Step And Flash Imprint Lithography Research Articles

Feature filling modeling for step and flash imprint lithography

The authors analyze the feature filling phenomena for step and flash imprint lithography (SFIL) via diffusion of a gas, entrapped in the features, through liquid imprint resist. The model and simulation for the dynamics of feature filling including gas dissolution during the SFIL imprint step is presented. Several factors including the gas concentration profile across the liquid resist drop, the filling progression, and the total filling time for different pattern configurations are investigated to quantify feature filling. Simulation results show that initial filling is pressure controlled and very rapid [∼O(1ms)]. The rest of the feature filling is diffusion controlled, but fast enough [∼O(1s)] to conclude that diffusion of entrapped gas is not a cause for nonfilling of features. Also, the result that the smaller size features fill faster than the larger ones (with the same depth) makes SFIL the prime contender for high resolution and high throughput next generation lithography.

Fabrication of Step-and-Flash Imprint Lithography (S-FIL) templates using XeF2 enhanced focused ion-beam etching

The fabrication of Step-and-Flash Imprint Lithography (S-FIL) templates with line widths of 50 nm is described in this work. The structures have been patterned using a Ga+ focused ion beam (FIB) in a quartz template. FIB milling is generally accompanied with re-deposition effects, which represent a hindrance to densely patterned nanostructures required in most NIL applications. To reduce these re-deposition effects, in this research, xenon difluoride (XeF2) enhanced FIB etching was applied that also increases the material removal rates in comparison to pure kinetic ion sputtering. To optimise the process when using XeF2 gas the following ion scanning parameters have been examined: ion dose, beam current, dwell time and beam overlap (step size). It has been found that the assisting gases at very low doses do not bring significant etching enhancements whilst the sputtering rates have increased at high doses. Using the XeF2 gas-assisted etching, FIB structuring has been used to fabricate <100 nm structures onto quartz S-FIL templates. The presence of XeF2 considerably enhances the etching rate of quartz without any significant negative effects on the spatial resolution of the FIB lithographic process and reduces the template processing time.

Step and flash imprint lithography for manufacturing patterned media

The ever-growing demand for hard drives with greater storage density has motivated a technology shift from continuous magnetic media to patterned media hard disks, which are expected to be implemented in future generations of hard disk drives to provide data storage at densities exceeding 1012 bits/in.2. Step and flash imprint lithography (S-FIL) technology has been employed to pattern the hard disk substrates. This article discusses the infrastructure required to enable S-FIL in high-volume manufacturing, namely, fabrication of master templates, template replication, high-volume imprinting with precisely controlled residual layers, and dual-sided imprinting. Imprinting of disks is demonstrated with substrate throughput currently as high as 180 disks/h (dual sided). These processes are applied to patterning hard disk substrates with both discrete tracks and bit-patterned designs.

A Decade of Step and Flash Imprint Lithography

Step and Flash Imprint Lithography (SFIL) was first reported ten years ago. The technology has advanced in many ways during the last decade. There are sophisticated, imprint tools available from commercial suppliers and high resolution templates can be purchased from several vendors. The materials and the process have evolved and matured to enable printing of sub 10nm structures, inverse tone printing, printing on both sides of disk drive substrates, printing in three dimensions to enable efficient production of CMOS wiring levels and printing of functional materials tailored to enable production of photonic crystals, insulators, etc. While great progress has been made in many areas, there remain concerns among some about defectivity and the throughput of the process.

