A paper must meet four criteria before it is publishable in a scientific journal. •The content of the paper must match the scope of the journal •The quality of the paper (method and execution of the research, as well as the writing) must be sufficiently high •It must present novel results (with the exception of review papers and the like) •The results must be significant enough to be worth reading about (and thus worth publishing). After a quick review of the first three items, I’d like to spend some time talking about the last item, paper significance.

For a feature of finite length, linewidth roughness leads to variations in the mean feature width. Typically, numerical simulations are used to explore this relationship. An analytical approach is used. Starting with a common expression for the power spectral density, an analytical expression relating critical dimension uniformity to linewidth roughness is derived. The derived expression matches simulation results extremely well and can be used to understand more fully the detrimental impact of feature roughness on lithographic results. Finally, based on this expression, a new metric of linewidth roughness is proposed.

Miniaturized cantilevers are one of the elementary structures that are widely used in many micro-devices and systems. The dynamic performance of micro-cantilevers having process dictated through perforations is investigated. High-aspect ratio, long silicon cantilevers, intended for improved performance through lowered stiffness are designed with a series of through holes and simulated along with similar nonperforated/solid cantilevers for comparison. A few perforated structures are also fabricated using silicon-on-insulator-based multiproject MEMS processes from MEMSCAP Inc. (Durham, North Carolina) by reduced mask level and eliminating complex substrate trenching step. The dynamic behavior of these fabricated structures is experimentally studied for both in-plane and out-of-plane directions. It is shown that, due to the presence of perforations, stiffness in planar direction is lightly affected, whereas in out-of-plane direction it is significantly reduced by <35% . Similarly, the variation of damping in both perforated and nonperforated beams, too, is thoroughly analyzed for the first few modes of vibration. Nevertheless, their frequency response variation of <10% for modal frequencies in both planar and out-of-plane directions as compared to the nonperforated counterparts, points to potential applications in several micro-systems including those based on comb drives.

We present the limit of a conventional photomask writer and new possibilities to meet various requirements of tight specifications for a sub-10 nm device. The issues of a variable shaped beam (VSB) writer and how to overcome the limit by computational techniques are discussed. Because VSB writing can use only one rectangular or triangular beam per shot, the complex design for computational lithography results in the increase of shot number to implement rounded or angled pattern. Based on model-based-fracturing, we have confirmed that the ideal curvilinear pattern can be optimized by using overlapping shots, and that they have the same patterning performance in mask and wafer. On the other hand, the multibeam writer can make ideally any kinds of shapes, even curvilinear design because the combination of small spots writes a design. In a real situation, each spot of multibeam writer is defined at fixed mesh and each beam has discrete dose level, so that there are fidelity errors if the pixel size is large or the dose level is not enough large. Here, we propose a “Buddhist cross” design as the evaluation pattern of digitization error in a multibeam writer. The “fidelity error” smaller than 0.5 nm error requires 5 nm pixel size and the required minimum number for dose level is 7 to implement a smaller error than 0.05 nm at one edge. To realize new technology for mass production, new data flow, model based pattern verification, and required computing power have been presented.

Robust inverse mask synthesis is computationally intensive, and its turnaround time continues to rise hand-in-hand with the ever-shrinking integrated circuit feature size. We report the development of a cascadic multigrid (CMG) algorithm for robust inverse mask synthesis, which starts from a relatively coarse mask grid and refines it iteratively in stages, so as to achieve significant speedup without compromising numerical accuracy. Since the CMG algorithm entails frequent changes of the computational grid size, we need to intentionally introduce an analytical circle-sampling technique for modeling the forward lithography imaging and employ an edge distance error as metric to guide mask synthesis. These two techniques work nicely with variable grid sizes and are well suited for our CMG algorithm. As a result, our algorithm achieves more than four times speedup over conventional methods that synthesize a mask on a fixed fine grid. Numerical results are presented to demonstrate the validity and efficiency of the proposed method.

We describe a fabrication method for arrays of microlenses of low f -number by using a surface coating and dispensing technology. We demonstrate how to achieve a low f-number by selectively changing the surface wettability, as well as how to precisely control the f -number through control of the dispensing time. This advance enables the fabrication of arrays of microlenses with diameters varying from 400 to 1400 μm, f -number as low as 0.95. In addition, the optical performance tests indicate that this method is suitable for high performance microlens array fabrication. This dispensing technology may be low cost and allow fast fabrication of high-speed microlens arrays, and may thus be particularly useful for biologically inspired advanced optical systems.

