Layer Antireflection Coatings Research Articles

Fabrication of Single Layer SiO2 and Si3N4 as Antireflection Coating on Silicon Solar Cell Using Silvaco Software

The main objectives was to investigate and enhance the short circuit current density, J sc and also to improve the efficiency of silicon solar cel l by fabricating a layer of silicon dioxide (SiO 2) and silicon nitride (Si 3N4) coatings on silicon solar cell. This fabrication carried out on high temperature during annealing process from 800-1050°C and variable thickness of antireflection coating (ARC) layer from 50-90 nm thick. The photovoltaic propert ies of Si 3N4 layer have been compared with SiO 2 layer to determine which material is suitable in fa bricating single layer ARC. Solar cell simulation could be useful for time saving and cost consumptio n. Problem statement: The Silvaco software is not widely used in designing the 2D solar cell devi ces because there are lots of 1D, 2D and 3D- simulation beside Silvaco software such as MicroTec, SCAPS-1D. Approach: The silicon dioxide (SiO 2) and silicon nitride (Si 3N4) coating have been modeled and fabricated on silic on solar cell by using Silvaco software packaging. Results: For SiO 2 results, the FF value is approximately 0.758 and η maximum 9.43%. In annealing process, the temperature becomes higher resulted increasing of pn junction depth. However, not to V oc and Jsc values, both parameters were slowly decreased when temperature increased. Meanwhile, when the thickness of SiO 2 layer is increased, the parameters of pn junction depth, J sc , Voc , FF and η were decreased slowly. As for Si 3N4 result, the calculated FF approximately 0.758 and η maximum is 9.57%. During annealing process, the temperature increasing constantly follows the increasing of pn junction de pth and Jsc , meanwhile the Voc is decreased slowly. In variable Si 3N4 thickness simulation, the output parameters of pn junction depth, J sc , Voc , FF and η were decreased when the thickness increased 10 nm each simulation. Conclusion: The optimum temperature during annealing process for SiO 2 is 950 °C, while for Si 3N4 is 1050 °C. For the thickness analysis, the optimum ARC thickness for SiO 2 and Si 3N4 layer is 50 nm both.

Hydrogen silsesquioxane-based hybrid electron beam and optical lithography for high density circuit prototyping

The authors report on a hybrid lithography process that integrates electron beam lithography (EBL) and optical photolithography. To maximize resolution and density, the EBL exposure is performed using a hydrogen silsesquioxane-based resist, while the photolithographic exposure is performed using standard positive or negative tone 248nm photoresists. Both exposures take place on a common underlayer consisting of an antireflective coating (ARC). During pattern transfer into the ARC layer, a composite image of the two lithographic exposures is formed creating a robust and versatile etch mask for further pattern transfer into the substrate. They demonstrate the utility of this technique by using it to pattern the active, gate, and wiring levels of complementary metal oxide semiconductor devices and circuits consisting of trigated Fin-based field effect transistors. These devices have a minimum active area pitch of 50nm, minimum gate pitch of 90nm, and achieve densities suitable for 15nm node static random access memory cells. Details of the exposure process and device fabrication are discussed along with electrical results from the resulting devices and circuits built using this technique.

Porous Si Layer by Electrochemical Etching for Si Solar Cell

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating(ARC) and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si ARC layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layers were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The structure of porous Si layers was investigated with SEM. The formation of a nanoporous Si layer about 100nm thick on the textured silicon wafer result in a reflectance lower than 5% in the wavelength region from 500 to 900nm. Such a surface modification allows improving the Si solar cell characteristics. An efficiency of 13.4% is achieved on a monocrystalline silicon solar cell using the electrochemical technique.

