This guest editorial by former Editor-in-Chief Chris Mack introduces JM3’s new co-editors-in-chief, Harry Levinson and Hans Zappe.

This is a list of reviewers who served the Journal of Micro/Nanolithography, MEMS, and MOEMS in 2019.

Dip-pen nanolithography (DPN) is a low-cost, versatile, bench-top technology for direct patterning of materials over surfaces. Our study reports on the production of two-dimensional optical grating nanostructures based on polymers, using DPN. The influence of both the ink composition and the dwell time were investigated. Prototypes of phase masks were manufactured, and their main characteristics were analyzed. The results in our work may contribute to improving the fabrication process of optical structures, including the production of microlenses with controlled focal length.

Background: Modern one-digit technological nodes demand strict reproduction of the optical proximity corrections for repeatable congruent patterns. To ensure this property, the optical and process simulations must be invariant to the geometrical transformations of the translation, rotation, and reflection. Simulators must support invariance both in theory, mathematically, and in practice, numerically. The invariance of compact modeling operators has never been scrutinized before.

Aim: We aim to examine manner and conditions under which optical simulations preserve or violate intrinsic invariances of exact imaging. We analyze invariances of Volterra operators, which are widely used in compact process modeling. Our goal is to determine necessary and sufficient conditions under which such operators become fully invariant

Approach: We use theoretical analysis to deduce full invariance conditions and numerical simulations to illustrate the results.

Results: The linear fully invariant operators are convolutions with rotationally symmetrical kernels. The fully invariant quadratic operators have special functional form with two radial and one polar argument and are not necessarily rotationally symmetrical. We deduced invariance conditions for the kernels of high-order Volterra operators.

Conclusions: We suggest to use fully invariant nonlinear Volterra operators as atomic construction blocks in machine learning and neural networks for compact process modeling.

Background: To ensure consistent and high-quality semiconductor production at future logic nodes, additional metrology tools are needed. For this purpose, grazing-incidence small-angle x-ray scattering (GISAXS) is being considered because measurements are fast with a proven capability to reconstruct average grating line profiles with high accuracy.

Aim: GISAXS measurements of grating line shapes should be extended to samples with pitches smaller than 50 nm and their defects. The method’s performance should be evaluated.

Approach: A series of gratings with 32-nm pitch and deliberately introduced pitchwalk is measured using GISAXS. The grating line profiles with associated uncertainties are reconstructed using a Maxwell solver and Markov-chain Monte Carlo sampling combined with a simulation library approach.

Results: The line shape and the pitchwalk are generally in agreement with previously published transmission small-angle x-ray scattering (SAXS) results. However, the line height and line width show deviations of   (  1.0  ±  0.2  )    nm and   (  2.0  ±  0.7  )    nm, respectively. The complex data evaluation leads to relatively high pitchwalk uncertainties between 0.5 and 2 nm.

Conclusions: GISAXS shows great potential as a metrology tool for small-pitch line gratings with complex line profiles. Faster simulation methods would enable more accurate results.

Background: Reliable photomask metrology is required to reduce the risk of yield loss in the semiconductor manufacturing process as well as for the research on absorber materials. Actinic pattern inspection (API) of EUV reticles is a challenging problem to tackle with a conventional approach. For this reason, we developed RESCAN, an API platform based on coherent diffraction imaging.

Aim: We want to verify the sensitivity of our platform to absorber and phase defects.

Approach: We designed and manufactured two EUV mask samples with absorber and phase defects, and we inspected them with RESCAN in die-to-database mode.

Results: We reconstructed an image of an array of programmed absorber defects, and we created a defect map of our sample. We inspected two programmed phase defect samples with buried structures of 3.5 and 7.8 nm height.

Conclusions: We verified that RESCAN, in its current configuration, can detect absorber defects in random patterns and buried (phase) defects down to 50  ×  50  nm².

