This PDF file contains the editorial “The Editorial Review Process” for JM3 Vol. 14 Issue 03

This PDF file contains the editorial “Special Section Guest Editorial: Alternative Lithographic Technologies IV” for JM3 Vol. 14 Issue 03

The routine “on demand” fabrication of features smaller than 10 nm opens up new possibilities for the realization of many devices. Driven by the thermally actuated piezoresistive cantilever technology, we have developed a prototype of a scanning probe lithography (SPL) platform which is able to image, inspect, align, and pattern features down to the single digit nanoregime. Here, we present examples of practical applications of the previously published electric-field based current-controlled scanning probe lithography. In particular, individual patterning tests are carried out on calixarene by using our developed table–top SPL system. We have demonstrated the application of a step-and-repeat SPL method including optical as well as atomic force microscopy-based navigation and alignment. The closed-loop lithography scheme was applied to sequentially write positive and negative tone features. Due to the integrated unique combination of read–write cycling, each single feature is aligned separately with the highest precision and inspected after patterning. This routine was applied to create a pattern step by step. Finally, we have demonstrated the patterning over larger areas, over existing topography, and the practical applicability of the SPL processes for lithography down to 13-nm pitch patterns. To enhance the throughput capability variable beam diameter electric field, current-controlled SPL is briefly discussed.

In this study, a stitching method other than soft edge (SE) and smart boundary (SB) is introduced and benchmarked against SE. The method is based on locally enhanced exposure latitude without throughput cost, making use of the fact that the two beams that pass through the stitching region can deposit up to 2× the nominal dose. The method requires a complex proximity effect correction that takes a preset stitching dose profile into account. Although the principle of the presented stitching method can be multibeam (lithography) systems in general, in this study, the MAPPER FLX 1200 tool is specifically considered. For the latter tool at a metal clip at minimum half-pitch of 32 nm, the stitching method effectively mitigates beam-to-beam (B2B) position errors such that they do not induce an increase in critical dimension uniformity (CDU). In other words, the same CDU can be realized inside the stitching region as outside the stitching region. For the SE method, the CDU inside is 0.3 nm higher than outside the stitching region. A 5-nm direct overlay impact from the B2B position errors cannot be reduced by a stitching strategy.

High-defect density in thermodynamics driven directed self-assembly (DSA) flows has been a major cause of concern for a while and several questions have been raised about the relevance of DSA in high-volume manufacturing. The major questions raised in this regard are: (1) What is the intrinsic level of DSA-induced defects? (2) Can we isolate the DSA-induced defects from the other processes-induced defects? (3) How much do the DSA materials contribute to the final defectivity and can this be controlled? (4) How can we understand the root causes of the DSA-induced defects and their kinetics of annihilation? (5) Can we have block copolymer anneal durations that are compatible with standard CMOS fabrication techniques (in the range of minutes) with low-defect levels? We address these important questions and identify the issues and the level of control needed to achieve a stable DSA defect performance.

Directed self-assembly of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) during laser thermal annealing at peak temperatures of 300°C–800°C for dwells of 1–10 ms has been explored. The enhanced mobility of polymer chains at these temperatures improves registration compared with conventional thermal anneals. PS-b-PMMA films (forming 15-nm line/space standing lamellae) were cast on chemically patterned substrates with a copolymer neutral layer and annealed by laser and hot plate. Annealing by hot plate or multiple laser scans resulted in well-aligned features over micron length scales. By laser annealing multiple times, defectivity was reduced by ∼60%. However, laser annealing for only 10 ms before performing a hot plate anneal reduced defectivity by <80%. We believe that this reduction arises from improved interfacial alignment of the film to the template during laser annealing near the order–disorder transition.

