Dept of EECS and 2 Applied Physics Program (fax)

Transcription

1 Hsu-Ting Huang, Brooke Stutzman 2, Wei Kong, and Fred L. Terry, Jr.,2 Dept of EECS and 2 Applied Physics Program (fax) fredty@umich.edu

2 Motivation and Background Demonstration of Spectroscopic Ellipsometry for Analysis Patterned Wafers Two-Channel Spectral Reflectometry as a Lower Cost / Higher Reliability Alternative to Full Spectroscopic Ellipsometry In Situ Measurements of Grating Evolution (The Motion Picture) Advantages of Near-Normal Incidence SE (RDS) for Topography Measurements Conclusions and Future Efforts

3 High-Speed, Nondestructive, Critical Dimension (CD) Measurement in Deep Sub- µm Regime Faster, More Accurate than CD-SEM Ex Situ & In Situ Applications Depth, Wall Angle (Wall Shape) In Situ Etch Monitoring In Line Photolithography Characterization In Situ Applications Favor Fixed Position (Single Angle of Incidence) Instrumentation for High Speed Spectral Methods

4 Basic Concept: Scattering (Diffraction) of Light from Features Produces Strong Structure in Reflected Optical Field Analyze Structure to Obtain Topography Information Periodic Structures (Gratings) Can Be Numerically Modeled Exactly

5 Single Wavelength Scatterometry Examine Structure in Specular and/or Diffracted Modes vs. Angle of Incidence at a Single Wavelength Naqvi, McNeil, and Co-workers (UNM) Elta, Terry, and Co-workers (U. Michigan) Texas Instruments, Sandia Systems Biorad Spectroscopic Ellipsometry and Reflectometry Examine Structure vs. Wavelength at Fixed AOI Terry and Co-workers (U. Michigan) Spanos and Co-workers (UCB), Timbre Technologies

6 Light Source Polarizer Analyzer Detector Eip Erp Eis Ers ρ α = = R R p s cos( = E E 2 Ψ rp rs ), / / E E Sample tan( sin( 2 Ψ cos( Tan(Ψ) And Cos( ) Are Measured by Ellipsometry Functions of wavelength and incident angle ip is β = = Ψ ) ) exp( i ) )

7 The Line is Sliced into a Number of Thin Layers Numerical Eigen-Matrix Solution for Maxwell s Equations Amplitudes & Phases of Different Diffraction Orders Are Obtained by Matching the EM Boundary Conditions Reflected Waves t - ε d θ ε Transmitted Waves

8 Let N be the number of harmonics retained for approximating the solution, s be the number of slices used for approximating grating profile, Then at each wavelength we need 4Ns linear equations for p-polarization 2(N+)s linear equations for s-polarization Typical: s, N~45-65

9 n= 2 N- N 4s x 2s 2s x s C C 2 = s x C N C N R i 2 (N+) Typical N~45-65, S Solve separately for E s and E p to generate tan(ψ) and cos( ) Run time is approximately ~ 2-5 min/forward simulation T i

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11 ~.35µm Line/Space Grating In Photoresist/3Å SiO 2 /Si Accurate Photoresist N(λ) Obtained by SE Measurement of Similarly Prepared Unpatterned Film Period Measured as.7 µm Using st Order Diffraction Angle at Multiple λ s

12 Photoresist Refractive Index Extracted by 3- Angle SE Measurement (65, 7, 75º) of Similarly Prepared Blanket PR Film on Si Thickness Extracted from Transparent Region (5-83nm) n Blanket Photoresist Refractive Index k (n,k) vs. λ Extracted by Direct Point by Point Fit n.8.3 k Some Uncertainty Due to PR Changes During SE Measurements and Due to Vacuum Curing of PR Gratings Wavelength (nm)

13 Grating Equation: sin(θ D )= sin(θ i )+mλ/p For m= (st Order Diffraction) λ=p[sin(θ D )- sin(θ i )] Measurements Done on Sopra GESP-5 in Scatterometry Mode at Nominal AOI=7 Sample Aligned to Plane of Incidence Using High Negative Order Diffracted Light (Backscattered Toward Polarizer Arm) Elimination of Period as a Free Variable Reduces Topography Extraction Problem Wavelength (um) Sony.35µm/.35µm Photoresist Grating Wavelength (um) Y=M+M*X M M.745 R Period (µm).7 Angle of Incidence sin(theta) st order diffraction peak

