar Time Avg. Temperature T(x) vs. Particle Weighting (pw) V = 500 10 pw = 1e9 pw = 4e9 pw = 16e9 e - e - e - ions ions ions 0 0 X (m) 0.03 0 X (m) 0.03 0 X (m) 0.03 Particle Weighting (Real Particles/Superparticle) more simulation particles

16 Motivation and Highlights Global Model of Electronegative Discharges for Neutral Radical Control Sungjin Kim, M. A. Lieberman, and A. J. Lichtenberg Control of neutral radical flux and ion flux for dielectric etch systems Effect of chamber geometry aspect ratio (height/diameter) Effect of pulsed power modulation

17 2003 Objectives Discharge equilibrium properties depending on: - Aspect ratio: Ratio of height to diameter (L/2R) - Non-rectangular power modulation waveform Simulation with the parameters of experimental systems Compare the simulation results with experimental results and with analytical global model.

18 Global model (spatially averaged model) Assumes uniform spatial distribution of plasma parameters over the volume of bulk plasma, with the bulk plasma density dropping sharply to edge values at the wall. Much simpler equation than other simulation methods (PIC, fluid model) Particle Balance Equation Assuming Te dn dt j = Ki, k ( Te ) nin i, k k AK V w j Γ j Wall reaction n j Electron Power Balance Equation d dt 3 2 en T e e = P Reaction set (electron & ion impact ionization, Dissociation, neutralization, charge exchange, etc) absorbed P collision _ loss P escape_ loss T e

19 Simulation Conditions Oxygen discharges at low pressure (10mTorr) were studied. (including O 2+, O -, electrons and O 2* ( 1 g ) ) Two different aspect ratios (L/2R) were studied. - aspect ratio = 1 (L=30cm/R=15cm), Power AVG = 200W - aspect ratio = 1/6 (L=5cm/R=15cm), Power AVG = 66W The average powers of both aspect ratios were adjusted to yield similar values of steady state positive ion flux (Γ + ) on the wall. Nearly sinusoidal waveform of power modulation was considered. (rise/fall time = 50% of the pulse period) The dependence on pulse period and duty ratio (50% & 25%) were studied.

20 Time-average flux ratio of O neutrals to O 2+ ions with various pulse periods Aspect ratio = 1 Aspect ratio = 1/6 140 130 Pulsed (50% duty) Pulsed (25% duty) CW Plasma 80 75 Pulsed (50% duty) Pulsed (25% duty) CW Plasma 120 70 Γ / Γ 110 Γ / Γ 65 100 60 90 55 80 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 50 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 Pulse Period (sec) Pulse Period (sec) Reducing the aspect ratio to 1/6 results in 43% of Γ O /Γ + reduction. 25% duty ratio pulse leads to 27% and 22% of Γ O /Γ + reduction at the pulse period of minimum neutral density.

21 Future Plans Kinetic Simulations Determine power depositions for dual frequencies Global Models Compare results with experiments (single and dual frequency) and analytic models

22 Plasma Sources for Feature Level Compensation and Control Workshop November 19, 2003 Berkeley, CA Mark Nierode and David Graves UC Berkeley

23 Milestones Year 1: September 3, 2003 ~ August 31, 2004 Develop 2-D, non-isothermal, compressible flow simulator for dual frequency capacitive discharge and for Centura.

24 Motivation and Highlights Fluid Simulation of Chemically Reacting Plasma Discharges Mark Nierode and David B. Graves Important to develop models of complex chemistry and transport in plasma etch reactors few studies with chemistry models and nonisothermal gas transport Comparisons to experiment initial results compared to ICP with diagnostics subsequent applications to capacitive discharges and Centura

25 2003 Objectives Investigate numerical challenges to using FEM package FEMLAB Begin construction of chemistry model and comparisons to experiment Incorporate ability to model transient gas flows

26 Simulation Summary 2-D Axisymmetric fluid model Neutral fluid Exchange mass, momentum, and energy with plasma fluid Many neutral species with an added emphasis on surface reactions Plasma fluid Collisional plasma (approximate) Power deposition, electron energy Commercial PDE Solver FEMLAB and MATLAB Example domain

27 Available Experimental Diagnostics QMS Fluxes of neutrals and ions at chamber wall Neutral density (APMS) OES Neutral species identification and temperature estimate Langmuir probe EEPF mean electron energy, T e, electron density Plasma potential Ion flux probe Positive ion fluxes at chamber wall FTIR Neutral species densities

28 Experimental Apparatus Jerry Hsu, UCB

29 Experimental Results Jerry Hsu, UCB 3 2.5 Current Conditions p = 10 mtorr P = 150 W NormalFlowRate DoubleFlowRate F CF CF2 CF3 CF4 C4F8 Ar (*0.1) Neutral Species 2 1.5 1 0.5 Figure: Dominant neutral species density measured by using Hiden. Note that Ar neutral density was multiplied by a factor of 0.1. 0 Density (10 13 cm -3 ) 18/2 sccm Ar/C 4 F 8 Questions How important are the surface reactions? Can we reproduce the experimental results? Can we describe the reformation of PFCs? Will the simulation translate to other tools?

30 Neutral Argon Results 20 sccm Ar, p=10 mtorr, P = 150 W Argon number density follows temperature profile Minimal pressure gradients

31 Plasma Density Electron Density Profile Comparison Number Density [#/m3] 5.0E+17 4.0E+17 3.0E+17 2.0E+17 1.0E+17 0.0E+00 FEMLAB P=150 W, p=10 mtorr Exp. Data Adjusted P=?, p=10 mtorr 0 5 10 Radius [cm] Electron density profile agrees reasonably well with Langmuir probe scan (Matt Radke, UCB) in experimental chamber

32 Electron Energy 150 W power dictated by Hsu experiments Electron temperature agrees with L&L global model 20 sccm Ar P=10 mtorr

33 Future Plans Compare results with experiments (single and dual frequency) and analytic models Provide input for feature profile simulators Transient/Pulsing Flows