Bare Wafer Research Articles

Multi-type particle layer improved light trapping for photovoltaic applications

This work discusses regular particle arrays as nanostructured front layers for possible application in photovoltaic devices yielding strongly increased forward scattering. I used a rigorous plane-wave method to investigate multi-type particle layers combining different radii and configurations. The absorbance was enhanced compared to the bare Si wafer and I demonstrated on mixing particles a broadband boost in the absorbance within the homogeneous wafer region, excluding parasitic absorption in the particle layer. I studied the efficiency enhancement for varying geometries. Multi-type layers made of Si disks with two different radii achieved up to 33% (24%) and with four different radii up to 40% (30%) improvement in the short circuit current and integrated absorbance, respectively, without yet standard anti-reflection coatings. Broadband efficiency enhancement for metal multi-type layers was not observed because they show strong parasitic absorption and boost the absorbance only in narrow wavelength regions.

Fabrication of direct Z-scheme Ta3N5-WO2.72 film heterojunction photocatalyst for enhanced hydrogen evolution

A combination of atomic layer deposition (ALD) and sol-gel techniques was applied to fabricate a direct Z-scheme Ta3N5-WO2.72 heterojunction film photocatalyst for improved H2 generation. The Ta3N5 was deposited by ALD on WO2.72 sol coated on Si wafer. Ta3N5 film coated on bare Si wafer showed 13.2μmol/g of H2 generation after 6h under irradiation by a 150W Xe lamp with a cut-off filter (λ>420nm). In comparison, the direct Z-scheme Ta3N5-WO2.72 heterojunction film demonstrated a more than two-fold increase in H2 production (31.9μmol/g). The efficiency of the Ta3N5-WO2.72 heterojunction film further increased to 46.4μmol/g upon coating with Pt nanoparticles by ALD. Additionally, the direct Z-scheme Ta3N5-WO2.72 heterojunction film generated 18 times more H2 than a Ta3N5-WO3 liquid-state (using NaI as the shuttle redox mediator) Z-scheme system prepared by mixing Ta3N5 and WO3 powders. The H2 generation of the direct Z-scheme Ta3N5-WO2.72 heterojunction film coated with Pt nanoparticles further increased to 3072.5μmol/g without the 420nm cut-off filter.

Low-frequency noise in bare SOI wafers: Experiments and model

Low-frequency noise (LFN) measurements are largely used for interface quality characterization in MOSFETs. In this work, a detailed investigation of LFN technique applied to pseudo-MOSFETs in bare silicon-on-insulator (SOI) substrates is provided. A physical model capable to describe the experimental results is proposed and validated using different die areas and inter-probe distances. The effective silicon area contributing to the noise signal, the impact of defects induced by probes and the possibility to extract interface trap density are addressed.

Effect of Rapid Thermal Processing on Light-Induced Degradation of Carrier Lifetime in Czochralski p-Type Silicon Bare Wafers

The electrical properties of Czochralski silicon (Cz-Si) p-type boron-doped bare wafers have been investigated after rapid thermal processing (RTP) with different peak temperatures. Treated wafers were exposed to light for various illumination times, and the effective carrier lifetime (τ eff) measured using the quasi-steady-state photoconductance (QSSPC) technique. τ eff values dropped after prolonged illumination exposure due to light-induced degradation (LID) related to electrical activation of boron–oxygen (BO) complexes, except in the sample treated with peak temperature of 785°C, for which the τ eff degradation was less pronounced. Also, a reduction was observed when using the 830°C peak temperature, an effect that was enhanced by alteration of the wafer morphology (roughness). Furthermore, the electrical resistivity presented good stability under light exposure as a function of temperature compared with reference wafers. Additionally, the optical absorption edge shifted to higher wavelength, leading to increased free-carrier absorption by treated wafers. Moreover, a theoretical model is used to understand the lifetime degradation and regeneration behavior as a function of illumination time. We conclude that RTP plays an important role in carrier lifetime regeneration for Cz-Si wafers via modification of optoelectronic and structural properties. The balance between an optimized RTP cycle and the rest of the solar cell elaboration process can overcome the negative effect of LID and contribute to achievement of higher solar cell efficiency and module performance.