Numerical calculation of the reflectance of sub-wavelength structures on silicon nitride for solar cell application

In this study, we calculate the spectral reflectivity of pyramid-shaped silicon nitride (Si 3N 4) sub-wavelength structures (SWS). A multilayer rigorous coupled-wave approach is advanced to investigate the reflection properties of Si 3N 4 SWS. We examine the simulation results for single layer antireflection (SLAR) and double layer antireflection (DLAR) coatings with SWS on Si 3N 4 surface, taking into account effective reflectivity over a range of wavelengths and solar efficiency. The results of our study show that a lowest effective reflectivity of 1.77% can be obtained for the examined Si 3N 4 SWS with the height of etched part of Si 3N 4 and the thickness of non-etched layer of 150 and 70 nm, respectively, which is less than the results of an optimized 80 nm Si 3N 4 SLAR (∼5.41%) and of an optimized DLAR with 80 nm Si 3N 4 and 100 nm magnesium fluoride (∼5.39%). 1% cell efficiency increase is observed for the optimized Si solar cell with Si 3N 4 SWS, compared with the cell with single layer Si 3N 4 antireflection coatings (ARCs); furthermore, compared with DLAR coated solar cell, the increase is about 0.71%. The improvement on the cell efficiency is mainly due to lower reflectance of Si 3N 4 SWS over a wavelength region from 400 to 600 nm that leads to lower short circuit current.

Fabrication of antireflective sub-wavelength structures on silicon nitride using nano cluster mask for solar cell application.

We have developed a simple and scalable approach for fabricating sub-wavelength structures (SWS) on silicon nitride by means of self-assembled nickel nanoparticle masks and inductively coupled plasma (ICP) ion etching. Silicon nitride SWS surfaces with diameter of 160–200 nm and a height of 140–150 nm were obtained. A low reflectivity below 1% was observed over wavelength from 590 to 680 nm. Using the measured reflectivity data in PC1D, the solar cell characteristics has been compared for single layer anti-reflection (SLAR) coatings and SWS and a 0.8% improvement in efficiency has been seen.

Modelling and Simulation Single Layer Anti-Reflective Coating of ZnO and ZnS for Silicon Solar Cells Using Silvaco Software

Modelling and Simulation Single Layer Anti-Reflective Coating of ZnO and ZnS for Silicon Solar Cells Using Silvaco Software

ZnO Nanostructures as Efficient Antireflection Layers in Solar Cells

An efficient antireflection coating (ARC) can enhance solar cell performance through increased light coupling. Here, we investigate solution-grown ZnO nanostructures as ARCs for Si solar cells and compare them to conventional single layer ARCs. We find that nanoscale morphology, controlled through synthetic chemistry, has a great effect on the macroscopic ARC performance. Compared with a silicon nitride (SiN) single layer ARC, ZnO nanorod arrays display a broadband reflection suppression from 400 to 1200 nm. For a tapered nanorod array with average tip diameter of 10 nm, we achieve a weighted global reflectance of 6.6%, which is superior to an optimized SiN single layer ARC. Calculations using rigorous coupled wave analysis suggest that the tapered nanorod arrays behave like modified single layer ARCs, where the tapering leads to impedance matching between Si and air through a gradual reduction of the effective refractive index away from the surface, resulting in low reflection particularly at longer wavelengths and eliminating interference fringes through roughening of the air-ZnO interface. According to the calculations, we may further improve ARC performance by tailoring the thickness of the bottom fused ZnO layer and through better control of tip tapering.

Effect of Additives on the Durability and Properties of Antireflective Films for Solar Glass Covers

Generally, single layer antireflective (AR) coatings are based on SiO2 for which the low refractive index is achieved by increasing the porosity of the films. On the other hand, the increase of porosity on any material results in a decrease of its mechanical properties. In addition to increasing the solar transmittance, it is equally important that the AR film is long-term stable for its application in solar collectors. In this sense, the objective of our work has been to develop a film that exhibits good AR properties and physical durability as well. In the present study, sol-gel silica films have been deposited on borosilicate glass. The effect of adding some organic compounds to the precursor solution in the properties of the films has been studied. Moreover, accelerated weathering tests have been performed in order to investigate the outdoor durability. A value of solar transmittance as high as 0.974 has been obtained by using a porosity promoter additive. However, the durability tests have shown the necessity of incorporating a hydrophobic additive to the precursor solutions in order to avoid the degradation of the optical properties of the films. 1.5% decrease in solar transmittance is observed after 1900h in the weathering chamber for films prepared with methyltriethoxysilane.