Stamping-Based Planarization of Flexible Substrate for Low-Pressure UV Nanoimprint Lithography

Patterning flexible substrates in nano scale is an important and challenging issue in the fabrication of next-generation devices based on a non-silicon substrate. Step and Flash imprint lithography (S-FIL) which is a room temperature and low pressure process offers several important advantages, such as the use of a smaller and therefore cheaper stamp or the possibility of the overlay imprinting, as a transparent stamp is utilized. However, it is very difficult to perform S-FIL on a flexible substrate successfully due to the high waviness. The waviness of a flexible substrate is not a constant value in contrast to a rigid substrate. It depends on the imprint pressure applied onto the substrate. In this paper, in section two, the effect of the imprint pressure on the waviness of the surface of the flexible substrate is examined. It is proved that the waviness of the surface of the flexible substrate could not be reduced sufficiently to assure a successful imprint at low imprint pressures. In the third section, a method of patterning polymer substrates using ultra-violet nanoimprint lithography (UV-NIL) is presented. The method consists of two stages, stamping-based planarization and S-FIL. In stamping-based planarization, a planarization layer of transparent polymer is formed onto the flexible substrate. Waviness of the blank stamp (in this study, glass wafer) is transferred to the planarization layer. S-FIL is performed with the nanoimprint tool IMPRIO100 directly onto the planarization layer employing a 1 x 1 in. quartz stamp. Optical microscope and SEM images of the successfully imprinted patterns were also presented.

Overcoming material challenges for replication of “motheye lenses” using step and flash imprint lithography for optoelectronic applications

In this article, the fabrication and characterization of two-dimensional (2D) and three-dimensional (3D) structures using focused ion beam milling onto templates for step and flash imprint lithography (S-FIL) is discussed. It has been discovered that the 2D linewidth and height are closely related to the ion dose. At low doses (∼1pC∕μm2), the surface of the quartz template swells, thus, affecting the shape of the subsequent imprint. Furthermore, it has been shown that during UV curing of the S-FIL resist, the polymeric resist layer contracts as it solidifies, resulting in a dimensionally reduced replication of the original structure. The authors introduce a method to overcome the problem for 3D patterns, using a “multilayer” imprinting technique and apply this technique to the fabrication of “motheye” lenses. With respect to the imprinted replica, they show that the feature profile using this approach has a high fidelity in comparison to the template structure, and thus motheye lenses can be consistently replicated employing the S-FIL technology.

Patterned wafer defect density analysis of step and flash imprint lithography

Acceptance of imprint lithography for complementary metal-oxide semiconductor (CMOS) manufacturing will require demonstration that it can attain defect levels commensurate with the requirements of cost-effective device production. This article specifically focuses on this challenge presenting the current status of defect reduction in step and flash imprint lithography (S-FIL). The results of defect inspections of wafers patterned using S-FIL are summarized. The masks or templates used to imprint wafers for this study were designed specifically to facilitate automated defect inspection. The templates were made by employing CMOS industry standard materials and exposure tools. The primary wafer inspection was performed using a KLA Tencor-2132 (KT-2132) automated patterned wafer inspection tool. Additional imprint inspections were carried out on a KT-eS32 e-beam inspection system. The first section of the article provides a brief background of S-FIL technology. Next, the defect types and potential sources are described. Section III contains recent results demonstrating defect reduction below 5cm−2 and the result of a high resolution e-beam inspection that provide insight into sub-50-nm S-FIL specific defects. A brief summary concludes the article.

Degradable Cross-Linkers and Strippable Imaging Materials for Step-and-Flash Imprint Lithography

The ability to produce tough, cross-linked networks that can, if necessary, be rendered soluble by an external stimulus such as acid or heat is highly desirable for a number of applications. An acetal containing diacrylate, 2,2-di(acryloyloxy-1-ethoxy)propane (ADA) (1), was synthesized by transketalization with 2-hydroxyethyl acrylate. Its photopolymerization kinetics were measured by real-time FT-IR and its degradation in acidic organic solvents was evaluated. Additionally, a diacrylate cross-linker containing a thermally labile Diels−Alder (DA) linkage (2) was synthesized and its reversibility was evaluated using solid-state NMR spectroscopy. The DA cross-linker (2) and ADA (1) were evaluated for use in Step-and-Flash Imprint Lithography (S-FIL). Finally, a dimethacrylate cross-linker containing a thermally labile urethane-oxime linkage (10) was synthesized. Its copolymerization with methyl methacrylate and reversibility were evaluated by size exclusion chromatography (SEC) and 1H NMR spectroscopy.

