Physical characterization of nanoimprinted polymer nanostructures using visible light angular scatterometry

To follow Moore’s law and the trend of devices to keep shrinking, the nanotechnology industry is challenged in finding a suitable technique for the mass production of integrated circuits with critical dimension in the sub-10 nm range. At the time this project started, EUV lithography, that employs light with a wavelength of 13.5 nm and thus requires the scanner to be kept under vacuum, was encountering difficulties in making its way into high volume manufacturing. Therefore different technologies were being explored as alternative to EUVL. The European project Single Nanometer Manufacturing for beyond CMOS devices (SNM) [1] aims at developing a manufacturing platform that routinely provides sub-10 nm resolution. To achieve that, fabrication processes based on Nano Imprint Lithography (NIL) are investigated. NIL is a low cost, high resolution and high throughput patterning technique, suitable for the mass production of devices. In NIL, a UV-transparent stamp is pressed on top of a substrate covered with polymer, called the NIL resist. The features on the stamp are imprinted in this polymer, that hardens under the exposure of UV light. The features on the polymer are then transferred into the underlying substrate using etching processes. To fabricate these stamps, we propose to use electron beam induced deposition (EBID)...

In this paper the bias table models for the wafer scale SmartNIL™ technology are addressed and validated using complete Scanning Electron Microscopy (SEM) characterizations and polynomial interpolation functions. Like the other nanoimprint lithography (NIL) technics, this replication technology is known to induce Critical Dimension (CD) variations between the master and the imprint, due to polymer shrinkage, soft stamp deformation or thermal expansion. The bias between the former and final object follows peculiar rules which are specific to this process. To emphasis these singularities, Critical Dimension (CD) uniformity analyses were analyzed onto 200 mm wafers imprinted with the HERCULES® NIL equipment platform. Dedicated masters were manufactured to capture the process signatures: horizontal and vertical line arrays, local densities ranging from 0.1 to 0.9 and minimum CD of 250 nm. The silicon masters were manufactured with 248 optical lithography and dry etching and treated with an anti-sticking layer from Arkema. CD measurements were made for the master and the replicates on 48 well selected features to build interpolations. The bias table, modelled by polynomial functions with a degree of 5 for the density and a degree of 3 for the CD, are compared between horizontal and vertical features, and between the center and the edge of the wafers. Finally the focus is made on the validation of the interpolations by comparing the computed bias and the experimental data.

Electron beam (EB) lithography using polymethylmethacrylate (PMMA) andoxygen gas reactive ion etching (RIE) were used to fabricate fine patterns in adiamond mould. To prevent charge-up during EB lithography, thin conductivepolymer was spin-coated over the PMMA resist, yielding dented line patterns 2μm wide and 270 nm deep. The diamond mould was pressed into PMMAon a silicon substrate heated to 130, 150 and 170ºC at 43.6, 65.4 and87.2 MPa. All transferred PMMA convex line patterns were 2 μ mwide. Imprinted pattern depth increased with rising temperature andpressure. PMMA patterns on diamond were transferred by the diamondmould at 150ºC and 65.4 MPa, yielding convex line patterns 2 μm wide and 200 nm high. Direct aluminium and copper patterns wereobtained using the diamond mould at room temperature and 130.8 MPa. Thediamond mould is thus useful for replicating patterns on PMMA and metals.

Raster-Atomic force nanolithography: New insights towards the fabrication of 3D nanostructures on PMMA and Silicon Nitride

Low cost, rapid fabrication of durable molds of grating arrays for nanoimprint lithography

The recent growth of information-communication facilities such as the Internet, mobile telecommunication and video-on-demand services has led to explosion of worldwide communication traffic, which increase demand for faster and denser communication infrastructures including optical communication networks. Distributed feedback laser diodes (DFB LDs) have been widely used as optical sources in networks because of their high selectivity and stability of wavelength. Although they had limitedly been used in longhaul and high-speed network at one time, they are now increasingly required in metro and end-user fields because of the increasing traffic. Thus, necessity for inexpensive DFB LDs increases rapidly. The characteristics of a DFB LD with uniform (constant period) gratings depend on the grating phase at the cleaved facet (Matsuoka et al., 1984). The variation of characteristics with the facet phase is a serious issue in view of productivity and usability of the LDs. One of the most effective ways of reducing the facet phase effect is to adopt phase-shifted gratings instead of uniform gratings (Kaden et al., 1992). The uniformities of the LD characteristics such as mode-stability and output power are improved by adopting phaseshifted gratings, thus the yield of LDs increase and their production cost is effectively reduced. In general, there are various fabrication methods for diffraction gratings of DFB LDs, for example, interference exposure, electron beam lithography (EBL), and optical projection exposure. Interference exposure cannot feasibly be used for fabricating phase-shifted gratings, because it exclusively generates exposure patterns with a uniform bright-and-dark period. Although EBL has sufficient resolution to be used for phase-shifted gratings, exceedingly expensive apparatus is necessary for volume production with sufficient throughput. For the optical projection method, a forefront stepper having sufficient resolution for gratings is also expensive, and the cost is too high for fabricating DFB LDs, of which production volume is relatively small compared to that of such semiconductor devices as LSIs. Nanoimprint lithography (NIL) has been studied by many organizations since the middle of the 1990s. Chou et al. indicated that sub-10-nm features could be formed by imprint, which started the era of NIL technology (Chou et al., 1995). A novel method of NIL using a UVcurable resin was introduced by Haisma et al (Haisma et al., 1996), and Bailey et al.

