Figure 1:Illustration of the RNIL process with the optical engine (not to scale).
In Roll-to-Roll manufacturing, the final products are created on a long, continuously rolling, flexible web, as illustrated in Figure 1. The process for Roll-to-Plate is almost identical, except that the imprints are created on rigid individual substrates (plates). For simplicity, we will describe the R2R process only.
This contrasts the traditional Plate-to-Plate (P2P) process whereby each product is manufactured individually by pressing a stamp into resin on a rigid substrate (wafer or plate).
Depending on the final product, a light curable resin is applied to the web across a selected area. A UV-transparent imprint roller with flexible stamps rotates with a surface speed matching the web speed. The optical engine is located inside the transparent imprint roller. When the uncured resin reaches the imprint roller, the stamp is pressed into the resin, and later the resin is cured by exposure to UV light. After leaving the transparent roller, the imprints may get a post-curing treatment.
Objectives and challenges
It is essential to understand the objectives and possible challenges of a typical RNIL high-volume manufacturing process to evaluate the performance of a specific optical engine.
Each machine should output as many products as possible. RNIL processes such as R2R and R2P offer nanoimprinting with very high rolling speeds, which can provide high throughput.
While the throughput should be high, the performance in terms of replication quality cannot be compromised. The fine structures must thus be imprinted error-free and reproducibly for 10,000s of products. By controlling the UV-light intensity, the stamp pressure, and the rolling speed, it is possible to obtain error-free imprints that demould easily from the stamp without leading to trapped air bubbles and defects. Illuminating every resin section with sufficient UV energy during curing is important to obtain consistent product performance.
A final consideration is the process’s power consumption, meaning the UV-light source naturally must be as power-efficient as possible.
Overview of optical engine
Based on the experience gathered over 20 years in the nanoimprint industry, Stensborg has developed a Nanoimprint Optical Engine that addresses the issues listed in the previous section.
The key function of the Stensborg Optical Engine is to provide the right amount of UV-light intensity in the nip. The main feature of the nip technology is that pressure is applied along a narrow line, as shown in Figure 2, rather than over a larger two-dimensional area in the conventional Plate-to-Plate (P2P) NIL process.
Figure 2: Pressure and illumination along a line in the nip design.
The smaller contact area of the nip design requires less imprinting force than wafer moulding / P2P nanoimprinting. The nip is ideally suited for high-speed, continuous RNIL processes, and the throughput can be very high, with up to 50 meters per minute in R2R production.
A further benefit of the nip solution is that the imprinting process can be precisely controlled, leading to better performance and reproducibility. The rolling speed and UV-light intensity can be reduced for imprinting very detailed structures to obtain even higher precision.
The Stensborg Optical Engine design is modular and scalable from small to large imprinting width. Along the width of the rolling substrate, the Optical Engine design can be scaled up to meters. The same basic Optical Engine is used inside our Desktop R2P NanoImprinter for prototyping and for any machines custom-built by our engineers for high-volume production.
Figure 1 provides a schematic side view of the Stensborg Optical Engine, which includes UV light sources and optics to focus the light from the LEDs to a line, as shown in Figure 2. In the following sections, we will describe the various parts in more detail.