Wide Process Window Research Articles

Characterization of pseudo‐single‐nucleus lateral crystallization method for silicon thin film

AbstractBased on the phase‐modulated excimer laser annealing method, an advanced crystallization technology called the “pseudo‐single‐nucleus lateral crystallization method” has been reported recently. Arrays of large rectangular Si grains of almost 6 μm × 5 μm in size were successfully grown by the new method with a sufficiently wide process window. The characterization of crystallized film was investigated by electron backscattering pattern (EBSP) method, Raman spectra and AFM, and it was confirmed that the two‐dimensionally large Si grain had a good crystallinity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hot-Spot Detection and Correction Using Full-Chip-Based Process Window Analysis

In semiconductor industry, lithography technology has advanced with higher numerical aperture (NA) and/or lower-wavelength scanner on a yearly basis, which made it possible to keep shrinking the pattern size of semiconductor devices. Unfortunately, since chip size shrinking is currently limited to 193 nm ArF immersion scanners, lithographers have no further help from the equipment side for technology development. At this time, obtaining a compact design of a semiconductor device having a wide process window will be a key solution to realize the semiconductor industry's primary goal of fabricating high-density products with high yield. For a given particular design layout, the capability to analyze how difficult the process will be, which regions need to be modified to enlarge the process margin, and to provide guidelines to obtain a high-quality design are some of the key issues for the design for manufacturability (DfM). Many electronic design automation (EDA) companies are aggressively developing the method for DfM to meet the requirement for improved designs. In this paper, we discuss a method of full-chip-level lithography simulation using the optical proximity correction (OPC) engine and the calculation of process-limiting index parameters: mask error enhancement factor (MEEF), image log slope (ILS), and focus sensitivity (FS). Furthermore, this work includes a method of the quantitative rating of each design.

Nanoparticle-based lift-off technique for ultra-thin nanoporous film preparation

Ultra-thin membrane with nanoscale through hole has great potential in biomedical applications, where precise controllability of porosity, pore size and film thickness is urgently required. The present work proposed a cost-effective way to prepare the ultra-thin nanoporous film with a promising controllability. Monodispersed nanoparticle, rather than photoresist, is used as the sacrificial material for this new lift-off process. By releasing the particles, holes can be achieved with predetermined characters. A 110 nm-thick nanoporous aluminum film with well-controlled pore’s diameter was successfully fabricated to validate the technique. The technique has wider process window and better applicability than other nanofabrication methods.

Eddy Current Induced Heating for the Solder Reflow of Area Array Packages

This paper presents a feasibility study of using eddy current induced heating for the solder reflow of area array packages. With a high frequency electromagnetic field, Sn 3.5% Ag lead-free solder balls were heated to melt and wet the solder pads on an organic substrate. The experimental results showed that such a solder reflow process could be implemented effectively in a wide processing window. With an infrared temperature sensor, it was found that the temperature difference between the solder balls and the FR4 board might reach 80 , indicating a rather localized heating mechanism. In addition, the heating and cooling rates during the soldering were found very high. This is another feature of the induction heating reflow process. It was also found that the generated temperature in the solder balls would depend on the size of the solder balls. This characteristic may be used to perform selective soldering of flip chip BGA packages. Furthermore, the developed soldering process was applied to the board level reflow of actual components. The result verified that the induction heating reflow is a feasible soldering process in actual applications.

Development of Developer-Soluble Gap Fill Materials for Planarization in Via-First Dual Damascene Process

