UV-NIL Technologies

SmartNIL® Imprint Process withLuxNIL® High Refractive Index
Resins for Augmented Reality
Optical Devices

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SmartNIL® Imprint Process with LuxNIL® High
Refractive Index Resins for Augmented Reality
Optical Devices
Introduction
Augmented, Virtual and Mixed realities (AR/VR/MR) enable smart solutions in realtime across a wide spectrum of industries from entertainment to communication tohealthcare. AR/VR/MR devices bend and combine light to create virtual images thatproject onto the physical world. To provide the widest viewing angle and maximize
the field of view (FOV), materials with refractive indices greater than 1.7 at 589 nm
are employed. High refractive index glasses are available, and nanometer scalestructures can be imprinted on these glasses economically by photo nanoimprint
lithography (UV-NIL or P-NIL); in this technique, a UV-curable resin is coated on thesubstrate, a working stamp with nanometer scale images is pressed onto the resin,
the resin is cured photochemically, and the working stamp is removed.

Key points
 UV-nanoimprint lithography
 High refractive index resins High precision imprints Sub-nm height gains

Wafer-level UV-NIL with high refractive index resins is a critical deliverable for semiconductor equipment andmaterials companies addressing the needs of AR/VR/MR device manufacturers. To become the de facto process for
AR devices, the resins must overcome a number of challenges including insufficient resin filling of the working stamp,difficulty in release of the wafer from the polymer working stamp, and poor imprint quality in the nano-structures. As
leaders in manufacturing equipment and materials, EV Group (EVG) and Addison Clear Wave Coatings (ACW) joined
forces in developing a ready to use, high volume wafer-level UV-NIL process with EVG’s SmartNIL® technology andACW’s LuxNIL® high refractive index resins.

ACW’s LuxNIL® High Refractive Index (RI) Resins
To achieve the requirements of AR/VR/MR devices and to enable mass production capability using SmartNIL®
processes, the LuxNIL® high RI resins must meet several performance objectives. The viscosity of the resins must
be low enough such that uniform ultra-thin coatings of 0.1 to 4 microns can be produced by spin coating. Afterremoval of solvent, the resins must maintain enough fluidity such that they fill the binary or the slanted nanostructures of the polymer working stamp by capillary action. The resins must be capable of imprinting with accurate
capture of the nanometer scale structures. Finally and importantly, the resins must be chemically inert so that they
do not etch nor deposit residues on the polymer working stamp thus changing the dimensions of the nano-structures
produced in multiple uses of the working stamp.
After processing, the cured films must be strong enough to maintain the structures when the working stamp isremoved from the cured resin layer, and the cured films must meet industrial level testing requirements without
significant deterioration of optical properties including refractive index, haze, optical clarity, and transmission. For
optical applications of AR/VR/MR, the refractive indices of the cured films must be >1.7 and, for many applications,>1.8 at 589 nm.
The bulk properties and environmental stabilities of three ACW LuxNIL® high RI resins studied in this work arereported in the Table. Thin films coated on glass were exposed to reliability performance testing of 85 °C and 85%
relative humidity for extended periods. The Table reports properties measured before and after the stress tests. Thefilms maintained high transmission and clarity with low haze, and the refractive indices and film thicknesses wereeffectively unchanged.

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Table. Properties of LuxNIL® films before and after 85 °C and 85% relative humidity exposure. aResin was coated on glass, heated at 100 °C for 1 minute to remove solvent, cured with 365 nm UV light, conditioned
at 150 °C for 4 hours, and then stressed at 85 °C and 85% RH. bThe RI and thickness were measured on samples
stressed for 360 hours; haze, clarity, and transmission were measured on 1 micron samples stressed for 1,000 hours.
cTransmission values are corrected for reflections.
aNano-Imprint Structures with EVG’s SmartNIL®
Process
To demonstrate nano-imprint manufacturing feasibility with
EVG’s SmartNIL® process, ACW’s LuxNIL® P276, P285 and P289
resins were studied with a PFAS-free polymer working stampwith a focus on the following properties:
A. Accuracy of nanoimprint structures with binary andslanted structures
B. Working stamp height change following multiple imprints
C. Resolution capabilities of the resins
The samples were replicated on the EVG HerculesNIL® system, afully integrated high volume manufacturing equipment that isdedicated for nano imprinting lithography and wafer-level optics.
All imprints were on glass wafers with AR/VR-like structures withdimensions of 200 nm and a pitch of 400 nm using EVG NILUV/AS5 working stamps which are PFAS-free. The final
characterizations were conducted by SEM and AFM for exact
determinations.
Accuracy of nanoimprint structures
An important requirement of AR/VR/MR market is the productionof imprinted structures with an exact replication of the shape ofthe original master template. In general, such fidelity is afunction of the fluidic properties of the material after the solvent
removal bake step, the compatibility of the resin with the chosen
working stamp material, and the proper process settings. In thepresent study, the LuxNIL® resins were investigated in terms of
their pattern replication on the PFAS-free working stamp. Figure
1 shows AFM measurements of the SmartNIL® process with theLuxNIL® resins. The results demonstrate perfect replication withsuperior pattern fidelity for all three materials.

