2. Transparent Films. Neha Singh October 2010

Transcription

1 2. Transparent Films Neha Singh October 2010

2 Course Overview Day 1: Introduction and Theory Transparent Films Microstructure EMA Surface roughness Ultra thin films Uniqueness test UV Absorption Point-by-point fit Day 2: Genosc Layer Absorbing Films If time permits: Non-idealities Grading (Simple and function-based ITO) Thickness non-uniformity Review Actual Samples 2

3 Transparent? No or very little absorption (k 0) Depends on wavelength range Typical transparent films in Visible wavelength range: SiO 2, polymers, MgF 2, ZnO, etc. Typical transparent films in NIR or IR wavelength range: Si, ZnSe, ZnS, etc. 3

4 Transparent Films Cauchy Dispersion Sellmeier Dispersion 4

5 Data features Oscillation patterns in ellipsometry data due to thin film interference Pattern affected by thickness and index ~n 0 ~n 1 ~n 2 Transparent - oscillations 5

6 Thickness Effects Thicker films have more interference oscillations 6

7 DEMONSTRATION Demo1_SiO2 on Silicon Roller-ball to get Thickness Pay attention to the generated data feature as thickness changes Roller-ball Click Shift-Click CTRL-SHIFT Click small step X10 X100 2 sio2_jaw nm 1 intr_jaw nm 0 si_jaw 1 mm 7

8 Examples Demo2_SiO2 on Si.dat and Demo3_SiO2 on Si.dat Fit for thickness, using roller-ball to find approximate value before regression.

9 Index effects Film index contrast to substrate affects the magnitude of Psi High contrast leads to high peaks Index also affects number of oscillations

10 Cauchy Dispersion Equation Cauchy dispersion equation describes index (n) as a function of wavelength λ Only for TRANSPARENT materials (k=0 or very small) 1.65 Index of refraction, n n(λ)=a+b/ λ 2 +C/λ 4 k(λ)= Wavelength (nm) 10

11 Cauchy Dispersion Equation A sets index range n (λ) = A +B / λ 2 + C / λ 4 k (λ) = 0 B and C give dispersion shape Wavelength, 11

12 Applications- Cauchy Material must be transparent. 4 SiO2 Si3N4 Si Index, n Wavelength in nm 12

13 Cauchy.mat Cauchy Layer Cauchy Parameters

14 Cauchy Procedure 1. Adjust An parameter to approximate index. Psi amplitude can help estimate. 2. Adjust thickness to match # of oscillations. 3. Fit Thickness and An. 4. Add Bn. Does it improve the MSE? 5. Add Cn. Does it improve the MSE? 14

15 DEMONSTRATION Demo4_SiN on Si.dat Cauchy for Index Roller-ball to get Thickness and Index Fit Window Edit Parms 1 cauchy nm 0 si_jaw 1 mm 15

16 Normal Dispersion Without absorption: Increasing index with decreasing λ Desired outcome with Cauchy layer is positive coefficients 16

17 Unphysical Dispersion Decreasing index with decreasing λ Anything other than increasing index with decreasing λ

18 Which results are physical? A= B= C= E-05 A= B= C= n (λ) = A +B / λ 2 + C / λ 4 A= B= C= A= B= C= 0.009

19 Examples Demo5_AlN on Si.dat Use roller-ball to find approximate thickness and index before regression.

20 Examples Demo6_SiOC on Si.dat Fit with Cauchy. Is result correct?

21 Poles (Sellmeier model) Add dispersion (curvature) to both ends of spectral range ε Center energies must be outside of spectral range Valid spectral range (transparent region) ε A ( ) n = 2 E E 2 n n E ε 1 reference ε 1 Sellmeier Photon Energy (ev) 21

22 Introduction to Genosc.mat ε 1 section Reference/graph section ε 2 section & oscillator list 22

23 Genosc ε 1 section Poles and e1offset used to match ε 1 shape Pole #2 dispersion ε 1 Pole #1 dispersion e1 Offset Photon Energy (ev) 23

24 Poles: What to Vary Do not fit Position, if Magnitude = 0. Do not fit Position of Pole#2. Pole#1 Magnitude, Pole#1 Position, and e1-offset often correlated 1. Fit Pole #1 Magnitude (see next page) 2. Add Pole#1 Position 3. Add Pole#2 Magnitude (should stay zero or very small) 4. Add e1-offset. Keep if improves fit, but remove if MSE stays the same. 24

25 Varying Pole Magnitude Index Simulation: Pole Position = 11eV Pole#1 Amp=100 Pole#1 Amp=150 Pole#1 Amp=200 Pole#1 Amp=250 Pole#1 Amp=300 Pole#1 Amp=350 Pole#1 Amp=400 Pole#1 Amp=450 Pole#1 Amp= Wavelength (nm) 25

26 DEMONSTRATION Demo1_SiO2 on Si.dat Use GENOSC e1-section to fit transparent film index. 26

27 Examples Demo7_Dielectric on Si.dat Use Genosc Layer to fit Dielectric index. Which fit parameter combination works best? (Goal: Fewest # of parameters that match data well)

28 Transparent Films Cauchy Dispersion Sellmeier Dispersion 28