Backside Surface Research Articles

Retention and release mechanisms of tritium loaded in plasma-sprayed tungsten coatings by plasma exposure

Depth profiles of tritium (T) loaded by gas and plasma in tungsten (W) coatings on ferritic steels have been examined by using a tritium imaging plate technique and their changes during storage and after annealing have been monitored. The depth profiles of T consisted of 4 components, (I) T trapped at impurities and defects newly introduced in the near surface region of the coating by plasma loading, (II) T trapped at the inner surfaces of the grains and dissolved in the grains resulting in a flat depth profile throughout the whole coating, (III) T dissolved and diffused into the substrate giving a decaying profile, and (IV) T trapped at the backside surface of the substrate. The results support that retention of T is mainly caused by pore diffusion of gaseous T followed by dissolution and trapping in/at each W grain, and dissolution of T into the F82H substrate to allow permeation . Release of T proceeds in an opposite way of retention but each component desorbs independently.

The Use of Light Diffracted from Grating Etched onto the Backside Surface of an Atomic Force Microscope Cantilever Increases the Force Sensitivity

A reflecting diffraction grating has been etched onto the backside of a standard cantilever for atomic force microscopy, and the diffracted light has been used to monitor the angular position of the cantilever. It is shown experimentally that for small angles of incidence and for large reflection angles, the force sensitivity can be improved by few times when an appropriate detection scheme based on the position sensitive (duolateral) detector is used. The first demonstration was performed with a one micron period amplitude diffraction grating onto the backside of an Al-coated cantilever etched by a focused ion beam milling for the experiments in air and an analogous 600 nm-period grating for the experiments in air and in water.

Investigation of the hot cracking susceptibility of laser welds with the controlled tensile weldability test

Due to significant developments over the last decades, laser beam welding has become a well-established industrial process offering high processing speeds and causing low component distortions. But an important issue currently preventing its intense use, especially in the energy or plant construction sector where high alloy steels are applied, concerns hot crack formation. Although considerable advances in understanding hot cracking mechanisms have been made, most of the known influencing factors are metallurgical in character. The thermo-mechanical effects are barely considered or quantified. Up to the present, there exist numerous hot cracking tests that were however conceived for welding methods other than laser beam welding. Considering the special features of the laser welding process, such as high cooling rates and the narrow process zone, results obtained with other welding techniques and test procedures cannot be transferred to laser beam welding. In this study, the laser beam weldability of various stainless steels was examined in terms of their susceptibility to hot cracking by means of the controlled tensile weldability test, which was proven to be suitable for use in conjunction with CO2 laser welding. This test allows the application of tensile strain at a variable fixed cross-head speed transverse to the welding direction. Full and partial penetration bead-on-plate welds were produced. In a first attempt to determine the impact of the applied external strain on the local transient strains and strain rates near the weld pool, an optical system was used to measure the backside surface of partial penetration welds. The results showed the influence of the strain and the strain rates on hot crack formation. Furthermore, a classification of the studied austenitic, duplex and ferritic stainless steels according to the established test criteria (critical strain and cross-head speed) was conducted.

Rotating-platform Has No Surface Damage Advantage Over Fixed-bearing TKA

Rotating-platform TKA, although purported to have superior kinematics, has shown no clinical advantages over those of fixed-bearing TKA. Our design-matched retrieval study aimed to investigate if differences in bearing wear damage exist between fixed- and mobile-bearing TKAs with similar condylar geometry. We asked whether (1) the rotating platform's more conforming tibiofemoral articulation would be associated with less severe damage; (2) the location of damage and wear would be similar on the tibiofemoral or backside surfaces of two contemporary designs with similar condylar geometry; and (3) the combined damage and deformation measured as thickness would differ between the two designs. We performed damage grading and damage mapping on 25 rotating-platform and 17 fixed-bearing inserts. The patient demographic data from each of these cohorts were comparable. Inserts were also laser-scanned from which we obtained thicknesses, and inferior surface three-dimensional scans, from which we determined dimensional changes. Rotating-platform and fixed-bearing inserts had similar tibiofemoral damage scores. However, the scores on the inferior surface of rotating platforms were greater, often as a result of third-body debris scratching observed on both damage mapping and three-dimensional scans. The extent of damage as a function of surface area was greater for rotating platforms, consistent with the greater tibiofemoral conformity. Dimensional changes on the inferior surfaces of the fixed bearing followed loading areas of the knee. However, no differences were seen in the thicknesses between fixed- and rotating-platform bearings. The increased total damage score on the rotating platform, coupled with increased surface area damaged and the propensity for third-body debris, indicates no damage advantage to this mobile-bearing design.