Although extreme ultraviolet lithography (EUVL) remains a promising candidate for semiconductor device manufacturing of the 1× nm half pitch node and beyond, many technological burdens have to be overcome. The “field edge effect” in EUVL is one of them. The image border region of an EUV mask, also known as the “black border” (BB), reflects a few percent of the incident EUV light, resulting in a leakage of light into neighboring exposure fields, especially at the corner of the field where three adjacent exposures take place. This effect significantly impacts on critical dimension (CD) uniformity (CDU) across the exposure field. To avoid this phenomenon, a light-shielding border is introduced by etching away the entire absorber and multilayer at the image border region of the EUV mask. We present a method of modeling the field edge effect (also called the BB effect) by using rigorous lithography simulation with a calibrated resist model. An additional “flare level” at the field edge is introduced on top of the exposure tool flare map to account for the BB effect. The parameters in this model include the reflectivity and the width of the BB, which are mainly determining the leakage of EUV light and its influence range, respectively. Another parameter is the transition width which represents the half shadow effect of the reticle masking blades. By setting the corresponding parameters, the simulation results match well the experimental results obtained at the IMEC’s NXE:3100 EUV exposure tool. Moreover, these results indicate that the out-of-band (OoB) radiation also contributes to the CDU. Using simulation, we can also determine the OoB effect rigorously using the methodology of an “effective mask blank.” The study demonstrates that the impact of BB and OoB effects on CDU can be well predicted by simulations.

Smoothing effects of postlithography plasma treatments on 22-nm lines and spaces are evaluated for two types of extreme ultraviolet photoresists, using five different plasma processes (Ar, H ₂ /Ar , HBr, H ₂ /N ₂ , and H ₂ ). Experimental results indicate a reduction in linewidth roughness of about 10% by using an H ₂ plasma smoothing process. This smoothing process is mainly triggered by the synergy of vacuum ultraviolet photons and H ₂ reactive species during the plasma treatment. Moreover, the smoothing process is dependent on the resist composition and the pattern dimensions. This paper shows the impact of different plasma conditions on roughness reduction for 22-nm lines.

We fabricated large-area stacked complementary plasmonic crystals (SC PlCs) by employing ultraviolet nanoimprint lithography. The SC PlCs were made on silicon-on-insulator substrates consisting of three layers: the top layer contacting air was a perforated Au film, the bottom layer contacting the buried oxide layer included an Au disk array corresponding to the holes in the top layer, and the middle layer was a Si photonic crystal slab. The SC PlCs have prominent resonances in optical wavelengths. It is shown that the fabricated PlCs were precise in structure and uniform in their optical properties. We examined the photoluminescence (PL) enhancement of monolayer dye molecules on the SC PlC substrates in the visible range and found large PL enhancements of up to a 100-fold in comparison with dye molecules on nonprocessed Si wafers.

This paper describes a method that contains a series of processes for producing three-dimensional (3-D) microstructures with a feature size in the submicrometer scale. It starts from using a metal contact printing lithography to pattern a thin metal film on the surface of a (100) silicon substrate. The metal film has a hole-array pattern with a hole diameter ranging from 300 nm to 800 nm and is used as an etching mask for silicon bulk machining to create concave pyramid-shaped surface microstructures. Using this bulk-machined silicon substrate as a template, polymer 3-D microstructures are replicated on top of a silicon dioxide (SiO ₂ ) layer. Finally, through a dry etching process, 3-D microstructures with a profile similar to the replicated polymer microstructures are formed on the SiO ₂ layer. Potential applications of these fabricated SiO ₂ microstructures in the light-emitting diode industry will be addressed.

Neural probes contain the potential to cause injury to surrounding neural cells due to a discrepancy in stiffness values between them and the surrounding brain tissue when subjected to mechanical micromotion of the brain. To evaluate the effects of the mechanical mismatch, a series of dynamic simulations are conducted to better understand the design enhancements required to improve the feasibility of the neuron probe. The simulations use a nonlinear transient explicit finite element code, LS-DYNA. A three-dimensional quarter-symmetry finite element model is utilized for the transient analysis to capture the time-dependent dynamic deformations on the brain tissue from the implant as a function of different frequency shapes and stiffness values. When micromotion-induced pulses are applied, reducing the neuron probe stiffness by three orders of magnitude leads up to a 41.6% reduction in stress and 39.1% reduction in strain. The simulation conditions assume a case where sheath bonding has begun to take place around the probe implantation site, but no full bond to the probe has occurred. The analyses can provide guidance on the materials necessary to design a probe for injury reduction.

