Continuous ALD deposition on flexible su

Continuous ALD Deposition on Flexible Substrates – Towards a Roll-to-Roll Process D C Cameron, P Maydannik, T O Kääriäinen, K Lahtinen Advanced Surface Technology Research Laboratory Mikkeli, Finland: 

Continuous ALD Deposition on Flexible Substrates – Towards a Roll-to-Roll Process D C Cameron, P Maydannik, T O Kääriäinen, K Lahtinen Advanced Surface Technology Research Laboratory Mikkeli , Finland

Continuous and roll-to roll ALD: 

Continuous and roll-to roll ALD Issues of coating with a moving substrate Results of continuous ALD coating in ASTRaL Implications of results Future directions – roll-to-roll systems ALD 2011 Cambridge 2

Batch system cycle: 

Batch system cycle ALD 2011 Cambridge 3 Precursor A Precursor B Purge Purge A Purge B Purge Stationary substrate Sequential exposure Time sequenced gas pulses

Features of batch system: 

Features of batch system Maximum substrate surface area is dependent on the chamber dimensions. ALD cycle time T fill : reactor chamber filling time T react : time for surface reaction to take place T purge : time to remove excess precursor and reaction byproducts T fill + T purge generally the most significant Dynamic gas flows flow uniformity issues Unwanted deposition on substrate walls ALD 2011 Cambridge 4

Continuous system: 

Continuous system Sequence of precursor and purge cycles can be achieved by static gas flows in spatially separated zones and by moving the substrate relative to the gas zones. ALD 2011 Cambridge 5 Precursor A Precursor B Purge Purge

Features of continuous system: 

Features of continuous system Static gas flows no dynamic gas flow effects No T fill precursor zones always have same gas concentrations No gas switching valves No limit to length of substrate it can be a roll-to-roll process Less wastage of precursors only deposition is on substrate since different zones are exposed to only one precursor No coating build up on system ALD 2011 Cambridge 6

Moving system configurations: 

Moving system configurations Eastman Kodak (US) atmospheric pressure moving coating head close substrate to head spacing Lotus Applied Technology* (US) roll-to-roll substrate transported between gas zones isolation by slits and purge zone TNO (Netherlands) rotating wafer system close substrate to head spacing LUT/ASTRaL* (Finland) rotating drum inside cylindrical chamber 1 mm substrate to chamber spacing gas separation by purge and exhaust zones test system for exploring issues of roll-to-roll process Levitech (Netherlands) moving wafers Solaytech (Netherlands) moving wafers ALD 2011 Cambridge 7 * Flexible Polymer coating

Continuous ALD – ASTRaL: 

Continuous ALD – ASTRaL ALD 2011 Cambridge 8

Continuous ALD tool: 

Continuous ALD tool ALD 2011 Cambridge 9 Precurs . A Exhaust Purge gas Precurs. B Beneq TFS200R

Process details: 

Process details Vehicle for studying the process parameters relevant to roll-to-roll Rotational speed up to 500 rev/min equivalent to ~2.5 m/s Flexible substrate size 300mm x 120 mm AL 2 O 3 from TMA + H 2 O as a test process PET and other polymer sheets 50 μ m ultrathin flexible Si Temperatures up to 200 o C Aim is to understand the process in detail ALD 2011 Cambridge 10

Issues raised by the moving system: 

Issues raised by the moving system Is it really ALD? Can we maintain isolation between gas zones? How fast can it operate? What are the limiting parameters? Is there a lack of flexibility in changing the length of individual precursor/purge zone exposure times? ALD 2011 Cambridge 11

Is it ALD?: 

Is it ALD? Linear dependence of thickness on number of rotation cycles ALD 2011 Cambridge 12

Is it ALD?: 

Is it ALD? Growth saturation with precursor dose ALD 2011 Cambridge 13 TMA setting 5 Water settiing 6

Dependence of growth rate on cycle time: 

Dependence of growth rate on cycle time ALD 2011 Cambridge 14 Anomalous deposition in some speed ranges. Why?

