The Potential of Ellipsometric Porosimetry

Transcription

1 The Potential of Ellipsometric Porosimetry A. Bourgeois, Y. Turcant, Ch. Walsh, V. Couraudon, Ch. Defranoux SOPRA SA, 26 rue Pierre Joigneaux, Bois Colombes, France Speaker: Alexis Bourgeois, Application Engineer Janvier 2008

2 SOPRA Presentation Manufacturer of optical systems Established in employees (12 PhDs) Application Lab with Clean room Over 700 systems installed worldwide Worldwide offices & partners: (Germany, USA, China, Taïwan, South-Korea, Japan ) Sopra is a scientific company. Our aim is to create and sale metrology systems dedicated to thin film metrology. 2

3 Optical Metrology Optical solutions for your research 3

4 Outline Quick introduction to understand Ellipsometric Porosimetry Spectroscopic Ellipsometry Adsorption The Ellipsometric Porosimetric techniques General Presentation Applications Application to Nanoporous materials Porous gradient Characterisation of treatments Further Developments Diffusion Experiments FTIR - EP Conclusion 4

5 Introduction Principle of Ellipsometric Porosimetry 5

6 Optical Metrology Challenge: Characterization of porous thin films Adsorption Spectroscopic ellipsometry Ellipsometric Porosimetry = In Situ equipment Optical solutions for your research 6

7 Ellipsometric Porosimetry (EP) EP measures the change of the optical properties and thickness of the materials during an adsorption experiment 2 different tools : + Adsorptive Change of optical properties EP-A : Atmospheric pressure, water as adsorptive Developped with LCMC, University Paris 6 EP: High vacum experiment, any adsorptive Developed under IMEC license Boissière, C., Grosso, D., Lepoutre, S., Nicole, L., Brunet-Bruneau, A., Sanchez, C., Langmuir 21(26), (2005). Baklanov, M.R., Mogilnikov, K.P., Polovinkin, V.G., and Dultsev, F.N., J. Vac. Sci. Technol. B, 18, 1385 (2000). 7

8 Advantages of the technique Non destructive Without contact No sample preparation No scratching Thin Films (even thickness < 50 nm) Multilayer samples Any substrates Ambient temperature Tunable total measurement time measurements < 15min Spot size (< 1mm 2 ) 8

9 Introduction Principle of Spectroscopic Ellipsometry 9

10 Spectroscopic Ellipsometry (S.E.) Step 1: Measurement S.E. is a non destructive optical technique that is able to measure optical properties and thickness of single and multi layers without any contact λ (spectral range) E i E P Detection Measured Parameters r p E S θ o E r r s Ambient (n 0, k 0 ) Thin Film 1 (n 1, k 1, T 1 ) Thin Film 2 (n 2, k 2, T 2 ) Thin Film i (n i, k i, T i ) Tan(Ψ) and Cos( ) Vs λ ρ = r r p s = Substrate (n s, k s ) j Tan( Ψ). e = f ( ni, ki, Ti ) Amplitude ratio Phase shift 10

11 Structure simulation Native Oxide Si 1, 2µm Glass - Substrate ρ = r r p s Tan(Ψ), Cos( ) Spectroscopic Ellipsometry (S.E.) Step 2: Regression on a modeled structure j = Tan( Ψ). e = f ( ni, ki, Ti ) Comparison Experimental Measurement Tan(Ψ), Cos( ) Automatic Modification Of the structure using an analysis software Simulation = Measurement Simulation Measurement We find: Thickness Optical Index 11

12 Introduction Principle of Adsorption 12

13 Gas Adsorption Principle Adsorption experiment = Cycle p/p 0 = Relative pressure of adsorptive Each step: 1 Adsorption Desorption Adsorbed Quantity a s n m = f ( p p 0 ) T 0 Time ~20 minutes 1. Increase of the partial pressure: Adsorption 2. Decrease of the partial pressure: Desorption 13

14 Pressure Increase 1 Reference adsorbate: NITROGEN Closed Tapering Pore 2 1. Micropores Filling 2. Adsorption 3. Condensation 3 Amount Adsorbed (cm 3 STP g -1 ) Gas Adsorption Experiment Adsorbed Quantity a s n m = f ( p p 0 ) T Relative Pressure F. Rouquerol, J. Rouquerol and K. S. W. Sing, Adsorption by powders and porous solids, Academic Press Inc. (1999). 14

15 Gas Adsorption Characterization of Porous Solids Amount Adsorbed (cm 3 STP g -1 ) capillary evaporation filled pore monolayer formation Micropore filling multilayer formation Relative Pressure capillary condensation pore volume total amount adsorbed capillary condensation pressure pore size number of molecules in monolayer specific surface area (e.g., BET method) 15

16 Ellipsometric Porosimetry Ellipsometry + Adsorption 16

17 Ellipsometer Porosimeter principle S.E. measurement Tan(Ψ), Cos( ) E E p E λ (UV, Vis) Window E s Porous Materials Si Substrate Vacuum Chamber Porous material Controlled adsorptive relative pressure + adsorptive Change of optical properties Measurement of SE parameters (T, n, k) Vs Relative pressure 17