Gap fill materials and planar-type bottom antireflective coating are needed for patterning metal trenches in the via-first dual damascene process. We have already reported on thermal cross-link gap fill materials and bottom antireflective coating as planarizing layers under a resist that can be spin-coated and etched faster than resists. In this study, developer-soluble gap fill materials were optimized in order to obtain excellent planarization, simplify the process, and increase wafer throughput. The developer-soluble gap fill materials using poly(4-hydroxystyrene) derivatives developed by an approach of the via-first dual damascene process was obtained by optimizing the concentration of the phenol group with solubility in the alkaline developer (0.26 N tetramethylammonium hydroxide, TMAH) and by thermal cross-link reaction. In addition to a superior via-filling performance, developer-soluble gap fill materials using poly(4-hydroxystyrene) derivatives showed a wide process window of prebake temperature, the controllable dissolution rate for the etch-back process, and a good CF4 etch rate of 1.4 times higher than that of a resist for etching the substrate. These results were attributed to the polymer structures of poly(4-hydroxystyrene) derivatives. Both dry plasma cleaning and wet developer cleaning can be used to remove residual gap fill materials after processing. This novel approach using developer-soluble gap fill materials as a new type of sacrificial material in an advanced lithography process makes this solution convenient for planarizing surfaces and is economically favorable owing to high throughput.

Lead-Free Stabilization for Pvc Pipes: The New Alternative

PVC remains the material of choice for the construction industry and pipe producers. However, environmental concern and regulations will lead to the elimination of lead based heat stabilizers over the next five years. This move to lead free stabilizers will cause pipe producers to re-evaluate their stabilizer options as they strive to keep the cost competitiveness of their PVC formulations. Thus, the challenge for stabilizer manufacturers is to propose new lead-free stabilizers for pipes with good performance and attractive costs. Rohm and Haas Company has developed a new stabilization system that is based on a derivative of the mercaptan chemistry which has been used for decades with conventional tin stabilizers. The patented technology includes organic based, heavy metal free compositions that contain blocked thiols, which under vinyl processing conditions, generate highly active stabilizing components. These innovative systems offer wide processing windows, give excellent early color, and can be adjusted to meet the various technical requirements of the pipe market. The stabilizing systems are odor free, and are compatible with all standard stabilizer systems. Additional benefits include reduced cross-linking leading to easier recycling. This new stabilizing systems are non toxic, contain no heavy metals, and are available as stabilizer system additives or as one-packs, offering excellent price/performance ratio. Here we present information detailing the stabilization mechanism and performance attributes (stabilization, rheology, and recycling data) on laboratory and industrial equipment.

Novel Optical Method for Widening Process Window of Phase-Modulated Excimer Laser Crystallization

A wide process window has been achieved for “the phase-modulated excimer-laser annealing” method of Si thin films. Ordinary and extraordinary light rays resulting from the birefringence effects of a crystal quartz plate, which is newly introduced within the optical path of the annealing system, generate a pair of projected images of a phase modulator. By adjusting their separation to be half the modulator pattern pitch, undesirable deformations, which appear in pair images owing to defocus, cancel each other out, resulting in a stable superposed image (light intensity profile) on the sample surface. It is shown by optical simulation and experiment that this “double-image method” widens the depth of focus from less than 2 µm to as wide as about ±6 µm.

Pattern transfer using poly(styrene-block-methyl methacrylate) copolymer films and reactive ion etching

Self-assembly block copolymers have drawn a lot of attention for its great potential on critical dimension (CD) control and line-edge roughness (LER) reduction, which become more and more crucial as the CD of transistors is only tens of nanometers nowadays. In this study, lamellar-forming poly(styrene-b-methyl methacrylate) copolymer which fabricates line patterns was chosen for its ability to provide higher aspect ratio and vertical sidewall profile in template stage, thus more suitable for the following etching process to substrate. A dry plasma etching process using pure oxygen and pure argon plasma as example chemical etching gas and physical etching gas, respectively, was studied. Etching selectivity and lateral etch rate, which are responsible for the final template height and CD loss, had been characterized on a capacitive reactive ion etching tool. The templates formed by the proposed process had high aspect ratios, excellent pattern fidelity, and low LER values. The PS lateral etch rate was small enough to provide a wide process window for retaining the CD of the pattern during the template forming process. Subsequent silicon etching using the PS template made by dry etching process yielded a steep and smooth sidewall profile.