Impact of Cu Contamination on Memory Retention Characteristics in Thinned DRAM Chip for 3-D Integration

The influence of Cu diffusion at the backside surface of a thinned dynamic random access memory (DRAM) chip for 3-D integration on memory retention characteristics was electrically evaluated. A DRAM test chip was bonded to a Si interposer at 300 °C for 2 min and thinned down to 30-μm thickness. The DRAM cell characteristics, which show 50% failure at 200 μs, were not degraded from the packaged sample (prethinning) even after chip bonding, chip thinning, and no-Cu postannealing for 30 min at 300 °C. Meanwhile, the DRAM cell array shows 50% failure at 70 μs after an intentional Cu diffusion from the backside surface for 30 min at 300 ° C. It means that Cu atoms at the back surface reach the Si-SiO2 interface of the front surface in active areas and cause functional failures such as increasing carrier recombination rate, consequently shortening retention time. However, the NMOS transistor characteristics show no significant change even after Cu diffusion. The on-current performance characterized by majority carriers is not an effective criterion to characterize sensitively the Cu contamination effect.

Performance evaluation of an off-grid photovoltaic system in Saudi Arabia

The paper presents the performance evaluation analysis of a 5.28 kW installed capacity isolated grid photovoltaic power plant installed at King Fahd University of Petroleum and Minerals, Dhahran Saudi Arabia in June 2010. The plant was equipped with temperature, solar radiation intensity, and PV (Photovoltaic) panel power output recording sensors for performance evaluation of the plant. The analysis presented the effect of PV surface temperature and dust collected on the panels on the power output of individual arrays and total power from complete plant. Furthermore, the PV panel performance was studied by DC (Direct current) performance ratio variation with PV panel backside surface temperature. Hourly mean energy yield was found to be decreasing with increasing PV panel surface temperature during the months of July & August 2010. The daily energy yield showed a decreasing trend with days of the month which could be accounted for dust accumulation on the PV panel surface. The DC performance ratio also showed a decreasing trend with increasing PV panel surface temperature.

Separation of Front and Backside Surface Recombination by Photoluminescence Imaging on Both Wafer Sides

In this paper, we present a method to separate the front and the backside surface recombination based on two photoluminescence images: one taken from the front side of the wafer and one from the backside. We use a 790-nm laser with a penetration depth in silicon of only 11 μm. At such a shallow charge carrier generation, the surface recombination of the illuminated side affects the minority carrier density to a greater extent than the recombination of the nonilluminated side. To utilize this effect, we calculate the ratio of the front side and the back side lifetime image. This ratio image allows an easy distinction not only of surface defects from bulk defects but of front surface recombination from back surface recombination as well. With a simple calculation, even quantitative surface recombination velocities can be obtained.

Computational development of a polyethylene wear model for the articular and backside surfaces in modular total knee replacements

A computational model to predict polyethylene wear in modular total knee replacements was developed. The results from knee simulator wear tests were implemented with finite element simulations to identify the wear factors of Archard's wear law. The calculated wear factor for the articular and backside surface was 1.03±0.22×10−7mm3/Nm and 2.43±0.52×10−10mm3/Nm, respectively. The difference in wear factors was attributed to differences in wear mode and wear mechanisms between the articular (mainly two-body rolling/sliding wear mode with an abrasive/adhesive wear mechanism) and the backside surfaces (mainly fretting wear mode with an adhesive wear mechanism).

Semi-quantitative assessment methods for backside polyethylene damage in modular total knee replacements

Two semi-quantitative grading methods (referred to as the Hood/Wasielewski-method and the Modified-method) were described and then applied to 52 retrieved tibial polyethylene inserts from modular total knee replacements. Their ability to assess backside surface damage was compared. The damage score correlation with the implantation period greater than 24 months was better using the Modified-method (R=0.524, p=0.006) than using the Hood/Wasielewski-method (R=0.328, p=0.102). Also, the Modified-method gave significantly higher damage scores for males with gamma-in-air irradiated polyethylene inserts whereas the Hood/Wasielewski-method did not. Thus, the damage score obtained using the Modified-method seemed to provide a better representation of clinical surface damage and possibly PE wear.