18 Ellipsometric porosimetry (EP) p/p 0 = Relative pressure of adsorptive 1 Adsorption Desorption SE measurement at each step p=p 0 tan Ψ(p/p ,λ) cos ( tan Ψ p= Longue ur d'onde (µm) Shift of the fringes cos Time ~20 minutes p=p p= Longueur d'onde (µm) Increase of the effective index of the layer (p/p 0,λ) filling of the pores 18

19 Ellipsometer Porosimeter System setup Turnkey software with easy way to create new recipes and control measurement SE spectra: Tp, Cd vs wavelength 4 adsorptives available: IPA, Methanol, Toluene, Water Measurement control Vacuum system control Field viewing camera 19

20 Isotherms Thickness and refractive index vs. p/p 0 p/p 0 1 Adsorption Desorption 0 SE measurement at each step Time ~20 minutes Classical SE analysis on each measurement Refractive index Vs p/p 0 1,5 300 Thickness Vs p/p 0 We obtain: Thickness n, k For each step Refractive Index 1,45 1,4 1,35 Thickness (nm) ,3 1,25 0 0,2 0,4 0,6 0,8 1 p/p 0 Ads Des Ads Additional information Des 0 0,2 0,4 0,6 0,8 1 p/p 0 20

21 Adsorption Isotherm We obtain: Lorentz-Lorenz equations V n = n 2 eff 2 eff 1 n + 2 n 2 init 2 init n n 2 ads 2 ads Fractional volume filled Vs rel. pressure Saturation point when all pores are filled in Accessible Porosity = 36% 0,40 Refractive Index 1,5 1,45 1,4 1,35 1,3 + Fractional volume adsorbed 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 Adsorbed Quantity ( p / p ) T ads sample V V = f 0 Ads Des 0,0 0,2 0,4 0,6 0,8 1,0 1,25 Ads Des 0 0,2 0,4 0,6 0,8 1 p/p 0 p/p 0 Classic isotherm Usual adsorption analysis 21

22 Isotherms Amount adsorbed and Thickness vs. p/p 0 Analysis of the adsorption experiment Fractional volume of adsorptive Vs p/p 0 Thickness Vs p/p 0 0, Fractional volume adsorbed 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 Classic adsorption information Ads Des 0,0 0,2 0,4 0,6 0,8 1,0 p/p 0 Thickness (nm) Additional information Ads Des 0 0,2 0,4 0,6 0,8 1 p/p 0 Starting points for the further analysis 22

23 Highlights applications Porous thin film characterization Hydrophobic samples Treatment characterization Diffusion properties FTIR EP 23

24 Very different porosity and PSD Solvent volume Porosity: 23.5% 59.0% 70.7% Ads Ads Des 0.70 Des TOLUENE TOLUENE n = 633 nm n = 633 nm Ads 0.20 Des 0.10 TOLUENE n = 633 nm Relative Pressure of Solvent Relative Pressure of Solvent Relative Pressure of Solvent Average radius of the pores: Solvent volume Solvent volume dv/d(lnr) Pore Radius (nm) Des TOLUENE 1.4nm dv/d(lnr) Des TOLUENE Pore Radius (nm) Collaboration with SIEMENS (NAPOLYDE) 6.6nm dv/d(lnr) Des TOLUENE 10.4nm Pore Radius (nm) 24

25 Porous TiO 2 in a multilayer Model Adsorption Analyse of ellipsometric spectra Isotherm Porous TiO nm Model ITO 131nm Glass Substrate Initial Measurement Porosity (%) Thickness > µm!!! 4.0 Measured at the end of adsorption 2.0 Adsoprtion Desorption RH (%) 25

26 Porous composite TiO 2 /SiO 2 Thickness ~ 50nm!!! Porosities ranging from a few percent to at least 70% Pore sizes from a few angströms to tens of nanometers Thickness values from few nanometers to micrometers Substantial variation between materials M. Houmard, D. Riassetto, F. Roussel, A. Bourgeois, G. Berthomé, J.C. Joud, M. Langlet, Appl. Surf. Sci., 254, 1354 (2007) 26

27 Hydrophobic porous thin films Water Toluene 1 p/p 0 = Relative pressure of adsorptive Adsorption Desorption 0 Time I = 75 I = 60 No shift of the ellipsometric spectra for water adsorption = No Water adsorption 1) The sample has no open porosity 2) The sample is hydrophobic 27

28 Hydrophobic Porous thin films Porosimetry Isotherms Refractive Index & Adsorbed Volume Using Lorentz-Lorenz Equations Distributions - Pores & Interconnects Using computation procedure BJH / Kelvin model γ 2 v RT ln l r k = ( p p ) 28 0

