Direct top-down ordering of diblock copolymers through nanoimprint lithography

Novel thermoplastic polymers with improved release properties for thermal NIL

Contact hole (CH) patterning by directed self-assembly (DSA) of polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymers (BCPs) is extensively studied. Based on statistical analysis of defectivity and CD measurements after DSA, a process window (PW) for CH shrink is experimentally determined as a function of guiding pattern dimensions and BCP molecular weights corresponding to BCP natural periods. This PW permits to define the suitable BCP molecular weight and the best guiding CD ranges required to achieve a desired DSA hole CD within a specific tolerance. As an example, for a DSA hole CD targeted at 19.5 nm with 10% tolerance, circular guiding patterns of 52 nm CD with 20% guiding CD latitude are needed using a 35-nm-natural-period cylindrical BCP. Furthermore, it is shown that the CH shrink PW is also dependent on the guiding pattern density and the DSA process conditions such as the self-assembly annealing and the spin coating conditions. The study also highlights an interesting property of commensurability between guiding pattern dimensions and BCP’s natural period that governs the DSA CH patterning for both CH shrink and CH doubling configurations. This permits one to predict the guiding pattern dimensions needed for CH patterning by DSA using a given BCP of known natural period.

Nanoimprint Lithography (NIL) has demonstrated its value in manufacturing nanostructures with extremely tight tolerances for the optics industry. Doing NIL process on single samples in the lab has been displayed for a long time in industry and academia. Scaling up from one good sample to full wafer and wafer to wafer uniformity for many wafers in a row, has some obstacles to overcome. In this paper, we discuss the process repeatability of manufacturing nanostructures starting from basic line/space through various other periodic and meta structures. Demonstrating the manufacturing capability using NIL for pattering also includes the other related process steps such as thin films and etching. We discuss key metrology, process control characterization, and process stability which include thin film RI uniformity, master to print replication uniformity, and post etch structural critical dimensions uniformity (CDU). Our NIL process has achieved 1.0nm σ on line widths at 45nm. This precision of replication includes all variation introduced from multiple stamps, wafer to wafer prints, and multiple sites within the wafer. This level of process control at the masking layer needs to be maintained for the finished structure.

This research investigates deformation behavior of polystyrene (PS) as a thermoplastic resist material for the thermal nanoimprint lithography (T-NIL) process. Molecular dynamics modeling was conducted on a PS substrate with dimensions 58 × 65 × 61 Å that was imprinted with a rigid, spherical indenter. The effect of indenter size, force, and imprinting duration were evaluated in terms of indentation depth, penetration depth, recovery depth, and recovery percentage of the polymer. The results show that the largest indenter, regardless of force, has the most significant impact on deformation behavior. The 40 Å indenter with a 1 µN of force caused the surface molecules to descend to the lowest point compared to the other indenters. An increase in indenter size resulted in higher penetration depth, recovery depth, and recovery percentage. Higher durations of imprint cycle (400 fs) resulted in plastic deformation of the PS material with minimal recovery (4 Å). The results of this research lay the foundation for explaining the effect of several T-NIL process parameters on virgin PS thermoplastic resist material.

Nanoimprint lithography (NIL), as a non-conventional pattern transfer technique, presents unique competitiveness in the fabrication of semiconductor structures for medium-to-low resolution, cost-sensitive, and high-volume applications, owing to its advantages in high resolution, high throughput, low cost, and scalability. Compared with conventional lithography, NIL achieves high-precision pattern transfer beyond the optical diffraction limitation by directly imprinting and transferring patterns through mechanical contact, without relying on complex optical systems, thereby significantly reducing equipment and operational costs. This article systematically reviews the fundamental principles of NIL and its major process types, including thermal nanoimprint lithography (T-NIL), ultraviolet nanoimprint lithography (UV-NIL), and roller nanoimprint lithography (R-NIL), elaborating on the characteristics and applicable scenarios of each in terms of resolution, process conditions, substrate compatibility, throughput, and cost. Furthermore, a multi-dimensional comparison is conducted to analyze NILs competitive positioning within the current universal lithography technology landscape, while potential future development directions are outlined. Although NIL still faces challenges such as limited mold lifetime and pattern flexibility, advancements in material engineering, process optimization, and technology integration are expected to broaden its industrialization prospects.