Line edge roughness (LER) measurement is one of the metrology challenges for three-dimensional device structures, and LER reference metrology is important for reliable LER measurements. For the purpose of LER reference metrology, we developed an LER measurement technique that can analyze LER distribution along the height of a line pattern, with high resolution and repeatability. A high-resolution atomic force microscopy (AFM) image of a vertical sidewall of a line pattern was obtained using a metrological tilting-AFM, which offers SI-traceable dimensional measurements. The tilting-tip was controlled with an inclined servo axis, and it scans the vertical sidewall along a line pattern with a high sampling density to enable an analysis of the LER height distribution at the sidewall. A horizontal cross-section of the sidewall shows sidewall roughness with sub-nm resolution. Power spectral density (PSD) analysis of the sidewall profile showed that the PSD noise in the high-frequency region was several orders of magnitude lower than the noise of typical scanning electron microscopy methods. AFM measurements were sequentially repeated three times to evaluate the repeatability of the LER measurement; results indicated a high repeatability of 0.07 nm evaluated as a standard deviation of LER at each height.

Nanoscale wear affects the performance of atomic force microscopy (AFM)-based measurements for all applications, including process control measurements and nanoelectronics characterization. To prevent or reduce AFM tip wear, an area of active research is required. However, most prior work has been on conventional AFMs rather than critical dimension AFMs (CD-AFMs). Hence, less is known about CD-AFM tip wear. Given that tip wear directly affects the accuracy of dimensional measurements, a basic understanding of CD-AFM tip wear is needed. Toward this goal, we evaluated the wear performance of electron beam deposited CD-AFM tips. Using a continuous scanning strategy, we evaluated the overall wear rate and tip lifetime and compared these with those of silicon-based CD-AFM tips. Our data show improved tip lifetime of as much as a factor of 5 and reduced wear rates of more than 17 times. Such improvements in wear rate means less measurement variability and lower cost.

Background: Design of microelectromechanical system based Bennet’s doubler kinetic energy harvester (KEH) is tricky as it has to satisfy the operating criteria of doubler circuit along with the harvester’s design constraints for its operation.

Aim: Design guidelines for an electrostatic KEH using Bennet’s doubler circuit along with its experimental validation are presented.

Approach: Bennet’s doubler circuit can work as a KEH only for a specific range of capacitance ratio across interdigitated electrodes of the harvester. The constraints on the resonant frequency of Bennet’s doubler harvester have been deduced to achieve operational capacitance ratio at both low and high vibrational frequencies. Finally, a test structure is fabricated, using silicon-on-insulator multiuser MEMS processes, and tested for capacitance ratio η greater than 1.366, a prerequisite for the operation of Bennet’s doubler circuit.

Results: Resonant operation of the test structure achieves capacitance ratio of 1.39 with a capability of harvesting energy density of 4.63  μJ/cm³. Further, an improved harvester design is also presented for η  =  1.5, based on the discussed guidelines that increase the energy density to 19.6  μJ/cm³.

Conclusions: We will present an insight into the design of Bennet’s doubler harvester for different vibrational frequencies, which is being widely explored for electrostatic energy harvesting.

Background: The piezoelectric microvibratory stage as a microelectromechanical system (MEMS) actuator can tilt around the X  /  Y axis and translate along the Z axis. However, when the vibratory stage is tilted around the X axis, it also has an undesirable tilting angle around the Y axis. It means that the X axis tilting and the Y axis tilting are not independent; therefore, it is significant to eliminate the coupling of two motions.

Aim: The coupling of X  /  Y tilting motion is studied theoretically and decoupled by optimization of structural parameters.

Approach: A structural model was established to analyze the reasons of the X  /  Y tilting coupling. Reasonable structure parameters of L-shaped piezoelectric beam were designed to eliminate the off-axis errors caused by X  /  Y tilting coupling.

Results: The reason of X  /  Y tilting coupling is that the stiffness of the L-shaped piezoelectric support beam mismatch in the X axis and Y axis directions. The appropriate width ratio of the two segments of the L-shaped piezoelectric beam can reduce the off-axis error effectively.

Conclusions: The test results show that the piezoelectric MEMS vibratory stage can achieve X  /  Y tilting motion with the relative off-axis error only at 1%.