DUV ( nm ) Characterization of Materials: A new instrument, the Purged UV Spectroscopic Ellipsometer,

Transcription

1 WISE 2000, International Workshop on Spectroscopic Ellipsometry, 8 9 May 2000 DUV ( nm ) Characterization of Materials: A new instrument, the Purged UV Spectroscopic Ellipsometer, Pierre BOHER,, SOPRA S.A., 26 rue Pierre Joigneaux, Bois-Colombes, France, 1

2 Outline of the talk: Introduction. Presentation of the purged UV spectroscopic ellipsometer. Experimental results: CaF 2 substrate LaF 3 film on CaF 2 substrate Photoresists and antireflective coatings Cr and CrOx layers on glass Transmittance of SiOF substrate Extended PUV range Conclusion 2

3 introduction: 157nm lithography successor of 193nm generation. Need to characterize accurately new materials (resists, ARC) and optics at this new wavelength. Strong correlation between thickness and indices due to low thickness values. Good candidate --> spectroscopic ellipsometry Need of additional photometric measurements (transmittance of the optics for example). New instrument: Purged UV ellipsometer 3

4 SE Basic theory Ellipsometry determines and analyzes the change of the polarization state of light after reflection on a sample incidence plan S elliptical polarization s θ0 E Ep rp Es rs E Ep Es surface N = n - jk ρ rp = = r s tan ψ e j 4

5 Advantages of ellipsometry Ellipsometry is an absolute technique ( no need of reference spectrum or reference sample ) Ellipsometry gives twice more informations than reflectometry ( ψ and instead of R ) The phase is very sensitive to surface layers As ellipsometry measures the polarization state and not the intensity, it is less sensitive to light intensity fluctuations. Ellipsometry allows to characterize directly the optical indices (n,k) of bulk materials : N = ( n jk) = sin θ ρ 1 + ρ 2 tan 2 θ0 5

6 Ellipsometer setup Minimized beam path. Deuterium lamp as source. Double monochromator included in the polariser arm (avoid photobleaching) MgF 2 Rochon polarizers on stepper motors. Detection by a photomultiplier in photon counting mode. 6

7 Ellipsometer characteristics Rotating analyser instrument. Spectral range nm extendable in the visible range. 3 measurement modes possible: >variable angle spectroscopic ellipsometry >Photometry (reflectance or transmittance) >Scatterometry 7

8 Goniometer Analyser arm Mapping stage Polariser arm + spectrometer Purged UV spectroscopic ellipsometer 8

9 PM tube in photon counting mode Fixed polariser Rotating analyser Retarder Sample Prism Grating Deuterium lamp Schematic view of the purged UV spectroscopic ellipsometer 9

10 Purged glove box SE system is installed inside a glove box with continuous H 2 O and O 2 purification. Dry nitrogen is injected continuously with automatic pressure adjustment. Filters can be regenerated automatically every 3- month. 10

11 Purged glove box One working face with three gloves to adjust sample and replace deuterium lamp. Samples up to 200mm diameter introduced with load lock Residual H 2 O and O 2 measured continuously (in the ppm range during normal working conditions ). 11

12 Purged Glove Box 12

13 Transmission Experiment Simulation CaF Wavelength (nm) Transmittance measurement on a CaF 2 substrate 13

14 Experiment Simulation 0.6 Tan Psi Cos Delta 0.1 Wavelength 157.6nm Roughness 5.4nm -0.6 CaF2 n=1.600± Angle of incidence (deg) Analysis of the SE measurement at 157.6nm on the CaF 2 substrate 14

15 Refractive index n Wavelength (nm) Refractive index of the CaF 2 substrate compared to the literature 15

16 0.6 Tan Psi nm 193nm 227nm 262nm 298nm Incidence angle (deg) SE measurements on LaF3/CaF2 sample 16

17 Cos Delta nm 193nm 227nm 262nm 298nm Incidence angle (deg) SE measurements on LaF3/CaF2 sample 17

18 0.6 Wavelength 157.6nm Experiment Simulation 0.6 Tan Psi 0.3 Roughness 3.3nm Cos Delta LaF3 Layer 400nm n = CaF2 Subtrate Angle of incidence (deg) Analysis of the SE measurement at 157.6nm on the LaF 3 /CaF 2 sample 18-1

19 SiO2 SiO2 Index of refraction n SiN Extinction coefficient k x100 SiN Wavelength (nm) Wavelength (nm) Measured dielectric constants of SiO 2 and SiN layers 19

20 1 Cos Delta deg 70deg 65deg Wavelength (nm) Variable angle measurement on a photoresist film 20

21 5 4 75deg 70deg Tan Psi deg Wavelength (nm) Variable angle measurement on a photoresist film 21

22 2.2 F2 ArF KrF 2 Refractive index n KrF resist ArF resist i-line resist ARC F2 resist Wavelength (nm) Refractive index of different resists and antireflective coatings 22

23 1 F2 ArF KrF 0.75 Absorption k 0.5 KrF resist ArF resist i-line resist ARC F2 resist Wavelength (nm) Extension coefficients of different resists and antireflective coatings 23

24 GESP Refractive index n PUV 157.6nm Extinction coefficient k Energy (ev) Dielectric constants of photoresist 1 measured with the GESP and PUV instruments 24

25 2.2 1 refractive index n GESP PUV Extinction coefficient k 157nm Energy (ev) Dielectric constants of photoresist 2 measured with the GESP and PUV instruments 25 0

26 Incident angle PHOTORESIST Canceled by ARC ARC SUBSTRATE * Reduction of the notching effect ---> lower line width fluctations * Reduction of the «swing» effect ---> periodic behaviour of the reflectivity 26

27 * Spectroscopic Ellipsometry provides : -Thickness: T - Refractive index : n(λ) - Extinction coefficient : k(λ) * The index profile : quality of the material * The knowledge of N and K allows to simulate the REFLECTIVITY of the material for any thicknesses, any angles of incidence and at any photolithographic wavelengths. The best conditions for the deposition process can be predicted 27

28 REFLECTIVITY SIMULATIONS Normal incidence PHOTORESIST Wavelength : nm R ARC Ambient : Photoresist SUBSTRATE 28

29 Extinction coefficient 0.2 Reflectance Refractive index Reflectivity at nm versus n & k using photoresist 1 Thickness=150 Å 29

30 n (CrOx) k (CrOx) n (Cr) k (Cr) Optical indices Wavelength (nm) Measured Refractive Indices of Cr oxide and Cr versus Wavelength. 30

31 0.4 Reflectance (%) Simulated reflectance Measured reflectance Thickness (µm) Measured and Simulation of reflectance of Cr Oxide on Cr on Glass at nm. 31

32 100.00% Transmittance (%) 75.00% 50.00% 25.00% 0.00% Wavelength (nm) Transmission of SiOF versus wavelength. 32

33 Tan Psi 4 0 Cos Delta Wavelength (nm) SE on SiO 2/ Si samples using extended PUV range 33

34 PUV Database 0.05 Refractive index n Extinction coefficient k Energy (ev) Optical indices of SiO 2 compared to litterature using extended PUV range 34

35 Conclusion: A new purged UV spectroscopic ellipsometer has been presented. Experimental results on: CaF 2 substrate. LaF 3 layer on CaF 2 substrate CrOx/Cr/glass structures. Photoresists and antireflective coatings SiOF transmittance Now the range is extended to nm 35