Silicon carbide thin films for EUV application deposited by means of Pulsed Laser Deposition (PLD) Gianni Monaco LUXOR-IFN Laboratory COST meeting Krakow, May 2010 COST-STSM-MP Report

Gianni Monaco COST meeting Krakow, 26 may 20102/24 Outline  SiC Carbides in the EUV;  PLD systems;  SiC thin films deposited at IOP-WAT Warsaw with Excimer laser;  Analysis of the films;  Some SiC thin film deposited at LUXOR with Nd-YAG.

Gianni Monaco COST meeting Krakow, 26 may 20103/24 List of pubblications on SiC and PLD lab.  P. Nicolosi, D. Garoli, M. G. Pelizzo, V. Rigato, A. Patelli, and F. Rigato, “VUV reflectance measurements and optical constants of SiC thin films” J. Electron Spectrosc. Relat. Phenom. 144–147, (2005).  D. Garoli, G. Monaco, F. Frassetto, M.G. Pelizzo, P. Nicolosi, L. Armelao, V. Matterello, V. Rigato “Thin film and multilayer coating development for the extreme ultraviolet spectral region” “Radiation Physics and Chemistry”, 75 (11), p , Nov 2006  G. Monaco, D. Garoli, R. Frison, V. Mattarello, P. Nicolosi, M. G. Pelizzo, V. Rigato, L. Armelao, A. Giglia, S. Nannarone, “Optical constants in the EUV soft x-ray (5÷152 nm) spectral range of B 4 C thin films deposited by different deposition techniques”, Proceedings SPIE, 6317, (2006).  D.Garoli, F. Frassetto, G. Monaco, P. Nicolosi, M.-G. Pelizzo, F. Rigato, V. Rigato, A. Giglia, S. Nannarone, “Reflectance measurements and optical constants in the extreme ultraviolet-vacuum ultraviolet regions for SiC with a different C/Si ratio” Appl. Opt. 45(22) (2006)  Gianni Monaco, M. Gastaldi, P. Nicolosi, M.G. Pelizzo, E. Gilioli, S. Rampino, S. Agnoli, G. Granozzi and N. Manuzzato, “Silicon carbide thin films for EUV and soft X-ray application” Eur. Phys. J. ST (2009).  Gianni Monaco, M. Suman, M. G. Pelizzo, P. Nicolosi, “Optical constants of silicon carbide deposited with emerging PVD techniques”, Proc. SPIE Vol (2009).

Gianni Monaco COST meeting Krakow, 26 may 20104/24 material properties CVD SiC Hot- pressed B 4 C MoAlSiZerodur® Density, ρ (kg m –3 ) x Coefficient of thermal expansion, α (K –1 x10 –6 ) Specific heat, C (J kg –1 K –1 ) Termic conductivity, κ (W m –1 K –1 ) Young's Modulus, E (GPa) Hardness KH (kg mm -2 ) low density high melting point low expansion coefficient can be polished to lower roughness than metals Carbides material

Gianni Monaco COST meeting Krakow, 26 may 20105/24 Reflecting materials for EUV  Presence of a great number of atomic resonance  radiation absorbed on very short distances  complex refractive index: n=1-  +ik (n=1-  )  Fresnel normal incidence reflectance: R=  (1-n)/(1+n)  2 =(  2 + k 2 )/4  Below 30 nm (Soft X-ray) , k « 1 =>R <  optics must be used at grazing incidence in order to take advantage of total reflection  Multilayers optics (ML’s)

Gianni Monaco COST meeting Krakow, 26 may 20106/24 Deposition of Silicon Carbide thin films for EUV CVD-techniques monocrystalline β-SiC with T≈ 1400°C high normal incidence reflectance (R > 40% for λ < 60nm) good stability Sputtering techniques (Ion beam, or magnetron) worse performances than CVD-SiC only amorphous SiC Suitable for multilayer lower temperature lower cost Reflectivity degradation Si atom C atom 1.89Å 3.08Å Larruquert et al.,Appl. Opt. 39 (2000); J. B. Kortright and D. L. Windt Appl. Opt. 27, 2841–2846 (1988) Fernandez-Perea et al. Proc. SPIE 6317, (2006)

Gianni Monaco COST meeting Krakow, 26 may 20107/24 SiC deposition techniques/2  HOW TO OBTAIN HIGH REFLECTIVE SiC AT LOWER TEMPERATURE THAN CVD PROCESS?  Plasma Enhanced-CVD (R.A.M. Keski-Kuha, Appl. Opt. 27 (1988).  With Pulsed Laser Deposition at around 800 °C is possible to obtain a crystalline SiC. Pelt et al. Thin Solid Films, 371 (2000). Let’s try Pulsed deposition techniques (as PLD)!

