Hybrid polymers are a class of materials especially suited for micro-optical applications due to their outstanding transmission and excellent stability towards temperature, chemicals and radiation. They are solvent-free viscous liquid and therefore UV-replication has become the most established process for their usage in micro-optics manufacture. However, they have also comparable processing behavior to classical photoresists and can be processed in versatile ways offering further possibilities for 2D and 3D structuring. Herein, we report on different UV-lithographical technologies to create high-aspect and high resolution pattern with hybrid polymers.
Greyscale lithography is applied to manufacture complex 2.5D and freeform microstructures in photoresists which serve as master for the pattern transfer into materials for permanent applications, often used in micro-optics. We present the results and the challenges in reproducible generation of deep greyscale patterns in a highly sensitive greyscale positive photoresist, mr-P 22G_XP, when using photomask-based mask aligner greyscale lithography in contrast to laser direct writing on which resist development had been focused. Furthermore, we show the influence of resist aging on the resist response, and ways to correct it by process adaption, as well as we conclude requirements to greyscale photomasks suitable to make use of the full potential of the mr-P 22G_XP resist dedicated for >100μm deep greyscale patterns.
The use of imprint resists in the frame of a multi-layer systems is a viable and also very effective approach to overcome critical challenges typically associated with the patterning and fabrication of demanding nano-patterned substrates like high-aspect ratio structures often applied e.g. in optical devices. The high etch performance of the systems needed for such pattern transfers is either realized by the fabrication of in situ etch masks or by the preparation of a metal hard mask after the imprint and subsequent etch processes. While it might seem counterintuitive at first glance, to split the different features and functions of one resist into different materials and layers, the overall fabrication process however becomes more inherent robust and is moreover also easier adaptable to changes and modifications like e.g. the use of other substrate materials). Herein, we present in detail different types of multi-layer material systems that are all realized by applying candidates of the mr-NIL210 resist series.
The ongoing advancement of lithographic manufacturing in micro- and nanopatterning rely on the commercial availability of innovative photoresists, polymers and photopolymers as well as complementary process chemicals: This allows to enhance current micro- and nanofabrication technologies by increasing the overall pattern complexity or general process simplicity. In this contribution, we demonstrate that material innovations have a significant part in enhancing micro- and nanofabrication by outperforming generic photoresists through cross-functionality as it is increasingly required in ever growing pattern complexity (e.g. advanced mix-and-match methods) or when additional material features are set by the final application.
We propose a novel approach of combined patterning technologies to manufacture individualized micro-optical components as required for the integration of system-level optical packaging, e.g. for coupling light into on-chip level waveguides. The presented work consists of an innovative combination of inkjet printing of available optical polymers onto a prepatterned substrate and UV-replication which enables the manufacturing processes for tailor-made polymeric hybrid and biconvex micro-optical components. For this, inkjet printing of the optical polymers InkOrmo or InkEpo is used as a dispensing technique for additive manufacturing. The ink is printed into designated cavities on a patterned substrate that shows either diffractive or refractive features. After UV-induced polymerization, the cured component is separated from the soft mold substrate. This results in a combination of either a diffractive and a refractive element or two convex refractive elements in one monolithic component. The refractive part on top is self-organized by the surface energy and the shape is adjusted with the amount of dispensed ink enabling to tune the refractive power of the lens. The diffractive structure or convex shape on the opposite side of the lens is obtained by replicating the shape of the prepatterned substrate. Such advanced micro-optic components allow in principle a higher degree of system integration and thus further system miniaturization by e.g. substituting a multi lens system with a single hybrid lens. This novel manufacturing concept is composed to cost-effectively implement design requirements, making tailor-made diffractive-refractive lenses easily accessible e.g. to the MEMS/MOEMS community.
Hybrid Polymers are a material class established in the industry for manufacturing of high-performance optical components, mainly patterned by (nano)imprint processes. Recently, the application range of Hybrid Polymers has been extended into bonding and passivation. In this context, patterning by classical UV-lithography has come into focus as an alternative patterning method to (nano)imprinting. By applying a two-stage curing process with a high intensity, low dose patterning step and a high dose flood exposure after development, it is possible to realize previously unattainable resolutions limits for Hybrid Polymers of 6μm L/S and aspect ratios of more than 3.