Fabrication of eight-step diffractive optical element for hologram-ROM

Summary form only given. Nanoscale metal-semiconductor-metal (MSM) photodetectors and MESFETs are key elements in ultra-fast optical and wireless communication systems. However, devices with sub-0.25 /spl mu/m feature sizes are typically fabricated using electron-beam lithography (EEL), which has high cost and low throughput. Nanoimprint lithography (NIL), on the other hand, has both low cost and high throughput, as well as sub-l0 nm resolution. We report the fabrication of MSM photodetectors on semi-insulating (SI) GaAs using NIL, and the examination of NIL on the quality of the nanoscale Schottky contact. We found that if the imprint pressure is 600 psi or lower, nanoscale GaAs MSM photodetectors fabricated using NIL are comparable to those fabricated by conventional EEL and photolithography, indicating no degradation to the photodetector Schottky contact induced by the imprint process.

Nanophotonics is wide field covering many interesting applications branching from cutting edge science including plasmonics, metamaterials, cavity quantum electrodynamics in high-Q cavities all the way to applied sciences like silicon nanophotonics for on chip optical interconnections and single frequency semiconductor light sources. Most of the practical device demonstrations in these fields utilize nanopatterned surfaces. Applications require patterning of nanoscopic gratings, photonic crystals, waveguides and metal structures. There are many wonderful demonstrations of nanotechnology-based lasers and other photonic components. However, difficult questions related to fabrication need to be addressed before these components enter any market. Demonstrations in the scientific literature have relied heavily on the use of direct writing lithography methods, such as electron beam lithography or focused ion beam lithography. These methods, although excellent for scientific studies, cannot be scaled up to allow cost effective production of nanophotonics. Lithography solutions developed for integrated circuits can produce extremely narrow linewidths and deliver high precision but are difficult to transfer to photonics fabrication. There exist many alternative lithography methods, but their scale-up to cost effective volume production is challenging. Since the introduction of nanoimprint lithography (NIL) in 1995 (Chou et al. 1995), there has been widespread interest in the development of NIL for various applications. As early as in 2003 NIL had gained substantial support and was chosen as one of MIT's Technology Review’s “10 Emerging Technologies That Will Change the World” (Technology Review 2003). The selection was justified by the fact that NIL can bridge the gap between lab level nanotechnology research and production level manufacturing requirements. In this chapter, we briefly review the state-of-the-art lithography methods and introduce nanoimprint lithography (NIL), a very cost effective lithography method for nanophotonics applications. In section two we will introduce soft UV-NIL, an imprint method using soft and flexible stamps, as a method for patterning compound semiconductor optoelectronics. Finally, in section three, we highlight some NIL activities based on soft-UV-NIL.

The high-volume production of semiconductor devices with sub-10 nm critical dimensions is challenging. We have investigated the feasibility of the fabrication of line-and-space patterns with a 7 nm quarter-pitch (7 nm space width and 21 nm line width) by electron beam (EB) lithography. In this study, the optimum beam size for the fabrication of line-and-space patterns with a 7 nm quarter-pitch was investigated from the viewpoint of the trade-off relationship between line edge roughness (LER) and sensitivity. When the peak charge was constant, the optimum beam size depended on the required sensitivity. When the total charge was constant, the beam size was required to be less than 1.6 nm for minimizing LER.

