There are primarily two types of NIL processes for large area nanopatterning:
1. Full-wafer NIL (or Plate-to-Plate (P2P) / Flat-to-Flat NIL), and
2. Roller type NIL. Roller type NIL can itself be divided into two types:
➢ Roll-to-Plate (R2P) or Roll-to-Flat NIL, and
➢ Roll-to-Roll (R2R) NIL.
During the initial stage of the inception of NIL, P2P processes were developed. In such methods, a rigid or hard mould is pressed against a resist (resin) layer deposited on a rigid substrate like silicon or quartz.
The P2P process was quickly applied in various fields like photonics, LEDs, and wafer optics. But very soon, the limitations of such a process start showing up.
In the P2P process, there is a full wafer contact or field contact. The full wafer contact requires very high pressure to fill the mould and there is no tolerance for non-uniformity of the resist surface. This led to the challenges of very high imprinting and demolding forces, accelerating the problems of mould and substrate damage, reduction in replication uniformity and trapped air bubbles and contamination issues. These said issues turn out to be sabotaging for many applications, and there has been a continuous push from research and commercial communities to find better and faster solutions.
This finally led to the development of roller-type NIL processes pioneered by Stephen Chou.
Roll-to-Plate (R2P) and Roll-to-Roll (R2R)
In the roller-type NIL, instead of two flat plates in P2P, there is a roller generally holding the mould and a movable platform or another roller bearing the substrate. Thus, in R2P, a roller and a platform move where the resist deposited substrate comes in contact with the mould installed on the roller to imprint the mould’s structures onto the resist.
This place, where the roller and the platform come in contact with each other, is called a “nip.” The nip in a roller type NIL is a line contact compared to a full field contact in plate-based or P2P lithography. The fact that it is line contact overcomes the longstanding challenges faced by conventional P2P NIL, i.e. maintaining pressure uniformity and seamlessly demolding large area imprinting.
Since the line contact needs less imprinting force, the mould and substrates are not damaged, allowing repeat patterning. Also, the process involves good replication fidelity and inherently is a continuous process leading to high throughput and large-scale manufacturing. Further, the mould and the substrate are demoulded in a peeling fashion due to the roller shape, allowing fewer demolding defects. Additionally, the rolling motion ensures less air trapped and better conformal contact between the mould and the resist irrespective of the surface uniformity or contamination.
To review the Stensborg Roll-to-Plate method using patented technology, click here.
Roll-to-Roll is in some respects better than R2P NIL to attain high-speed, large-area patterning with advanced throughput. Like its Roll-to-Plate counterpart, Roll-to-Roll offers processing featuring high production rates and yields but with more automatic opportunities that help reduce the manufacturing costs through economy of scale. Because of that, the cost upfront may be high, but the RoI on that will be even greater with the aforementioned economic advantages found during production. However, since the R2R process needs two rollers, the flexibility for the mould and substrate materials gets limited. Also, as it is fast-paced, sometimes the lateral dimensions and replication fidelity can be compromised.
Summary – Don’t Get Flattened By The Wrong Roll
Stensborg Patented HoloPrint® Explained – Watch Video.
In summary, the choice to roll or not to roll is entirely up to you and your production objectives. But if you are looking for faster, high throughput large-scale patterning, roller type lithography would be recommended compared to conventional P2P or full wafer NIL.
In terms of prototyping, testing the technology and pilot-scale production, Roll-to-Plate could be the way to go. Also, if the large-scale patterning needs to be done on conventionally rigid substrates like glass and silicon but with high throughput, R2P provides the best solution.
However, nothing beats Roll-to-Roll if the production needs to be further scaled up and be completely continuous. Big Roll-to-Roll setups require huge initial investments. Therefore, companies and research labs that plan to take the production of their devices on Roll-to-Roll can start with Roll-to-Plate prototyping machines like HoloPrint® uniA6 DT and then transfer the optimised parameters smoothly onto bigger roller type machines without the fear of unsuccessful investment of their valuable time and money.
As both Roll-to-Plate and Roll-to-Roll NIL leaders for the last 20+ years, our team at Stensborg has devoted our resources and industry experts to the bigger-picture initiatives – ensuring that the efforts taken by our clients will foster results that both they and the economy can collectively gain from.