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Figure 1. AFM results of binary with 400 nm depthnano-imprint structures of LuxNIL® P276, P285, andP289 with SmartNIL® processes.
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Height gain from multiple imprints

A single perfect replication is not sufficient performance for a bulk manufacturing process. The EVG SmartNIL®
process is a highly cost-effective technology when multiple replications from the same polymer working stamp give
useful imprinted surfaces. Thus, each of the three LuxNIL® resins was applied in 25 imprints on a single workingstamp, and heights of structures on the imprints were measured. Figure 2 shows the results. The observed averageheight gains were 0.64 nm/imprint (P276 and P289) and 0.80 nm/imprint (P285). These uncommonly small heightgains, which are groundbreaking results for materials with refractive indices as high as 1.96 at 633 nm, reflect thegood compatibility of the resins with the polymer working stamp.

Figure 2. Height gain over 25 imprints for ACW LuxNIL® P276, P285 and P289.

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Resolution capabilities of the resinsHigh resolution capability of the resins is necessary for the replication of sharp edges. This property was investigatedusing a dedicated resolution master. The smallest features on this master are 50 nm, and there are complex
meander structures on the template which are more challenging than simple line and space structures since they
contain 90° curves. The AFM results of the resolution tests, illustrated in Figures 3-5, demonstrate that each of theLuxNIL® resins achieved an exceptional resolution of 50 nm.

Figure 3-5. Resolution tests.

In summary
EVG’s SmartNIL® process with ACW’s LuxNIL® resins produces high resolution structures with high refractive indicesin multiple replications on inexpensive working stamps. These are necessary properties and performance standards
for economical bulk manufacturing of optical components that can be incorporated into AR/VR/MR devices.

EV Group SmartNIL® Process Summary
The process flow consists of two steps: First, manufacturing multiple low-cost polymer working stamps (WS) froma previously manufactured master and then utilizing them for the actual imprints during the second step. This
intermediate approach avoids wearing out the original master template and improves the overall production
economics, as the achievable number of imprints is increased tremendously. The NIL process is depicted in detailin Figure 6. To ensure defect-free WS fabrication, the master is coated with an anti-sticking layer applied by spin
coating. The WS material is then dispensed directly on the master, also by a spin coating process. Next, thetransparent SmartNIL® backplane is attached to the coated master. The WS polymer is cured with UV light froman LED, and the WS is demolded from the master. Upon completing this process, the actual SmartNIL® imprinting
process begins, where a dedicated material is applied onto the substrate by the same method as used for the WSfabrication, e.g., spin coating. After removal of the solvent in a short “bake” step, the WS and the substrate withthe dispensed material are brought into contact. Similar to the WS fabrication, this step is followed by UV curingand demolding, allowing multiple imprints to be made with the final structures.
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Figure 6. The EV Group SmartNIL® Process.

High Refractive Index LuxNIL® Resins
Addison Clear Wave Coating’s LuxNIL® resins provide films with refractive indices in the range of 1.70 to 1.97 at
589 nm that are suitable for high volume wafer-level photo nanoimprint lithography manufacturing. In addition to
the essential high refractive indices, these resins were developed with an eye towards chemical inertness andcompatibility with contemporary equipment, processes and working stamps as demonstrated by the studies
conducted here. As immersive experiences in AR/VR/MR mature and markets grow, additional requirements forhigh RI materials undoubtedly will surface; ACW is poised to continue vigorous research and development
activities to ensure delivery to device manufacturers of the most technologically advanced imprint resins.
Scan the QR code below to download a copy of this whitepaper.

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