Status and Prospects for VUV Ellipsometry (applied to high-k and - PowerPoint PPT Presentation

Status and Prospects for VUV Ellipsometry (applied to high-k and low-k materials) N.V. Edwards Advanced Products Research and Development Laboratory Semiconductor Products Sector, Motorola, Inc.

Requires invention/ potential showstopper Development required Solution known

Outline Quick Introduction to Ellipsometry 1 • Why do we need the VUV? VUV SE: Initial Challenges 2 • Instrumentation and analysis Applications and Advantages of VUV SE 3 • Increased sensitivity to film thickness • Increased access to unique spectral features VUV SE of High- k Materials 4 • Thickness, bandgap, interface layer VUV SE of Low -k Materials 5 • Porosity, low index inclusions 6 Conclusion

1 Introduction: What is ellipsometry? • Traditional SE can be static or dynamic, 1770 to 190 nm – In-line metrology (thickness, index) – Material diagnostics (band gap, alloy composition, strain) – Optical constants (index of refraction, dielectric constant) – Control/ monitoring of, e.g, • Semiconductor growth • Etching • Deposition of proteins on semiconductors

1 Introduction: What is ellipsometry? • Traditional SE can be static or dynamic, 1770 to 190 nm – In-line metrology (thickness, index) – Material diagnostics (band gap, alloy composition, strain) – Optical constants (index of refraction, dielectric constant) – Control/ monitoring of, e.g, • Semiconductor growth • Etching • Deposition of proteins on semiconductors VUV: <190 nm or > 6.5 eV

1 Introduction: What is ellipsometry? • Why do we need VUV? – Lithography • 157 nm • EUV – Front end processing • Thin high k films – Back end processing • Porous low –k interlayer dielectrics Potential applications for analyzing any “transparent” dielectric and wideband gap semiconductor

1 Introduction: What is ellipsometry? Detector ϕ Source Exit Entrance Optics Optics χ i χ f Sample χ f / χ i → ρ

1 Introduction Real and imaginary part of dielectric function, ε = ε 1 + i ε 2 ρ Optical Real(Dielectric Constant), ε 1 4.0 2.5 Imag(Dielectric Constant), ε 2 ε 1 ε 1 HfO 2 ε Constants ε 2 2 3.5 2.0 3.0 1.5 2.5 1.0 2.0 0.5 Index of refraction n , 1.5 0.0 Extinction coefficient k, 0 2 4 6 8 10 Photon Energy (eV) n = n + i k 2.8 0.60 Index of refraction ’n’ Al 2 O 3 Extinction Coefficient ‘ K ’ n   ( ) 1 1 k  +  2 2 2 2.4 0.40 n σ = ε 2 + 1 1      νε  2   2.0 0.20   ( ) 1 1  +  2 2 2 k σ = ε 2 − 1 1      νε  2   1.6 0 0 300 600 900 1200 1500 1800 W avelength (nm )

2 Challenges: Instrumentation Measurements made: • in air (any transparent medium will do) Quartz and air • with quartz optical elements absorb below 190nm

2 Challenges: Instrumentation The world’s first VUV ellipsometer at the BESSY-I synchrotron source but not quite appropriate for industrial use……..

Challenges: Instrumentation 2 Xenon → Deuterium quartz → MgF 2 Spectral Range: 131 to 1770nm or 0.7 to 9.5 eV Available A.O.I. = 20° to 80° Compensator for high accuracy measurements of transparent region However, reducing data to optical constants still was not routine

2 Challenges: Data Reduction for VUV SE Detector ϕ Source Exit Entrance Optics Optics χ i χ f Sample χ→ρ→ε 131 to 1770 nm Experimental Data 80 300 Sample Properties: Exp Ψ -E 65° ∆ -E 65° Exp 60 200 d , n, k, ε ∆ in degrees Ψ in degrees composition 40 100 Model roughness bandgap 20 0 porosity 0 -100 0 2 4 6 8 10 Photon Energy (eV)

2 Challenges: Data Reduction χ i χ f ambient ε a 2-phase model: substrate ε s 2  − ρ  1 = ϕ + ϕ ϕ 2 2 2   ε sin sin tan s + ρ 1   3-phase model: ambient ε a * d � } < ε > overlayer ε o substrate ε s ( )( ) ε ε ε ε ε ε n   π − − 4 id 2 a s s o o a  s  ε ( ) sin ε = + − ϕ s ε ε ε ε   λ −   o s a a

2 Challenges : Data Reduction * Model assumes mathematically sharp interfaces * Information is returned over the penetration depth of light in the heterostructure (penetration depth is a function of λ ) } overlayer ε o substrate ε s ε s * Must account for: • Inorganic/ organic contamination Significant for VUV SE } • Roughness of high and low k films • Interface layers

2 Challenges : Data Reduction ε s : Substrate is foundational; ε s Substrate = Si Fitting up to DUV is routine; Si optical constants are well known: Aspnes, Herzinger Jellison, Yasuda No optical constants for Si in VUV Si OSG

