Polysilicon Films Research Articles

Deposition Contribution Rates and Simulation Model Refinement for Polysilicon Films Deposited by Large-Sized Tubular Low-Pressure Chemical Vapor Deposition Reactors.

Tunnel oxide passivating contact cells have become the mainstream form of high-performance photovoltaic cells; however, the key factor restricting the further improvement of tunnel oxide passivating contact cell performance lies in the deposition process technology of high-quality polysilicon films. The experimental optimization cost for the deposition of large-sized polysilicon films in low-pressure chemical vapor deposition reactors is enormous when conducted in the temperature range of 800-950 K; hence, the necessity to develop effective computer simulation models becomes urgent. In recent years, our research group has conducted two-dimensional simulation research on large-sized, low-pressure chemical vapor deposition. This article focuses on analyzing the influence of gas-phase chemical reactions on the contribution rate of polysilicon film deposition under a mixed atmosphere of H2 and SiH4. The findings indicate that when using SiH4 as the precursor reactants with a gas pressure not exceeding 100 Pa, SiH4 contributes more than 99.6% to the deposition of polysilicon films, while the contribution rate of intermediates from chemical reactions to film deposition is less than 0.5% with 860-900 K. The influence of temperature on the contribution rate of gas-phase intermediates is negligible. It is found that simulating complex multi-step chemical reactions is highly resource-intensive, making it difficult to achieve the three-dimensional simulations of large-sized tubular LPCVD reactors. Based on the in-depth analysis of the mechanism and simulation results, a simplified model neglecting the complex multi-step chemical reaction process has been proposed. Through employing this refined and simplified model, the two-dimensional simulation of the polysilicon thin films deposition process in the large-sized tubular low pressure chemical vapor deposition reactor will become more effective and resource efficient.

Structure and electrical properties of polysilicon films doped with ammonium tetraborate tetrahydrate

Here, p-type polysilicon films are fabricated by ex-situ doping method with ammonium tetraborate tetrahydrate (ATT) as the boron source, named ATT-pPoly. The effects of ATT on the properties of polysilicon films are comprehensively analyzed. The Raman spectra reveal that the ATT-pPoly film is composed of grain boundary and crystalline regions. The preferred orientation is the (111) direction. The grain size increases from 16−23 nm to 21−47 nm, by ~70% on average. Comparing with other reported films, Hall measurements reveal that the ATT-pPoly film has a higher carrier concentration (>1020 cm−3) and higher carrier mobility (>30 cm2/(V·s)). The superior properties of the ATT-pPoly film are attributed to the heavy doping and improved grain size. Heavy doping property is proved by the mean sheet resistance (R sheet,m) and distribution profile. The R sheet,m decreases by more than 30%, and it can be further decreased by 90% if the annealing temperature or duration is increased. The boron concentration of ATT-pPoly film annealed at 950 °C for 45 min is ~3 × 1020 cm−3, and the distribution is nearly the same, except near the surface. Besides, the standard deviation coefficient (σ) of R sheet,m is less than 5.0%, which verifies the excellent uniformity of ATT-pPoly film.

Low-thermal-budget electrically active thick polysilicon for CMOS-First MEMS-last integration

Low-thermal-budget, electrically active, and thick polysilicon films are necessary for building a microelectromechanical system (MEMS) on top of a complementary metal oxide semiconductor (CMOS). However, the formation of these polysilicon films is a challenge in this field. Herein, for the first time, the development of in situ phosphorus-doped silicon films deposited under ultrahigh-vacuum conditions (~10−9 Torr) using electron-beam evaporation (UHVEE) is reported. This process results in electrically active, fully crystallized, low-stress, smooth, and thick polysilicon films with low thermal budgets. The crystallographic, mechanical, and electrical properties of phosphorus-doped UHVEE polysilicon films are studied. These films are compared with intrinsic and boron-doped UHVEE silicon films. Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM) are used for crystallographic and surface morphological investigations. Wafer curvature, cantilever deflection profile and resonance frequency measurements are employed to study the mechanical properties of the specimens. Moreover, resistivity measurements are conducted to investigate the electrical properties of the films. Highly vertical, high-aspect-ratio micromachining of UHVEE polysilicon has been developed. A comb-drive structure is designed, simulated, fabricated, and characterized as an actuator and inertial sensor comprising 20-μm-thick in situ phosphorus-doped UHVEE films at a temperature less than 500 °C. The results demonstrate for the first time that UHVEE polysilicon uniquely allows the realization of mechanically and electrically functional MEMS devices with low thermal budgets.