To demonstrate the possibility of using electron beam-induced deposition (EBID) masks for sub-10 nm pattern transfer into silicon, first experiments were carried out by using 20- to 40-nm EBID masks, which were etched by different chemistries. It is experimentally verified that recipes based on hydrogen bromide, chlorine, and boron trichloride can selectively etch silicon when using 20- to 40-nm masks made by EBID. We observed an enhancement of the height ratio, i.e., the ratio of the height of structures before and after etching, up to a factor of 3.5 when using chlorine chemistry. To demonstrate the pattern transfer of sub-10 nm structures, further experiments were carried out using 8- to 20-nm EBID masks in combination with hydrogen bromide, chlorine, and fluorine chemistries. Fluorine chemistry provided the best results in terms of surface smoothness and height ratio. In this case, 7.4-nm lines were successfully transferred into silicon, resulting in 14.3-nm-wide lines with a height ratio of ∼5.

A fast and flexible fabrication method that allows the creation of silicon structures of various geometries is presented. It is based on the combination of focused ion beam local gallium implantation, selective silicon etching, and diffusive boron doping. The structures obtained by this resistless method are electrically conductive. Freely suspended mechanical resonators of different dimensions and geometries have been fabricated and measured. The resulting devices present a good electrical conductivity which allows the characterization of their high-frequency mechanical response by electrical read-out.

Measurement and control of line edge roughness (LER) is one of the most challenging issues facing patterning technology. As the critical dimensions (CDs) of patterned structures decrease, an LER of only a few nanometers negatively impacts device performance. Here, Mueller matrix (MM) spectroscopic ellipsometry-based scatterometry is used to characterize LER in periodic line-space structures in 28-nm pitch Si fin samples fabricated by directed self-assembly patterning. The optical response of the MM elements is influenced by structural parameters like pitch, CDs, height, and side-wall angle, as well as the optical properties of the materials. Evaluation and decoupling MM element response to LER from other structural parameters requires sensitivity analysis using scatterometry models that include LER. Here, an approach is developed that can be used to characterize LER in Si fins by comparing the optical responses generated by systematically varying the grating shape and measurement conditions. Finally, the validity of this approach is established by comparing the results obtained from power spectral density analysis of top down scanning electron microscope images and cross-sectional transmission electron microscope image of the 28-nm pitch Si fins.

The conventional optical lever detection technique involves optical components and their precise mechanical alignment. An additional technical limit is the weight of the optical system in cases where a top-scanner is used with high-speed and high-precision metrology. An alternative represents the application of self-actuated atomic force microscopy (AFM) cantilevers with integrated two-dimensional electron gas (2-DEG) piezoresistive deflection sensors. A significant improvement in the performance of such cantilevers with respect to deflection sensitivity and temperature stability has been achieved by using an integrated Wheatstone bridge configuration. Due to employing effective crosstalk isolation and temperature drift compensation, the performance of these cantilevers was significantly improved. In order to enhance the speed of AFM measurements, we present an adaptive scanning speed procedure. Examples of AFM measurements with a high scanning speed (up to 200  lines/s) committed to advanced lithography process development are shown.

Due to its high resolution and applicability for large area patterning, nanoimprint lithography (NIL) is a promising technology for photovoltaic (PV) applications. However, a successful industrial application of NIL processes is only possible if large-area processing on thin, brittle, and potentially rough substrates can be achieved in a high-throughput process. The development of NIL processes using the SmartNIL technology from EV Group with a focus on PV applications is described. The authors applied this tooling to realize a honeycomb texture (8  μm period) on the front side of multicrystalline silicon solar cells, leading to an improvement in optical efficiency of 7% relative and a total efficiency gain of 0.5% absolute compared to the industrial standard texture (isotexture). On the rear side of monocrystalline silicon solar cells, the authors realized diffraction gratings to make use of light trapping effects. An absorption enhancement of up to 35% absolute at a wavelength of 1100 nm is demonstrated. Furthermore, photolithography was combined with NIL processes to introduce features for metal contacts into honeycomb master structures, which were initially realized using interference lithography. As a final application, the authors investigated the realization of very fine contact fingers with prismatic shape in order to minimize reflection losses.

