Automated measurement and analysis of sidewall roughness using three-dimensional atomic force microscopy.

As semiconductor device architecture develops, from planar field-effect transistors (FET) to FinFET and gate-all-around (GAA), there is an increased need to measure 3D structure sidewalls precisely. Here, we present a 3-Dimensional Atomic Force Microscope (3D-AFM), a powerful 3D metrology tool to measure the sidewall roughness (SWR) of vertical and undercut structures. First, we measured three different dies repeatedly to calculate reproducibility in die level. Reproducible results were derived with a relative standard deviation under 2%. Second, we measured 13 different dies, including the center and edge of the wafer, to analyze SWR distribution in wafer level and reliable results were measured. All analysis was performed using a novel algorithm, including auto flattening, sidewall detection, and SWR calculation. In addition, SWR automatic analysis software was implemented to reduce analysis time and to provide standard analysis. The results suggest that our 3D-AFM, based on the tilted Z scanner, will enable an advanced methodology for automated 3D measurement and analysis.

"Multipoint Force Feedback" Leveling of Massively Parallel Tip Arrays in Scanning Probe Lithography.

Nanoscale patterning with massively parallel 2D array tips is of significant interest in scanning probe lithography. A challenging task for tip-based large area nanolithography is maintaining parallel tip arrays at the same contact point with a sample substrate in order to pattern a uniform array. Here, polymer pen lithography is demonstrated with a novel leveling method to account for the magnitude and direction of the total applied force of tip arrays by a multipoint force sensing structure integrated into the tip holder. This high-precision approach results in a 0.001° slope of feature edge length variation over 1 cm wide tip arrays. The position sensitive leveling operates in a fully automated manner and is applicable to recently developed scanning probe lithography techniques of various kinds which can enable "desktop nanofabrication."

Direct-write patterning of bacterial cells by dip-pen nanolithography.

The ability of dip-pen nanolithography (DPN) to generate nano- or microarrays of soft or hard materials (e.g., small molecules, DNA, proteins, nanoparticles, sols, and polymers) in a direct-write manner has been widely demonstrated. The transporting of large-sized ink materials such as bacteria, however, remains a significant challenge with this technique. The size limitation of the water meniscus formed between the DPN tip and the solid surface becomes a bottleneck in such diffusion-based molecular transport experiments. Herein, we report a straightforward "stamp-on" DPN method that uses a nanostructured poly(2-methyl-2-oxazoline) hydrogel-coated tip and carrier agents to generate patterns of micrometer-sized Escherichia coli JM 109 bacterial cells. We demonstrate that this approach enables the deposition of a single bacterial cell array on a solid surface or arrays of layers of multiple cells by modulating the viscosity of the "ink" solution. Fluorescence microscopy images indicated that the deposited bacterial cells were kept alive on Luria-Bertani-agar layered solid surfaces after DPN patterning.

Fabrication of pseudo-crystal nanostructures of TiO2 particles under UV-irradiation.

Colloidal titanium dioxide (TiO2) suspensions were synthesized by hydrolysis of titanium isopropoxide in the presence of acetic acid. When TiO2 colloids were subjected to bandgap excitation (ultraviolet [UV] irradiation), the colloidal solution exhibited yellow coloration, leading to the trapping of holes and electrons on the particle surfaces. The absorption spectra indicated a distinct absorption band in the UV and visible region. Dried-drop film of the UV-irradiated TiO2 suspension on the mica surface was characterized by scanning electron microscopy (SEM). SEM images showed that "crystal-like" network structures of TiO2 nanoparticles had formed dramatically on the solid surface. The resulting networks ranged in size from 100 nm to 500 nm and had crystal-growth patterns, while also having almost similar rectangular shapes. It seems that the individual particles, with electron or hole scavengers such as oxygen in ambient conditions, make contact with a number of neighbors, thereby forming self-assembled three-dimensional nanoparticle-based pseudo-crystalline structures.