Toward nanoporous composite membranes with tailored block copolymers as selective layer

This review concentrates on the applications of nanoimprint lithography (NIL) and hot embossing for the fabrications of nanolectronic devices, nanophotonic metamaterials and other nanostructures. Technical challenges and solutions in NIL such as nanofabrication of templates, removal of residual resist, pattern displacement in thermal NIL arising from thermal expansion are first discussed. In the nanofabrication of templates, dry etch in plasma for the formation of multi-step structures and ultra-sharp tip arrays in silicon, nanophotonic chiral structures with high aspect ratio in SiC are demonstrated. A bilayer technique for nondestructive removal of residual resist in thermal NIL is described. This process is successfully applied for the fabrication of T-shape gates and functional high electron mobility transistors. However, pattern displacement intrinsically existing in thermal NIL/hot embossing owing to different thermal expansions in the template and substrate, respectively, limits its further development and scale-up. Low temperature even room temperature NIL (RTNIL) was then proposed on HSQ, trying to eliminate the pattern distortion by avoiding a thermal loop in the imprint. But, considerable pressure needed in RTNIL turned the major attentions to the development of UV-curing NIL in UV-curable monomers at low temperature. A big variety of applications by low-temperature UV-curing NIL in SU-8 are described, including high-aspect-ratio phase gratings, tagging technology by nanobarcode for DNA sequencing, nanofluidic channels, nanophotonic metamaterials and biosensors. Hot embossing, as a parallel technique to NIL, was also developed, and its applications on ferroelectric polymers as well as metals are reviewed. Therefore, it is necessary to emphasize that this review is mainly attempted to review the applications of NIL/embossing instead of NIL technique advances.

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

ABSTRACTTo investigate template releasing process in nanoimprint lithography, template releasing energy (i.e. surface energy between the template and the resist polymer) in various releasing conditions is evaluated using multi-axial controlled releasing system. The releasing energy is in proportion to the surface free energy of the template, but does not depend on the velocity of releasing. Also, a peeling mode where the template is released from a single side and a lift-off mode where the template is removed in the perpendicular direction to the resist are examined. The result shows that the releasing energy by peeling mode is lower than that by lift-off modes.

Polymer photonic band-gaps fabricated by nanoimprint lithography

Nanoimprint lithography (NIL) is one of the most promising technologies for nanofabrication because it can create nano- and microscale structures and devices in a cost-effective manner. In the NIL process, a mold with patterns on its surface comes in contact with a polymer film on a substrate. The patterns are transferred to the polymer film and then the mold is separated from the film. Mechanical contact between the mold and the polymer film, and between the film and the substrate, is inevitable. In some cases, during the separation process, adhesion and friction forces at the interfaces can deform and fracture the transferred patterns and detach the polymer film from the substrate. Thus, controlling the adhesion and friction between the materials in contact is very important in achieving a successful pattern transfer and making the NIL process a robust nanofabrication technique. Many theoretical and experimental research efforts have been made to clarify the tribological phenomena in NIL and to reduce defects due to adhesion and friction. This article describes the tribological problems encountered and reviews the related research.

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.

Block copolymer (BCP) lithography as a low-cost and simple process emerges to become an important patterning technique in microelectronic manufacturing. In this work, self-assembly of a triblock copolymer was used to prepare silicon nanowire FinFET devices on the SOI substrate. The original pattern was formed on the block copolymer layer via self-assembly, and then transferred to the Si layer by dry etching that stops at the interface of Si and box oxide. The minimum critical dimension of the device can be as small as 8 nm, and the performance is extensively evaluated. This type of FinFET device shows high transconductance (g m ) 150 µS, signifies extremely low off current (I OFF ) ~50 pA, and high on/off current ratio (I ON /I OFF ) up to 3×10 6.

Demolding, the process to separate stamp from molded resist, is most critical to the success of ultraviolet nanoimprint lithography (UV-NIL). In the present study we first investigated adhesion and demolding force in UV-NIL for different compositions of a model UV-curable resist containing a base (either tripropyleneglycol diacrylate with shorter chain length or polypropyleneglycol diacrylate with longer chain length), a cross-linking agent (trimethylolpropane triacrylate) and a photoinitiator (Irgacure 651). The demolding force was measured using a tensile test machine after imprinting the UV resist on a silicon stamp. In general, the shorter monomer shows a larger demolding force. Decreasing the cross-linking agent content from 49 to 0 wt% results in a decreased adhesion force at the resist/stamp interface thereby facilitating the demolding. Demolding stress in general is mainly generated due to shrinkage of the resist in the UV curing step and also adhesion and friction at the stamp/resist interface in the subsequent demolding step. In the second part of this study the effect of resist compositions on the stress generation was studied by numerical simulation of the curing and demolding steps in UV-NIL. Input parameters required for the simulation were determined experimentally. As the cross-linking agent content increases the fracture strength of the resist also increases. At the same time, shrinkage stress due to cure and also adhesion at the stamp/resist interface both increase. By normalizing the overall maximum local stress by the fracture stress of the resist, we found that there is an optimum for the cross-linking agent content that leads to the most successful imprinting. In the third part of our study a simple method was developed to obtain the polymerization shrinkage stress exerted on the sidewalls of resist/stamp interface in UV NIL. This method is based on the measurements of demolding force which is the sum of adhesion and friction forces. The mean polymerization shrinkage stress on the sidewalls can readily be decoupled from overall demolding force by independently measuring the friction coefficient, adhesion force, and geometries of stamp structures. The polymerization shrinkage stress on the sidewalls is overall larger than adhesion and increases by adding more cross-linking agent to the resist composition.

Computational study of material optimization on de-molding process in nanoimprint lithography