Imprint Lithography Templates Research Articles

Automating the mode of the electron-probe control of templates for imprint lithography

Problems of selecting the optimum parameters of electron-probe systems when scanning areas on the order of 1 cm2 with resolutions of 3–20 nm and the real-time control of these parameters during scanning are considered. The obtained dependences open the possibility of solving certain problems in fully automating the acquisition of information.

Fabrication of three-dimensional imprint lithography templates by colloidal dispersions

Self-aligned imprint lithography (SAIL) enables the patterning and alignment of submicron-sized features on metre-scaled flexible substrates in the roll-to roll (R2R) environment. SAIL solves the problem of precision interlayer registry on a moving web by encoding all the geometry information required for the entire patterning steps into a monolithic three-dimensional mask that is imprinted on the thin film stack deposited on a flexible substrate. Soft molds made of plastics or elastomers cast on a silicon master have been used as stamps to pattern the 3D masks because of their low cost and ease of fabrication. However, the durability of these stamps is one factor that limits their efficiency in a R2R process. Fluorothermoplastics are low cost imprint stamp materials with great mechanical strength and chemical compatibility but with low gas permeability that trap air bubbles in the photopolymer during the imprint process. This paper describes the strategy for increasing gas permeability of fluorothermoplastics by introducing voids or pores in the stamp material by fabricating the stamps with aqueous colloidal dispersions of tetrafluoroethylene–hexafluoropropylene copolymer (FEP) nanoparticles. The basic idea is that the hard fluorinated particles, whose modulus is too high to deform during drying, remain as hard spheres and lead to a porous packing when drying is complete. The selection of suitable additives to eliminate cracks created by capillary stresses during water evaporation is also described in this paper.

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.

Fabrication and validation of fused silica NIL templates incorporating different length scale features

A cost effective methodology for pattering of Nano Imprint Lithography (NIL) templates incorporating different length scale features is proposed. The approach relies on selecting the optimum processing window of different technologies for cost effective micro- and nano-patterning. Very promising results were obtained when first fused silica templates were structured by F2 laser ablation at 157 nm. It was demonstrated that nano-scale features and complex 3D micro-scale features could be machined with a Focused Ion Beam (FIB) over the existing topography produced by laser ablation. Thus, a large area (up to several square centimeters) of the NIL templates is easily patterned with micro- and even meso-scale features by laser ablation while nano- and micro-scale features could be introduced locally by FIB machining. Through S-FIL process such templates were validated and the nano- and micro-structures were accurately replicated in one imprinting step.

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.

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.

Comprehensive defect analysis methodology for nano imprint lithography

Because of the non traditional elements involved in both the manufacture of nano imprint lithography (NIL) templates [T. DiBiase, J. Maltabes, B. Reese, M. Ahmadian, SPIE 6151 (2006)] and the resulting features printed on substrates, methods and procedures for effectively locating, tracking and identifying defect mechanisms need to be modified and refined from the traditional methods employed by the semiconductor industry [I. Peterson, G. Thompson, T. DiBiase, S. Ashkenaz, R. Pinto, Yield Management Solutions, KLA-Tencor Spring, (2000)]. Since NIL involves pattern structures defined at 1× magnification, there is no defect “forgiveness” such as with conventional 4× optical reduction lithography. In addition, NIL is performed with the patterning tooling (template) in full contact with the casting material (in this case, UV curable monomer) used to define the final features on the substrate of interest. Surface chemistry and substrate interactions quickly become obvious crucial factors in defect formation mechanisms. This article describes a few non-traditional approaches to working with the extreme dynamic range of defect types found in the step and repeat NIL process.

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.