Bi-layer in-situ phosphorus doped poly-Si films by PECVD for blistering-free high-efficiency industrial TOPCon solar cells

The passivating contact concept stands out as one of the most promising and industrially viable photovoltaic (PV) technologies. Further improving the quality of physical contact has become a focus of ongoing research. The film blistering issue has been identified as one of the major bottlenecks for the polysilicon (poly-Si) films deposited by the PECVD approach. In this study, we investigated how the in-situ phosphorus (P) doping level within the poly-Si films contributes to the occurrence of blistering. Our investigations into the film blistering mechanisms reveal that a high in-situ P-doping suppresses hydrogen release levels and reduces the accumulation of residual stress during annealing, which leads to the blistering-free appearance, especially observed in heavily P-doped poly-Si films. However, as excessive P-doping could weaken the interfacial passivation quality, we propose a bi-layer structure of P-doped poly-Si films which allows the doping profile to be tailored and maintain good quality passivating contacts. Based on the bi-layer structure, we fabricated industrial-sized tunnel oxide passivated contact (TOPCon) solar cells, which attained an average efficiency of 23.84%. Our work not only presents a promising strategy for improving the performance of passivating contacts via the PECVD approach but also underscores the significant potential for its widespread implementation in industrial TOPCon solar cell manufacturing.

The preparation of polysilicon films on highly boron doped silicon substrates and their effects on Cu out-diffusion

The impurity gettering efficiency of the polysilicon film significantly hinders the out diffusion of Cu in the heavily boron-doped mono-silicon substrate. Moreover, as the thickness and layer count of the polysilicon film increase, its gettering effectiveness is further enhanced.

Blistering-free carbon-doped polysilicon (n+) passivating contact with high surface passivation properties prepared by industrial tube PECVD

Tube plasma-enhanced chemical vapor deposition (PECVD) has garnered attention as a promising large-scale production tool for in-situ doped polysilicon due to its high capacity and low equipment cost. In this work, we explore the use of carbon (C)-doped a-Si:H (n+), deposited by tube PECVD, for tunnel oxide passivated contact (TOPCon) solar cells. By introducing carbon atoms into polysilicon, blistering-free polysilicon films with excellent passivation properties can be obtained. The optimized sample with C-doped polysilicon (n+) exhibits remarkable surface passivation with a single-sided saturation current density (J0,s) of 1.25 fA/cm2, an implied open-circuit voltage (iVoc) of 751 mV, and a corresponding effective lifetime exceeding 18 ms at a minority carrier concentration of 1 × 1015 cm−3. UV Raman measurements reveal that C doping suppresses the crystallization of polysilicon, leading to a significant stress in the film. Despite excessive C doping, the contact resistivity extracted from the TLM method remains below 13.6 mΩ cm2. As a result, a champion conversion efficiency of 23.64 % was achieved in a small-sized proof-of-concept n-type TOPCon solar cell. This demonstrates the feasibility of fabricating C-doped polysilicon (n+) prepared by tube PECVD for high-efficiency and low-cost TOPCon solar cells.