14 7 Sharp Reflection Resonances Change with Topography 6 tan(psi)-measured 5.5 tan(ψ) 4 3 cos( ) Wavelength (µm) cos(delta)-measured Wavelength (µm)

15 tan(psi)-measured tan(psi)-fit cos(delta)-measured cos(delta)-fit 8.5 tan(ψ) cos( ).92 um.534 um 83.9º Wavelength (µm).36 um um

16 Sharp Features in Spectroscopic Ellipsometry Data Are Very Sensitive to Detailed Shape of Lines in Grating These Sharp Features Are Known as Wood s Anomalies R.W. Wood, Phys. Rev., p. 928 (935) {further commenting on his observations from 92-92} Detailed Fitting Using Vector Diffraction Theory Can Yield Accurate Quantitative Information Some Important Questions: Optimal Measurement Modes Best Methods for Analysis (Inverse Problem) & Issues of Uniqueness

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18 Similar to Ellipsometer but Fixed Prisms (No Moving Parts) Measures R s 2, R p 2 tan(ψ) Key Is Availability of Adequate Low Cost, High Speed, Broad Wavelength Range Spectrometer 6ms Integration Time/2Hz Sampling Rate (Full Spectral) with Easy Upgrade to 3ms/4Hz Low Construction Cost (~$7K) Very Good Reproducibility and Near SE Level Accuracy Demonstrated

19 2CSR Incident 2CSR Reflected

20 Real-Time Etch Monitoring: Blanket Film SiO 2 Etched in CF 4 at 5 & W Thickness from Fit to Both R p 2 & R s 2 6ms Integration Time, s Sampling Time Thickness Repeatability σ d =.22Å Etch Rate Standard Deviation σ e =.37Å/s Thickness (Angstroms) Thickness (A) Etch Rate (A/s) time (s) Etch Rate (Angstroms/s)

21 tan(ψ ) Tan(ψ) Vs wavelength, SE and TCSR AOI=73º SE TCSR Wavelength (µm)

22 Grating with.35 µm line/space width Grating In Photoresist/ 37Å SiO 2 Si Period Measured as.7 µm Using st Order Diffraction Angle at Multiple λ s Etch experiment Modified GEC Etching Chamber mtorr, sccm O 2,5 W 3.56 MHz RF Blanket PR Etch Rate ~.5 nm/s Simple Test Case / Photoresist Trim Process Used to Reduce Gate CD Below Photo Limitations

23 Model Experimental Data Rs 2, Rp 2 vs. λ Calculated Rs 2, Rp 2 vs. λ Nonlinear Regression of Depth, CD and Wall Angle Adjust the Parameters Initial Guess Optimized Parameters

24 Time = 7 sec R P 2 R S CSR Rp ^2 RCWA Rp ^2 2CSR Rs ^2 RCWA Rs ^ Height:.757 µm TopWidth:.54 µm Bottom:.343 µm WallAngle: 82.9º Wavelength (um)

25 Time = 67 sec R P 2 R S CSR Rp ^2 RCWA Rp ^2 2CSR Rs ^2 RCWA Rs ^ Wavelength (um) Height:.436 µm TopWidth:.76 µm Bottom:.54 µm WallAngle: 84.9º

26 Depth:.679 µm Top:.8 µm Bottom:.24 µm WallAngle: 84.5 Etch Time: 2 sec Depth:.638 µm Top:.3 µm Bottom:.269 µm WallAngle: 83.8 Etch Time: 24 sec Depth:.49 µm Top:.85 µm Bottom:.96 µm WallAngle: 83.5 Etch Time: 45 sec Depth:.435 µm Top:.77 µm Bottom:.53 µm WallAngle: 85 Etch Time: 6 sec

27 Topwidth (um) Depth (um) Top Width (um) Depth (um) E+ 9.E+.E+ 2.3E+ 2.5E+ 2.7E+ 2.9E+ 2 2.E E+ 2 Etching Time (sec)

28 Feature Height (nm) Top Width (nm) 78 Real-time-pr- 8 Feature Height (nm) Y = M + M*X M M R Y = M + M*X M 98.9 M R Time (s) Top Width (nm)

