Roll-to-Roll Integrated Deposition, Lithography, and Etching on Flexible Corning Willow Glass for Electronics Device Fabrication Robert Malay, Christian Bezama, Mark Poliks, Ming-Huang Huang, Sean Garner, and Scott Pollard
Outline Flexible Corning Willow Glass The Center for Advanced Microelectronics Manufacturing Fabrication on the Rolls Multi-layer Alignment and Registration Analysis Double Sided Alignment and Patterning Reactive Ion Etching Etching Titanium Etching Glass Fabrication of Devices using Wafer on Web Technique: TFTs Interposer Substrates ITO and Copper Mesh Antennas Anti-reflective coatings Conclusions
Flexible Corning Willow Glass Any material made thin enough is flexible. 100 um and 150 um glass, developed by Corning Inc. shows promise as a substitute for polymer films, showing increased thermal stability, optical transparency, and hermiticity. Flexibility also enables the ability to be processed Roll-to-Roll (R2R), dramatically increasing throughput. Willow Glass coated with aluminum, being conveyed over rollers
The Center for Advanced Microelectronics Manufacturing Fabrication of devices on the glass took place at the Center for Advanced Microelectronics Manufacturing (CAMM), at SUNY Binghamton. Processes used for Device fabrication included: Conveyance and Inspection Physical Vapor Deposition (Sputtering) Slot-Die Coating Projection Photolithography Wet Chemical Processing Equipment Available at CAMM for Electronics Fabrication. From top left clockwise: Wet Chemical Process, Sputter Deposition, Conveyance and Inspection, Photolithography.
Fabrication on the Rolls: Lithography The Azores projection lithography system was used to pattern the layer geometries on the surface of the web. Virtual panels of designated geometries were exposed in a repeating patterns across the width of the web. First layer geometries were exposed and patterned with corresponding alignment fiducials for subsequent layer alignment.
Multi-layer Devices on Glass Rolls Using the alignment fiducials patterned onto the glass, multi-layer TFT patterns were generated. Various square features were used to determine the alignment quality at different points on the plate. The difference in the x-axis and y-axis positions of the first layer and the second layer were used to determine the overall alignment of the plate.
Average X-axis Displacement Lithography Alignment: X- Axis From the charts, as the geometries are observed from left to right, the displacement of the second layer shifts to the right. Second layer displacement also shifts to the right when moving from the machine side of the web (top) to the operator side (bottom). Indication of pull from web handlers during movement. Overall, the average x-axis displacement for the plates was -2.5 +/- 7.5 um. Average Displacement Plate Row 15 10 5 0-5 -10-15 5 4 3 2 0 10 20 Exposure Position Contour Plot of X axis Displacement Across Plate 30 40 X Mean < -10.0-10.0-7.5-7.5-5.0-5.0-2.5-2.5 0.0 0.0 2.5 2.5 > 5.0 5.0 Plate Column 1 1 2 3 4 5 6 7
Lithography Alignment: Y- axis Y-axis alignment can be seen to be shifted to the top as exposure position across the web moves to the right. There is almost no change in displacement between geometries across the width of the web. Indicates plate rotation Average y-axis displacement was 0 +/- 8 um. Total displacement due to stage and roll handler displacement. Can be remedied with localized alignment marks. Average Distance From Center Plate Row 10 5 0-5 -10 5 4 3 2 0 Average Y Displacement 10 Plate Column 1 1 2 3 20 Exposure Position Contour Plot of Y Axis Displacement Across Plate 4 5 6 30 7 40 Y Mean < -8-8 -4-4 0 0 4 4 > 8 8
Double Sided Alignment and Patterning Geometries on both sides of the web were desirable for interposer substrates. Manual windows were etched into the back side metal layers to allow for access to the alignment fiducials on the patterned side. Alignment marks and other features were visible using the alignment system through the glass. These marks were used to expose features onto the backside of an already patterned glass roll.
Double Sided Alignment and Patterning Rolls with both sides exposed were able to be patterned R2R and diced for inspection. Due to not having a mirrored mask of the geometries, the x-axis displacements could not be found. However, y-axis displacement was found to be similar to that of the multi-layer alignment, approximately 0.2 +/- 7 um. Given correct mask orientation, fine alignment of double-sided rolls is feasible.