A semi-analytical model for semiconductor solar cells

A semi-analytical model is constructed for single- and multi-junction solar cells. This model incorporates the key performance aspects of practical devices, including nonradiative recombination, photon recycling within a given junction, spontaneous emission coupling between junctions, and non-step-like absorptance and emittance with below-bandgap tail absorption. Four typical planar structures with the combinations of a smooth/textured top surface and an absorbing/reflecting substrate (or backside surface) are investigated, through which the extracted power and four types of fundamental loss mechanisms, transmission, thermalization, spatial-relaxation, and recombination loss are analyzed for both single- and multi-junction solar cells. The below-bandgap tail absorption increases the short-circuit current but decreases the output and open-circuit voltage. Using a straightforward formulism this model provides the initial design parameters and the achievable efficiencies for both single- and multiple-junction solar cells over a wide range of material quality. The achievable efficiency limits calculated using the best reported materials and AM1.5 G one sun for GaAs and Si single-junction solar cells are, respectively, 27.4 and 21.1% for semiconductor slabs with a flat surface and a non-reflecting index-matched absorbing substrate, and 30.8 and 26.4% for semiconductor slabs with a textured surface and an ideal 100% reflecting backside surface. Two important design rules for both single- and multi-junction solar cells are established: i) the optimal junction thickness decreases and the optimal bandgap energy increases when nonradiative recombination increases; and ii) the optimal junction thickness increases and the optimal bandgap energy decreases for higher solar concentrations.

Semiconductor nanopores formed by chemical vapor deposition of heteroepitaxial SiC films on SOI(100) substrates

The authors investigated the formation of nanometer-scale pore (nanopore) arrays by chemical vapor deposition (CVD) of heteroepitaxial SiC films on Si(100) membranes prepared by anisotropic etching of silicon on insulator substrates from the back-side surfaces. SiC heteroepitaxial films with thicknesses of ∼10 nm were grown by pulse jet CVD of CH3SiH3 gas. During the SiC growth, inverted pyramidal pits with {111} facets grew into the Si membranes due to the surface diffusion of Si atoms outward from the bulk Si. Nanopores were formed at the tips of the inverted pyramidal pits. The pore sizes were found to be dependent on the existence of the buried oxide layers under the Si membranes. It is suggested that maintaining the {111} facets during the SiC growth on the Si membrane is essential for smaller size (∼nm) pore formation.

Retrieval analysis of modular total knee replacements: Factors influencing backside surface damage

Retrieved knee implants were examined to investigate the influence of patient and implant related factors on backside damage. Fifty-two implants of three different models were examined that all had cemented tibial trays without screw holes. A semi-quantitative grading system supplied backside damage scores (BDS) for each polyethylene (PE) tibial insert. Evidence was obtained to support the use of a constraining partial-peripheral locking mechanism and polished tibial tray surface (particularly for male patients) to reduce backside damage. Overall, male patients in the present study were associated with higher body mass and higher BDS compared with female patients. Furthermore, PE inserts sterilized by gamma-in-air had higher BDS than PE inserts sterilized in inert environments (gas–plasma or ethylene–oxide). Also, the proximal surfaces of tibial trays that had been grit-blasted showed embedded particles that may have increased backside damage. While none of these overall findings was unexpected, the present study provided detailed supporting analysis based on data from clinical retrievals, which may further support the use of a polished tibial tray combined with partial-peripheral locking mechanism to reduce BDS.