REMOTE MEASUREMENTS OF WATER SURFACE POLLUTION BY THE METHOD OF LASER LOCATION

As it was shown in the nature investigations,the most area of water in the Azerbaijan shore of Caspian Sea is covered by oil film, the square of which depends on direction of wind. The research of pollution's of environment by the mean of optical apparatus of remote sounding, mounted on the board of flying apparatus or space satellites is one of intensely developing directions. The theory of measuring of oil film's thickens by the help of laser location in detail described. The principles of straight¬-line spreading of electromagnetic waves, reflecting of electromagnetic energy by objects and constant speed of their propagation are laid in the basic of location. We have developed lidar for controlling of pollutions of water surface, where helium-neon laser “LGI-102” having power 3mW working in the pulse regime is used as beam radiator. During the experiment the laser was mounted on the plain ground on the distance 1-meter from water surface. The prism was placed in the road of propagation of laser beam and used for direction of radiation under the angle 45 on water surface. Integral photo transducer on the base of local mono-and polycrystalline silicon films with linear output was used in the photo detector device. Photo transducer was made in hybrid form on the base of two crystals: photo sensitive poly-silicon film and unpack operational amplifier 740UD4. Keywords: Pollution, water surface, oil film, laser location, lidar, photo detector.

Regionalizing Nitrogen Doping of Polysilicon Films Enabling High-Efficiency Tunnel Oxide Passivating Contact Silicon Solar Cells.

Tunnel oxide passivating contact (TOPCon) solar cells (SCs) as one of the most competitive crystalline silicon (c-Si) technologies for the TW-scaled photovoltaic (PV) market require higher passivation performance to further improve their device efficiencies. Here, the successful construction of a double-layered polycrystalline silicon (poly-Si) TOPCon structure is reported using an in situ nitrogen (N)-doped poly-Si covered by a normal poly-Si, which achieves excellent passivation and contact properties simultaneously. The new design exhibits the highest implied open-circuit voltage of 755mV and the lowest single-sided recombination current density (J0 ) of ≈0.7 fAcm⁻2 for a TOPCon structure and a low contact resistivity of less than 5 mΩ·cm2 , resulting in a high selectivity factor of ≈16. The mechanisms of passivation improvement are disclosed, which suggest that the introduction of N atoms into poly-Si restrains H overflow by forming stronger Si-N and N-H bonds, reduces interfacial defects, and induces favorable energy bending. Proof-of-concept TOPCon SCs with such a design receive a remarkable certified efficiency of 25.53%.

24.18% efficiency TOPCon solar cells enabled by super hydrophilic carbon-doped polysilicon films combined with plated metal fingers

Electroplating technology which has the potential of reducing silver consumption and lowering fabrication costs has been widely used in the photovoltaic (PV) devices. However, the poor wettability of the polysilicon film limits the application of the electroplating technology on tunnel oxide passivated contact (TOPCon) solar cells (SCs). In this work, we propose a carbon (C)-doped polysilicon with highly polar C–Si bonds to improve the surface wettability of polysilicon film. By reducing the hydrogen bubble retention during plating, a uniform, dense, and void-free Ni seed layer can be obtained. To maintain the good conductivity of polysilicon, a double-layer polysilicon structure consisting of a C-doped and a C-free polysilicon films was constructed for TOPCon device fabrication. The new design shows an excellent passivation quality with an implied open-circuit voltage (iVoc) of 745 mV for the lifetime sample and a good contact performance with a low contact resistivity (ρc) of 2–3 mΩ cm2 between plated grids and polysilicon films. Finally, the proof-of-concept TOPCon devices with the double-layer polysilicon structure and plated metal electrodes deliver a remarkable power conversion efficiency (PCE) of 24.18%. Therefore, the C-doped polysilicon combined with the electroplating technology demonstrated in this work shows great potential to obtain high-efficiency and low-cost TOPCon SCs in the PV industry.