Recently, directed self-assembly (DSA) has emerged as a promising lithography solution for cut manufacturing. We perform a comprehensive study on the DSA aware mask optimization problem to provide a DSA friendly design on cut layers. We first formulate the problem as an integer linear programming (ILP) to assign cuts to different guiding templates, targeting both conflict minimization and line-end extension minimization. As ILP may not be scalable for very large size problems, we then propose two speed-up strategies. The first one is to decompose the initial problem into smaller ones and solve them separately, followed by solution merging without much loss of quality. The second one is using the set cover algorithm to decide the DSA guiding pattern assignment, and then legalize the template placement. Our approaches can be naturally extended to handle arbitrary DSA guiding template patterns with complicated shapes. Experimental results show that our methodologies can significantly improve the DSA friendly, i.e., both the unresolved pattern number and the line-end extensions can be reduced.

A lossless electron-beam layout (EBL) data compression algorithm, LineDiff Entropy v2.0, and its low-complexity, high-performance hardware decoder for multiple electron-beam direct-write lithography systems are proposed. The algorithm compares consecutive data scanlines and encodes the data based on the change/no-change of pixel values and the lengths of pixel sequences. Then, the compaction steps of data omission, merging, and encoding of consecutive long identical scanlines are applied. Unique short codes are assigned to data with high occurrence frequency. The hardware decoder is designed as three circuit blocks that perform entropy decoding, decompaction, and EBL data generation through parallel outputs. The results demonstrate that our algorithm can achieve excellent compression performance and that the hardware decoder can decompress data at very high data rates.

Variation in the shape of directed self-assembly (DSA) prepatterns caused by lithographical process variability is one of the significant contributors to the placement error in DSA patterning. DSA-aware printing assist features (PrAFs) can be used to reduce the sensitivity of DSA prepatterns to lithographical process variability, with the printed sidelobes resulting from these PrAFs being “sealed” during the DSA step of the process. For instance, in a graphoepitaxy DSA process, where confinement wells are formed by deep ultraviolet (DUV) lithography, the process window of the DUV lithography process may be improved by using PrAFs, as long as the confinement wells resulting from these PrAFs are sized and shaped so that they do not etch transfer into the substrate due to etch-resistant outcomes of the DSA process. A method to optimize the placement of these DSA-aware PrAFs is presented, along with a method utilizing a regular array of etch-resistant confinement wells with localized modifications of their size or shape to form etch-transferrable features. Both methods are tested and verified in simulations of DUV lithography and DSA.

E-beam direct write (EBDW) process window (PW) simulations were performed on critical layers in Altera designs of the 20-nm node (minimum metal half-pitch 32 nm). For selected layout clips, a direct comparison is made with 193i simulation results. Local interconnect and Via0 (single patterning) and Metal1 (litho-etch-litho-etch double patterning) layers are considered. The EBDW dose latitude was found to exceed that of the 193i process by a factor of 4. As the electron beam total spot size is of the order of the critical dimension for the considered node, interplay between neighboring features is low. This results in straightforward data preparation with typically two kernels and “clean” PWs. The latter are mainly limited by edge placement errors of line ends. The curves for the various simulation sites roughly overlap, as opposed to the 193i case in which they significantly differ. In EBDW, the performance of square vias equals that of rectangular vias, enabling a denser via packing.

Making the best use of the characteristic features in nanocrystalline Si (nc-Si) ballistic hot electron source, an alternative lithographic technology is presented based on two approaches: physical excitation in vacuum and chemical reduction in solutions. The nc-Si cold cathode is composed of a thin metal film, an nc-Si layer, an n+-Si substrate, and an ohmic back contact. Under a biased condition, energetic electrons are uniformly and directionally emitted through the thin surface electrodes. In vacuum, this emitter is available for active-matrix drive massive parallel lithography. Arrayed 100×100 emitters (each emitting area: 10×10  μm²) are fabricated on a silicon substrate by a conventional planar process, and then every emitter is bonded with the integrated driver using through-silicon-via interconnect technology. Another application is the use of this emitter as an active electrode supplying highly reducing electrons into solutions. A very small amount of metal-salt solutions is dripped onto the nc-Si emitter surface, and the emitter is driven without using any counter electrodes. After the emitter operation, thin metal and elemental semiconductors (Si and Ge) films are uniformly deposited on the emitting surface. Spectroscopic surface and compositional analyses indicate that there are no significant contaminations in deposited thin films.