Cu Retardation Performance of Extrinsic Gettering Layers in Thinned Wafers Evaluated by Transient Capacitance Measurement

The behaviors of Cu diffusion at backside surface of thinned wafer with extrinsic gettering layer in three-dimensional (3-D) LSI were electrically and quantitatively evaluated by capacitance-time (C–t) analysis and Zerbst plot. In order to electrically evaluate Cu diffusion characteristics, MOS capacitors were fabricated using the thinned wafer of 100-μm thickness. To compare the gettering ability to Cu diffusion, three types of extrinsic gettering layers were prepared on the back surface of thinned wafers by mechanical grinding and following CMP, DP, and UPG methods. For accelerated Cu diffusion test, thin Cu layer was deposited on the back surface as a contamination source and Cu atoms were artificially diffused into the substrate by annealing at 300°C for various times. In the CMP treated wafer, the C–t curves of MOS capacitor are most severely degraded and transient time tf is more seriously decreased after annealing. The gettering efficiency of the DP treated wafer is enhanced about 50% as compared with the CMP treated wafer and 20% as compared with the UPG treated wafer, respectively, after annealing for 60 min. The DP treated wafer shows most good gettering ability to Cu diffusion.

Post Damage in Contemporary Posterior-Stabilized Tibial Inserts: Influence of Implant Design and Clinical Relevance

The mechanisms of damage at the polyethylene post in 3 contemporary tibial insert designs were evaluated and compared with a historical standard (Insall-Burstein II; Zimmer, Warsaw, Ind). One hundred five gamma sterilized posterior-stabilized tibial inserts were revised after an average of 4.7 years (0.05-13.6 years). Retrievals were classified according to their designs: Insall-Burstein II (n = 28); PFC (Johnson & Johnson, Raynham, Mass; n = 30); NexGen (Zimmer; n = 32); and Scorpio (Stryker Orthopaedics, Mahwah, NJ; n = 15). Reasons for revision and patient details were available. Surface damage scoring and photogrammetry were performed on all the retrieved tibial inserts. Oxidation analysis was carried out for traceable historical, gamma air-sterilized and conventional, gamma inert-sterilized tibial inserts (n = 61) with the use of infrared spectroscopy. The posts for all 3 contemporary designs exhibited damage similar to the historical controls. Articular, post, and backside damage scores significantly increased with implantation time. Post damage was insensitive to design and patient factors but was exacerbated by oxidation. An association between damage at the post and articular surface was also confirmed. Logistic models suggested an interaction between post damage, backside surface damage, and implant loosening.

Organic vapor sensors based on functionalized macroporous Si using single and double-side electrochemical etching

Organic sensors for ethanol vapor detection were developed by means of electrochemical etching of crystalline silicon as initial substrate following two procedures: front side etching (FSE) and front- and backside (double) surface etching (DSE). The first consists on the attack of the crystalline silicon surface by hydrofluoric acid (HF) in presence of a constant current flow to form a layer of vertically oriented pattern of pores with diameters in the 2-5µm range and a thickness of about 50µm. The second procedure is similar to the first one but allowing a similar etching to the opposite side of the silicon wafer. The etching times for both surfaces were adjusted in such a way to produce a free standing porous layer of around 300µm in thickness. The samples produced by FSE and DSE were submitted to a functionalization methodology using 4-aminopyridine to cover the porous surface. The obtained specimens were mounted in a holder with two soldered contacts and placed in a testing chamber where different flows of ethanol vapors were injected. Conductance responses of both kinds of sensors were recorded and compared between them and with respect to nontreated crystalline silicon samples in terms of sensing capability, reproducibility, and response times. The results indicate that both FSE and DSE sensors have improved sensing properties compared to the nontreated surfaces.

Surface-Texturing of Single-Crystalline Silicon Wafers

In this work, alkaline-based anisotropic etchants, tetramethylammonium hydroxide (TMAH) and potassium hydroxide (KOH)/isopropyl alcohol (IPA) solutions, have been used for the surface texturing of the single-crystalline silicon wafers used for solar cells. The pyramid morphology produced by the surface texturing can reduce the surface reflection of the incident light and increase the light absorption so that the efficiency of the solar cells can be increased. The experimental data shows that the optimized surface texturing has been obtained with 5 wt. % TMAH anisotropic etching at 80 °C. The surface reflectance of the polished front surface can be reduced to 17 % and the surface reflectance of the unpolished backside surface can be reduced to 3 %, respectively. This result shows that the anisotropic etching can effectively reduce the surface reflectance. While for the surface texturing with KOH/IPA mixture, the front surface reflectance can only be reduced to 35 % and the backside surface reflectance can only be reduced to 5 %, respectively. Besides, debris of Si nano-crystals exists around the pyramid base area when texturing with the KOH/IPA mixture.