Elucidation of high-power fibre laser welding phenomena of stainless steel and effect of factors on weld geometry

The fibre laser has been receiving great attention due to its advantages of high efficiency, high power and high beam quality, and is expected to be one of the most desirable heat sources for high-speed and deep-penetration welding. In this study, therefore, in bead-on-plate welding of Type 304 stainless steel plates with 6 kW fibre laser, the effects of laser power, power density and welding speed on the formation of sound welds were investigated with four laser beams of 130, 200, 360 and 560 µm in spot diameter, and their welding phenomena were clarified with high-speed video cameras and an x-ray transmission real-time imaging system. The weld beads showed a keyhole type of penetration at any diameter, and the maximum penetration of 11 mm in depth was obtained at 130 µm spot diameter and 0.6 m min−1 welding speed. It was found that the laser power density exerted a remarkable effect on the increase in weld penetration at higher welding speeds, and sound partially penetrated welds without welding defects such as porosity, underfilling or humping could be produced at wide process windows of welding speeds between 4.5 and 10 m min−1 with fibre laser beams of 360 µm or 560 µm in spot diameter. The high-speed video observation pictures and the x-ray images of the welding phenomena at 6 m min−1 welding speed and 360 µm spot diameter show that a sound weld bead was formed owing to a long molten pool suppressing and accommodating spattering and a stable keyhole generating no bubbles from the tip, respectively.

A novel STI etching technology to mitigate an inverse narrow width effect, and improve device performances for 90 nm node and beyond CMOS technology

A new STI (shallow trench isolation) with automatic top corner rounding (ATCR) to improve 90 nm CMOS narrow width device performance has been studied in detail. Experimental results show that the ATCR mitigates the inverse narrow width effect, and increases the driving current (Idsat) by 8% together in a unit process step, thus getting easy process control and cost down benefits, which cannot be achieved through conventional methods. Additionally, the ATCR attained a better trench depth uniformity, and thus a wider process window (20–50 s) than that of the conventional method. Furthermore, the technique does not degrade the gate oxide integrity and junction leakage current; thus the developed ATCR STI technique is more suitable for 90 nm and beyond narrow width CMOS technologies.

Effects of bonding frequency on Au wedge wire bondability

This paper studies the effect of bonding frequency on bondability of Au wire on a PCB bond pad. The wire bonding was performed at two different frequencies, 62 kHz and 138 kHz, and at varying bond pad temperatures between 60 and 110 °C. It is shown that the bond strengths of the wires bonded at a high frequency were generally higher than those bonded at a low frequency for all temperatures studied. Two distinct wire failure modes were observed for the wires bonded at the high frequency: the wires with high pull strengths failed at the bond neck, while those with low pull strengths failed mainly within the bonded wire body. This resulted in a large pull strength data scatter, which was explained by the high Q factor of the high frequency transducer. The bondability obtained for the high bond power end was much higher for the high frequency, giving rise to a wider process window in terms of bond power for the high frequency bonding. The wire bonding performance was compared between the “open” and “closed” loop bonding systems. The minimum bond powers required for successful bonds in the closed loop system were significantly lower than those required in the open loop system (e.g. 20–40 mW vs. 110–135 mW at 90 °C). The closed loop system was able to correct the resonance frequency shift, thus maintaining an almost constant bond power during bonding. In the open loop system, in contrast, a high bond power needs to be continuously supplied because of the power drop. This causes an excessive energy to be transmitted to the bonded wire, resulting in weakened wire due to excessive deformation.

Near-infrared femtosecond laser crystallized poly-Si thin film transistors

Polycrystalline silicon (poly-Si) thin film transistors (TFTs) fabricated by near-infrared femtosecond laser annealing (FLA) are demonstrated. The FLA-annealed poly-Si channels exhibit low tail-state, deep-state, and midgap-state densities of grain traps. Characteristics such as field-effect mobility, threshold voltage, and subthreshold slope for FLA-annealed poly-TFTs are comparable to those of conventional approaches. A wide process window for annealing laser fluences was confirmed by examining the changes in electrical parameters for transistors with various channel dimensions.