Characterisation of the SilSpin etch-back process for nanolithography with CHF&lt;SUB align=right&gt;3 and O&lt;SUB align=right&gt;2 gas chemistry

This study characterises the SilSpin™ etch-back process within the reverse tone Step and Flash Imprint Lithography (SFIL/R). Currently, the S-FIL/R operational specifications to etch the SilSpin material require a reactive ion etching platform which etches the polymers at a slower rate than a high density plasma reactor. The goal was to develop empirical etch models and determine the process parameters in the etching process using a magnetically enhanced reactive ion etching reactor with CHF3 and O2 gas chemistry. The experimental approach taken uses a 24 factorial design to characterise the relationships between the process factors and etch responses. The factors in the design are: reactor pressure, power, gas flow and magnetic flux. The factors and their interaction levels to uniformly etch the SilSpin were determined along with the best set of operating parameters. Using these results in conjunction with response surface methodology enabled the development of empirical etch behaviour models.

Fabrication of complex 3D structures using Step and Flash Imprint Lithography (S-FIL)

In this paper, the use of Focused Ion Beam (FIB) milling as an alternative technology to electron-beam lithography in production of complex 3-D-structures such as “Motheye” lenses for Step and Flash Imprint Lithography (S–FIL) templates is discussed. Alterations introduced to conventional template fabrication techniques and the advantages and disadvantages of the proposed template fabrication method over conventional routes are discussed. Comparing the template and replication, we show that the surface topographies are almost identical, and thus FIB milled structures can be consistently replicated employing the S–FIL technology.

Highly parallel fabrication of nanopatterned surfaces with nanoscale orthogonalbiofunctionalization imprint lithography

Large areas of nanopatterns of specific chemical functionality are needed for biologicalexperiments and biotechnological applications. We present nanoscale orthogonalbiofunctionalization imprint lithography (NOBIL), a parallel top-down imprinting andlift-off technique based on step-and-flash imprint lithography (SFIL) that is able to createcentimetre-scale areas of nanopatterns of two biochemical functionalities. A photoresistprecursor is polymerized with a template in place, and the thin resist layer is etched tocreate an undercut for lift-off. Gold nano-areas on a silicon dioxide background are thenindependently functionalized using self-assembly that translates the nanopattern into acell-adhesive/cell-rejective functionality pattern. We demonstrate the technique by creatingfibronectin areas down to a pattern size of 60 nm against a polyethylene glycol(PEG) background, and show initial results of cells stably seeded over an array of1 mm2 areas of controlled size and pitch.

Fogging effect correction method in high-resolution electron beam lithography

We report on a fogging effect correction (FEC) method to be used in high-resolution e-beam lithography (EBL). In the new version of the previously presented PROX-In software tool, originally developed to determine the numerical proximity parameters for the proximity effect correction (PEC), was now implemented also the possibility of correcting large-range pattern distortion effects in connection with the modified PROXECCO TM tool from PDF Solutions. This allows a complex exposure optimization by dose modulation of long-range fogging and/or loading effects with the standard PEC method using the same corrector. The presented approach is fast and effective, does not use any special additional technology steps and uses only standard high-resolution measuring techniques. The reviewed method was successfully implemented into mask production at different absorber stacks. It is also used for the determination of FEC input parameters and complex exposure optimization in e-beam direct write and step and flash imprint lithography (SFIL) template manufacturing with sub-50 nm resolution capability.