Study on epitaxial silicon thin film solar cells on low cost silicon ribbon substrates

Heavily B-doped silicon ribbons were prepared by modified silicon sheets from powder (SSP) technique using 9 N purity electronic-grade silicon powder. Utilizing the SSP ribbons as substrates, crystalline silicon thin film (CSiTF) solar cells have been fabricated by direct epitaxy method. As-prepared CSiTF solar cells were characterized by illuminated and dark I– V characteristic measurement, Suns- V oc measurement, quantum efficiency (QE) and reflectance measurement. The results show that the CSiTF solar cells have poor performance with typical efficiency η only about 4.25%, and nearly all the characteristic parameters are far away from the ideal values. By detailed analysis and discussion on the measured results, it was found that grain boundary (GB) recombination in the active layers and electrical leakage at the edge of the PN junctions play a major role in deteriorating the performance of the CSiTF solar cells, which lead to higher dark saturation current I s and lower parallel resistance R sh, respectively. By improving the preparation process, such as optimization of the epitaxy process, use of remote plasma hydrogen passivation (RPHP), optimization of the metallization and use of double layer anti-reflection (DLAR) coatings, etc., all the characteristic parameters of the CSiTF solar cells have been greatly improved, and the best efficiency value increased to 8.02%.

Effect of thin-film imaging on line edge roughness transfer to underlayers during etch processes

For the patterning of sub-100 nm features, a clear understanding of the origin and control of line edge roughness (LER) is extremely desirable, from a fundamental as well as a manufacturing perspective. With the migration to thin photoresists coupled with bottom antireflective coating (ARC)-hardmask underlayers, LER analysis of the developed resist structures is perhaps an inaccurate representation of the substrate roughness after the etch process, since those underlayers can play a significant role in increasing/decreasing linewidth variations during the image transfer process and hence can impact the device performance. In this article, atomic force microscopy is used to investigate the contribution of the imaging resist sidewall topography to the sidewall roughness of the final etched feature in thin photoresists, ARC, and hardmasks. Resist systems suitable for 248 and 193 nm lithography as well as fluorine-containing resists were processed using N2-H2 or fluorocarbon plasma etch. It is shown that the interaction of different etch chemistries with existing sidewall profiles can result in loss of the original morphological information and creation of new spatial frequency domains that act as physical templates for subsequent image transfer processes. Excessive roughness transfer into the hardmask layer due to insufficient resist thickness or inadequate etch resistance originates from striation propagation from the resist layer into the hardmask layer. In the case of fluorine-containing materials, a decreased etch resistance and reduced initial film thickness values give rise to critical underlayer roughening during plasma etch. Based on the results shown, it is predicted that advanced resist systems for 157 nm lithography and beyond will require the use of ARC layers with built-in hardmask properties in those particular cases in which patterning of deep trenches is needed, in order to maintain LER values within acceptable levels.

Diluted Low Dielectric Constant Materials as Bottom Antireflective Coating Layers for both KrF and ArF Lithography Processes

In this paper, we report on a bottom antireflective coating (BARC) layer for both KrF and ArF lithography processes. The antireflective layers are composed of diluted low-dielectric constant materials, such as bisbenzo(cyclobutene) (BCB), fluorinated poly(arylene)ether (FLARE) and SiLK. By adding an optimized thickness of diluted low-dielectric constant materials, the reflectance of less than 1% at the resist/silicon substrate interface can be achieved. Diluted low-dielectric constant materials also have great potential to be used as BARC layers on various highly-reflectance substrates for metal-interconnect applications. Using this structure, it is easy to reduce reflectance without adding an extra BARC layer for patterning low-dielectric materials. After the lithography procedure, the diluted low-dielectric constant layer need not be removed.