Imprint lithography template fabrication for emerging market applications

Imprint lithography template fabrication for emerging market applications

Polyvinyl alcohol templates for low cost, high resolution, complex printing

Templates for imprint lithography and MxL (molecular transfer lithography) are generated by adhesion of a spin-cast film of polyvinyl alcohol (PVA) to a carrier comprised of materials selected for conformability or distortion reduction. Template formation using both polymeric carrier materials and rigid materials, including quartz and glass carrier materials, is demonstrated. The absence of a carrier material altogether to form a suspended thin film is shown to be feasible. The rigid template material is formed by bonding the PVA patterned film to a rigid carrier while still connected to the master pattern, and it is demonstrated that separation occurs at the PVA-silicon master pattern interface. Form factors for the templates include a 25mm×25mm patterned film attached to a 65mm×65mm glass substrate, a full 100 mm pattern bonded to a quartz substrate, and a 100 mm mask of Mylar™ bonded with a patterned PVA film for MxL applications. These carrier materials are developed in a form factor compatible with commercial nanoimprint lithography tools, and for standard contact aligners adapted to perform MxL processing.

Inspection of templates for imprint lithography

Masks of any next generation lithography (NGL), such as imprint lithography, must eventually achieve and maintain the very low defect counts of current production masks. This requires typically fewer than 10 or even no defects over the entire field. We describe an inspection methodology and how it can be applied to the imprint template. Special test patterns etched onto the template enable both a die to die comparison, to find nuisance defects, and also calibration of sensitivity to different types of preprogrammed defects. A state of the art deep ultraviolet photomask inspection system (KLA-Tencor model 526) can detect these rare events with about 70nm threshold for imprint masks with reflection mode contrast. Initial scans are made at various stages of the imprint process: the newly processed mask, after dicing, and after several imprints. The scans show mostly isolated point defects at a density of ∼10–100permm2. This is an encouraging start for a new NGL, and reductions are expected from better processes, equipment, and handling. In the future viable mask inspection at the 45–22nm node will be very demanding for these 1× masks and will require sensitivities approaching 10–20nm defect size. To this end, special masks suitable for electron (e)-beam inspection are being made and show good contrast and immunity to e-beam charging.

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 step and flash imprint lithography templates using a variable shaped-beam exposure tool

If imprint lithography is to be considered as a viable method for fabricating high density silicon-based circuits, an infrastructure must be established that is capable of supplying users with 1X templates. It is critical, therefore, that tools are available that can expose, inspect, and repair these templates. The purpose of this work is to present initial step and flash imprint lithography template results using a shaped-beam system. A Leica SB350 MW was used to expose ZEP 7000 resist. The SB350 is a variable shaped-beam tool with 50 kV electron optics. A Motorola template pattern transfer process was used to obtain final images in the template. Trenches as small as 33 nm were resolved, as were 44 nm holes. Further improvements may be possible by increasing the operating voltage to 100 kV, and further increasing the e-beam system line edge acuity.

Simulating fabrication and imprinting distortions in step-and-flash imprint lithography templates

Simulating fabrication and imprinting distortions in step-and-flash imprint lithography templates

Initial study of the fabrication of step and flash imprint lithography templates for the printing of contact holes

Step and flash imprint lithography (S-FIL) is an attractive method for printing sub-100-nm geometries. Relative to other imprinting processes, S-FIL has the advantage of the template being transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, minimizing magnification and distortion errors. As a result, it may be possible to use S-FIL to build integrated circuits. The purpose of this work is to investigate the fabrication methods needed to form templates capable of printing sub-100-nm contact holes. A positive resist process is used to image both holes and pillars on the template. After fabrication, the templates are used to print both contacts and pillars. The dense 80-nm imprinted contacts measure 65 nm, a consequence of undersizing on the template. For relaxed pitches, contacts smaller than 30 nm are observed. Pillars as small as 50 nm are also cleanly printed. At 40 nm, pillar size is inconsistent, and missing pillars are evident. Modifications to the template fabrication process will be necessary to study the feasibility of printing even smaller contacts and pillars.

Simulating fabrication and imprinting distortions in step-and-flash imprint lithography templates

Step-and-flash imprint lithography (SFIL) is a novel approach for producing chips with sub-45-nm features. The technology uses a quartz template to imprint a dispensed polymer solution on the device wafer in a 1 × pattern-transfer process. The accuracy of the imprint fabrication technology requires minimization of the errors associated with the template fabrication, appropriate dispensing of the polymer, and reduction of template distortion during the interaction with the polymer and the device wafer as a result of the imprint. In this paper, two key issues, template fabrication and polymer dispensing, are investigated with numerical models in order to characterize the response of system components during the SFIL process. The template distortion during fabrication is simulated using finite-element models and the polymer solution dispensing is modeled using computational fluid dynamics simulations.

