Roll-to-Roll ALD Deposition of Al 2 O 3 Barrier Layers on PET

Transcription

1 Roll-to-Roll ALD Deposition of Al 2 O 3 Barrier Layers on PET W. A. Barrow and E. R. Dickey Lotus Applied Technology AIMCAL Fall Technical Conference 2009 Amelia Island Plantation, Florida 20-Oct-2009

2 Why ALD for Barrier Films? Exceptional barrier properties reported for very thin, single layer oxide films Mlil Multiple groups reporting 10-3 to 10-6 g/m 2 /day for single films as thin as nanometers on polymer substrates ALD films are conformal Coats uniformly inside scratches, pits, irregularities Good results from single layers even on extremely rough surfaces ALD films may be very dense but stress-free High density achieved without plasma or addition of kinetic energy High density may be achieved in completely amorphous films

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6 Conventional vs. Roll-to-Roll ALD Conventional ALD cycle Roll-To-Roll ALD cycle N 2 Precursors sequentially introduced and purged into same space H 2 O TMA Substrate Pump Substrate is transported back and forth between zones which constitute the components of the ALD cycle N 2 H 2 O TMA Substrate Pump H 2 O N2 Pump N 2 H 2 O TMA Substrate Pump TMA N 2 H 2 O TMA Substrate Pump

7 Key Process Differences No pulsing valves required Extremely high coating rate possible No time required to purge or saturate volumes Only the substrate itself is coated No other surface is exposed to both precursors Precursors may be recycled Trapping may be done in exhaust line prior to combining with other precursor

8 Experimental Overview Al 2 O 3 barrier films fabricated in conventional cross- flow ALD reactor at 50 C and80 C Benchmark comparison to results from other researchers Baseline for comparison of roll-to-roll results Al 2 O 3 barrier films fabricated in roll-to-roll ALD reactor at 75 C Band or cycling mode True roll to roll mode

9 Characterization WVTR measurements made using Illinois Instruments model C, 90% RH Two test cells for each measurement Thickness measurements Conventional ALD reactor - Ran silicon witness coupons and measured using ellipsometry Roll coater - Ran quarter wave coatings and measured thickness optically to calibrate thickness per cycle

10 Equipment - Conventional ALD P400 cross-flow reactor manufactured dby Planar Systems

11 Equipment Flexible Substrate Reactor Band Configuration i Each full revolution of band constitutes in one ALD cycle R2R Configuration Each full pass results in 8 ALD cycles

12 Al 2 O 3 Barrier Films Films deposited on PET in conventional cross-flow reactor Determine saturation characteristics i for process Establish baseline for WVTR performance vs. thickness Characterize WVTR performance vs deposition temperature t Films deposited in Band Mode in flexible substrate reactor Compare saturation characteristics to confirm ALD growth mode Compare WVTR performance vs. thickness and web speed Films deposited in roll-to roll mode in flexible Films deposited in roll to roll mode in flexible substrate reactor

13 Al 2 O 3 Saturation in a Conventional ALD Reactor 1.60 Å/cycle) on Rate ( Depositi C, 30 sec purges 80 C, 30 sec purges 80 C, 90 sec purges 80 C, 150 sec purges 80 C, 180 sec purges Precursor Pulse Time (sec)

14 Dependence of Al 2 O 3 Barrier Properties on Thickness from a Conventional Reactor WVT TR (g/m 2 /d day) Double-Sided, 50 C Double-Sided, 80 C Single-Sided, 80 C WVTR Measurement Floor Al 2 O 3 Thickness (Å) Results generally in agreement with published values

15 Dependence of Al 2 O 3 Barrier Properties on Deposition Temperature in a Conventional Reactor WVTR (g/m 2 /da ay) Å Al2O3 WVTR Measurement Floor ALD Deposition Temperature ( C)

16 Saturation Characteristics For Al 2 O 3 in the Roll-to-Roll Reactor in Band Mode Al 2 O 3 Growth Ra ate (Å/cyc cle) CVD Starvation Saturation Dwell Time of Web in Each Precursor Zone (seconds)

17 Barrier Characteristics For Al 2 O 3 in the Rollto-Roll Reactor in Band Mode WV VTR (g/m 2 /day) Conventional ALD, 80 CC Web Speed 0.5 m/s Web Speed 0.3 m/s WbS Web Speed d m/s WVTR Measurement Floor ALD Cycles

18 WVTR Performance vs Web Speed (Band Mode) Excellent WVTR performance achieved at up to about 0.3 m/s web speed WVTR performance degrades gradually up to about 1 m/s web speed Above 1 m/s web speed the growth mode changes from ALD to CVD (including vapor phase reactions generating powder)

19 Cause of Degradation of Process at High Web Speed - Water Purge Pattern of film growth on chamber walls above 1 m/s suggest that failure of fh 2 O purge occurs at high h speed. This effect was observed for TiO2 barriers deposited in the web coater, but the effect was much weaker (got decent barriers at up to 10 m/s) Currently evaluating several approaches to improve H 2 O purge, including: Utilize azeotropes (alcohols, HCl, etc.) to help remove excess H 2 O or inhibit the reaction between H 2 O vapor and TMA Replace H 2 O with a precursor that does not tend to form excess adsorbed layers (O3, O2 plasma, etc.) Use a plasma in the purge zone to remove excess H 2 Of from the web.

20 Al 2 O 3 in True Roll-to-Roll Mode Effects of Web Speed and Thickness WV VTR (g/m 2 /day) Conventional ALD, 80 C Web speed 0.15 m/s Web speed 0.30 m/s WVTR Measurement Floor Number of ALD Cycles

21 WVTR Performance vs Web Speed (True Roll-to-Roll Mode) Good WVTR performance achieved at 0.15 m/s web speed Performance degradation compared to band mode is thought to be caused by web handling Manual speed control lknob poor control of acceleration No tension control Web must be rolled and unrolled on the drive and take-up spools once for every 16Å of film deposited

22 Conclusions High quality Al 2 O 3 films have been grown in novel ALD reactor for flexible substrates High barrier properties demonstrated with very thin films Barrier quality it higher speeds limited by H 2 O purge Working on several approaches to improve H 2 O purge New approach has potential for very low cost coating of clear barriers Extremely simple machine and process Low substrate temperatures Good barriers produced at 75 C Very high h precursor utilization possible