Isotope Effect in Electrical Characteristics of Polysilicon Based-Photodetector

The electrical conduction of polysilicon can be improved through the passivation of defects located at grain boundaries. Most passivation proceeds by hydrogen bonding to dangling bonds of silicon. However, more research is needed on the reliability of the Si-H bond. A process using deuterium instead of hydrogen can be expected to improve the performance of silicon devices because Si-D bonds have much higher stability than Si-H bonds. In this study, we have investigated how the isotope effect appears in polysilicon applications. For this purpose, a photodetector composed of a polysilicon film incorporated with hydrogen or deuterium was prepared, and then, current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}\text{)}$</tex-math> </inline-formula> characteristics, photo response, and degradation thereof were investigated. Hydrogen and deuterium incorporation was performed by both furnace annealing and ion implantation methods. It was found that in order for the isotope effect to occur in polysilicon grain structure, the density of grain boundary must be maintained properly, and there must be no additional damage during the hydrogen or deuterium process. Through this study, it was confirmed that the electrical characteristics and the reliability of the polysilicon based-photodetector were improved by forming a Si-D bond inside the polysilicon with the furnace annealing.

20.4: Activation of Doped Silicon Film Using Semiconductor Blue Light Diode Laser Annealing

We have investigated activation annealing of the doped poly silicon film of LTPS TFT by using CW semiconductor blue light diode laser. It has been found that by full melting and re‐crystallization, the sheet resistance can be reduced significantly to 1/3 of which can be realized by using conventional RTA treatment. We will report the experiment results in the paper.

The Effect of Defect Charge and Parasitic Surface Conductance on Aluminum Nitride RF Filter Circuit Loss

When AlN thin films are deposited directly on the high-resistance silicon (HR-Si) substrate, a conductive layer will be formed on the HR-Si surface. This phenomenon is called the parasitic surface conduction (PSC) effect. The presence of the PSC effect will increase the power consumption of electronic components. Therefore, it is necessary to reduce the PSC effect. In prior technology, the polysilicon layer is usually used as the trap-rich layer to reduce the PSC effect. Experiments show that compared to AlN films deposited directly on HR-Si, the AlN substrates with polysilicon introduced on HR-Si have less radio frequency (RF) loss. To verify the effect of polysilicon on RF loss, polysilicon films of three different thicknesses and several different roughnesses were introduced. The results show that the thickness of the polysilicon will affect the RF loss, while the roughness has almost no effect on it. The polysilicon trap-rich layer can reduce the RF loss, which gradually becomes smaller as the polysilicon thickness increases.

Parametric Analysis of Electrostatic Comb Drive for Resonant Sensors Operating under Atmospheric Pressure

The microelectrostatic comb resonator’s issues with high driving voltage and strong feed‐through coupling noise limit its practical use. In earlier studies, the design and structural optimization of microcomb resonators generally focused on lowering beam stiffness and raising electrostatic force density to enhance resonance displacement and lower driving voltage. However, for a microresonator that performs high‐speed resonance in the air, it is required to consider the three influencing elements of the electrostatic field, structural mechanics, and fluid mechanics to achieve the best dynamic resonance amplitude. In this paper, the parametric analysis of the comb‐driven resonator is carried out. First, the comb‐driven electrostatic force and all air‐damping terms are investigated using an electrostatic force analytical model considering edge effects, a damping analytical model simplified based on the thin‐film damping model, and the finite element model. The analysis results agree with the simulated results. To more accurately quantify the dynamic electrostatic force and damping coefficient, the electrostatic–structure–fluid three‐field indirect coupling model was used, and the law of the resonant amplitude of the resonator as a function of the structural parameters was obtained. The results show that, for the electrostatic comb resonator that oscillates at atmospheric pressure, to obtain a high‐voltage driving efficiency, a thin polysilicon film can be used to design narrow comb fingers that are dense in the vertical direction and loose in the lateral direction. To validate the accuracy of the model and the results of parameter analysis, an electrostatic comb‐drive resonator with shapes optimized from numerical simulations was fabricated. The results show that the driving efficiency is enhanced by 102%, with the chip area increased by 29%, which shows the superiority of parameter optimization.