Greyscale lithography for the manufacture of complex 2.5D and freeform microstructures in photoresists receives increasing attention from industry for the fabrication of advanced micro-optical elements. The thus obtained structures serve as master or template for different methods of pattern transfer into materials for final, permanent applications, such as refractive and diffractive lenses, blazed gratings, beam-shapers etc. However, many such applications require large structure heights beyond 100 μm which was not easily accessible until now. We present a novel photoresist, mr-P 22G_XP, enabling greyscale lithography of very deep patterns. Issues limiting the pattern depth caused by the photoresist chemistry were addressed. Greyscale pattern depths of 120 μm were possible with an easily accessible set-up with this prototype, with a well-considered choice of photoresist ingredients, and lithography process adjustments focusing on laser direct writing, with the prospect of even deeper patterns up to 140–150 μm.
Nanoimprint lithography (NIL) is one of the most promising technology platforms for replication of nanometer and micrometer scale 3D topographies with extremely high resolution and throughput, as needed for e.g. photonic or optical applications. One of the remaining challenges of 3D NIL, however, is the fabrication of high quality 3D master originals – the initial patterns that are replicated multiple times in the NIL process. Here, we demonstrate a joint solution for 3D NIL where NanoFrazor thermal scanning probe lithography (t-SPL) is used to pattern the master templates with singlenanometer accurate 3D topographies. 3D topographies from polymer resist master templates are replicated using a HERCULES NIL system with SmartNIL technology. Furthermore, 3D patterns are transferred from the resist into a silicon substrate via reactive ion etching (RIE) and the resulting silicon master template is used for producing polymeric working stamps into OrmoStamp and, finally, replicas into optical grade OrmoClearFX material. Both replication strategies result in very high-quality replicas of the original patterns.
The fabrication of optical interconnects has been widely investigated for the generation of optical circuit boards. Twophoton absorption (TPA) lithography (or high-precision 3D printing) as an innovative production method for direct manufacture of individual 3D photonic structures gains more and more attention when optical polymers are employed. In this regard, we have evaluated novel ORMOCER-based hybrid polymers tailored for the manufacture of optical waveguides by means of high-precision 3D printing. In order to facilitate future industrial implementation, the processability was evaluated and the optical performance of embedded waveguides was assessed. The results illustrate that hybrid polymers are not only viable consumables for industrial manufacture of polymeric micro-optics using generic processes such as UV molding. They also are potential candidates to fabricate optical waveguide systems down to the chip level where TPA-based emerging manufacturing techniques are engaged. Hence, it is shown that hybrid polymers continue to meet the increasing expectations of dynamically growing markets of micro-optics and optical interconnects due to the flexibility of the employed polymer material concept.
A step-and-repeat nanoimprint lithography (SR-NIL) process on a pre-spin-coated film is employed for the fabrication of an integrated optical device for on-chip spectroscopy. The complex device geometry has a footprint of about 3 cm2 and comprises several integrated optical components with different pattern size and density. Here, a new resist formulation for SR-NIL was tested for the first time and proved effective at dramatically reducing the occurrence of systematic defects due to film dewetting, trapped bubbles, and resist peel-off. A batch of 180 dies were imprinted, and statistics on the imprint success rate is discussed. Devices were optically characterized and benchmarked to an identical chip that was fabricated by electron-beam lithography. The overall performance of the imprinted nanospectrometers is well-aligned with that of the reference chip, which demonstrates the great potential of our SR-NIL for the low-cost manufacturing of integrated optical devices.
Hybrid polymers have been already widely applied in photonic applications to manufacture microlenses or 2D and 3D waveguides. Thus, they are promising candidates to manufacture optical systems down to the chip level. A brief review on hybrid polymers consisting of both inorganic and organic functional units and thus combine superior material properties in just one material class will be given in this report. The material properties, which can be adjusted to the application in wide ranges enable to fabricate micro-optical elements (e.g. microlenses) using replication techniques such as UV-assisted replication or nano-imprint lithography. Aside of their applicability in 2D, emphasis will be in particular on the evaluation of hybrid polymer materials for two-photon absorption lithography, which is employed to directly manufacture sophisticated 3D photonic structures impossible to be generated with conventional 2D techniques.
We report on our development strategy of photo-curable resists for nanoimprint lithography (NIL) based on modularity. Starting with a basic formulation, we address two topics: the integration of fluorinated additives and the enhancement of the dry etching stability. We prove both concepts by the introduction of two different resists derived from the same basic formulation. The viscosity of the novel resist materials was optimized for inkjet dispensing at room temperature (RT). The novel resist materials can be applied either in NIL batch processes or in high-throughput roller processes. Batch-wise imprints were performed on various substrates such as Si or plastics, demonstrating the distinctive application versatility of the novel materials. Dry etching of spin-coated thin films on Si wafers was performed, demonstrating an etch stability versus Si of 3.5:1 by using the resist formulation with improved etching stability. Roll-to-roll NIL at high throughput on large areas was performed with web speeds of up to 30 m min−1 with different stamp materials. We conclude that all resists reported herein can be deposited via inkjet dispensing at RT, are suitable for continuous high-throughput imprinting on flexible substrates, and are applicable in step-wise NIL processes with good etch resistance in dry etch processes.