We present an optimization methodology for the template designs of subresolution contacts using directed self-assembly (DSA) with graphoepitaxy and immersion lithography. We demonstrate the flow using a 60-nm-pitch contact design in doublet with Monte Carlo simulations for DSA. We introduce the notion of template error enhancement factor (TEEF) to gauge the sensitivity of DSA printing infidelity to template printing infidelity and evaluate optimized template designs with TEEF metrics. Our data show that source mask optimization and inverse lithography technology are critical to achieve sub-80 nm non-L₀ pitches for DSA patterns using 193i.

Line edge roughness (LER) and line width roughness (LWR) are analyzed based on the frequency domain 3σ LER characterization methodology during pattern transfer in a self-aligned double patterning (SADP) process. The power spectrum of the LER/LWR is divided into three regions: low frequency, middle frequency, and high frequency regions. Three standard deviation numbers are used to characterize the LER/LWR in the three frequency regions. Pattern wiggling is also detected quantitatively during LER/LWR transfer in the SADP process.

Power spectral density (PSD) analysis is an important part of understanding line-edge and linewidth roughness in lithography. But uncertainty in the measured PSD, both random and systematic, complicates interpretation. It is essential to understand and quantify the sources of the measured PSD’s uncertainty and to develop mitigation strategies. Both analytical derivations and simulations of rough features are used to evaluate data window functions for reducing spectral leakage and to understand the impact of data detrending on biases in PSD, autocovariance function (ACF), and height-to-height covariance function measurement. A generalized Welch window was found to be best among the windows tested. Linear detrending for line-edge roughness measurement results in underestimation of the low-frequency PSD and errors in the ACF and height-to-height covariance function. Measuring multiple edges per scanning electron microscope image reduces this detrending bias.

Lack of progress in reducing linewidth roughness of lithographic features has led to investigations of the use of postlithography process smoothing techniques. However, it remains unclear whether such postprocessing will sufficiently reduce the detrimental effects of feature roughness. Thus, there is a need to understand the efficacy of postprocessing on not just roughness reduction, but on the negative device impacts of roughness. We derive model equations of how roughness impacts lithographic performance and incorporates smoothing using postprocessing. These models clearly show that postprocess smoothing works best by increasing the correlation length. Increasing the correlation length is very effective at reducing high-frequency roughness that impacts within-feature variations but is less effective at reducing low-frequency roughness that impacts feature-to-feature variations. It seems that postprocess smoothing is not a substitute for reducing the initial roughness of resist features.

A rapid three-dimensional (3-D) ultraviolet (UV) lithography process for the fabrication of millimeter-tall high aspect ratio complex structures is presented. The liquid-state negative-tone photosensitive polyurethane, LF55GN, has been directly photopatterned using multidirectionally projected UV light for 3-D micropattern formation. The proposed lithographic scheme enabled us to overcome the maximum height obtained with a photopatternable epoxy, SU8, which has been conventionally most commonly used for the fabrication of tall and high aspect ratio microstructures. Also, the fabrication process time has been significantly reduced by eliminating photoresist-baking steps. Computer-controlled multidirectional UV lithography has been employed to fabricate 3-D structures, where the UV-exposure substrate is dynamically tilt-rotating during UV exposure to create various 3-D ray traces in the polyurethane layer. LF55GN has been characterized to provide feasible fabrication conditions for the multidirectional UV lithography. Very tall structures including a 6-mm tall triangular slab and a 5-mm tall hexablaze have been successfully fabricated. A 4.5-mm tall air-lifted polymer-core bowtie monopole antenna, which is the tallest monopole structure fabricated by photolithography and subsequent metallization, has been successfully demonstrated. The antenna shows a resonant radiation frequency of 12.34 GHz, a return loss of 36 dB, and a 10 dB bandwidth of 7%.

