Plasma Activated EB-PVD of Titanium and its Compounds by Means of Large Area SAD

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1 AIMCAL 2005 Myrtle Beach, SC, USA, October 19th, 2005 Plasma Activated EB-PVD of Titanium and its Compounds by Means of Large Area SAD E. Reinhold, C. Steuer VON ARDENNE Anlagentechnik GmbH, Dresden, Germany C. Metzner, B. Scheffel Fraunhofer Institut Elektronenstrahl- und Plasmatechnik, Dresden, Germany

2 Plasma Activated EB-PVD of Titanium and its Compounds by Means of Large Area SAD Outline 1 Introduction 2 Description of Experiments 3 Coating Results 4 Results of Process Enlargement 5 Conclusions and Outlook The joint project of VON ARDENNE and FEP concerning the development of large area plasma activation of EB-PVD has been sponsored by the Department of Economy and Labour of Saxony. 2

3 Introduction Industrial applications of EB-PVD of metal strip: Steel strip: Corrosion protection (stacks of metals and oxides) Preparation for soldering (copper coatings) Catalytic properties (aluminum, titanium oxide) High resistance / low resistance (silicon dioxide / metals) Al strip: Enhanced reflectance (metals + low / high index layer pairs) Solar absorption (metal / metal oxide gradient layers, AR layers) Cu strip: Solar absorption (metal / metal oxide gradient layers, AR layers) High conductivity (metals, noble metals) Plastic web: Metallization of web (capacitors, barrier coatings) Inorganic oxide coatings (transparent barrier) Optical coatings on web (reflective, antireflective, holographic) Partial substitution of glass substrates (solar cells...) Applications of web and thin metal foils come close to each other. Industrial profitable PVD of flexible substrates requires high rates. 3

4 Introduction 4

5 Introduction 5

6 Introduction Possibilities of improvement of layer properties: Ion assisted reactive EB-PVD: Combination of an ion source and EB evaporation Enhancement of the reactivity of the process gas leads to stoichiometry stabilization of evaporated compounds as oxides. Plasma activated (reactive) EB-PVD: Combination of a plasma generating equipment and EB evaporation Enhancement of the reactivity of the evaporated material leads to stoichiometrical compounds, improved density, hardness,... Spotless arc activated deposition (SAD): An additional crucible-near anode is installed. Crucible is the cathode. A diffuse arc is ignited between the anode and the hottest zones on the evaporant. 6

Introduction Principle arrangement of the SAD equipment 5 4 6 3 1 2 1

7 Introduction Principle arrangement of the SAD equipment Crucible (cathode) 4 EB gun 2 Anode 5 Metal strip 3 Gas manifold 6 Plasma cloud 7

8 Introduction Advantages and limitations of SAD: + High plasma densities with 60% ionisation degree can be achieved. + The additional equipment in the process-surrounding of the EB evaporator is less expensive than other plasma generation tools. + The position of the arc on the evaporant coincides with the location of the electron beam generated vapor source. Therefore the activated vapor distribution may be similar to the initial EB vapor distribution. - Only some refractory metals allow the ignition of a diffuse arc on the evaporant. Examples: Mo, Zr, Ta, W, Ti. Questions regarding coating of titanium and its compounds: Which coating rates can be achieved today using SAD in case of titanium and its compounds titanium dioxide and titanium nitride? Which layer properties can be achieved by means of SAD? Is it possible to extend the SAD process to large area dimensions? 8

Description of Experiments Stage 1: Free span metal strip coating 1 2 3 8 9 4 5 7 6 8 Technical data of the lab coater MAXI: Max. strip width: 280 mm Max.

9 Description of Experiments Stage 1: Free span metal strip coating Technical data of the lab coater MAXI: Max. strip width: 280 mm Max. strip thickness: 500 µm Max. substrate speed: 60 m/min 1 Unwinder 2 Heating 3 Sputter etching 4 EB gun 5 Crucible (cathode) 6 Anode 7 Gas manifold 8 Measurement devices 9 Upwinder 9

10 Description of Experiments Stage 1: Free span steel strip coating Feature Titanium Titanium oxide Titanium nitride Crucible Cooled copper Cooled copper Cooled copper Evaporant Titanium Titanium Titanium EB acc. voltage 40 kv 40 kv 40 kv EB power 60 kw 27 kw 17 kw Process gas / Oxygen Nitrogen Gas flow / sccm 2000 sccm Proc. pressure 2 x 10e-5 mbar 2.3 x 10e-3 mbar 2 x10e-3 mbar Arc current 200 A A 100 A Bias voltage / 130 V pulsed DC 100 V pulsed DC Measurements: Layer thickness: GDEOS, Ellipsometry Optical constants: Ellipsometry Hardness: Nanoindentation 10

Description of Experiments Stage 2: Metal foil coating on a cooling drum 5 4 7 6 9 8 3 2 1 1 Winding system 2 IR