The critical dimension (CD) of lithographic patterns is the most significant indicator for evaluating the imaging performance of photoresists, and its value is seriously affected by process conditions. However, the lithographic imaging system is highly nonlinear, and extensive exposure experiments are needed to obtain the desired CD. This consumes lots of time, manpower, and cost in screening for optimal process conditions. Here, we report a combined electron beam lithography (EBL) experiment and recurrent neural network (RNN) study on the CDs of metal oxide nanoparticle photoresists, and establish a CD RNN model. Leveraging the RNN model, a process condition filter is developed to screen suitable process conditions. The experimental results demonstrate that the prediction accuracy of the CD model exceeds 93%, and the photoresist patterns under the screened process conditions can satisfy the requirements of a preset CD. This work opens up a novel perspective for accurate EBL process modeling, and provides guidance for EBL experiments.

Electrochemical transducers are frequently used to electrochemically deposit, synthesize and/or sense chemical compounds in material science, chemistry and biology. Traditionally this is done in fairly large volumes; generally several milliliters to even full production scale tanks, however, for high throughput measurements and combinatorial experiments smaller volumes are generally preferred. To probe small volumes small electrodes with preferable high density are needed. Presented in this paper is how to fabricate interdigitated electrodes by electron beam lithography (EBL) and also how to make large quantities by nanoimprint lithography (NIL) to enable combinatorial studies of cells or materials in microsystems (Lab-on-a-Chip Systems).Interdigitated electrodes are shown to have additional advantages compared to simple disk or rod electrodes, such as being able to perform redox cycling experiments. The collection efficiency for the electrodes with pitch of 400 nm and width of 200 nm fabricated by EBL has been found to be round 87% when characterized electrochemically using ferro-/ferricyanide. The shape of the cyclic voltammograms for the electrodes are also in good agreement with the theoretical expectations for ultramicroelectrodes. Hence, these electrodes should be ideal candidates for combinatorial and high-throughput studies based on electrochemical methods.Furthermore, a fabrication process based on nanoimprint lithography (NIL) is demonstrated, this could potentially ease fabrication and reduce cost of devices. The NIL process is based on thermal imprinting in PMMA 950k and LOR 0.7A.

Patterns written by laser direct write have a critical dimension (CD) bias dependence on the dose similar to other direct write methods, such as electron beam lithography, which can be explained by the exposure intensity distribution (EID) of the laser beam. In this study, a comprehensive model based on the EID is proposed to understand the pattern CD bias dependence on the dose, which is known as the exposure latitude. This model was supported by the results of the exposure tests on MicroChem S1800 resist on an Si wafer using the Heidelberg DWL66+ laser writer. The exposure latitudes of the patterns at both micrometer and submicrometer scale were measured. At the micrometer scale, the exposure latitudes were found to have no measurable dependence on the pattern size and the local pattern density. This conclusion does not hold at the submicrometer scale where the length scale is comparable to the width of the laser beam. This study proposes a way to convert the experimental exposure latitude data into the EID functions and fit these functions by assuming a Gaussian laser beam intensity distribution. All empirical observations are found to agree with the predictions made by the EID model. The authors also show that this model can help achieve dimensional accuracy, especially when there is a change in the exposure process. Moreover, it can be used to analyze and minimize the CD inconsistency between different runs found in the experiments. To reduce such inconsistency, overexposing combined with a negative bias applied to the pattern is suggested.

Sloped and stepped 3D structures were added to surface-patterned resists using grey-scale electron beam lithography and thermal reflow. A poly(methyl methacrylate) resist with moderate initial molecular weight of 120 kg/mol was chosen, which enabled processing with both nanoimprint and electron beam lithography. Using proper exposure doses, a molecular weight distribution was generated that allowed a selective thermal postprocessing of the exposed steps while the imprinted gratings on top of the resist were preserved. This allows fabricating mixed structures of microprisms surrounded by large-area nanogratings in the same resist layer. Working stamps were casted from the template pattern and subsequently replicated using thermal nanoimprint. As a possible application, backlight devices with arrays of light outcoupling prisms can be seen.

Nanoimprint lithography (NIL) technology has aroused great interests in both academia and industry due to its high resolution, low-cost, and high-volume nanopatterning capability. And as an expoxy resin-based negative amplified photoresist, SU-8 is an ideal candidate for NIL because of its low-glass-transition temperature, low-volume shrinkage coefficient, and good optical properties. In this reviewing paper, we highlight the major technical achievements in NIL on epoxy resin and its applications for bio- and nanophotonic structures. NIL was also applied for the duplication of imprint templates, originally fabricated by e-beam lithography (EBL) followed by reactive ion etch (RIE), using a SU-8/ SiO 2/PMMA tri-layer technique. And nanoimprint properties were systematically investigated for optimization. The developed nanoimprint process for different applications indicates promising industrial potentials in the next generation lithography resolution.