We investigated the physical sputtering of low-energy argon bombardment onto α-quartz and amorphous quartz substrate using dynamics simulations. We reported the effects of etching selectivity, the effect of surface temperature, T_s, and the effect of incident energy, E_i on sputtering yield. The second generation charge-optimized many body (COMB10) potential was utilized to model the interatomic potential of quartz substrates. Simulations were conducted at incident energies of E_i=50, 100, and 150 eV and substrate temperatures of T_s=300, 500, and 800 K. α-quartz shows higher sputtering yield compared to amorphous quartz at any given incident energy, E_i and substrate temperature, T_s. α-quartz has also produced more stoichiometric yield compared to amorphous quartz.

A step-and-repeat nanoimprint lithography (SR-NIL) process on a pre-spin-coated film is employed for the fabrication of an integrated optical device for on-chip spectroscopy. The complex device geometry has a footprint of about 3  cm² and comprises several integrated optical components with different pattern size and density. Here, a new resist formulation for SR-NIL was tested for the first time and proved effective at dramatically reducing the occurrence of systematic defects due to film dewetting, trapped bubbles, and resist peel-off. A batch of 180 dies were imprinted, and statistics on the imprint success rate is discussed. Devices were optically characterized and benchmarked to an identical chip that was fabricated by electron-beam lithography. The overall performance of the imprinted nanospectrometers is well-aligned with that of the reference chip, which demonstrates the great potential of our SR-NIL for the low-cost manufacturing of integrated optical devices.

Extreme ultraviolet (EUV) lithography is considered to be the most promising option to continue with the downscaling of integrated circuits in high-volume manufacturing. One of the main challenges, however, is the development of EUV resists that fulfill the strict sensitivity, resolution, and line-edge roughness specifications of future nodes. Here, we present our EUV resist screening results of a wide range of EUV resists in their developmental phase from our collaborators from around the world. Furthermore, we have carried out extensive experiments to improve the processing parameters of the resists as well as to identify the optimal wafer pretreatment methods in order to optimize the adhesion of the resist to the substrate. We show that even though significant improvements in performance of chemically amplified resists have been achieved, pattern collapse is still the major process-limiting factor as the resolution decreases below 14 nm half-pitch.

Predicting the lithography impact of a phase defect embedded in a mask used for extreme ultraviolet lithography on the printed image on wafer is a challenging task. In this study, two types of measurement tools were employed to characterize the phase defects. The prior measurement tool was a scanning probe microscope used for measuring the surface topography of phase defects, and the second was an at-wavelength dark-field inspection tool capable of capturing a phase defect and then calculating the defect detection signal intensity (DSI) from those images. A programmed phase defect mask with various lateral sizes and depths was prepared. The sizes and DSIs were then measured. The measured data indicated that the DSIs did not directly correlate with the phase defect volumes. The influence of the phase defects on the printed image on a wafer was also calculated using a lithography simulator. The simulation results indicated that the printed critical dimensions (CDs) were strongly correlated with the DSIs rather than with the phase defect volumes. As a result, the influence of the phase defect on the printed CD can be predicted from the values of the DSIs.

The nanomechanical properties of solvent-cast polymer thin films have been investigated using PeakForce™ Quantitative Nanomechanical Mapping. The samples consisted of films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) obtained after the dewetting of toluene solution on a polymeric brush layer. Additionally, we have probed the mechanical properties of poly(styrene-b-methyl methacrylate) block copolymers (BCP) as randomly oriented thin films. The probed films have a critical thickness <50  nm and present features to be resolved <42  nm. The Young’s modulus values obtained through several nanoindentation experiments present a good agreement with previous literature, suggesting that the PeakForce™ technique could be crucial for BCP investigations, e.g., as a predictor of the mechanical stability of the different phases.