11 Description of Experiments Stage 2: Metal foil coating on a cooling drum Winding system 2 IR heater 3 Glow discharge 4 Sputtering 5 EB gun 6 Cooling drum 7 Crucible system (cathode) 8 Anode 9 Gas manifold 11

Description of Experiments Stage 2: Metal foil coating on a cooling drum Process enlargement: - Doubling of the substrate width - Doubling of the coating distance - Coating of thin stainless steel

12 Description of Experiments Stage 2: Metal foil coating on a cooling drum Process enlargement: - Doubling of the substrate width - Doubling of the coating distance - Coating of thin stainless steel foils EB-figure: Double source: Jumping beam; Two filled ellipses Distance 600 mm Technical data of FOBA 600: Substrate width 600 mm Substrate thickness µm Max. speed 1000 m/min Movable cooled copper crucible Temperature cooling drum: -20 C 12

13 Description of Experiments Stage 2: Metal foil coating on a cooling drum Feature Crucible Evaporant EB acc. voltage EB power Process gas Gas flow Proc. pressure Arc current Bias voltage Measurements: Titanium Titanium oxide Titanium nitride Cooled copper Cooled copper Cooled copper Titanium Titanium Titanium 60 kv 60 kv 60 kv 100 kw 52 kw 44 kw / Oxygen Nitrogen / 8000 sccm 4000 sccm < 1 x 10e-4 mbar 2 x 10e-3 mbar 2 x 10e-3 mbar 1000 A 800 A 600 A / 120 V pulsed DC 120 V pulsed DC Layer thickness: GDEOS, ellipsometry Optical constants: Spectral ellipsometry 13

14 Coating Results Stage 1: Free span metal strip coating Feature Titanium Titanium oxide Titanium nitride Coating rate 400 nm/s nm/s 30 nm/s Dyn. dep. rate 5500 nm x m/min nm x m/min 420 nm x m/min Appearance metallic brilliant transparent golden Optical constants n(550nm) = k(550nm) 0.01 Hardness Process stability: 2h (limitation by crucible) Dense plasma on the evaporant 7 10 GPa Diffuse arc is steered by the hottest zone on the titanium melt (electron beam impingement) 30 GPa 14

15 Coating Results Stage 1: Free span metal strip coating Refractive index at various coating rates depends on: Reactive gas inlet Substrate temperature Arc parameters Bias voltage Titanium dioxide refractive index at various SAD rates 15

Results of Process Enlargement Stage 2: Metal foil coating on a cooling drum a) EB-evaporation without SAD b) Start of SAD: diffuse arc ignition c) High density plasma of the SAD process Double

16 Results of Process Enlargement Stage 2: Metal foil coating on a cooling drum a) EB-evaporation without SAD b) Start of SAD: diffuse arc ignition c) High density plasma of the SAD process Double source distribution: Distance of two EB heated zones up to 600 mm Diffuse arc is split and steered by both overheated regions One anode for two sources Large area SAD by superposition of two plasma generation zones 16

17 Results of Process Enlargement Stage 2: Results of metal foil coating on a cooling drum Feature Coating rate Dyn. dep. rate Appearance Optical constants Hardness Titanium oxide 50 nm/s 600 nm x m/min transparent n(550nm) = 2.3 k(550nm) 0.01 Titanium nitride 36 nm/s 430 nm x m/min golden 33 GPa Double source reactive SAD allows long term stable and homogeneous deposition of extended substrates with coatings from titanium compounds. Crucible movement lead to an increased process duration of 8h. High rates can be achieved in spite of reduced vapor utilization (increased coating distance). 17

18 Results of Process Enlargement Stage 2: Metal foil coating on a cooling drum Layer thickness s(nm) Position across the substrate x(mm) Average layer thickness distribution of the titanium dioxide coating 18

19 Conclusions and Outlook Titanium and its compounds can be coated by means of (reactive) SAD at high and stable rates. The dynamic deposition rate of titanium dioxide amounts to approximately 1000 nm x m/min. Comparison 1: The same rate can be achieved with more than 20 dual cylindrical magnetrons. This means that the equipment costs of SAD compared with sputtering solutions are considerably lower. There is the possibility of substitution of expensive titanium suboxides as evaporant by low cost titanium. Comparison 2: The price of Ti 3 O 5 is about 140 USD/kg. Compared with this the price of titanium is only about 5 USD/kg. This means that the coating costs can be reduced drastically in the case of reactive SAD. The experiments have displayed that the SAD process can be extended to a large area technology. There are no limitations regarding substrate widths. The way into several industrial applications is opened now. 19

20 Conclusions and Outlook Coatings from titanium and its compounds on various substrates and their applications: Coating Titanium Titanium oxide Substrate Stainless steel Aluminum Aluminum Stainless steel, ceramics Application Catalysts Roof elements Enhanced reflectors Photocatalytic applications Titanium oxynitride Titanium nitride Copper Steel, others Solar absorbers Decorative coatings Fuel cells SAD can be expected in these industrial application fields! 20

21 Thank you for your kind attention! 21

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