Large Area 4H SiC Products for Power Electronic Devices

Efforts to develop 150 mm 4H SiC bare wafer and epitaxial substrates for power electronic device applications have resulted in quality improvements, such that key metrics match or outperform 100 mm substrates. Total dislocation densities and threading screw dislocation densities measured for 150 mm wafers were ~4100 cm-2 and ~100 cm-2, respectively, compared with values of ~5900 cm-2 and ~300 cm-2 measured for 100 mm wafers. While median basal plane dislocation counts in 150 mm samples exceed those of the smaller platform, a nearly 45% reduction was realized, resulting in a median density of ~3900 cm-2. Epilayers grown on 150 mm substrates likewise exhibit quality metrics that are comparable to 100 mm samples, with median thickness and doping sigma/mean values of 1.1% and 4.4%, respectively.

Efficient Capture of Particles Via Rotating Magnetic Beads in a Microfluidic Channel

Even with stringent levels of detection the CDC estimates 48 million people a year suffer from food poisoning (1, 2). While it is true that deaths from food poisoning are rare, the economic impact from food poisoning is estimated at $77 billion dollars a year (3). Rapid and efficient detection in food safety applications has two primary challenges. First, the FDA detection level for bacterial contamination is one live cell per 20 grams of food material, a large volume. The practicality of finding one prokaryotic cell in the volume requires pre-concentration as a crucial step in improving the reliability of the test. Second, it is possible to find multiple strains of a given bacteria in a sample. Each of these strains will have similar morphology but different pathological results. Thus a system is required that is strain specific which can also process large quantities of sample. Techniques for cell sorting in microfluidic systems have received a lot of attention recently. The most popular methods to separate the cells are based upon physical characteristics, such as size, shape, weight, density or elasticity. These systems often utilize passive structures that rely on flow conditions or size exclusion principles. However, sorting via this method is not useful for food safety applications because of the strain problem previously described. Labeling the targets with fluorescent or bead-based signals is inefficient due to the large sample volumes involved in food safety testing. This work presents a system that captures dilute concentrations of particles from a bulk fluid (4, 5). The particles are captured by magnetic beads inside a microfluidic channel. The magnetic beads are actuated by rotating around soft magnetic features using an external magnetic field. The magnetic bead sweeps through the fluid, increasing the chances of the particles coming into contact with the magnetic bead by increased fluid mixing and flow agitation (6). Protein and antibody coatings on the magnetic bead then capture the target particles from the bulk fluid and trap it with the magnetic bead. This system is easily multiplexedacross multiple channels to process large quantities of fluid sample and incorporated into a portable system.The system described here uses commercially available magnetic beads (Dynabeads M-280, Life Technologies) and soft magnetic features of permalloy (80/20 NiFe). The soft magnetic features are made by electron beam evaporation onto a bare glass wafer. A standard photolithography process with wet etching of the excess metal was used to produce the soft magnetic features. A layer of silicon dioxide is deposited via plasma enhanced chemical vapor deposition (PECVD) over the entire wafer to protect the soft magnetic features from oxidation during experiments. Finally a PDMS microfluidic channel is created from standard PDMS molding and placed over the wafer to create a fully sealed channel. Magnetic beads are pumped into the array where the magnetic forces from the external magnetic field and the soft magnetic features distribute the beads across the entire array. In this work fluorescent particles (Fluorspheres, 1 µm diameter) are pumped through the array of rotating magnetic beads at various conditions and images taken of the fluorescent particles capture in the array. These particles are analogous in size to common bacteria sought in food safety testing. The goal is to quantify the effectiveness of this system to capture targets from the bulk fluid under different flow and geometric conditions. The conditions considered in this work are flow rate, bead rotation speed, the ratio of magnetic bead diameter to channel height and the packing density of the magnetic features in the array.

Characterization of Boron Diffusion Phenomena According to the Specific Resistivity of N-Type Si Wafer

This paper is directed to characterize the boron diffusion process according to the specific resistivity of the Si wafer. N-type Si wafers were used with the specific resistivity of 0.5-3.2 omega-cm, 1.0-6.5 omega-cm and 2.0-8.0 omega-cm. The boron tribromide (BBr3) was used as boron source to create the PN junction on N-type Si wafer. The boron diffusion in N-type Si wafer was characterized by sheet resistance of wafer surface, secondary ion mass spectroscopy measurements (SIMS) and surface life time analysis. The degree of boron diffusion was depended on the variation in specific resistivity and sheet resistance of the bare N-type Si wafer. The boron diffused N-Si wafer exhibited the average junction depth of 750 nm and boron concentration of 1 x 10(19). N-type Si wafer with the different specific resistance considerably affected the boron diffusion length and life time of Si wafer. It was found that the lifetime of boron diffused wafer was proportional to the sheet resistance and resistivity. However, optimization process may necessary to achieve the high efficiency through the high sheet resistance wafer, because the metallization process control is very sensitive.