Requirements for control of critical dimension (CD) become more demanding as the integrated circuit (IC) feature size specifications become tighter and tighter. Critical dimension control, also known as CDC, is a well-known laser-based process in the IC industry that has proven to be robust, repeatable, and efficient in adjusting wafer CD uniformity (CDU) [Proc. SPIE6152, 615225 (2006)]. The process involves locally and selectively attenuating the deep ultraviolet light which goes through the photomask to the wafer. The input data for the CDC process in the wafer fab is typically taken from wafer CDU data, which is measured by metrology tools such as wafer-critical dimension—scanning electron microscopy (CD-SEM), wafer optical scatterometry, or wafer level CD (WLCD). The CD correction process uses the CDU data in order to create an attenuation correction contour, which is later applied by the in-situ ultrashort laser system of the CDC to locally change the transmission of the photomask. The ultrashort pulsed laser system creates small, partially scattered, Shade-In-Elements (also known as pixels) by focusing the laser beam inside the quartz bulk of the photomask. This results in the formation of a localized, intravolume, quartz modified area, which has a different refractive index than the quartz bulk itself. The CDC process flow for improving wafer CDU in a wafer fab with detailed explanations of the shading elements formation inside the quartz by the ultrashort pulsed laser is reviewed.

We present an approach for the creation of guiding patterns to direct the self-assembly of block copolymers. A neutral layer of a brush polymer is directly exposed by electrons, causing the cross-linking of the brush molecules, and thus changing its local affinity. The advantage relies on the achievable resolution and the reduction of the process steps in comparison with deep UV and conventional electron beam lithography, since it avoids the use of a resist. We envision that this method will be highly valuable for the investigation of high-chi directed self-assembly materials and complex guiding pattern designs, where pattern placement and resolution are becoming critical.

High-sensitivity and low-noise extreme ultraviolet (EUV) mask pattern defect detection is one of the major issues remaining to be addressed in device fabrication using extreme ultraviolet lithography (EUVL). We have designed a projection electron microscopy (PEM) system, which has proven to be quite promising for half-pitch (hp) 16-nm node to hp 11-nm node mask inspection. The PEM system was integrated into a pattern inspection system for defect detection sensitivity evaluation. To improve the performance of hp 16-nm patterned mask defect detection toward hp 11-nm EUVL patterned mask, defect detection signal characteristics, which depend on hp 64-nm pattern image intensity deviation on EUVL mask, were studied. Image adjustment effect of the captured images for die-to-die defect detection was evaluated before the start of the defect detection image-processing sequence. Image correction of intrafield intensity unevenness and L/S pattern image contrast deviation suppresses the generation of false defects. Captured images of extrusion and intrusion defects in hp 64-nm L/S patterns were used for detection. Applying the image correction for defect detection, 12-nm sized intrusion defect, which was smaller than our target size for hp 16-nm defect detection requirements, was identified without false defects.

Change in the cross-sectional profile of a photoresist (PR) pattern due to shrinkage was evaluated to investigate the mechanism of electron beam-induced shrinkage. A scanning transmission electron microscope (STEM) was used to observe the cross-sectional profiles of PR lines after atomic-layer deposition of metal oxide and carbon deposition on the sample surface. A HfO₂ thin layer enhanced the profile contrast in the STEM measurements without blurring the edge, which enabled the precise cross-sectional measurement of the PR patterns. We found interesting features associated with shrinkage from the detailed profile change obtained using this method, such as a rounding of the pattern top, a necking of the sidewall profile, a rounding of the foot in the pattern on the organic underlying layer, and voltage-independent sidewall shrinkage under a large electron beam dose. These behaviors along with the results from a Monte Carlo simulation are discussed. Consequently, these observations experimentally clarified that the elastic deformation effect and the impact of the secondary electrons emitted from the spaces around the pattern into the sidewall are important to interpret the change in the shape of the pattern induced by shrinkage.

The spectral emission properties of a droplet-based laser-produced plasma are investigated in the vacuum ultraviolet (VUV) range. Measurements are performed with a spectrograph that operates from 30 to 180 nm with a spectral resolution of 0.1 nm. The emission spectra are recorded for different metal droplet targets, namely tin, indium, and gallium. Measurements were performed at different pressure levels of the background gas. Several characteristic emission lines are observed. The spectra are also calibrated in intensity in terms of spectral radiance to allow absolute emission power estimations from the light source in the VUV region. The presented experimental results are relevant for alternative light sources that would be needed for future wafer inspection tools. In addition, the experimental results help to determine the out-of-band radiation emission of a tin-based extreme ultraviolet (EUV) source. By tuning the type of fuel, the laser energies, and the background gas, the laser-produced plasma light source shows good capabilities to be operated as a light source that covers a spectral emission range from the EUV to the sub-200 nm range.

