This PDF file contains the editorial “What Can a JM3er Do for the Green Earth?” for JM3 Vol. 7 Issue 01

Reports the microfabricated nickel clamps for packaging of optical fibers in photonics devices. When the fiber is inserted into the silicon V groove, the microfricated clamps fix it in the V groove. Compared with the traditional silicon V grooves, this approach only involves one additional sputtering, photolithography, and electroplating process. Two single-mode optical fibers were fixed into the silicon V groove by the nickel clamp; the measured insertion loss is lower than 0.1 dB.

As silicon processes scale toward the 45-nm node using conventional 0.25-magnification, the feature sizes on the photomask are below the ArF (193.3 nm) laser wavelength. At these scales, traditional scalar and paraxial approximations used for optical image modeling are no longer valid. Thick-mask and vector-based rigorous models are equired to account for mask topographic effects and large incident angles at the reticle plane in ultra-high numerical aperture (NA) systems. Experimental depolarization measurements through advanced optical reticles at 193 nm are compared to rigorous finite-difference timedomain vector-based electromagnetic simulations. The validated simulation model is extended to explore the impact of polarization purity, mask absorber profile, mask film properties, and Fresnel effects through the pellicle on the imaging process window and requirements for optical proximity correction (OPC) in immersion imaging. The model has shown that line-end pullback has a strong correlation with mask shadowing under TE-polarized off-axis illumination (OAI).

Optical proximity correction (OPC)is a mandatory resolution enhancement technique (RET) to ensure the printability of layout features in silicon. The most prominent OPC method, model-based OPC, alters the layout data for the photomask that enables drawn layout features to be accurately reproduced by lithography and etch processes onto the wafer. This technique in various forms has now become standard in integrated circuit (IC) manufacturing at 0.18 μm and below. However, model-based OPC is computationally expensive and its runtime increases with technology scaling. The cell-based OPC approach improves runtime by performing OPC once per cell definition, as opposed to once per cell instantiation in the layout. However, cell-based OPC does not comprehend intercell optical interactions that affect feature printability in a layout context. This leads to printability, and consequently, performance and leakage, degradation. In this work, we propose auxiliary pattern-enabled cell-based OPC to improve printability of cellbased OPC, while retaining its runtime advantage. Auxiliary patterns (AP) are nonfunctional poly features that are added around a standard cell to "shield" it from optical proximity effects. We present the AP- ased OPC approach and demonstrate its advantages over cell-based and model-based OPC in terms of printability as well as timing and eakage variabilities. AP-based OPC improves the edge placement error over cell-based OPC by 68%. To enable effective insertion of AP in cell instances at a full-chip layout level, we propose a dynamic programming (DP)-based method for perturbation of detailed placement. Our approach modifies the detailed placement to allow opportunistic insertion of AP around cell instances in the design layout. By perturbing placement, we achieve 100% AP applicability in designs with placement utilization less than 70%. AP-based OPC also reduces leakage and timing variability compared to conventional cell-based OPC. We further demonstrate that AP insertion achieves timing and leakage variability comparable to that of model-based OPC.

A potential alternative extreme ultraviolet (EUV) light source for lithography is studied. The ZaP (z-pinch) Flow Z-Pinch experiment is studying the effect of sheared flow on gross plasma stability. In the experiment, hydrogen gas is used to produce plasma with quiescent periods in the magnetic mode activity, which are 2000 times longer than other plasma concepts for creating EUV light, in a configuration with 300 times the volume. Similar results are found with xenon gas. An EUV detector designed using an AXUV100, silicon/zirconium filtered photodiode with an 11- to 18-nm bandpass is used to detect EUV emissions within that spectrum and the total power of the emissions. EUV emissions in 17.4% of the z-pinch have lasted longer than 16 μs, with an average power of 550 kW. The total EUV power potential inband at 13.5 nm from 17.4% of the z-pinch is calculated to be 140 W at the intermediate focus, with a total 100-cm z-pinch emission potential of 800 W at 1 kHz. Based on this information, the ZaP Flow Z-Pinch experiment is a promising EUV light source for lithography if properly scaled and optimized for EUV light production.