29 Thin films with a porosity gradient SiOCH porous thin films (low-k) Spin coated (sol gel) From a pre-polymère MSQ solution in PGMEA Thermal treatment ( C) Hydrophobic material Integration of the porous thin film Seal the porosity : avoid diffusion Make the surface hydrophilic : increase adherence properties Post-treatment: N 2 O plasma Effect of the treatment? A. Bourgeois, A. Brunet-Bruneau, V. Jousseaume, S. Fisson, B. Demarets, J. Rivory, Thin Solid Films , 366 (2004). 29

30 Graded porosity Ethanol adsorption n (600nm) Reference 1.45 Top layer: 65nm Modified by N 2 O treatment n (600nm) Densification After N 2 O treatment Width of the hysteresis loop p/p Botom layer: 230nm non modified p/p 0 After N 2 O treatment Modified layer Porous SiOCH Si Substrate N 2 O treatment Porous SiOCH Si Substrate Densification of the top of the thin film (porosity decrease) The pore size is not modified by the treatment 30

31 Hydrophilic behaviour induced by the post-treatment Water adsorption Sample SiOCH SiOCH-N 2 O K 2.2 >3 Top layer: 65 nm 1.38 Contact Angle 105 <10 n (600nm) Chemisorption n Relative Humidité Humidity relative (%RH) (%HR) Substitution of Si-CH 3 bond by Si-OH Absorbance (a.u.) Untreated porous SiOC Porous SiOC after N 2 O plasma treatment OH CH x Si-CH 3 Si-O-Si Si-(CH 3 ) x Modified layer Porous SiOCH Si Substrate Wavenumber (cm -1 ) Top layer: becomes hydrophilic Botom layer unchanged: remains hydrophobic 31

32 Water degradation on treated materials ELLIPSOMETRY Measurement Tan Psi Cos Del Adsorbed volume H2O (%) Adsorption Isotherm Adsoprtion Desorption 40.0 Ads. Vol. = 18.5% Adsorbed volume H2O (%) Adsorption Isotherm Adsorption Desorption RH Ads. Vol. = 34.3% Adsorbed volume H2O (%) Adsorption Isotherm Adsorption Desorption p/p All the isotherms measured after cycle 4 are similar Adsorbed volume H2O (%) Ads. Vol. = 35.2% The shape becomes similar to that of the reference sample Successive Water Adsorptions The shape of the isotherm is changing Adsorption Isotherm Adsorption Desorption p/p 0 Ads. Vol. = 35.2% p/p

33 Advanced Applications: Combination of SE and images recorded with the CCD camera: Diffusion experiments 33

34 Lateral Diffusion Description of an ideal system Porous thin films could be ideal materials to study diffusion process cm Porous material 100 nm Non porous layer Porous material Silicon substrate Silicon substrate Vacuum Saturated pressure of adsorptive (toluene) 0 Time Experiment: Adsorptive diffusion vs. time 34

35 Lateral Diffusion Diffusion Vs Time Sample edge Solvent diffusion 1171µm Vacuum t = 0s t = 266s t = 1230s Lateral change of colour toluene penetrates inside the porous layer from its edge Non porous layer Porous material t = 2556s D = 876µm 2 /sec for toluene Silicon substrate Diffusion coefficient (D) is calculated using the following diffusion law : D = (πl 2 )/(4t), (Shamiryan and Maex, 2003) 35

36 Lateral diffusion Diffusion profile Experiment: Adsorptive diffusion vs. position (at a given time) Optical measurement is moved along x axis Volume fraction of Toluene absorbed (% of total volume) Measured at t = 2556s Distance from the edge (mm) x Non porous layer Porous material xsilicon substrate Sample edge 0 x Mapping of the amount adsorbed on a line perpendicular to the edge of the sample 36

37 Infrared Ellipsometry Porosimetry FTIR Ellipsometer Porosimeter 37

38 Setup Using the GES5E upgradeable platform FTIR Spectroscopic Ellipsometry 500cm -1 to 7000cm -1 MCT or DTGS detector EP + FTIR FTIR Ellipsometric Porosimeter Advantages: Possibility to measure thick films (over ~20µm) Possibility to check functionalization of porous films by following evolution of absorption peaks Chemical Bonds 38

39 Infrared Ellipsometry Porosimetry Porous silicon 11 µm Porous Si Silicon substrate Si-O bond -OH bond Water Adsorption Porous silicon is already oxidized Presence of -OH bonds before EP cycle Increase of the amount of water adsorbed during the experiment 39

40 Conclusion EP: Porous Thin Films EP gives quantitative, accurate and repeatable measurement for: Porosity Pore size distribution for meso & microporous distribution Film thickness and refractive index Mapping of this parameters Small spot for edge exclusion control EP gives information on: Surface chemistry of pores Effect of a treatment Porous thin film behavior in a process integration scheme EP advantages: 4 adsorptives available Suitable for measurement on final product No specific preparation of samples (no scratch of the layer) Fast porosity measurement ~20 minutes Non-destructive (it is also a non-contact technique) Measured at room temperature It is an absolute characterization No need to know the optical properties of the dense skeleton of the porous materials (i.e. EMA) 40

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