Low Dielectric Constant Polymer Materials as Bottom Antireflective Coating Layers for both KrF and ArF Lithography

In this paper, we demonstrate a new bottom antireflective coating (BARC) layer for both KrF and ArF lithography. The antireflective layers are composed of a novel low-dielectric constant polymer material (SiLK) and its etching hard-mask layer. By adding an optimized hard-mask layer, the reflectance of less than 1% at the resist/silicon substrate interface can be achieved. SiLK also has great potential to be used as BARC layers on various highly-reflectance substrates for metal-interconnect applications with large thickness-controlled tolerance. By using this novel structure, it is easy to reduce reflectance without adding an extra BARC layer for patterning low-dielectric materials. In this paper, suitable etching characteristics and thermal stability of SiLK-based BARC layers are also described.

Design and simulation of antireflection coating systems for optoelectronic devices: Application to silicon solar cells

Reflectance calculation for various single-, double- and triple-layer Antireflection coatings (ARCs) on silicon substrate are presented. A calculation program is developed to determine the optimum thickness and the refractive index of each layer at a single wavelength for optoelectronic applications and through the visible spectrum for photovoltaic applications. Ta 2O 5, ZnS, Al 2O 3 single layer, MgF 2/Zns double layer and MgF 2/Al 2O 3/ZnS triple layer ARC systems are deposited on silicon substrate using electron beam and thermal evaporation as deposition techniques. The reflectance as a function of the wavelength of AR coating systems on silicon substrate is measured. All curves show good accordance between the theoretical and the experimental reflectance. As application in the photovoltaic field, a ZnS single-layer AR coating is evaporated on concentrator silicon solar cells. Spectral response and current–voltage characteristics are measured before and after ZnS ARC deposition to estimate the improvement of the cell performances. Short-circuit current and cell efficiency are increased by about 31% and 29.4%, respectively.

Performance of different etch chemistries on titanium nitride antireflective coating layers and related selectivity and microloading improvements for submicron geometries obtained with a high-density metal etcher

Different chemistries were evaluated in a metal etcher with a high-density plasma source that was used to etch a titanium nitride antireflective coating (ARC). A composite film structure consisting of aluminum (with 0.5%–1% Cu) as the underlying layer, a titanium nitride ARC layer, and titanium nitride as the barrier layer were used for the standard stack, while titanium nitride and aluminum layers alone were used for the initial characterizations of the process. Conventional BCl3/Cl2 chemistry was used initially to etch both the titanium nitride ARC layer and the underlying aluminum layer. The performance of BCl3/Cl2 chemistry on the titanium nitride ARC layer as well as on the composite stack was evaluated. Partial etch measurements were taken to calculate the composite microloading and resist selectivity values. Different etch chemistries were then employed for the ARC layer while keeping conventional BCl3/Cl2 chemistry for the aluminum layer, and the difference in process performances were evaluated. Fluorine additives along with chlorine as the main etchant gave very high etch rate values for the titanium nitride layer. CHF3 was added as the fluorine source for the current study. When the titanium nitride layer was etched with chemistries having faster etch rates, CHF3 added chemistries in the current study, a remarkable improvement in the composite microloading was observed, compared to the microloading values obtained with conventional chemistry. An improved etch rate uniformity was another noticeable performance improvement. Possible mechanisms for these trends are explained in this article. The experimental portion of this article will provide details relating to the etcher and the film structure used for the study. The results and discussion section will give details of the process performance and a comparative evaluation of different titanium nitride chemistries, as well as possible mechanism for the trends observed.