We present a series of baseline techniques for inspection, cleaning, repair, and native defect mitigation of extreme ultraviolet (EUV) masks. Deep-ultraviolet inspectors are capable of inspecting patterns down to about 45 nm in pitch on wafer. Cleaning methods involving both chemical and physical forces have achieved good particle removal efficiency while minimizing absorber shrinkage and have realized 90% PRE in removing particles from the backside of an EUV mask. In addition, our compensation method for native defect repair has achieved partial success.

We report about optical spectrometry using gold nanostructures printed on top of an integrated optical waveguide. The optical waveguide is a single-mode buried waveguide made from a combination of photo-polymerizable materials and is fabricated by photolithography on a glass substrate. To detect the electric field inside the waveguide, a gold nanocoupler array of thin lines (50 nm thick and 8 μm in length) is embedded on top of the aforementioned waveguide. They are produced by e-beam lithography. Both waveguide ports are polished, and the output port, in particular, is coated with a thin gold layer to assimilate a mirror and hence, it enables the creation of stationary waves inside the structure. Stationary waves generated inside the guide constitute a spatial interferogram. Locally, light is out-coupled using the nanocouplers and allows measuring the interferogram structure. The resulting pattern is imaged by a vision system involving an optical microscope with the objective lenses of different magnifications and a digital camera mounted on top of the microscope. The 5× objective lens demonstrates a superior performance in retrieving the investigated spectrum compared to 20× and 100× objectives. Fast Fourier transform is performed on the captured signal to extract the spectral content of the measured signal.

Influences of phase defect structures on extreme ultraviolet (EUV) microscope images were examined. Phase defects on the bottom of a multilayer (ML) do not always propagate vertically upward to the ML’s top surface. For this study, two types of masks were prepared. One was an EUV blank with programmed phase defects made of lines in order to analyze the inclination angle of the phase defects. The other was an EUV mask that consists of programmed dot type phase defects 80 nm wide and 2.4 nm high with absorber patterns of half-pitch 88-nm lines-and-spaces. The positions of the phase defects relative to the absorber lines were designed to be shifted accordingly. Transmission electron microscope observations revealed that the line type phase defects starting from the bottom surface of the ML propagated toward the ML’s top surface, while inclined toward the center of the EUV blank. At the distances of 0 and 66 mm from the center of the EUV blank, the inclination angles varied from 0 to 4 deg. The impacts of the inclination angles on EUV microscope images were significant even though the positions of the phase defect relative to the absorber line, as measured by a scanning probe microscope, were the same.

In this study, we developed a microarray bio-MEMS device that could trap PC12D (rat pheochromocytoma cells) cells to examine the intercellular interaction effect on the cell activation and the axonal extension ability. This is needed to assign particular patterns of PC12D cells to establish a cell functional evaluation technique. This experimental observation-based technique can be used for design of the cell sheet and scaffold for peripheral and central nerve regeneration. We have fabricated a micropillar-array bio-MEMS device, whose diameter was approximately 10 μm, by using thick photoresist SU-8 on the glass slide substrate. A maximum trapped PC12D cell ratio, 48.5%, was achieved. Through experimental observation of patterned PC12D “bi-cells” activation, we obtained the following results. Most of the PC12D “bi-cells” which had distances between 40 and 100 μm were connected after 24 h with a high probability. On the other hand, “bi-cells” which had distances between 110 and 200 μm were not connected. In addition, we measured axonal extension velocities in cases where the intercellular distance was between 40 and 100 μm. A maximum axonal extension velocity, 86.4  μm/h, was obtained at the intercellular distance of 40 μm.

In optical lithography for microchip manufacturing, it is important that the focal ranges of all patterns in the layout be closely aligned in order to maximize a common process window. In practice, large pattern-dependent variations in the position of the best focus are observed, which have been traced back to phase errors induced on the image-forming beams by scattering from mask topography. We show that this degradation mechanism can be exploited as a source of corrective phase shift, allowing pattern-dependent focus shifts to be controlled purely by changing the details of the mask layout, without requiring a significant change in the mask-making process. Phase distortions in the imaging beams are corrected by the optimized insertion of orthogonally oriented subresolution jogs into existing edges in the layout, thereby introducing a tailored scatter contribution whose quadrature component has the opposite sign from that of the primary edge.