Introducing gallium in silicon and thin film polysilicon using self assembled monolayer doping

• Gallium compound synthesized to form Ga molecular monolayers on silicon surface. • Ga monolayer doping in silicon and thin film polysilicon demonstrated. • Junction depth of 200 nm with a dose 1.6*10 15 Ga atoms/cm 2 demonstrated in n -Si. • Near uniform doping in polysilicon films is achieved with 20% electrical activation. Monolayer Doping (MLD) is a technique involving the formation of a self-assembled dopant-containing layer on the substrate. The dopant is subsequently incorporated into the substrate by annealing, forming a diffused region. Following MLD, samples were capped with silicon dioxide and rapid thermal annealed (RTA). In this work, gallium doping using MLD has been demonstrated. Gallium containing compound Tris (2,4 pentanedionato) gallium(III) was synthesized, and shown to be suitable for monolayer doping silicon substrates and deposited thin film polysilicon. Secondary ion mass spectroscopy (SIMS) and spreading resistance probe (SRP) measurements were performed to determine the dopant profiles and dopant electrical activation. These results showed that a dose of 1.6*10 15 atoms/cm 2 was received, and the gallium dopant produced a 0.2 µm junction in n -type silicon. For polysilicon, the entire 0.4 μm film was evenly doped, with a concentration greater than 10 19 atoms/cm 3 throughout.

Exploration of Phosphorus Oxide in Heavily Phosphorus-Doped Polysilicon Films of Tunneling Oxide Passivation Contact Solar Cells

Exploration of Phosphorus Oxide in Heavily Phosphorus-Doped Polysilicon Films of Tunneling Oxide Passivation Contact Solar Cells

Comparing the Gettering Effect of Heavily Doped Polysilicon Films and Its Implications for Tunnel Oxide‐Passivated Contact Solar Cells

In addition to excellent surface passivation and carrier selectivity, the structure based on the heavily doped polysilicon layer on an ultrathin silicon oxide interlayer also demonstrates strong impurity gettering effects. Herein, the gettering strength of a range of phosphorus‐ or boron‐doped polysilicon films from different fabrication techniques is assessed and compared. Iron, one of the most common metallic impurities in silicon, is used as a tracer impurity to quantify the gettering strength (segregation coefficient). A comparison of the experimental results to the literature, combined with measurements of the electrically active and inactive dopant concentrations, enables us to suggest the main gettering mechanisms in different polysilicon films. The differences in the segregation coefficients of the phosphorus‐doped polysilicon films for iron are within one order of magnitude, in spite of their different combinations of gettering mechanisms. On the other hand, boron‐doped polysilicon films show a large variation in their gettering effects, although the predominant gettering mechanisms are all attributed to electrically inactive boron, according to the current understanding of the gettering mechanisms from the literature. Finally, the impact of different polysilicon gettering effects on the efficiency of tunnel oxide‐passivated contact (TOPCon) cells is simulated and discussed.

Effects of PECVD preparation conditions and microstructures of boron-doped polysilicon films on surface passivation of p-type tunnel oxide passivated contacts

We investigate the effects of plasma-enhanced chemical vapor deposition (PECVD) preparation conditions and microstructures of the boron-doped polysilicon films on the passivation quality of p-type tunnel oxide passivated contact (p-TOPCon) integrated with plasma-assisted N2O oxidation (PANO) SiOx. The B2H6 gas flow, activation temperature, substrate temperature, H2 dilution ratio, and carbon (C)-doped polycrystalline silicon insertion layer are investigated. The best passivation based on plane-surface n-type CZ-Si lifetime sample manifests an implied open-circuit voltage (iVoc) of 706 mV, a single-sided saturation current density (J0,s) of 17.9 fA/cm2, and an effective lifetime (τeff) of 2.25 ms at 1 × 1015 cm−3, showing a slight improvement compared with the controlled sample featuring an iVoc of 703 mV. Although this passivation quality is one of the best specifications of the p-TOPCon featuring PANO SiOx so far, it is insufficient for industry application. Detailed experimental studies and a numerical simulation suggest that the passivation quality is probably weakened by the boron-induced defects located at the interfacial and beneath the SiOx, whose harmful influence is difficult to offset by the field-passivating effect. Generally, we provide new insight into the bottleneck of the p-TOPCon's passivation and then discuss the new strategies for improving the p-TOPCon's passivation in this paper.