Factorial Design: Reactive Ion Etching A mixed-level full factorial experimental design was implemented in order to assess the behavior of a newly working reactive ion etching unit in the GVE. Titanium and glass wafers were taped to the web using the Wafer-on-Web (WOW) technique, using polyimide tape as a hard mask for step height verification. Wafers were run through the etching unit sequentially, simulating R2R processing. Step height was measured using a Dektak XT stylus profilometer. Factor Level 1 Level 2 Level 3 Level 4 Power (W) 100 300 500 700 Oxygen Partial Pressure (%) System Pressure (mtorr) 0 5 10 15 150 300 450 N/A Temperature (C) 20 125 N/A N/A
Factorial Design: Titanium Etching The significant interaction effects seen in the Pareto and the Normal plot are the temperature/power interaction, and the temperature/oxygen interaction. The BD effect agree with previous studies on titanium etching, as the reaction is primarily dominated by the reaction mechanism between SF 6 and Ti, and follows the Arrhenius Equation The radiant heat from the drum can lead to decreased mean free path in the plasma, leading to the negative AD effect. Shih, M., Lee, W., Tsai, C., Tsai, P., & Chen, C. (2011). Decomposition of SF6 in an RF Plasma. Journal of the Air and Waste Management Association,52(11), 12741280 Term D A B AD BD BC ABC AC CD C BCD AB ABD ACD ABCD 0 Lenth s PSE = 4.56313 Percent 99 95 90 80 70 60 50 40 30 20 10 Pareto Chart of the Effects for Titanium Etching (response is Avg Dif, α = 0.05) 10 11.73 20 Effect 10 5 1-4 AD -2 Normal Plot of the Standardized Effects (response is Avg Dif, α = 0.05) 0 2 BD 4 A Standardized Effect B 6 30 8 D 40 Factor A B C D Factor A B C D Name Power O2 Pressure Temp Effect Type Not Significant Significant Name Power O2 Pressure Temp
Factorial Design: Glass Etching Contrary to the titanium etching, only main effects are significant for the glass etching; power and temperature. Both variables have a positive effect as the level is increased. This agrees with the literature, as the etching mechanism is dominated by the physical bombardment of the glass adatoms. Higher power increases the kinetic energy of the impinging ions, and temperature increases the potential leaving energy of the glass adatoms Term D A ABCD ACD B AB CD BC C BCD ABC ABD AC AD BD 0 5 Lenth s PSE = 3.51188 Percent 99 95 90 80 70 60 50 40 30 20 10 Pareto Chart of the Effects for Glass Etching (response is AVG Diff, α = 0.05) 9.03 10 15 Effect 20 6 5 1-3 -2 Normal Plot of the Standardized Effects (response is Avg Dif, α = 0.05) -1 0 1 2 3 Standardized Effect 25 4 30 5 A Factor Name A Power (W) B O2 Partial Pressure (%) C System Pressure (mtorr) D Temperature (C) D Effect Type Not Significant Significant Factor A B C D Name Power O2 Pressure Temp
Wafer on Web Fabrication of Devices To expedite process characterization and design verification, devices were fabricated on wafers using the WOW technique. Wafers were loaded onto carrier webs, conveyed through the sputter process, and carefully removed from the web. The rest of the fabrication process was carried out on wafer scale devices in the Nanofabrication Laboratory (NLAB). 1. Malay et al, Passive and Active Integration on Flexible Glass Substrates, Electronic Components and Technology Conference, 2015
Results and Analysis: TFTs on Wafers Leakage Current sweep of TFTs fabricated with GVE deposited oxide show exponential increase in current up to 20V, where it remains constant until breakdown at 65V. This shows that the oxide deposited in a R2R format is of a high enough quality as to be suitable for transistor devices. Drain current measurements in relation to gate voltage show an on/off ratio of approximately 10 8. 1. Malay et al, Passive and Active Integration on Flexible Glass Substrates, Electronic Components and Technology Conference, 2015 15
Results and Analysis: Interposers on Wafers Leakage current measurement between lines in the interposer show high isolation in the picoamp range. Lines probed were measured down to 1 um, showing very fine pitch features are possible using R2R deposited materials. Layers showed alignment registration down to 1 um. 1. Malay et al, Passive and Active Integration on Flexible Glass Substrates, Electronic Components and Technology Conference, 2015
Results and Analysis: Antennas on Glass Antennas were fabricated on the glass using both ITO and plated copper mesh. ITO patches were fabricated with a transmission at 550nm greater than 90%, and a sheet resistance of 7-11 ohm/sq. Copper mesh antennas were fabricated on glass sheets, using batch sputtering for seed layer and electroplating to the desired thickness (~1-2um). 1. Poliks, M. D., Sung, Y., Lombardi, J., Malay, R., Dederick, J., Westgate, C. R.,... Daly, C. (2017). Transparent Antennas for Wireless Systems Based on Patterned Indium Tin Oxide and Flexible Glass. 2017 IEEE 67th Electronic Components and Technology Conference (ECTC). doi:10.1109/ectc.2017.314 2. Lombardi, J., Malay, R., Schaffner, J., Song, H., Huang, M., Pollard, S.,... Talty, T. (2018). Copper Transparent Antennas on Flexible Glass by Subtractive and SemiAdditive Fabrication for Automotive Applications. Electronic Components and Technology Conference.
Results and Analysis: Antennas on Glass ITO Antennas showed a maximum gain of -48 db at approximately 5.6 GHz, showing general agreement with the simulation. The simulated and measured gain show general agreement, indicating good performance. The non-uniformities around the edge can be attributed to reflections in the testing range. 1. Poliks, M. D., Sung, Y., Lombardi, J., Malay, R., Dederick, J., Westgate, C. R.,... Daly, C. (2017). Transparent Antennas for Wireless Systems Based on Patterned Indium Tin Oxide and Flexible Glass. 2017 IEEE 67th Electronic Components and Technology Conference (ECTC). doi:10.1109/ectc.2017.314 2. Lombardi, J., Malay, R., Schaffner, J., Song, H., Huang, M., Pollard, S.,... Talty, T. (2018). Copper Transparent Antennas on Flexible Glass by Subtractive and SemiAdditive Fabrication for Automotive Applications. Electronic Components and Technology Conference.
Results and Analysis: Anti- Reflective Coating Antireflective coatings were fabricated in the GVE using ITO and Al-SiO x. Features were not patterned, but fine control of the sputtering thickness was critical for good coatings. Greater than 90% transmission and less than 5% reflection in VLT was obtained via spectroscopic ellipsometry at 0º and 30º 1. Sung, Y., Malay, R. E., Wen, X., Bezama, C., Soman, V. V., Huang, M.,... Klotzkin, D. (2018). Anti-Reflective Coating on Flexible Glass Substrates. Applied Optics,57(9), 2202-2207.
Conclusions and Thanks Fully R2R fabricated Multi-layered and double-sided alignment and patterning have been demonstrated on flexible glass. A R2R reactive ion etcher has been shown to appreciably etch titanium and glass substrates. Devices fabricated on the glass show good performance. This work was funded and supported by Corning Research and Development Corporation.