Gianni Monaco COST meeting Krakow, 26 may 20108/24 PLD deposition systems Features:  Very high heating rate of the target surface (108 K/s ).  deposition of crystalline film demands a much lower substrate temperature  stoichiometry of the target can be retained Particulate generation  can be connected to two macroscopic processes: exfoliational and hydrodynamical-sputtering.  Related to the laser parameters: wavelength, fluence and pulse duration  The particulate content decreases with the wavelength

Gianni Monaco COST meeting Krakow, 26 may 20109/24 PLD Deposition facility at the MUT

Gianni Monaco COST meeting Krakow, 26 may /24 Experimental Set-up  Silicon Carbide β-SiC (crystalline) target  Substrates  Single Crystal Sapphire orientated on the 0001 C-plane (for heteroepytaxial grow)  Si (111) (for for heteroepytaxial grow)  Si (100) (for further analysis)

Gianni Monaco COST meeting Krakow, 26 may /24 Deposited samples SampleSubstrate Temp (°C)RF etching (min) Base pressure (torr) Fluence (J/cm 2 ) Freq (Hz) Laser energy Distance (mm)AtmosphereTime (min) 1SiRT x mJ-Vacuum30 2SiRT x mJ-Vacuum30 3SiRT x Vacuum60 4SapRT x Vacuum60 5SiRT 153 x (ca)Vacuum90 6SiRT 153 x (ca)Vacuum90 7Si538 No1x (ca)Vacuum90 8Sapp538 No1x (ca)Vacuum90 9Si min (10 -2 mbar Ar) 1x Vacuum45 10Si min (10 -2 mbar Ar) 1x (ca)114880Vacuum75 11Sapp min (10 -2 mbar Ar) 4.5x x (ca)114880Vacuum75 12Sapp min (10 -2 mbar Ar) 4.5x x Vacuum120 13Sapp min (10 -2 mbar Ar) 3.5x x Vacuum120 14Si(111) min (10 -2 mbar Ar) 3.5x x Vacuum120 15Sapp min (10 -2 mbar Ar) 3.5x x Vacuum120 16Sapp min (10 -2 mbar Ar) 3.5x x Vacuum120 17Si(111) min (10 -2 mbar Ar) 3.5x x Vacuum90 18Sapp min (10 -2 mbar Ar) 3.5x x Vacuum90 19Sapp min (10 -2 mbar Ar) 3.5x x Vacuum90 20Sappca min (10 -2 mbar Ar) 5x Ar (6x10 -3 torr) Sappca min (10 -2 mbar Ar) 5x Ar (6x10 -3 torr) Si(111)ca min (10 -2 mbar Ar) 5x Ar (6x10 -3 torr) 120  Frequency: even if an higher repetition rate would have resulted in an higher deposition rate, we chose a rate of 1 Hz for all the deposition. Our goal was to get a crystalline, hence organized, structure and this could be better accomplished if the atoms on the substrate surface have longer time intervals in order to organize themselves.  Laser fluence: laser fluence was chosen very low. The deposition threshold of Silicon Carbide with excimer nm is 1 J/cm 2 and we choose to be around that value to get less particulate and give raise to a slower crystallization process. The two deposition carried at 3 J/cm 2 (sample 5 and 6) where used to locate the plume position and direction inside the chamber.  Substrates: Silicon (111) and Sapphire were used for two reasons: they have low lattice mismatch with 3C-SiC and can be suitable for heteroepitaxial growth (3C-SiC has 4.36 Å, Sapphire 4.75 Å on its face [0001], Si (111) has 9.23 Å), while Silicon (100) (cubic, lattice constant 5,43 Å) is mainly used as a test sample for successive characterization such as film thickness and composition.  Temperature: the temperature is another crucial parameter in our process. As said in the previous document in which the project has been exposed, the crystalline CVD silicon carbide is obtained at a temperature as high as 1400 °C, but with PLD we are trying to demonstrate that it is possible to obtain the same structure at lower temperature. We planned to keep the deposition temperature around 900° C for all the samples to help the crystalline growth.  For the last three samples 20, 21, 22 we tried to help film crystallization by use of Ar bombardment keeping a mild temperature of 650° C.

