Grayscale laser lithography is capable of producing continuous-relief (2.5D) structures down to the micro- and nanoscale for applications such as micro-optics, micro-electromechanical systems and functional surfaces. The present work evaluates build accuracy by employing benchmark artefacts having an active area of up to 1 mm × 1 mm and a structure depth of up to 50 μm with a resolution of 1 μm as models for the production of 2.5D structures with a wide range of representative features in terms of elevation, slope, curvature, aspect ratio and area density. The topography of manufactured samples is determined via laser scanning confocal microscopy and 3D optical microscopy based on white light interferometry, with alignment algorithms developed within MATLAB employed to evaluate local build error over the entire surface. Further to the incident laser energy density within each region, the applied energy in adjacent regions is found to influence build accuracy due to the laser intensity distribution, light scattering and photochemical reaction effects, with the area density and aspect ratio of model features found to be of strong influence on outcomes. The results imply that greater build accuracy can be achieved by basing process parameters on not only the local model height but also that within adjacent regions. The present work was performed within the Horizon Europe project “Automated Maskless Laser Lithography Platform for First Time Right Mixed Scale Patterning” (OPTIMAL, Grant Agreement No. 101057029), with the aim of facilitating automated approaches for error correction and accuracy optimization.
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.
In this paper, a patterning approach via i-line grayscale exposure is presented. The i-line wafer stepper (NIKON NSR2205i11D) together with specialized grayscale reticles from Benchmark Technologies (USA), manufactured with half-toning technique, are used. The positive tone and low contrast grayscale ma-P 1275G photoresist is manufactured by Micro Resist Technology (Berlin, Germany) and used in this work; it is part of the ma-P 1200G grayscale resist series and can cover a thickness range of 5 μm to 14 μm. The lithographical pattering process is performed on 6-inch wafers. Essential parameters like the contrast curve measured in the resist as well as after the dry etching are evaluated. Different 2.5D structures like micro lens arrays, blazed gratings, frustums and Fresnel lenses are fabricated by i-line stepper gray scale lithography and ma-P 1275G demonstrating its excellent behavior to generate 2.5D grayscale patterns. For the characterization of the generated 2.5D grayscale patterns a stylus profilometer, atomic force microscopy (AFM), scanning electron microscopy (SEM) and confocal microscope are used. In this paper the process of setting up a grayscale exposure with an i-line stepper and a grayscale reticle and the need to adapt the grayscale reticle in different iterations is presented and discussed.
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.
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.
In this paper the development of an intra-level mix and match (ILM&M) process, an expression for the exposure of one resist layer with at least two different exposure technologies, for the negative tone resist mr-EBL 6000.5 (micro resist technology, Germany) is demonstrated. Process development is conducted on a layout with photonic integrated circuit (PIC) related waveguides (WG), ring resonators and coupling structures on 150 mm silicon wafers with a 1000 nm SiO2 layer and a 450 nm low pressure (LP) Si3N4 layer on top. In order to match the intended structure dimensions perfectly, the ideal exposure dose has to be determined with an i-line wafer stepper and in parallel with an e-beam lithography (EBL) system. In addition, different post exposure bake (PEB) processes and their influence on resulting structures, which are investigated by means of CD-SEM and profilometer measurements are investigated. It is shown, that regarding pattern fidelity, coupling structures exposed by EBL match the layout design better than those exposed by the i-line stepper. For the purpose of further optimizing the matching of generated coupling structures to the targeted design, different proximity effect correction (PEC) parameter sets are applied. CD-SEM measurements reveal the PEC parameter set which is most suitable for generating the targeted coupling structures. By combining the measurement results of structures exposed with different exposure doses and selecting the best PEC parameter set regarding structure dimensions and pattern fidelity, a processing recipe for an e-beam/i-line stepper ILM&M with the negative tone resist mr-EBL 6000.5 is successfully established.
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.
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.
In this paper, we describe a lithographic technique of exposing complex patterns with an advanced resist processing that connects the high resolution of electron beam lithography and the fast exposure of optical i-line stepper lithography via an Intra Level Mix and Match (ILM&M) approach. The key element of our approach is that we use two successive exposures on one single resist layer directly followed by a single resist development. Process and resist characterization of negative tone resist ma-N 1402 as well as a resolution study for each lithographic tools involved. Lithographic performance of negative tone resist ma-N 1402 has shown structures with dimensions of 55 nm with 300 nm pitch for ebeam lithography (VISTEC SB254, shaped beam) and 350 nm structures for i-line stepper (Nikon NSR 2205i11D). Resist footing problem in structures exposed by i-line stepper is solved by introducing a 200 nm thick bottom antireflective coating AZ BARLI II in ILM&M resist processing sequence. A general processing recipe for electron beam/i-line stepper ILM&M with negative tone resist ma-N 1402 is successfully developed and patterns with different dimensions ranging from sub 100 nm to μm scale were reproducibly fabricated on the same resist layer.