Low doping in-situ strategy leading to polysilicon based TFTs exhibiting high stability under stress effects and enhanced electrical performances

In the present work, we investigate the effect of low phosphorus doped polysilicon thin films. These later are deposited on glass substrates by low pressure chemical vapor Deposition (LPCVD) technique and are in situ doped with phosphine adjunction to silane. Doping levels are reported by the phosphine to silane ratio Γ varying from 0 (undoped layer) to heavily doped layer almost 1.2 × 10–3. Films are characterized by different techniques as Photothermal Deflection Spectroscopy (PDS), photoluminescence measurements and x-ray diffraction of polycrystalline layers. The last one reveals that doping concentration giving modification in crystallite size and presence of microstrain, so a clear reduction in the Eg value was observed for the slightest doped layer (Γ = 3.7 × 10–7) by comparaison with the undoped one ((Γ = 0). Results give evidence of an optimum doping level to obtain higher polysilicon films quality. Polysilicon film quality has been correlated to phosphorus doping levels. Thin film transistors (TFTs) are fabricated on glass substrate using a top gate four mask process at low temperature (<600 °C). Electrical characterizations highlight significant improvements in the TFTs performances using slightly doped film instead of undoped one as active layer. Based on Levinson’s model, density of states within the grain boundaries is also found to be the lowest. Stability under stress is enhanced too. For slightly doped films, electrical characterizations indicate that both threshold voltage and density of states NT within the grain boundaries have their lowest values. Although, the field effect mobility μ records its highest values. Additionally, low doping levels enhances the TFT stability under stress. As a result, the in situ low doping strategy opens the way to manufacture polysilicon electronic devices exhibiting high electrical performances and a rather high stability under stress effects.

Method for improving electrical property of polysilicon film used to light absorption layer of photodetector

Method for improving electrical property of polysilicon film used to light absorption layer of photodetector

Phosphorus oxides in heavily doped polysilicon films

In tunneling oxide passivation contact (n-TOPCon) photovoltaic devices, poly-Si (n&lt;sup&gt;+&lt;/sup&gt;) films with high-concentration phosphorus doping are the key materials for electron selective passivation. Its optical and electronic properties strongly depend on the chemical configuration and physical phase, and also on high temperature annealing and structural relaxation in the recrystallization process. The poly-Si (n&lt;sup&gt;+&lt;/sup&gt;) films grown on SiO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;/n-Si substrates by low pressure chemical vapor deposition technology are investigated, while the microstructure of the film is studied by using X-ray photoelectron spectroscopy with depth etching, high-resolution transmission electron microscopy and X-ray diffraction analysis. It is found that the binding energy values of the two fitted peaks (O2 and O3) of O 1s state of the thin film are situated at 532.1 and 533.7 eV, corresponding to the bonding of O—Si and O—P, respectively. The binding energy values of the two fitted peaks (P2 and P3) of P 2p state are located at 132.4 and 135.1 eV, corresponding to O—P* bonding with the same origin. Electronic microscopy and light diffraction analyses show that the polycrystalline silicon film has the characteristic of (111) preferential orientation, and the space of crystal plane is 0.313 nm, for which the average grain size is in a range of about 43.6–55.0 nm. However, the mechanical deformation and grain boundaries are generated in the annealing process at 920 ℃ along (111) crystal cluster, resulting in the localized monocrystalline state within large grains. The comprehensive analyses of thermodynamic function parameters of formation enthalpy, reaction entropy, heat capacity, formation energy and Gibbs free energy and energy minimum principle analysis indicate that there exist conditions for forming Si—O and P—O bonds in the polysilicon film, and thus the bonding state of silicon and phosphorus oxides are formed.