2 Challenges: Data Reduction Can’t we just extrapolate optical constants? Big problems 0.70 Model Fit Exp pR 40° 0.60 0.50 Reflection 0.40 Reflectivity data 0.30 Model fit (with extrapolated optical constants) 0.20 0 2 4 6 8 10 Photon Energy (eV) No! Need to determine VUV optical constants Si for Si. Approach: • 9 thermal oxide samples grown on Si, OSG from ~8 Å to 2200 Å thick • multiple angle of incidence (45 to 75°) • multi-sample analysis

2 Challenges: Data Reduction • interface layer of 9.4 Å for all samples • fit parameters coupled in interface and SiO 2 layers, except for Amp, E1 offset • could NOT fit data without interface layer SiO 2 : Tauc-Lorentz oscillator Amp= 40.024 , En= 10.643, C= 0.72608, Eg= 7.5258 Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 E1 offset= 1.263 Interface Layer: Tauc-Lorentz oscillator Amp= 158.67 , En= 10.643, C= 0.72608, Eg= 7.5258 Interface Layer Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 Si: Parameterized Semiconductor Layer E1 offset= 1.5705

2 Challenges: Data Reduction • interface layer of 9.4 Å for all samples • fit parameters coupled in interface and SiO 2 layers, except for Amp, E1 offset • could NOT fit data without interface layer Multi-Sample Analysis SiO 2 : Tauc-Lorentz oscillator Amp= 40.024 , En= 10.643, C= 0.72608, Eg= 7.5258 Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 E1 offset= 1.263 Interface Layer: Tauc-Lorentz oscillator Amp= 158.67 , En= 10.643, C= 0.72608, Eg= 7.5258 Interface Layer Pole 1: Pos= 13.167, Mag= 94.386 Pole 2: Pos= 0.135, Mag= 0.0127 Si: Parameterized Semiconductor Layer E1 offset= 1.5705

SiO 2 /Si: Selected Fits from Multi-Sample Analysis Challenges: 2 Fig. 1 a 40 40 Data Reduction Data: ε 1 , blue 30 ε 2 , green 30 Model: red 20 Thinnest Sample: < ε 2 > < ε 1 > 10 20 SiO2 7.5 Å 0 10 Int. Layer 9.4 Å -10 Si Substrate -20 0 0 2 4 6 8 10 Photon Energy (eV) Fig. 1 b 100 300 80 200 ∆ in degrees Ψ in degrees 60 Thickest Sample: 100 SiO2 2189.3 Å 40 0 Int. Layer 9.4 Å 20 0 -100 Si Substrate 0 2 4 6 8 10 Photon Energy (eV)

2 Challenges: Data Reduction X 1C X 1V 2.8 Si Optical Constants New CP: X 1v -X 1C transition < ε 1 > 2.3 50 pseudodielectric function New Critical Point: X 1v -X 1C transition 30 1.8 < ε 2 > 7.2 7.7 8.2 < ε 1 > 10 Motorola Aspnes -10 Herzinger Jellison -30 Yasuda 0 2 4 6 8 10 energy in eV

2 Challenges: 2.00 Data Reduction Index of refraction n 1.90 1.80 SiO 2 Optical Constants 1.70 1.60 Don’t extrapolate 1.50 optical constants! 1.40 This work 0 2 4 6 8 10 Palik, et al. Photon Energy (eV) Herzinger, et al. 0.060 Extinction Coefficient k 0.050 0.040 0.030 0.020 0.010 0.000 0 2 4 6 8 10 Photon Energy (eV)

2 Challenges: 2.00 Data Reduction Index of refraction n 1.90 1.80 SiO 2 Optical Constants 1.70 1.60 Don’t extrapolate 1.50 optical constants! 1.40 This work n w 0 2 4 6 8 10 o n k n Palik, et al. Photon Energy (eV) o i t u l o S Herzinger, et al. 0.060 Extinction Coefficient k 0.050 0.040 0.030 0.020 0.010 0.000 0 2 4 6 8 10 Photon Energy (eV)

3 Applications and Advantages of VUV SE 1. Optical Constants from VUV SE 3. Achieved: ARC n and k from 131 to 1770 nm design and experimental 2.00 0.060 verification for 1.90 0.050 Extinction Coefficient ' k ' improved contrast Index of refraction ' n ' 1.80 0.040 at desired inspection 1.70 0.030 wavelengths 1.60 0.020 1.50 0.010 1.40 0.000 0 300 600 900 1200 1500 1800 Wavelength (nm) ] % 2. Reflectivity/ W [ y a heterostructure t v i e v l e i design t n c g e t simulation h l f e [ n R m ] Thickness[Å] Litho applications are numerous and obvious….

3 Applications and Advantages of VUV SE 2.8 Si 2.3 50 pseudodielectric function 30 1.8 7.2 7.7 8.2 10 -10 -30 0 2 4 6 8 10 energy in eV SiO 2

3 Applications and Advantages of VUV SE 2.8 Si 2.3 50 pseudodielectric function 30 1.8 7.2 7.7 8.2 10 -10 -30 0 2 4 6 8 10 energy in eV SiO 2 High- k Low-k Gates ILDs SiO 2 SiO 2 SiON TEOS Metal oxides OSGs • Increased sensitivity to film thickness • Increased access to unique spectral features