In this contribution, we present the results of a systematic material variation for the development of a resist material for high resolution positive tone electron beam lithography (EBL). Several acrylic copolymer materials with different compositions, that is varying mass fractions of the comonomers and different molecular weights, were synthesized and – as resist solutions – evaluated in terms of EBL performance at acceleration voltages of 30 kV and 100 kV. The resist material exhibiting the best combination of the desired properties, named mr-PosEBR, is two times more sensitive than PMMA 495k and performs comparably to the known high resolution resist ZEP520A at 30 kV. For example, a grating pattern with 29 nm wide lines with a period of 100 nm could be lithographically generated in films of mr-PosEBR with an area dose of 100 μC/cm2. In terms of resolution, single lines of only 35 nm width could be fabricated via metal liftoff. Furthermore, the dry etch stability of mr-PosEBR in a CF4/SF6 process is similar to the one of ZEP520A. Consequently, via dry etching nano patterns in mr-PosEBR could be smoothly transferred into the underlying Si substrate with high fidelity. Moreover, mr-PosEBR was evaluated as electron beam grayscale patterning and reflow resist. It was shown that the resist exhibits a good grayscale and reflow performance very similar to PMMA 120k and ZEP520A. Via these well controllable processes the generation of a wide variety of features and applications is possible.
Microlithography uses a variety of resists and polymer materials to create patterns and lithographic structures on several
types of substrates. Excellent adhesion of the resists and polymers to the substrate is a prerequisite for successful
patterning and pattern transfer. This paper presents the results of an investigation of the effects of an adhesion promoter,
SurPass, on the lithographic process when used in combination with a variety of resists, and substrate materials. SurPass
is a waterborne, non-hazardous, cationic organic surface active agent that promotes adhesion by modifying the substrate
surface energy without deposition, chemical change or impact on electrical properties of the substrate material. The
effectiveness of SurPass in combination with several novolac and epoxy resists on various substrate materials will be
presented.
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.
Photostructurable polymers, such as SU-8, have large potential impact on the field of MEMS/NEMS, allowing simple
fabrication of plastic MEMS/NEMS devices with nearly vertical sidewalls and high aspect ratios using standard
photolithographic procedures. Functional properties (as electrical conductivity or photoluminiscence) can be added to a
photostructurable polymer by doping the material with nanoparticles and/or nanocrystals. We present here the case in
which the resulting material presents opto-thermal properties if it is combined with an undoped polymer. From all the
different mechanisms for heating the structure, opto-thermal actuation is interesting from the point of view that it is
possible to obtain a mechanical energy transduction without requiring physical contact or proximity interaction, i.e.
devices can be moved merely by focusing light on it.
LIGA is a well-established process to fabricate metallic micro parts with high resolution, high precision and very low sidewall
roughness by means of X-ray lithography and electroplating. Typical mask substrate materials, e.g. beryllium, carbon based foils,
Si3N4 or SiC show different disadvantages such as low X-ray transparency or high toxicity or high prices or low conductivity or high
thermal expansion or surface porosity causing X-ray scattering. Due to the amorphous structure of vitreous carbon this mask material
proved to significantly reduce the amount of side wall striations, leading to extremely smooth pattern sidewalls. For the fabrication of
X-ray masks, PMMA with its unique features such as high aspect ratio patterns with high precision, exhibits low sensitivity and the
layers preparation is not easy. SU-8, an epoxy-based UV and X-ray sensitive, chemically amplified negative tone photoresist exhibits
high aspect ratio patterns with vertical sidewalls. The difficult remove of the resist after the electroplating process significantly
hinders the inspection of the fabricated X-ray mask. We present the suitability of an UV sensitive, chemically amplified, aqueous-alkaline
developable, and easy removable positive tone photoresist, XP mr-P 15 AV for the fabrication of X-ray masks by means of
UV lithography on vitreous carbon substrates.
There is an increasing need for highly viscous and easy to process thick and ultra thick photoresists for the production of Micro-Electro-Mechanical-Systems (MEMS) and advanced packaging. Here we present results with some novel positive tone photoresists formulated for this purpose. For that we transfered the concept of chemically amplified resists (CARs), originally designed to meet the IC-industry demands for miniaturization and higher resolution, to highly viscous resists. Various polymeric materials have been tested regarding their use in thick CARs. Appropriate resist formulations were developed and their lithographic performance was investigated in a thickness range of 50-150 microns. The CARs are sensitive to UV400.
KEYWORDS: Electron beam lithography, Photoresist materials, Electron beams, Picture Archiving and Communication System, Deep ultraviolet, Etching, Photoresist processing, Lithography, Ultraviolet radiation, Absorbance
Results of electron beam exposure of a DUV sensitive negative tone photoresists composed of a novolak/aromatic bisazide system are presented. Contents of the components of the resist solution were varied to cover a wide range of film thicknesses and to attain optimal performance of the resist. Dense patterns with dimensions of 100 nm and below of the resists patterned by electron beam exposure demonstrate its excellent resolution capability and the possibility to generate patterns with steep side walls and high aspect ratios.
A series of AZ-compatible negative photoresists composed of a novolak resin and azide sensitizers for the micro and nano-lithography is presented. The ma-N 2400 and ma-N 300 are sensitive to light of the deep UV region (248 nm, 254 nm, 308 nm), the ma-N 400 and ma-N 1400 are sensitive to light of the mid UV region, the latter has a high sensitivity to the i-line (365 nm). The thickness of the resist layers prepared by spin coating is up to 8 micrometers depending on the composition of the resist solution. All resists are non-swelling during aqueous alkaline development after exposure. Using special lithography, these photoresists have a resolution capability up to 0.1 micrometers . The resistance to wet etch solutions and to dry etch gases is superior and higher than that of the most positive resists based on novolak.
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