Image placement issues for ITO-based step and flash imprint lithography templates

Step and flash imprint lithography (SFIL) is an attractive, low-cost method for printing sub-100 nm geometries. The imprint process is performed at low pressures and room temperature, which minimizes magnification and distortion errors. Since SFIL is a 1× lithography technology, the template will require precise image placement in order to meet overlay specifications for multiple level device fabrication. In order to simplify the template fabrication process and facilitate post fabrication scanning-electron-microscope-based inspection, an integrated charge dissipation layer, such as indium tin oxide (ITO), is desired that is transparent to the SFIL exposure wavelength. The use of low-stress dielectric films such as SiON for the image relief layer minimizes the pattern distortions (&amp;lt;9 nm, mean+3σ) that occur after the pattern transfer process. Although ITO uniformity was also significantly improved by switching the ITO deposition process to an MRC sputter deposition system, image placement results were adversely affected.

Step and flash imprint lithography template characterization, from an etch perspective

As a means of studying process windows with short turnaround time while avoiding substrate-to-substrate repeatability issues, Step and Flash Imprint Lithography templates were fabricated with physical masking of quadrants during dry etching used to introduce process perturbations. For every 20 s of descum (Ar/O2 etch) time, critical dimensions (CD) were observed to change approximately 2.6 nm on sub-100 nm features. Similarly, increasing Cr overetch time by 20% resulted in a positive CD change of 3.8 nm. Line edge roughness decreased with increasing descum and Cr overetch times. Best overall performance was observed for a 20 s descum used in conjunction with a 110% Cr overetch. Of four tip types studied, sharpened silicon atomic force microscopy tips were able to accurately measure etch depth of 80 nm trenches, but geometrical considerations limited sidewall angle determination to greater than 100°. Cross-sectioning of features on 6×6×0.25 in. quartz plates was successfully accomplished using a focused ion beam technique with typical sidewall angles of about 95° observed on 150 nm features. Finally, minimal microloading was observed for the ICP-based quartz etch process. Feature sizes ranging from 70 nm up to 8 μm possessed an average etch depth of 88.8 nm with a 1.2 nm (1 sigma) variation.

Improved step and flash imprint lithography templates for nanofabrication

Step and flash imprint lithography (SFIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes, SFIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, which minimizes magnification and distortion errors. Several different methods for fabricating templates are presented in this study. One scheme addresses some of the weaknesses associated with a solid glass substrate by incorporating a conductive and transparent layer of indium tin oxide (ITO) on the surface of the substrate. Features are defined on the templates by patterning a thin layer of PECVD oxide that is deposited on the ITO layer. A second method bypasses the oxide etch process by imaging a thin layer of hydrogen silsesquioxane (HSQ). By using a combination of these two methods, it is also possible to form multi-tiered structures on a template. Templates with features as small as 20 nm have been fabricated using the methods described above. The templates were then used to imprint patterns on 200 mm silicon wafers. It appears that any feature defined in the template is faithfully replicated on the wafer.

Fabrication of multi-tiered structures on step and flash imprint lithography templates

Step and flash imprint lithography (SFIL) replicates patterns by using a transparent template with relief images etched into its surface. Recent work has examined alternative methods for template fabrication. One scheme incorporates a conductive and transparent layer of indium tin oxide (ITO) on the surface of the substrate. Features are defined on the templates by patterning a thin layer of PECVD oxide that is deposited on the ITO layer. A second method bypasses the oxide etch process by imaging a thin layer of hydrogen silsesquioxane (HSQ). By combining or iterating the two methods, it is possible to form multi-tiered structures on a template. Two and three tier structures were fabricated on silicon wafers and templates. A two layer structure was fabricated on a quartz photoplate by patterning PECVD oxide and subsequently patterning a second tier using HSQ. The resulting relief structures were successfully replicated on wafers using SFIL.