Heterojunction solar cells on flexible silicon wafers

ABSTRACTCurrent large-scale production of flexible solar devices delivers cells with low efficiency. In this paper we present an alternative path to organic or inorganic thin films. Our cells combine the remarkable surface passivation properties of the silicon heterojunction solar cells design, and the quality of n-type Cz wafers. The cells were manufactured on 50-70 µm-thick wafers. The cells have and efficiency of 17.8-19.2%, open-circuit voltages of 735-742 mV, short-circuit currents of 34.5-35.5 mA/cm2, and fill-factors of 72-75%. The cells are not as flexible as bare wafers. Thin cells are particular sensitive to the additional stress introduced by the busbars and the soldered ribbons. For radiuses of curvature over 8cm the cells efficiency remains the same, for radius equal to 6cm the cell efficiency drops less than 2%, and for radius equal to 4cm the drop is less than 3%. The broken fingers due to smaller bend radius lead to higher series resistance and subsequently lower field-factors.

B-Spline X-Ray Diffraction Imaging — Rapid non-destructive measurement of die warpage in ball grid array packages

Next generation “More than Moore” integrated circuit (IC) technology will rely increasingly on the benefits attributable to advanced packaging (www.itrs.net[1]). In these increasingly heterogeneous systems, the individual semiconductor die is becoming much thinner (25 to 50μm, typically) and multiple dies can be stacked upon each other. It is difficult to assess non-destructively, non-invasively and in situ the stress or warpage of the semiconductor die inside these chip packages and conventional approaches tend to monitor the warpage of the package rather than the die.This paper comprises an account of a relatively new technique, which we call B-Spline X-Ray Diffraction Imaging (B-XRDI) and its application, in this instance, to the non-destructive mapping of Si semiconductor die lattice misorientation inside wire bonded encapsulated Low-profile Fine-pitch Ball Grid Array (LFPGA) packages. B-XRDI is an x-ray diffraction imaging technique which allows the user to reconstruct from a series of section x-ray topographic images a full profile of the warpage of the silicon semiconductor die inside such a chip package. There is no requirement for pre-treatment or pre-processing of the chip package and we show that synchrotron-based B-XRDI mapping of wafer warpage can be achieved with angular tilt resolutions of the order of 50μrad≈0.003° in times as short as 9–180s (worst case X–Y spatial resolution=100μm) for a full 8.7mm×8.7mm semiconductor die inside the fully encapsulated LFBGA packages. We confirm the usefulness of the technique by correlating our data with conventional warpage measurements performed by mechanical and interferometric profilometry and finite element modelling (FEM). We suggest that future developments will lead to real-time, or near real-time, mapping of thermomechanical stresses during chip packaging processes, which can run from bare wafer through to a fully encapsulated chip package.

Photocurrent Response of Two ­Metal(II) Complexes Based on Rigid Ligands

AbstractTwo metal(II) complexes formulated as Cd3L(L1)3(H2O) (1) and Zn3L(BTC)2(H2O)·7H2O (2) {L = 4‐[4‐(1H‐imidazol‐1‐yl)phenyl]‐2,6‐di(pyridin‐4‐yl)pyridine, H2L1 = 2,5‐bis(3′‐carboxylphenyl)pyridine, H3BTC = 1,3,5‐benzenetricarboxylic acid} were synthesized and structurally characterized by single‐crystal X‐ray diffraction. Complex 1 displays a two‐nodal (3,7)‐connected 3D architecture with a novel (4.62)(48.610.83) topology, in which a Cd3 unit with a Cd···Cd separation of 3.5 Å is observed. Complex 2 possesses two kinds of Zn2 units, and it shows a (3,4,7)‐connected 3D architecture with a novel (4.62)6(43.66.811.10)2(64.82) topology. Complexes 1 and 2 both exhibit quasireversible redox properties, and a photocurrent could be produced on the two complexes upon visible‐light illumination (650 nm > λ > 350 nm). However, different photocurrent responses were observed on the two complexes, and complex 1 yielded a photocurrent density that was higher than that of the bare Si wafer and complex 2, probably because of different charge‐transfer impedances at the interfaces and charge‐carrier concentrations in the photoelectrodes.