Quantifying release in step-and-flash imprint lithography

Step-and-flash imprint lithography (S-FIL) is a leading candidate as the next-generation lithographic technique for replicating sub-10-nm features. The success of this technique is largely connected to the proper control of the interface formation and separation during the imprinting process. In particular, the release process of the imprinted layer from the master template is not straightforward. During release, the path of interface separation must follow precisely the complex topography of geometric features on the sub-100-nm length scale. While the issue of release is currently being addressed, more work is required to understand the underlying mechanisms in controlling release to increase the robustness of this technique in order to make it industrially viable. In this article, the authors describe a metrology for quantifying release in S-FIL. They show that the surface property and the elastic modulus of the template material control the release characteristics. They demonstrate that substituting the rigid template with a soft, elastomeric template can drastically lower the separation force necessary for release.

Implementation of an imprint damascene process for interconnect fabrication

Advanced integrated circuits require eight or more levels of wiring to transmit electrical signal and power among devices and to external circuitry. Each wiring level connects to the levels above and below it through via layers. The dual damascene approach to fabricating these interconnected structures creates a wiring level and a via level simultaneously, thereby reducing the total number of processing steps. However, the dual damascene strategy (of which there are several variations) still requires around 20 process steps per wiring layer. In this work, an approach to damascene processing that is based on step-and-flash imprint lithography (SFIL) is discussed. This imprint damascene process requires fewer than half as many steps as the standard photolithographic dual damascene approach. Through use of a template with two tiers of patterning, a single imprint lithography step can replace two photolithography steps. Further improvements in efficiency are possible if the imprint material is itself a functional dielectric material. This work is a demonstration of the compatibility of imprint lithography (specifically SFIL) with back-end-of-line processing using a dual damascene approach with functional materials.

Direct pattern transfer for sub-45 nm features using nanoimprint lithography

Recent advancements made in step and flash imprint lithography (S-FIL) have enhanced the attractiveness of nanoimprint technology for sub-100 nm resolution. Improvements in the area of material dispensing and refinement of the etch barrier itself have resulted in more uniform printing while producing a much thinner residual layer. These improvements, coupled with changes to the etch processes have facilitated direct pattern transfer of sub-45 nm line/space (1:3) features. This leading-edge research could define the pathway for nanoimprint to become a competitive solution for advanced high resolution pattern transfer.

Simulation of fluid flow in the step and flash imprint lithography process

Step and flash imprint lithography (SFIL) is a photolithography process in which the photoresist is dispensed onto the wafer in its liquid monomer form and then imprinted and cured into a desired pattern instead of using traditional optical systems. The mask used in the SFIL process is a template of the desired features that is made using electron beam writing. Several variable sized drops of monomer are dispensed onto the wafer for imprinting. The base layer thickness at the end of the imprinting process is typically about 50 nm, with an approximate imprint area of 1 in 2. This disparate length scale allows simulation of the fluid movement between the template and wafer by solving governing equations of fluid mechanics simplified by lubrication theory. Capillary forces are also an important factor governing fluid movement; a dimensionless capillary number describes the relative importance of these forces to the viscous forces in the fluid. This paper presents a simulation to model the flow and coalescence of the multiple fluid drops and the effect the number of drops dispensed has on imprint time. The imprint time is shown to decrease with increasing numbers of drops or with an applied force on the template. Appropriate filling of features on the template is an important issue in SFIL, which is presented in this study by simulating the interface movement into and around the feature by a modified boundary condition on the governing equations. It is found that above a critical aspect ratio, features do not fill and fluid does not spread outside the mask edge. The simulation provides a predictive tool for understanding and optimizing fluid management in SFIL.

Selective dry etch process for step and flash imprint lithography

In order for Step and Flash Imprint Lithography (S-FIL) to be considered a viable printing technology to produce sub-100 nm geometries, a reliable pattern transfer etch process needs to be established. Unlike optical lithography processes, imprinting features via S-FIL creates a residual layer of several hundred angstroms thick, which requires a break-through etch prior to etching the transfer layer. Of greater concern is the etch barrier used as the imaging layer for S-FIL technology. The incorporated silicon content is limited to approximately nine percent, and the formulation is geared toward achieving mechanical properties for the imprinting process. As a result, typical oxygen-based plasmas used for transferring more conventional bi-layer structures are not compatible with the current S-FIL resist stack. A reducing chemistry using ammonia (NH 3) plasma has been developed in providing a selective etch process for pattern transfer using S-FIL technology. The development of this NH 3-based process was a key enabler in the fabrication of the world’s first surface acoustic wave filters patterned via S-FIL technology.