A new, relatively simple experimental technique for generating arbitrary, two-dimensional patterns with high visibility and higher resolution than allowed by the Rayleigh criterion has been developed. The theoretical and experimental details of the method, based on repeated phase-coherent interference of four beams on a multiphoton absorber, are described. A sample pattern generated by numerical computer simulation of the technique is also shown.

Nowadays, features with sizes smaller than 10 nm can be obtained with electron beam lithography. For such small structures, high exposure doses are required to stay away from the shot noise limit. We investigated the effect of high-dose electron exposure of silicon substrates and subsequent dry development by reactive ion etching. We found that silicon can be directly patterned at electron doses ranging from 0.05 to 3.06 C/cm². The effect of backscattered electrons is seen as a halo around the patterns. In the given dose range, a gradual transition from positive tone low-dose to negative tone high-dose behavior is observed. It is demonstrated that the patterning is likely to be caused by structural changes of the silicon substrate, resulting in different etch rates in exposed and unexposed areas. X-ray photoelectron spectroscopy analysis has been applied to determine if the thickness of the native oxide in the irradiated areas is different from the thickness at a reference position not irradiated. Small but significant differences have been observed, the largest increase being 0.3 nm.

One of the methods used for fabrication of microelements is ion track lithography, and especially deep proton lithography. Structural depth of the produced elements depends on the energy of the protons. Equally important are the deposited dose and the time of development. One type of element where the thicknesses or depths are important is channels, used in microfluidic setups or used as rectangular waveguides. The waveguides can be obtained both by filling in with a different material and by the change of the refraction index. The shape of the obtained channels is important in both applications. The advantage of deep proton lithography is the possibility of influencing the shape of the channels by controlling the parameters of the radiation process. When using deep proton lithography to fabricate channels, it is necessary to precisely measure the dose deposited inside the material. A new method of channel fabrication, where the deposited dose is measured in the plane before the target, is presented. This is done with the use of a novel deep proton lithography setup operating in air. Experimental results are presented for such a setup built for the tandem accelerator in Erlangen, Germany.

Visible light angular scatterometry is applied to characterize the geometry and physical properties of sub-100-nm-wide polymer gratings fabricated using nanoimprint lithography and electron beam lithography. Measurement sensitivities to small variations in linewidth and slope angle were evaluated theoretically, which suggests that TM polarized incident light offers improved sensitivity for the measurements of sub-45-nm critical dimensions (CDs). A variable angle scatterometer using a red laser is built, and measurement results of various polymethylmethacrylate (PMMA) gratings with sub-100-nm CDs reveals good accuracies and fit well to the scanning electron microscopy (SEM) measurements. In addition to geometry and dimension measurements, new functionality is implemented in the modeling to characerize polymer residue thickness, polymer flow dynamics, and evidence of stress in the nanoimprinted polymer gratings. Scatterometry is also applied to detect possible undercut line profiles resulting from electron beam lithography. The results promote using this low-cost and noninvasive technique to characterize polymer nanostructures as well as understand and control the underlying lithographic processes.

We propose a new fabrication method of an x-ray grayscale mask using micro-electro-mechanical-systems (MEMS) technologies, and also report on successful fabrication of three-dimensional (3D) microstructures on a polymethylmethacrylate (PMMA)sheet by using only a single x-ray exposure. We showed that silicon can be diagonally etched by optimizing the etching condition in a reactive-ion-etching (RIE) process. It is well known that the absorbers of an x-ray mask can be made into 3D shapes. Here, we describe how this process can be extended to fabricate an x-ray grayscale mask by using a tapered-trench-etching technique. With such a mask, we carried out experiments on x-ray lithography (XRL) using a beam line BL-4 in the synchrotron radiation facility TERAS of National Institute of Advanced Industrial Science and Technology (AIST). The dose energy used for the exposure was 150 mA·h, and the subsequent resist development was done by a GG developer at room temperature for 16 h. The sidewalls in the upper part of the PMMA resist structure were inclined and rounded. In particular, the shape of the PMMA resist structure of the lines with 20-μm width (also referred as 20-μm lines) could be processed to achieve a halberd-like shape. Thus, the effectiveness of the grayscale mask in adjusting to the varying thicknesses of absorber was confirmed by XRL experiments. Moreover, we showed that the final shape of PMMA resist structures after XRL was predictable by calculations.