A review of electrical characterization techniques for ultrathin FDSOI materials and devices

The characterization of nanosize SOI materials and devices is challenging because multiple oxides, interfaces and channels coexist. Conventional measurement methods need to be replaced, or at least updated. We review the routine techniques that proved efficient for the evaluation of bare SOI wafers (essentially the pseudo-MOSFET) and of MOS structures (transistors and gated diodes). Informative examples are selected to illustrate the typical properties of advanced SOI wafers and MOSFETs. We will show how the ultrathin film and short-channel effects affect the interpretation of the experimental data.

Improvement of Triboelectric Efficiency using SnO2 Friction Layer for Triboelectric Generator

The triboelectric property of a material is important to improve an efficiency of triboelectric generator (TEG) in energy harvesting from an ambient energy. In this study, we have studied the TEG property of a semiconducting which has yet to be explored so far. As a counter triboelectric material, PET and glass are used. Vertical contact mode is utilized to evaluate the TEG efficiency. thin film is deposited by atomic layer deposition on bare Si wafer for various thicknesses from 5.2 nm to 34.6 nm, where the TEG output is increased from 13.9V to 73.5V. Triboelectric series are determined by comparing the polarity of output voltage of 2 samples among , PET, and glass. In conclusion, , as an intrinsic n-type material, has the most strong tendency to be positive side to lose the electron and PET has the most strong tendency to be negative side to get the electron, and glass to be between them. Therefore, the -PET combination shows the highest TEG efficiency.

Characterization and removal of polysilicon residue during wet etching

Process optimization of polysilicon removal by wet etching with alkaline chemicals in a gate-last device integration scheme was investigated. Initial surface condition of the polysilicon layer, spreading properties of wet etching chemicals, and generation of hydrogen bubbles during wet etching were revealed as key parameters affecting the degree of polysilicon residue after wet etching both in patterned structures and on non-patterned bare wafers. Wet etching starting from a hydrophilic polysilicon surface showed successful polysilicon removal (no residues) compared with a hydrophobic polysilicon surface, indicating that the spreading and wetting properties of the wet etching chemical on polysilicon surface is very important in the polysilicon wet etching process. Therefore, it is believed that chemicals showing lower contact angles on the polysilicon surface may be suitable to enhance process efficiency. Furthermore, hydrogen gas generated during silicon wet etching can hinder polysilicon removal, causing significant residues after processing. Ultrasonication or addition of IPA in the wet etching solution can be an alternative method for preventing the hydrogen bubble effect.

A multijunction of ZnIn2S4 nanosheet/TiO2 film/Si nanowire for significant performance enhancement of water splitting

Photoelectrodes with a specific structure and composition have been proposed for improving the efficiency of solar water splitting. Here, a novel multijunction structure was fabricated, with Si nanowires as cores, ZnIn2S4 nanosheets as branches, and TiO2 films as sandwiched layers. This junction exhibited a superior photoelectrochemical performance with a maximum photoconversion efficiency of 0.51%, which is 795 and 64 times higher than that of a bare Si wafer and nanowires, respectively. The large enhancement was attributed to the effective electron–hole separation and fast excited carrier transport within the multijunctions resulting from their favorable energy band alignments with water redox potentials, and to the enlarged contact area for facilitating the electron transfer at the multijunction/electrolyte interface.

Split-Capacitance and Conductance-Frequency Characteristics of SOI Wafers in Pseudo-MOSFET Configuration

Recent experimental results have demonstrated the possibility of characterizing silicon-on-insulator (SOI) wafers through split $C$ – $V$ measurements in the pseudo-MOSFET configuration. This paper analyzes the capacitance and conductance versus frequency characteristics. We discuss the conditions under which it is possible to extract interface trap density in bare SOI wafers. The results indicate, through both measurements and simulations, that the signature due to interface trap density is present in small-area samples, but is masked by the $RC$ response of the channel in regular, large-area ones, making the extraction in standard samples problematic.

Physical Continuity and Vertical Alignment of Block Copolymer Domains by Kinetically Controlled Electrospray Deposition

The fabrication of block copolymer (BCP) thin films is reported with vertically aligned cylindrical domains using continuous electrospray deposition onto bare wafer surfaces. The out-of-plane orientation of hexagonally packed styrene cylinders is achieved in the "fast-wet" deposition regime in which rapid evaporation of the solvent in deposited droplets of polymer solution drives the vertical alignment of the self-assembled structure. Thermally activated crosslinking of the polybutadiene matrix provides kinetic control of the morphology, freezing the vertical alignment and preventing relaxation of the system to its preferred parallel orientation on the nontreated substrate. Physically continuous vertically oriented domains can be achieved over several micrometers of film thickness. The ability of electrospray deposition to fabricate well-ordered and aligned BCP films on nontreated substrates, the low amount of material used relative to spin-coating, and the continuous nature of the deposition may open up new opportunities for BCP thin films.