Nanofabrication with step and flash imprint lithography

Step and flash imprint lithography (SFIL) has made tremendous progress since its initial development at The University of Texas at Austin in the late 1990s. The SFIL process went from laboratory to commercialization in under five years, and the number of technical hurdles that must be cleared before it is recognized as fully competitive with optical or EUV lithography for sub-50-nm patterning is dwindling. Patterning resolution has been demonstrated down to 20 nm, with the limit so far being only the template fabrication process. The SFIL method was developed from the beginning with the precision overlay/alignment requirements of multilevel device fabrication in mind. It was recognized that it would be inherently easier to achieve overlay and alignment accuracy with a constant temperature and low pressure imprinting process, and already tool designers have built on SFIL's advantages to produce tools that are viable for multilayer device fabrication. Early tools have demonstrated better than 10-nm alignment resolution, and no insurmountable fundamental issues have been identified that would prevent alignment resolution from reaching the tight tolerances required for integrated circuit manufacturing. With any contact printing method, process-generated defects are a concern, but the SFIL process has proven to be surprisingly robust with an inherent self-cleaning mechanism for removing particle contamination. Furthermore, new template surface treatments have been developed that improve mold lifetime and minimize defect generation. SFIL shows promise as a low cost manufacturing tool for a wide variety of semiconductor, microelectromechanical, optoelectronic, microfluidic, and other devices. This work summarizes the state of development of step and flash imprint lithography and discusses its potential as a general nanofabrication tool.

Repair of step and flash imprint lithography templates

In order for step and flash imprint lithography (S-FIL) to become a truly viable manufacturing technology, infrastructure including template repair must be commercially available. Extensive template repair studies were undertaken using RAVE’s nm 650 tool which is predicated on an AFM platform and relies upon a nanomachining technique for opaque defect removal. On S-FIL templates, the standard deviation for depth repairs in quartz from the target depth was found to be 3.1nm (1σ). At 21.5nm (1σ), the analogous spread in edge placement data for opaque line protrusions was somewhat higher. Trench cuts through lines were successfully created with a minimum size of about 55nm. The effectiveness of the repairs on the template was verified by imprinting experiments. The range of depth offsets studied (−15to+15nm) had no bearing on the imprinting process. The edge placement on wafers virtually mirrored the edge placement of the repaired templates. Connections between features which were created by trench cuts on the template were filled with the imprint monomer and measured slightly larger than the minimum gap size. Finally, imprinted wafers were used to pattern transfer features into 100nm of oxide.

Fabrication of a surface acoustic wave-based correlator using step-and-flash imprint lithography

We report the surface acoustic wave (SAW) correlator devices fabricated using nanoimprint lithography. Using step-and-flash imprint lithography (S-FIL), we produced SAW correlator devices on 100mm diameter z-cut LiNbO3 devices and an aluminum metal etch process. On the same chip layout, we fabricated SAW filters and compared both the filters and correlators to similar devices fabricated using electron-beam lithography (EBL). Both S-FIL- and EBL-patterned correlators and SAW filters were analyzed using a bit-error rate tester to generate the signal and a parametric signal analyzer to evaluate the output. The NIL filters had an average center frequency of 2.38GHz with a standard deviation of 10MHz. The measured insertion loss averaged −31dB. In comparison, SAW filters fabricated using EBL exhibited a center frequency of 2.39GHz and a standard deviation of 100kHz. Based on our preliminary results, we believe that S-FIL is an efficient and entirely viable fabrication method to produce quality SAW filters and correlators.