Through-silicon vias (TSV) are very important for wafer-level packaging as they provide patterning holes through thick silicon dies to integrate and interconnect devices which are stacked in the z-direction. For economic processing, TSV fabrication primarily needs to be cost effective, especially for a high throughput. Furthermore, a lithography process for TSV has to be stable enough to allow patterning on prestructured substrates with inhomogeneous topography. This can be addressed by an exposure process which offers a large depth of focus. We have developed a mask-aligner lithography process based on the use of a double-sided photomask to realize aerial images that meet these constraints.

Increasing board-to-board and chip-to-chip computational data rates beyond 12.5 Gbs will require the use of single-mode polymer waveguides (WGs) that have high bandwidths and are able to be wavelength division multiplexed. Laser direct writing (LDW) of polymer WGs provides a scalable and reconfigurable maskless procedure compared to common photolithography fabrication. LDW of straights and radial curves are readily achieved using predefined drive commands of the two-axis direct drive linear stage system. Using the laser direct write process for advanced WG structures requires stage-drive programming techniques that account for specified polymer material exposure durations. Creating advanced structures such as WG S-bends into single-mode polymer WG builds provides designers with the ability to affect pitch control, optical coupling, and reduce footprint requirements. Fabrication of single-mode polymer WG segmented radial arcs is achieved through a smooth radial arc user-programmed defined mathematical algorithm. Cosine and raised-sine S-bends are realized through a segmentation method where the optimal incremental step length and bend dimensions are controlled to achieve minimal structure loss. Laser direct written S-bends are compared with previously published photolithographic S-bend results using theoretical bend loss models. Fabrication results show that LDW is a viable method in the fabrication of advanced polymer WG structures.

Recently, we have developed a detector structure known as the resonator quantum-well infrared photodetector or R-QWIP. With this structure, we demonstrated quantum efficiency as high as 70% in single detectors and 30% to 40% in focal plane arrays (FPAs) with a 9-μm cutoff. We designed a broadband, 10-μm cutoff R-QWIP FPA using a more accurate refractive index. To achieve the theoretical prediction, the substrates of the detectors have to be removed completely to prevent the escape of unabsorbed light out of the detectors. The height of the diffractive elements (DE) and the thickness of the active resonator must also be uniformly produced within a 0.05-μm accuracy. To achieve these specifications, two optimized inductively coupled plasma (ICP) etching processes are developed. Using these etching techniques, a number of single detectors were fabricated to verify the analysis before FPA production. In general, test data support the theoretical predictions.

Bonding of a copper surface in a nonvacuum environment has been studied for the purpose of reducing manufacturing costs. Cu-Cu bonding in ambient air is demonstrated by using propylene carbonate (PPC) as a passivation layer. The decomposition of the PPC passivation layer during bonding would protect the copper surface from oxidation by providing a shielding gas atmosphere between the copper surface and the air. Further, the PPC passivation layer would also overcome the degradation of copper surface during storage in the atmosphere.

Nano thinfilm transistor (TFT) is fabricated at the root of a beam, which becomes the maximum stress area when the beam is bent. In this process, a probe is used to bend the beam and produce GPa-order mechanical stress. The electrical characteristic of TFT under different GPa stress has been studied. Threshold voltage V_T, relative drain current change ΔI_ds/I_ds, and transconductance g_m present a nonlinear relationship with increasing GPa-order stress. Analyzed from experimental results, channel piezoresistivity effect below 1.82 GPa stress, energy valley splitting, large change of valence effective mass from 1.82 to 2.08 GPa, and interface effect above 2.08 GPa are the factors of nonlinear change of parameter with GPa-order mechanical stress.