F4280 Technology of Thin Film Deposition & Surface Treatments 10. PECVD Lenka Zajíčková Faculty of Science, Masaryk University, Brno & Central European Institute of Technology - CEITEC lenkaz@physics.muni.cz spring semester 2024 E3RMO UNIUER5ITV OF" TECHNOLOGV UNI 10. PECVD 10.4 Plasma Polymerization Understanding the Plasma Polymerization Plasma Polymerization in Pulsed RF Discharges Amine Plasma Polymers Carboxyl Plasma Polymers F4280 10. PECVD Lenka Zajíčková 3/14 •Je asm Plasma polymerization is a subset of plasma enhanced CVD It produces organic thin films with specific functional groups originating from the monomer structure. Plasma polymers do not have the typical structure of polymers (impossible to find a repeated unit, structure is highly branched and cross-linked). Yasuda scheme: t\ťiiíniíin 1 * M, M- * M,-Mj —1 Cross-cycle r ckiíoii ■**Mk-M*—i 1st pathway (M») - similar to a standard free radical polymerization mechanism, 2nd pathway (-M*) - difunctional mechanism, "polymer" can grow in multiple directions by multiple pathways off one species =>■ a very rapid step-growth polymerization: F4280 10. PECVD Lenka Zajíčková 4/14 Different Types of Plasma Polymers Organosilicon plasma polymers hexamethyldisiloxane CH3 CH3 H3C-SÍ-O-SÍ-CH3 i 1 CH3 CH3 Carboxyl/ester/anhydride films acrylic acid methyl methacrylate 0 i? II CH2 H2C^OCH3 HO maleic anhydride Amine films NH2 NH ► barrier and protective coatings ► hydrophilic/hydrophobic surface ► cross-linking improvement (stabilization of organic functionalities by co-polymerization) ► interfacial adhesion, ► grafting of molecules with specific functionalities (reverse adhesion), ► improvement of cell colonization (tissue engineering), ► immobilization of biomolecules (biosensors, drug delivery systems). ► interfacial adhesion, ► improvement of cell colonization (tissue engineering), ► immobilization of biomolecules (biosensors, drug delivery systems). F4280 0. PECVD Lenka Zajíčková nderstanding the Plasma Polymerization 5/14 Description of plasma polymerization by macroscopic kinetic approach involving a composite ("Yasuda") parameter W/F (l/l/ power, F monomer flow rate) proportional to the energy delivered per one molecule of monomer in gas phase D. Hegemann etal. Plasma Process Polym 7(2010) Arrhenius plot - describing gas-phase 889 processes: w W d act |dep F d (1) s gas mass deposition rate f?m, apparent activation energy Ea, absorbed power density W, gas flow F -11.0 -11.5 £ -12.0 O) -12.5 c -13.0 -13.5 -14.0 -14.5 ■ 7 Pa A 10 Pa T 15 Pa *■ 20 Pa 4 30 Pa p=0.98 for both fits 0.00 0.01 0.02 0.03 0.04 0.05 (W/F)-1|dep [cm3/J] (again for the example of plasma polymerization of HMDSO in CCP) F4280 10. PECVD Lenka Zajíčková 6/14 10.4.1 Understanding the Plasma Polymerization Effect of ion bombardment (plasma-surface interaction) should not be forgotted especially for low pressure CCP discharges! and its not only about the ion energy - it is about ion energy flux Energy dissipated per deposition rate R ^surf mean R l~, ion flux, Emean mean ion energy D. Hegemann etal. Appl. Phys. Lett. 101 (2012) 211603 60 80 100 120 140 160 power [W] (again for the example of plasma polymerization of HMDSO in CCP) F4280 10. PECVD Lenka Zajíčková 7/14 10.4.2 Plasma Polymerization in Pulsed RF Discharges Quest for retaining monomer structure in plasma polymers - too much energy in plasmas! ► decreasing power (some limits apply) ► excluding ion energy flux (higher pressures, atmospheric pressure namely) ► pulsed CCP discharges pulse repetition frequency fpuls = 1/(fcn + W) O Q_ on toff duty cycle (DC) DC _ ^on řon+ř0ff x 100% Simplification (1 parameter instead of 2): mean RF power Paver = Pon x DC time Macroscopic approach uses P, aver W/F = aver Q [J/cm3] F4280 0. PECVD ka Zajíčková 8/14 mine nasma Hoiymers Reactivity of primary amines is important for ► adhesion enhancement ► immobilization of biomolecules (for enzyme electrodes, immunosensors etc.) NH2NH2NH£ -H-l- substrate gluteraldehyde (GA) PBS *~ 1 h r.t. O O. 11 P OJ N __N _N substrate NH2 antibody (AL-U1)^ PBS 12 h 5°C V N 1) .N OP N N N -I-1-1- s ubs trale USA antigen -» PBS 10 min r.t. R1 \ H H N _N _N substrate ► cells interaction with surfaces (artificial tissue engineering) Cells interact with surfaces via extracellular matrix (ECM) ECM contains proteins like fibronectine that bonds well to protonated surfaces such as NH2 surfaces at neutral pH. F4280 10. PECVD ka Zajíčková 9/14 SAM of cysteamine