Gianni Monaco COST meeting Krakow, 26 may /24 AFM analysis of the deposited samples Sapphire substrate Sample n°4 Sample n°5 Sample n°8 Sample n°15 Sample n°18

Gianni Monaco COST meeting Krakow, 26 may /24 Samples thicknesses  Silicon Carbide has an absorption dip centered at 795 cm −1 that could be ascribed to TO-phonon mode of SiC in its cubic or hexagonal phase 825 cm cm -1

Gianni Monaco COST meeting Krakow, 26 may /24 Samples number 5 and 6 (high fluence=of 3 J/cm 2 90 Samples thicknesses

Gianni Monaco COST meeting Krakow, 26 may /24 SEM images Sample n°8 Sample n°19

Gianni Monaco COST meeting Krakow, 26 may /24 XRD spectra of the samples  43° 21° and 38° are due to the Sapphire substrate.  3 spectra show different features: SiC8, SiC12 and SiC19 (Sapphire peaks disappear) The feature of these spectra, as retrieved in the Instrument database (ICCD-JCPDS), cannot be attributed to any of the SiC crystalline structure. Sapphire 003 Sapphire 006 Sapphire

Gianni Monaco COST meeting Krakow, 26 may /24 EUV Reflectance measurements  Source: hollow cathode or spectral lamps ( nm)  Monochromator: Johnson Onaka – normal incidence  Detector: Channel Electron Multiplier or photomultiplier  Sample and detector on manual stages  Polarization factor known (from to 40 nm)

Gianni Monaco COST meeting Krakow, 26 may /24 EUV Reflectance

Gianni Monaco COST meeting Krakow, 26 may /24 EUV Reflectance /2

Gianni Monaco COST meeting Krakow, 26 may /24 Conclusions of the STSM  Hard to find evidences of 3C-Silicon Carbide! I.The films are crystalline but are simply too thin to be revealed with the utilized techniques. This could sound strange if we think that we placed the substrates in the position of the sample n°5 which was demonstrated to have a thickness of 60 nm. Since we have kept the same target-substrate distance, the explanation surely lies in the laser fluence which is three times higher compared to the other samples. II.The samples are not crystalline, films are too thin and we cannot see any film by the utilized techniques (such as IR which is not sensitive to amorphous structure). III.Contamination of the surface, due to the residual atmosphere and to the clamp (made in stainless steel) prevails with respect to deposited films. Hence, it is difficult to see the IR absorption and the XRD spectra since the crystalline structure has not been formed, or some other structure have been formed instead crystalline SiC.  A TEM analysis could probably help to solve the first and the second uncertainties, while an XPS could be helpful for the third uncertainties. Nevertheless, with the results we obtain we can exclude the third supposition since the reflectance it is not affected by the presence of absorbing elements, such as Oxygen, that would lower the Reflectance yield compared to the substrate.

Gianni Monaco COST meeting Krakow, 26 may /24 Appendix: further LUXOR Laser: Nd:YAG (λ = 1064 nm) with variable repetition rate and 6ns Incidence angle of 45° on the target P ≈ 8.7 x mbar Magnetic field intensity on target: 100 – 200 Gauss Variable target-permanent magnet distance Can guest more than one target Ceramic heater (up to 1500 °C depending by the vacuum) Five samples deposited (different position relative to the target) Permanent magnet B z substrates

Gianni Monaco COST meeting Krakow, 26 may /24 Appendix: further LUXOR/2 Si (111) Si(100) Sapphire Fluence 1.4 J/cm 2, T=650°C, 10 Hz or 2 Hz Repetition rate

Gianni Monaco COST meeting Krakow, 26 may /24 Appendix: further LUXOR/3

Gianni Monaco COST meeting Krakow, 26 may /24 Acknowledgments  Institute of Optoelectronics Prof Henryk Fiedorowicz, Dr. Waldemar Mróz, Artur Prokopiuk, Michael L. Korwin-Pawlowski and Sylwia Burdyńska, BoguslawBudner  LUXOR-INF Laboratory Prof. Piergiorgio Nicolosi, Dr. Suman Michele, Dr. Maria G. Pelizzo, Dr. Zuppella Paola  Dr. Garoli Denis and Dr. Natali Marco for SEM and XRD measurements  COST project  Thank you for your attention!