29 Real-Time In Situ CD Monitoring/Control Status Kernel Based Learning Algorithm Interpolation Scheme Fully Automated on Modified GEC Reactor st Demonstration of Fully Automated Endpoint-On-Target-CD Accomplished on 2/4/ in GEC Reactor with ms Level Execution Speeds Further Tests Found that the KBL Approach is too Sensitive to Noise and Systematic Experimental Error New Algorithm Developed and Tested Using a Nonlinear Convex Hull Estimation Technique Initial Testing is Highly Successful Speed Optimization Underway Further Tests and Theoretical Analysis is Underway Joint Effort with Ji-Woong Lee and Prof. Pramod Khargonekar

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31 Maximizes Sensitivity to the Pattern R = (R p -R s ) = at Normal Incidence on Unpatterned Wafers Maximizes the Illumination of Sidewalls Reflectance Difference Spectroscopy (RDS) Established III-V Epi Growth Monitor / Detects Oriented Surface Molecular Bonds (Dimmers) Detection Limit of R/R 5-5 z E p Es

32 Simulation Study: Normal vs. Oblique Incidence for Slightly Modulated PR Gratings Flat film: PR Si Sub Very shallow grating: PR Si Sub Å Å 5 Å.2 R/R R/R - 6 Incidence 75 Incidence

33 CD = 5Å Å Poly Poly Poly Depth = 25Å SiO 2 5Å Si Substrate Target: To extract CD & depth separately from SE measurement. α = cos(2ψ), [α = - ( R/R)/2] β = sin(2ψ) cos( )

34 Varying the CD, Step = 2% (5nm) α.5 β.5 Nearly Orthogonal CD & Depth Variation Separated µm Varying the Grating Depth, Step = 2% (nm) µm α.5 β µm µm

35 Varying the CD, Step = 2% (5nm).8.8 α.6.4 β.6.4 Nearly Parallel CD & Depth Strongly Correlated µm Varying the Grating Depth, Step = 2% (nm).8 µm α.6.4 β µm µm

36 Lam TCP94SE Plasma Etching System Cl 2 /HBr Si Main Etch Recipe Nominal Etching Rates: Oxide 5.43Å/sec Poly 52.Å/sec Times: 6, 77, 97, 6, 35, 54, 74 sec

37 Model Experimental Data α, β vs. λ Calculated α, β vs. λ Nonlinear Regression of Depth, CD and Wall Angle Adjust the Parameters Initial Guess Optimized Parameters

38 Incidence at 7 Etching Time : Experiment : Theory α λ (µm) β λ (µm)

39 alpha, beta Angle of Incidence=7 Degrees alpha measured alpha fit beta measured beta fit CD (µm) Depth (µm) Wall Angle SE & RCWA.323 ±.6.33 ± ±.29 SEM.323 ±.5.34 ± ± wavelength (µm)

40 Etch Depth (µm) SE/RDS Etch Depth (um) SEM Etch Depth (um) Etch Time (s) The depths extracted from the SE measurement are in very good agreement with those measured from SEM. The time evolved data shows strong potential for In Situ etch monitoring.

41 Single Angle of Incidence Spectroscopic Ellipsometry is Highly Sensitive to CDs in Deep Sub-µm Regime Operation in Near-Normal (RDS) Mode Improves the Ability to Separately Extract Topography Parameters (Depth, CD, and Wall Angle) Experimentally Demonstrated Capability on.35µm Line/Space Structures Simulations Show Potential to Resolve CDs of 5nm and Below Easy to Implement with Existing Commercial SEs Alternative Implementation with Two-Channel Spectral Reflectometer

42 Improving Ease & Speed of Analysis Understanding Error Limits Errors Induced By Parameterization of Shapes Variations in Lines Uniqueness Issues Overlap of Grating/Non-Grating Patterns NIST ULSI Metrology Conference (Kong, Huang, Terry) Demonstration in Process Control Applications Real Time RIE Endpoint Control Etch to Target CD Use with RTSE on Lam 94 Near Normal 2CSR on Lam 94 Experimental Demonstrations on Smaller Structures More Complex Test Patterns

43 Funding from DARPA/AFOSR MURI Center for Intelligent Electronics Manufacturing (AFOSR GRANT NO. F ) Semiconductor Research Corporation (Contract 97- FC85) {project ended} NIST-ATP: Intelligent Control of the Semiconductor Patterning Process Valuable Technical Assistance Jeff Fournier Pete Klimecky Dennis Schwieger