We present the design of a micro-electro-mechanical-system (MEMS)-based power disconnect for use with the proposed 42-V automotive power systems. High-voltage power systems are prone to arcing, which occurs during power disconnections. The high arcing current may lead to severe damage on the systems and may expose electric shock hazards to humans. The objective of the MEMS-based power disconnect we propose is to eliminate arcing occurrence in the systems. To eliminate arcing, one alternative is to electronically terminate the power supply to the system prior to the physical disconnection. The integrated MEMS force sensor on the power disconnect will be activated as a service technician disconnects the connector. The power supply to the system will be electronically shut off to prevent arcing during the physical interruption. The MEMS force sensor on the disconnect has an overall dimension of 3600 μm××1000 μm×10 μm and is fabricated with the Micragem fabrication process. A displacement reduction mechanism is incorporated into the sensor design to increase the sensitivity of the force sensor. Results show that the sensor is capable of measuring a maximum force input of 10.7 mN, resulting from a 20-μm displacement on the sensing structure.

We report the modeling and characterization of adaptive voltage controlled electro-optic microlenses. First, we utilize finite element analysis (FEA) to simulate the induced electro-optic effect in lanthanum-modified lead zirconate titanate (PLZT). FEA simulation provides microlens parameters such as phase and focal length. A simple z-scan method is developed to fully characterize the adaptive voltage controlled linear lens. Experimental z-scan results are shown to match the theoretical predictions from FEA.

We demonstrate optical critical dimension measurement of lines in silicon grating targets using back focal plane scatterfield icroscopy. In this technique, angle-resolved diffraction signatures are obtained from grating targets by imaging the back focal plane of a brightfield microscope that has been modified to allow selection of the angular distribution and polarization of the incident illumination. The target line profiles, including critical dimension linewidth and sidewall angle, are extracted using a scatterometry method that compares the diffraction signatures to a library of theoretical signatures. Because we use the zero-order component of the diffraction, the target features need not be resolved in order to obtain the line profile. We extracted line profiles from two series of targets with fixed pitch but varying linewidth: a subresolution 300-nm-pitch series, and a resolved 600-nm-pitch series. Linewidths of 131 nm to 139 nm were obtained, with nanometer-level sensitivity to linewidth, and a linear relationship of linewidth obtained from scatterfield microscopy to linewidth measured by scanning electron microscopy was demonstrated. Conventional images can be easily collected on the same microscope, providing a powerful tool for combining imaging metrology with scatterometry for optical critical dimension measurement.

Polarimetric imaging applications at the 2-to-5-μm or midwave infrared range use large pixel-count focal plane arrays (FPAs) with small pixel sizes. We report on the design, fabrication, and characterization of micropolarizers for the 2-to-5-μm regime. These micropolarizers will be used in conjunction with a FPA and will be in the near field of the imaging device. The pixel pitches for some commercial FPAs are small enough that the finite apertures of the polarizing devices may significantly affect their performance, because their aperture dimension varies between three and five waves. We are interested in understanding the effect on the extinction ratio due to variations in the edge terminations of a polarizer with a small aperture. Edge terminations are the spaces between the first and last wire with the perimeter of the aperture of the polarizer. To verify these effects, we fabricated micropolarizers with apertures of 5 to 20 μm and with termination edge spaces of one-quarter and three-quarters of the wiregrids period. The devices measured extinction ratios from 50:1 for the smallest aperture to 200:1 for the largest. Simulations and measurements show that the extinction ratio is larger for the smaller termination edge spacing.