Effect of SnO2 on improvement on the microwave dielectric properties of Ba2Ti9O20

Effect of SnO2 addition on the crystal structure/microstructure and the related microwave dielectric properties of the Ba2Ti9O20 were systematically investigated. Incorporation of SnO2 markedly stabilized the phase constituent and microstructure for the Ba2Ti9O20 such that high quality materials can be obtained in a much wider processing window. The sintered density of the Ba2Ti9O20 increased linearly, but the microwave dielectric constant (K) decreased monotonically, with the SnO2 doping concentration. The quality factor (Qxf) of the materials increased firstly due to the addition of SnO2, but decreased slightly with further increase in SnO2 content. The best microwave dielectric properties obtained are K = 38.5 and Qxf = 31,500 GHz, which occurs for the 0.055 mol SnO2-doped and 1350 °C/4 h sintered samples. These properties are markedly better than those for undoped materials (K = 38.8 and Qxf = 26,500 GHz).

Low Density Sub-Critical CO2-Blown Solid-State PLA Foams

This paper presents a characterization of the PLA-CO2 system for solid-state foaming process with a particular goal of producing low density foams. The diffusivity of CO2 in PLA increases with increasing saturation pressures. The results show that low relatively density (lower than 10%) can be achieved in a wide processing window. The cell size can vary from tens of microns to several hundreds of microns depending on the solid-state foaming process parameters. There are significant differences in relative density and cell size for 2 and 3 MPa saturation cases, which are likely due to the much higher crystallinity at 3 MPa (26.4%) compared to 2 MPa (9.7%). Foams with cell size of around 300 μm and relative density of 3% were produced at 2 MPa saturation. It was observed that the higher the gas pressure, the higher the rate of gas-induced crystallization. Further, the gas-induced crystallization as well as the gas concentration in PLA during sorption reach their respective maximum values at approximately the same time for all gas pressures explored. For specimens saturated at 2 MPa, there is a substantial jump in crystallinity (from 5.2% to 23.4%) after foaming.

ＬＴＧ法を用いて作製したＳｍ１＋ｘＢａ２−ｘＣｕ３Ｏｙ薄膜の配向性と成長様式

We have reported high-Jc Sm1+xBa2-xCu3Oy (SmBCO) films prepared by a low-temperature growth (LTG) technique. Despite the low-substrate temperature, the LTG-SmBCO films showed complete c-axis orientation and cube-on-cube texture. In addition, the LTG-SmBCO films showed a Jc of 0.28 MA/cm2 (77 K, B//c, B=5 T), because these included high-dislocation densities and nanosize low-Tc particles. In this study, we discuss the mechanism of c-axis orientation and crystal growth for high-Jc LTG-SmBCO films. We newly suggest a model for “Nucleated growth on c-axis oriented Seed layer (NCS)" to understand the c-axis orientation mechanism for LTG-SmBCO films. Based on the NCS model, when the LTG-SmBCO films nucleated on a seed layer have two-dimensional (2D) nuclei with a 1 unit SmBCO step cell height, the interfacial energy between the nucleus and the seed layer and the critical Gibbs free energy of the nucleus are lower than those of PLD-SmBCO films. Therefore, the LTG-SmBCO films show high crystal quality and a wide processing window for biaxial orientation. We suggest that the LTG technique is effective for not only increasing Jc in magnetic fields, but also improving the processing window and crystal quality.

Growth of ternary PbTiOx films in a combination of binary oxide atomic layer depositions

Ternary PbTiOx films were deposited at 240°C on Pt-covered Si substrates using a combination of liquid injection atomic layer depositions of binary TiOx and PbO films. Ti(OC3H7)2(C11H19O2)2 [Ti(Oi−Pr)2(DPM)2] and Pb(C11H19O2)2 [Pb(DPM)2] dissolved in ethylcyclohexane and H2O were used as source materials. The deposition rates of Pb and Ti were enhanced in the ternary process compared to their binary processes under comparable deposition conditions. The Pb∕Ti ratio of PbTiOx films saturated with an increase in Ti precursor input, while it continued to increase with an increasing Pb precursor input. The self-regulated growth nature of the Pb–O layer in the binary film growth was lost in the mixed PbTiOx process as a result of interaction with the predeposited Ti–O layer. It was confirmed that for the PbTiOx film to grow on Pt substrates, an initial incubation period is required. Both Pb–O and Ti–O layers shared a common incubation period of up to ten sequences. The incubation period was shortened by increasing the input of Pb precursor. It was independent of the input of the Ti precursor and the order of precursor supply. This variable incubation period was considered as a potential key issue for growing stoichiometric and uniform multicomponent films over three-dimensional (3D) structures. The order of precursor supply affected the effective deposition rate after the incubation period. A sequence starting with a Ti precursor injection showed a higher growth rate than a sequence that started with a Pb precursor supply. A PbTiOx film was deposited on a 3D substrate precoated with an Ir layer to demonstrate the uniformity in film thickness and cation composition. Although the present PbTiOx process does not have an ideal wide-process window in the cation composition, the PbTiOx film showed uniform coverage and the distribution of cation composition over the hole structure was within ±10%.