High quality 3D shapes by silicon anodization

AbstractIn this paper some process considerations and optimizations of anodization for three‐dimensional (3D)‐structuring of silicon are discussed. For the shape controlling of etched form different approaches, such as frontside masking design, local backside doping and surface pre‐structuring are presented. Influences of the opening size and etch depth on the shape of the etching form are investigated. The surface quality of the resulting 3D structures is critically dependent on the specific process parameters and process flow. Best surface quality was obtained for electropolishing in 7 wt.% hydrofluoric acid (HF) at applied current densities of 100–300 mA/cm2. Application of 3D silicon forms for injection moulding is demonstrated and further implementations of the process for optical and fluidic devices are discussed.magnified image 3D silicon shapes fabricated using anodization process with local backside doping design.

CELLO measurement technique for local identification and characterization of various types of solar cell defects

AbstractThe CELLO technique allows to measure local data for a large number of solar cell parameters like bulk life time, back side surface recombination velocity, diffusion coefficient, and serial resistance. Inhomogeneities of these parameters induce lateral current flow in forward direction, which mixes the effects of the different defect types. Even if all local parameters would be known, a complete simulation is needed to obtain information about the local efficiency. Direct CELLO measurement at e.g. the working of the solar cell or at open circuit allows extracting this combined information directly. Examples for this will be presented in this paper, dealing with multicrystalline silicon solar cells showing a variety of defect types.Mainly to save measurement time several frequencies are applied simultaneously as a Laser intensity perturbation signal and analyzed by FFT deconvolution. The frequencies can be applied simultaneously to 3 confocal Lasers with different wavelength, i.e. penetration depths. Typically 4 frequencies are analyzed simultaneusly in order to maintain a good signal to noise ratio. This features will be discussed shortly as well. Especially the application of a deep penetrating Laser significantly increases the robustness of the fitting procedure and allows to separate reliably bulk and surface recombination and mobility dependencies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Backside SERS studies of inhibitor transport through polyelectrolyte films on Ag-substrates

In situ backside surface enhanced Raman spectroscopy (in situ-SERS) was newly employed for the study of the transport of inhibiting molecules through a polymer film. The barrier properties of layer-by-layer polyelectrolyte films (PE) composed of polyacrylic acid and polyallylamine hydro-chloride layers on Ag-surfaces were compared between untreated, thermally crosslinked, and Ag-nanoparticles containing samples. IB-SERS enabled the study of the transport of 2-mercaptobenzimidazole (MBI) as an inhibitor through the film. Water barrier properties of the treated PE films determined by Electrochemical Impedance Spectroscopy were correlated to the MBI diffusion kinetics. The PE stability against MBI diffusion and thermal treatment was analyzed by Infra-Red Reflection Absorption Spectroscopy (IRRAS). IRRAS showed that the thermally treated PE films formed chemical crosslinking via amide bonds and lowered the diffusion of water and the water uptake in the films. Moreover, the MBI diffusion kinetics can be followed by means of SERS. However, MBI adsorption at the PE film/metal interface was not detected after the heat treatment. In this case the adsorbed PE on the Ag surface was not substituted by the competing adsorption of MBI. Moreover, the presence of Ag-nanoparticles in the film decelerated MBI diffusion to the SERS substrate due to the trapping effect of MBI molecules.

Evaluation of Cu Contamination at Backside Surface of Thinned Wafer in 3-D Integration by Transient-Capacitance Measurement

The influence of Cu contamination at backside surface of a thinned wafer in three-dimensional LSI was electrically evaluated by capacitance-time (C-t) measurement. A MOS capacitor was fabricated using a thinned wafer of 50-μm thickness. The (C-t) curves of the MOS capacitor were severely degraded even after initial annealing at 300 °C for 5 min. It means that Cu atoms at the back surface reach the Si-SiO2 interface of the front surface, and the generation lifetime is significantly reduced. The quantitative relationship between the generation lifetime and surface concentration of Cu atom was evaluated. The (C-t) measurement is a highly promising method to electrically characterize the influence of Cu contamination on device reliability in fabricated LSI wafers.