In this study, we present a novel approach combining nano-scale imprint lithography (NIL) and reactive ion etching (RIE) to fabricate high-quality surface relief gratings (SRGs). This study provides valuable insights into the challenges and optimizations in fabricating SRGs from TiO2 layers using the combination of NIL and RIE. The work was performed with SCHOTT RealView® substrates coated with a 100 nm TiO2 layer and a NIL mask with pattern widths of 200 nm and a pitch of 400 nm. The substrates were processed using the SmartNIL® method to prepare the NIL mask. The advantage of removing the residual layer before the actual structuring of the TiO2 using argon plasma was demonstrated in our research. This led to a significant increase in the selectivity between TiO2 and the NIL resist UV/OA R18. Through the employment of a two-step etching process, which involved the removal of the residual layer with argon plasma and the use of a BCl3-based reactive process with high ion energy, TiO2 structures with a height of 100 nm and a sidewall angle of 75° were successfully created. An effective selectivity of 0.84 was achieved for this two-step process.
Since its beginning in the 90’s NanoImprint Lithography (NIL) has been continuously improved to target the different industry requirements. Using an intermediate soft stamp media was one of the main improvements and has now become a standard technology. Based on that technology, EVG introduces a full wafer imprinting solution, whereas the size of the stamp corresponds to the size of the wafer to imprint. Results obtained at CEA-Leti using this solution, with respect to uniformity, sub-50nm resolution, repeatability, and high aspect ratio patterns, are today state of the art and allow NIL to be considered as an HVM technology. Nevertheless, further development is carried out on different aspects such as overlay (OVL) which is the scope of this work.
Different contributors of OVL as translation, rotation but also distortion are dissociated and analyzed. Alignment repeatability is studied. Additionally, imprint to imprint OVL correction terms are applied. A dedicated methodology has been established and allows to obtain global OVL signature. According to the above, main process contributors are highlighted and studied in the paper to separate influence of each of them. Finally, different ways to improve overlay are discussed and some of them - which could be linked to hardware, process or both - are evaluated. Overall, the OVL status obtained and first improvements bring NIL technology closer to the alignment requirements of the industry.
This poster presentation was prepared for the Optical Architectures for Displays and Sensing in Augmented, Virtual, and Mixed Reality (AR, VR, MR) IV Conference at the SPIE AR | VR | MR 2023 Symposium.
Scaling up from prototype to high volume manufacturing is a challenge for many technologies. In particular for waferlevel manufacturing of advanced freeform micro-optics, there is a gap which needs to be addressed. The combination of two-photon grayscale lithography (2GL), step and repeat nanoimprint lithography (S&R NIL) followed by SmartNIL® replication enables to expand design freedom while still being able to scale up from prototype to high volume manufacturing. This entire process flow was used to pattern microstructures with challenging freeform geometries which are required for emerging devices and applications across the photonics market. Additionally, to further increase the flexibility and performance of the devices, it is possible to use advanced high refractive index materials, which, so far, have been limited to applications in sub-micrometer thin layers, for freeform micro-optics and micro lens arrays. The results presented in this work provide an overview of the versatility and recent achievements of NIL in terms of structure sizes and shapes using different imprint resins to obtain even more design flexibility for freeform micro-optics and micro lens arrays.
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