(Invited) Nanofab Lab . in a Box!™ for Teaching and Outreach

Creating patterned nanowires or highly ordered nanostructures is normally a difficult and expensive project that requires use of a multimillion dollar clean room, expensive tools such as an electron beam lithography tool and highly trained technical team to use and maintain the instruments and laboratory. Once the first copy is made, traditional lithographic patterns need to be reproduced starting from bare wafers. Each and every copy of the nanowire circuits requires new wafers, many hours of patterning, photoresist developing, vacuum deposition and selective removal of materials. Once made, characterizing the product requires additional specialized equipment and skills. For all the work involved, there are no short cuts. The full complexity for making patterned nanowires delays hands on nanotechnology until graduate level classes for most students. The undergraduate research group at University of Wisconsin – Stevens Point has introduced a practical alternative to these techniques for a wide variety of materials (metals, alloys, semiconductors and conductive polymers). Electroplate and Lift Lithography simplifies making patterned nanowires to two steps: electroplate the material on an ultrananocrystalline diamond template and lift the resulting structures away using Scotch tape. Making duplicate copies is accomplished in minutes by repeating the process on the non-sacrificial template. By growing wires for a longer duration, the patterned wires can be characterized with a simple USB powered microscope. The lack of expensive consumables or capital equipment makes this accessible to students even in rural, inner-city or tribal school districts. As a STEM outreach activity, this provides some extraordinary opportunities for students and provides a pathway for high school students to make novel microwire/nanowire research contributions while they are still in high school. A volunteer from the audience will make nanowires and microwires in a live demonstration of the technique. Warning for general high school and undergraduate audiences: After making wires, participants are not allowed to claim “I am no good at science” because you will have performed cutting-edge science. The amazing proof will be the wires that you may keep to show your friends! Figure 1

S1320104 光学的ナノ異物検出を可能とする高感度液相プローブ計測法の研究

There are high demands for inspecting way of bare Si wafer working surface in several tens ran scales with progressing of nanoscale processing technology to detect fine defects. However, it is difficult to find nanoscale particulate defects by conventional methods which are based on scattered light's intensity from defects because its intensity is extremely weak when defects are very small. Then, we conduct research for novel inspecting method of fine particulate defects by using liquid probe system. It uses volatile and inactive liquid for probe capturing automatically plural defects simultaneously by applying property of liquid which build conical film around particles on Si wafer surface with its evaporation. By observing optical multiple interference by these liquid film, it is enabled to detect nanoscale defects optically. In this report, we simulated the optical response and conducted basic experiment to verify our proposed concept and showed possibility of finding fine particulate defects on Si wafer surface.

Evaluation of Hindrance to the Growth of SiN Passivation Layer by Contamination of Fluoride Ions in Front Opening Unified Pod (FOUP)

We have investigated the hindrance to the deposition growth of silicon nitride (SiN) passivation layer from the contamination by airborne molecules in the front opening unified pod (FOUP). In particular, an artificial contamination of FOUP by fluoride ions as the source of the contaminants is utilized to elucidate the influence of contamination on the wafer surface. When the bare wafer surface is exposed to fluoride ions in the contaminated FOUP, the deposited thickness of the SiN layer is observed to decrease to a maximum of 11 A from our experimental condition. On the other hand, there is no appreciable variation in the thickness of deposited SiN layer stored in the pre-cleaned FOUP. Based on the analytical results of wafer surfaces and FOUPs, we believe that the contamination of fluoride ions on wafer surfaces is originated from the contaminated surface of FOUP. Therefore, we conclude that it is necessary to clean and monitor the inside of FOUP on a regular basis, especially after wet or dry etching processes, which generates gaseous impurities.

In Situ Characterization of Bias Instability in Bare SOI Wafers by Pseudo-MOSFET Technique

Bias instability is a reliability issue affecting the electrical characteristics of a MOS transistor when the gate is stressed with relatively high voltage. For the first time, we characterize the instability of bare SOI wafers using the pseudo-MOSFET technique. The effect of positive and negative stress pulses on the properties of both hole and electron channels is systematically investigated using measure-stress-measure and on-the-fly methods. The origin of the instability, the dependence of the degradation with time, and the recovery after the stress are discussed.