Large Area, 38 nm Half-Pitch Grating Fabrication by Using Atomic Spacer Lithography from Aluminum Wire Grids

We wrapped 150 nm period aluminum wire grid polarizer (WGP) with AlSiOx by using atomic layer deposition at 250 degrees C. The nanometer precision coating defined the spacer to double the spatial frequency of the 100 mm diameter grating fabricated by using a legacy immersion holography setup at 351 nm wavelength. Half-pitch grating of approximately 38 nm was demonstrated with good pattern uniformity, excellent repeatability, and a wide processing window. We believe 10 nm half-pitch grating over even larger areas are viable, overcoming one major hurdle to commercialize nanoimprint.

Development of 300mm MOCVD HfSiOx Process

This paper reports on the development of a 300mm MOCVD HfSiOx process. Alkylamido Hf and Si are used as precursors for HfSiOx deposition. A Design of Experiments (DOE) approach is applied to explore the effects of the precursor ratio and deposition pressure on the film composition. A wide process window from 20 to 80% Hf concentration range for deposited HfSiOx was targeted for the process optimization. Furthermore the process is optimized towards growth rate, uniformity, process stability. It is found out that the deposition rate and the process pressure have a significant impact on the HfSiOx layer within wafer uniformity. The results of a process monitoring over 50 days with a recipe of 50% Hf concentration show a very good stability for film thickness, film uniformity and Hf concentration as well.

Continuous Fabrication of Sound Semi-Solid Slurry for Rheoforming

An alternative method has been proposed for the continuous and sample production of SSM slurry for the rheo-forming process. The process named “Low Superheat Pouring with a Shear Field (LSPSF)” dose not use the conventional stirring process, instead, it uses solidification conditions to control nucleation, nuclei survival and grain growth by means of low superheat pouring, vigorous mixing and rapid cooling during the initial stage of solidification combined with thereafter a much slower cooling. The method has been applied to A356, 201 and A380 Al-alloys. The primary phases present in average equivalent diameter of 40-70μm, 35-50μm and 50-70μm for A356, 201 and A380, respectively. The morphology of primary phases is nearly spherical with shape factor of 0.78-0.86, 0.71-0.83 and 0.85-0.96 for A356, 201 and A380, respectively. For each of those alloys, there is no eutectic entrapped within the primary phase. The advantages of the LSPSF include process simplicity with high efficiency, easy incorporation into existing metal forming installation without infrastructure changes and a wide process window for pouring temperature.

Single‐polymer composites based on slowly crystallizing polymers

AbstractAn approach of using slowly crystallizing polymers to form single‐polymer composites (SPCs) was investigated. The method was demonstrated using poly(ethylene terephthalate) (PET) as a model system, with which two distinct physical forms, namely, amorphous PET films and highly crystalline PET fibers can be readily obtained. Because of the large difference between the rubbery softening temperature of the amorphous phase and the melting temperature of the crystalline phase, the new process is characterized by its wide process window and enhanced manufacturability. The heating temperature and holding time were found to play a profound role in influencing the properties of the SPC. Excellent fiber–matrix interfacial adhesion was obtained at heating temperature 180°C and holding time 10 s. The results also indicated that the heating rate plays a significant role in affecting the fusion and adhesion of the composite. With reduced heating rates, the fusion and adhesion properties are rapidly deteriorated. POLYM. ENG. SCI., 46: 1223–1230, 2006. © 2006 Society of Plastics Engineers