NH2 l-S I I NH2 NH2 NH2 -S (3-Aminopropyl)triethoxysilane (APTES) ^ -o i RO^Si—NH2 -O -°\ -O—Si—NH2 Polyethyleneimine (PEI) NH- 1 ^N-L^NJ-4n--[nh2 O L HJ™ ^NH2 Yj-nJ----jgJ —[fjH2 O L HJm ^NHz Ni ----TNH2 Hjm Plasma polymerization - alternative to the conventional methods NH __^ Example of plasma polymerized cyclopropylamine optimized for sensing performace a) c 03 0,98 0,96- Z3 o 03 £i 0,94- 1380 C"H bend. 0,92- 0,90 3500 3000 2500 2000 1500 wavenumber (cm") F4280 0. PECVD Lenka Zajíčková 10/14 Surface plasma treatment, e.g. in N2 or NH3 discharges unstable functionalization of a thin near-surface layer with rather short duration Deposition from vapors of amine monomers: ► allylamine ► diaminocyclohexane ► ethylenediamine ► cyclopropylamine (CPA) ► etc. usually in pulsed RF discharges, substrate floating or grounded Deposition from gas mixtures: ► NH3/CH4 ► NH3/C2H4 usually in continuous wave RF discharges, substrate at RF electrode Allylamine - commonly used due to presence of vinyl group (free radical polymerization) but highly toxic flammable chemical compound Cyclopropylamine - promising monomer for amine-rich coatings, non-toxic, vapor pressure of 32 kPa at 25 °C. F4280 10. PECVD Lenka Zajíčková 11/14 CPA Plasma Polymerization at Low Pressure ► in RF (13.56 MHz) capacitively coupled discharges ► in CPA/Ar mixtures ► continuous wave and pulsed modes ► fon = 660 fis, tos = 1340/xs ► fpuls = 500 Hz, DC = 33% reactor R3, substrate at floating potential reactor R2, substrate at RF electrode gas mixture gas mixture blocking matching rf generator capacitor unit ► Ar 28 seem, CPA 0.1-1.0 seem ► pressure 120 Pa RF power 20-30 W ► electrode diameter 80 mm ► interelectrode distance 185 mm rf generator - |_C =k= blocking capacitor matching unit ► Q(Ar) = 28 seem, Q(CPA) = 2.0 seem ► pressure 50 Pa ► RF power 30-250 W electrode diameter 420 mm ► interelectrode distance 55 mm F4280 10. PECVD Lenka Zajíčková 12/14 10.4.4 Carboxyl Plasma Polymers c o \ OH Plasma processing of carboxyl plasma polymers by PECVD from simple molecules ► H20/C02 [1] ► C2H4/C02 [2] by plasma (co-)polymerization of COOH-based monomers ► acrylic acid (AA) [2,3,4] ► maleic anhydride (MA) [5,6] HO O II CH2 acrylic acid maleic anhydride [1] N. Medard, J.-C Soutif, F. Poncin-Epaillard, Langmuir, 2002, 18, 2246 [2] D. Hegemann, E. Koerner, S. Guimond Plasma Process. Polym. 2009, 6, 246 [3] L. Detomasso, R. Gristina, G. Senesi, R. d'Agostino, P. Favia, Biomaterials 2005, 26, 3831 [4] A. Fahmy, R.Mix, A. Schonhals, J. Friedrich Plasma Process. Polym. 2011, 8, 147 [5] A. Manakhov, M. Moreno-Couranjou, N. D. Boscher et al., Plasma Process. Polym. 9 (2012) 435 [6] M. M. Brioude, M.-P. Laborie, A. Airoudj et al., Plasma Process. Polym. 12 (2015) 1220 DBD plasma polymerization of acryic acid in He A.J. Beck, R.D. Short, A. Matthews, Surf Coat Technol 203 (2008) 822-825: ► percentage of functional groups by fitting XPS C1s signal (~ 289.3 eV binding energy for C(0)=0, i.e. carboxyl and ester groups) ► films with high retention of the monomer structure for low energetic conditions (low W/F) up to 29.7 % of COOR ► Bioapplications require sufficient stability in aqueous media but cross-linking improves the layer stability at expenses of the functional group concentration. ► Plasma co-polymerization offers an additional possibility to tune the film stability and carboxyl functionalization efficiency Thomas etai Plasma Process. Polym. 4 (2007) S475 Manakhov et al. PPP 9 (2012) 435 - copolymerization of maleic anhydride (MA) and vinyltrimethoxysilane (VTMOS) in DBD S i 0.6 kW 0.1 ml/min £C0\0R, c = o COOR 1.0 kW 0.1 ml/min 1.2 kW 0.05 ml/min t n—n—" i" ' i"—|-1-1- i ' i i III| 295 290 285 280 BE (eV) a) £2r---*sj_o-ch3 O-CH3 (80 b) 0 ^? -9-0- 6 cl) ■(Si) -H,0 OCHj CH2—I—Si —CCH3 OCH3 ■H,0 HOOC COOH OH ■ CH,—1—Si—OH ■ OH !Sl, F4280 10. PECVD Lenka Zajíčková 14/14 Co-polymerization of MA and C2H2 ► dielectric barrier discharge at 6.6 kHz, 12 W Q^O\xP + HC ► distance between dielectrics 1.6 mm \=/ ► top electrode made of two parts, each 55 x 20 mm, spaced by 20 mm ► rectangular bottom electrode 150 x 60 mm ► central gas inlet, 9 mm in diameter ► buffer chamber distributing gas flow into a slit, 2 mm wide and 48 mm long MA : C2H2 flow rate ratio varied by changing flow rate of C2H2 and Ar through MA. ► Ar flow rate through MA bubbler Qai—ma = 0.25-1.5 slim QMa = 0.06-0.33 seem ► C2H2 flow rate Qc2H2 = 2-3 seem ► total Ar flow rate Qat-ma + Oat = 1.5 slim