Electromigration Induced Failure as a Function of Via Interface

ABSTRACTFailure of test structures composed of pairs of W vias connected by lengths of Al/0.5%Cu conductor were compared as a function of the position of the via with respect to the conductor link. In one configuration, the current was passed from first level to a conductor link on second level and in the other the current was passed from second level to one on the first. In each case the links were identical in cross section, length and composition. There was a significant difference in the performance with respect to electromigration lifetime between these configurations as well as a difference in the failure mode. In the first level links, where the current passed first through a a 350A thick TiN ARC (Anti-Reflective Coating) layer and then a 150A Ti layer, the lifetime was significantly shorter than that of the second level samples where the current was passed across an interface of Al3Ti intermetallic compound. In addition, the failure mode was different, the first metal links failing directly under the via whereas in second metal link, the failures were away from the via in the metal link itself.

Low noise figure (7.2 dB) and high gain (29 dB) semiconductor optical amplifier with a single layer AR coating

An angled facet strained MQW semiconductor laser amplifier with integrated mode expanders has been designed and fabricated. A device with simple single layer antireflection coatings exhibited a maximum of 29 dB fibre-to-fibre gain with a minimum noise figure of 7.2 dB at 26 dB gain and a saturation output power of 7.5 dBm. This gain is equal to the highest reported for an SLA operating at 1.5 µm while the noise performance is superior to that in any published work.

Ashing residues on TiN antireflective coating layers

Residues appearing on the surface of the TiN antireflective coating (ARC) layer after a resist ashing process were investigated by transmission electron microscope and field emission Auger electron spectroscopy. These residues tend to appear linearly in the center of Al lines covered with the TiN ARC layer, and are generally called the ‘‘backbone.’’ We found that a triangular product mainly composed of Al atoms appears in the center of the resist surface in the final stage of the ashing process and that a thin layer, about 10 nm thick, including Ti atoms, is formed to cover the triangular product and the resist surface. Due to the small solubility of the thin layer including Ti atoms to the alkaline stripper, the triangular product under the thin layer remains as a backbone residue. We demonstrate that the formation of the backbone depends on the distribution of Al and Ti atoms in the sidewall polymer.

Twenty-four percent efficient silicon solar cells with double layer antireflection coatings and reduced resistance loss

Significant performance increase for silicon solar cells is reported. This has been achieved by a combination of several mechanisms. One is the reduction of recombination at cell surfaces using atomic hydrogen passivation of silicon/silicon dioxide interfaces. Joule resistive losses in the cell have been reduced by a process which allows different thickness for fine and coarse features in the top cell metallization. Finally, reflection losses have been reduced by the use of a double layer antireflection coating. For successful incorporation, this required the development of techniques for growing the surface passivating oxide very thin, without reducing its passivation qualities. The cells display a monochromatic light energy conversion efficiency of 46.3% for 1.04 μm wavelength light, also the highest ever for a silicon devices.

Effect of TiN ARC on Electromigration Performance of Tungsten Plug Via

ABSTRACTThe effect of TiN Anti-Reflective Coating (ARC) layer capping of metal, in a multilevel interconnect system, on the reliability of the tungsten (W) plug has been investigated. EM study on Kelvin via showed that the thin TiN ARC Kelvin via lifetime exhibited a reduction of one order of magnitude compared to that of the thicker ARC thickness (1000Å) when they were stressed in a certain direction. A new testing technique, used to investigate the effect of ARC thickness on the W-plug electromigration (EM) performance, is discussed. The simulation results of current distribution confirmed the proposed failure model of EM performance of W-plug via with different ARC thickness.

Optical properties and structure of thermally evaporated tin oxide films

Tin oxide films have been grown by thermal evaporation of SnO 2 powder from a resistively heated alumina crucible. Analysis by X-ray diffraction and Rutherfold backscattering spectrometry has shown that the films are of an amorphous nature, with a typical stoichiometry of SnO 1.3. Detailed optical measurements have shown that the films have a refractive index close to two and a negligible extinction coefficient over the 2–10 μm wavelength range. Such films appear to be well suited to the fabrication of simple, single layer anti-reflection coatings for use on both germanium and silicon in the infrared.