What could cause anomalous growth?: 

What could cause anomalous growth? Existence of a gas boundary layer on the substrate surface precursor trapping in the boundary layer drag through of gas between the precursor zones causing CVD reaction Water carry over to TMA zone slow desorption of excess water molecules CVD reaction between excess water in TMA zone and TMA How to differentiate between them? ALD 2011 Cambridge 15

Boundary layer entrainment: 

Boundary layer entrainment Detection of gas entrainment using He tracer ALD 2011 Cambridge 16 purging purging tracing gas (He) injection precursor 1 inlet to pump M reactor moving substrate mass spectrometer

Results: 

Results 17 Port 2 Port 1 Port 4 Port 3 ALD 2011 Cambridge Purge Purge

Explanation: 

Explanation It is assumed that the He can reach the first exhaust port by two methods: Leakage through the reactor wall-to-substrate space (approx. constant). Entrainment on surface of moving substrate through the boundary layer. The width of the boundary layer, w  1/ √v where v is the relative linear velocity of the moving surface and the purge gas*. quantity of gas arriving at port 1 per second  wv , that is,  √ v He signal at port 1 is Q  A + B √v Similarly, at port 4, He signal is  A - B √v ALD 2011 Cambridge 18 * A. Arzate , P.A. Tanguy , Chem. Eng. Sci . 59 (2004) 3527.

continued: 

continued The amount of He reaching Port 2 is that which leaks past the exhaust zone at Port 1 (which will be proportional to the Port 1 signal), plus that which outdiffuses from the boundary layer in the purge zone. The outdiffusion rate from the boundary layer will depend approximately on the concentration gradient across the boundary layer which will vary with the width of the boundary layer (  1/√v ) the remaining amount of He in the boundary layer Thus the outdiffusion of He as a function of time in this zone is Q  exp(const x vt ) Combining the effects in the precursor zone and the purge zone, we can model the signal at Port 2. ALD 2011 Cambridge 19

Port 2: 

Port 2 Modelled and measured data ALD 2011 Cambridge 20

Dependence of growth rate on cycle time: 

Dependence of growth rate on cycle time ALD 2011 Cambridge 21

Anomaly due to gas entrainment?: 

Anomaly due to gas entrainment? No anomalous effects at relevant rotation speed Gas entrainment is not the reason for growth rate excess ALD 2011 Cambridge 22 Region where anomaly occurs

Adsorption of excess water on surface: 

Adsorption of excess water on surface When TMA terminated surface arrives in H 2 O zone Initially, water molecules react and then form an OH terminated surface Subsequent molecules are adsorbed on surface Surface concentration of adsorbed molecules increases due to balance between arrival rate and desorption rate desorption rate depends on binding energy and temperature after initial reaction period, concentration grows approximately according to [ 1-exp(- t / )] where   exp(E/ kT ) When substrate with adsorbed water arrives in the purge zone Water molecules desorb desorption rate depends on binding energy and temperature Amount of excess water remaining on entry to TMA zone causes CVD growth depends on balance between amount adsorbed and amount desorbed and can be modelled. ALD 2011 Cambridge 23 bonded O-H terminated layer adsorbed water layer

Results: 

Results Model displays the same features as the measured data. shows similar variations with deposition temperature and speed Water adsorption is likely to be the reason Need a non-water process for lower temperatures ozone plasma oxidation ALD 2011 Cambridge 24

Roll-to-roll development: 

Roll-to-roll development ALD 2011 Cambridge 25 h Web handling system -Feed-out/in Tension control Pre/post treatment ALD Processing zone multiple spatial gas zones one sided coating B A N Precursor delivery Heated process drum - 500mm wide up to 10 m/min Web coating system

Conclusions: 

Conclusions Low pressure continuous coating behaves generally as conventional ALD However, some anomalous behaviour because of the moving substrate Boundary layer gas entrainment and leakage effects do not seem to be important, even with a significant substrate to chamber gap Processes can be reasonably modelled Need non-water processes for low temperature at higher speeds 500 mm web roll-to-roll system will be available next year. ALD 2011 Cambridge 26

Acknowledgements: 

Acknowledgements TEKES (Finnish Funding Agency for Technology and Innovation) project Roll-to-Roll ALD European Regional Development Fund ALD 2011 Cambridge 27