The high throughput and large area nanostructuring of flexible substrates by continuous roller processes has great potential for future custom applications like wire grid polarizers, antireflection films, or super-hydrophobic surfaces. For each application different material characteristics have to be considered, e.g. refractive index, hydrophobicity, or dry etch stability. Herein, we show experimental results of nanoimprint lithography resist developments focused on inkjetable and photo-curable resists suitable for high throughput production, especially roll-to-roll NIL. The inkjet deposition of the novel materials is demonstrated by the use of different state-of-the-art inkjet printheads at room temperature. A plate-to-plate process on silicon substrates was successfully implemented on a NPS300 nano patterning stepper with previously inkjet dispensed NIL resist. Furthermore, we demonstrate a throughput of 30 m min-1 in a roller NIL process on PET. Dry etching of unstructured thin films on Si wafers was performed, and it was demonstrated that the etch stability in Si is tunable to a value of 3.5:1 by a concise selection of the resist components. The surface roughness of the etched films was measured to be < 2 nm, after etching of around 100 nm of the resist films what is an essential factor for a low line edge roughness. All resists reported herein can be deposited via inkjet dispensing at room temperature, are suitable for continuous high throughput imprinting on flexible substrates, and are applicable in step-wise NIL processes with good etch resistance in dry etch processes.
Thick photoresists, e.g. up to 1 mm layer thickness, are widely used for the manufacture of high aspect ratio
microstructures, e.g. as mould for the fabrication of metallic micro parts. Such resists or materials exhibit high
mechanical and chemical stability to non-deformably withstand a pattern transfer process, e.g. by electroplating. After
the pattern transfer a solvent based removal is difficult or not possible in many cases. A selective mould removal –
without the damage of electroplated metal structures – is required for the fabrication of single micro parts. As second
application example UV curable and strongly crosslinkable inorganic-organic hybrid polymers such as OrmoComp ® and
OrmoStamp ® are used in UV moulding. The cleaning and rework of these moulds or also of stamps for nanoimprint
lithography (NIL) is a challenging task with increasing importance. The life time of an expensive master mould or stamp
as well as of the replicated working stamps is important, and therefore the ability to rework such stamps without any
defect or decreased resolution. Hence, we demonstrate the application of a plasma-assisted removal using the STP 2020
etching tool from MUEGGE [1] for remote dry etching of strongly crosslinked materials, i.e. the development of
processes for the isotropical etching of highly crosslinked photoresists and hybrid polymer materials will be presented. In
combination with this specific etching tool this technique shows a high potential to make plasma-assisted removal ready
for industrial production.
Advanced micro- and nanofabrication processes are constantly evolving from academic R&D environment towards real
production technology. Therefore, the availability of suitable polymers for optical applications plays a crucial role to
satisfy not only application based requirements but also the compatibility to industrial production technologies. In this
context, UV-curable hybrid polymers, i.e. inorganic-organic materials obtained by sol-gel chemistry, were recently
implemented into mass production environment, e.g. for micro-lenses in mobile device applications.
In this contribution, we report on the development of innovative hybrid polymers and their tailoring towards an easy and
fast processing with reliable and reproducible performance output for industrial large-scale production. Based on a
discussion on standard process parameters with respect to optimize the material’s performance, the technical demands of
industrial manufacture to the hybrid polymers will be subsequently reviewed by giving selective examples. This will be
complemented by a brief description of current R&D activities adapting hybrid polymers to future patterning
technologies.
We present a new platform for the optical analysis of biomolecules based upon the polysaccharide chitosan. The versatile, stable, and compatible nature of chitosan makes it an ideal material for integrating biological materials in microfabricated systems. Chitosan’s pH-responsive solubility allows electrochemical deposition, while its chemical reactivity enables facile coupling of proteins, oligonucleotides, and other biomolecules by covalent bonds. This work demonstrates the spatially selective assembly of a fluorescent molecule on chitosan and its applicability to microscale optical transducers. We define multimode waveguides and fluidic channels on a Pyrex wafer using a single layer of SU-8. Our implementation of sidewall patterning of transparent electrodes (indium tin oxide) on SU-8 structures is demonstrated and can be highly beneficial to fluorescent signal transduction. In this optical configuration, normally incident excitation light illuminates a chitosan surface on the vertical face of a collector waveguide intersected by a microfluidic channel. We demonstrate the collection of the optical signal in the integrated waveguide and analyze the signal by coupling the waveguide to a grating spectrometer.
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