Deposition Of Silicon Nitride Layer Research Articles

Plasma enhanced atomic layer deposition of silicon nitride using magnetized very high frequency plasma

To obtain high-quality SiN x films applicable to an extensive range of processes, such as gate spacers in fin field-effect transistors (FinFETs), the self-aligned quadruple patterning process, etc, a study of plasma with higher plasma density and lower plasma damage is crucial in addition to study on novel precursors for SiN x plasma-enhanced atomic layer deposition (PEALD) processes. In this study, a novel magnetized PEALD process was developed for depositing high-quality SiN x films using di(isopropylamino)silane (DIPAS) and magnetized N2 plasma at a low substrate temperature of 200 °C. The properties of the deposited SiN x films were analyzed and compared with those obtained by the PEALD process using a non-magnetized N2 plasma source under the same conditions. The PEALD SiN x film, produced using an external magnetic field (ranging from 0 to 100 G) during the plasma exposure step, exhibited a higher growth rate (∼1 Å/cycle) due to the increased plasma density. Additionally, it showed lower surface roughness, higher film density, and enhanced wet etch resistance compared to films deposited using the PEALD process with non-magnetized plasmas. This improvement can be attributed to the higher ion flux and lower ion energy of the magnetized plasma. The electrical characteristics, such as interface trap density and breakdown voltage, were also enhanced when the magnetized plasma was used for the PEALD process. Furthermore, when SiN x films were deposited on high-aspect-ratio (30:1) trench patterns using the magnetized PEALD process, an improved step coverage of over 98% was achieved, in contrast to the conformality of SiN x deposited using non-magnetized plasma. This enhancement is possibly a result of deeper radical penetration enabled by the magnetized plasma.

Atmospheric-Pressure Plasma-Enhanced Spatial Atomic Layer Deposition of Silicon Nitride at Low Temperature

Atmospheric-Pressure Plasma-Enhanced Spatial Atomic Layer Deposition of Silicon Nitride at Low Temperature

Reactivity of different nitriding agents with chlorine-terminated surface during atomic layer deposition of silicon nitride

The atomic layer deposition (ALD) of silicon nitride using silicon chloride was simulated by density functional theory (DFT) calculation to compare different nitriding agents. We chose the NSiCl2*/SiCl*-terminated Si3N4 substrate as the adequate chlorine-terminated substrate. We confirmed that the thermal ALD reaction using NH3 or N2H4 is energetically favorable and found that the reaction with N2H4 shows an activation energy of 1.77 eV, which is lower than 3.30 eV of the reaction with NH3. In the plasma-enhanced ALD (PEALD) process using NH3 plasma, NH2− ion and H⋅ radical remove the Cl atoms of the Si3N4 surface to form active sites for the following reaction, –SiNH2* group or –Si*. N⋅ radicals in N2 plasma may not remove the Cl atoms because the recombination reaction is more favored. The PEALD process using NH3 plasma showed a growth rate of 0.09 nm/cycle at 300 °C, but the growth rate of the process using N2 plasma is negligible, which is in good agreement with our DFT calculations.

Remote plasma atomic layer deposition of silicon nitride with bis(dimethylaminomethyl-silyl)trimethylsilyl amine and N2 plasma for gate spacer

The silicon nitride (SiNx) atomic layer deposition with bis(dimethylaminomethylsilyl)-trimethylsilyl amine precursor and N2 remote plasma was investigated. The process window ranged from 250 to 400 °C, and the growth rate was about 0.38 ± 0.02 Å/cycle. The physical, chemical, and electrical characteristics of the SiNx thin films were examined as a function of deposition temperature and plasma power. Based on the results of spectroscopic ellipsometry and x-ray photoelectron spectroscopy, the growth rate and state of binding energy showed little difference depending on the plasma power. The better film properties such as leakage current density and etch resistance were obtained at higher deposition temperatures and higher plasma power. High wet etch resistance (wet etch rate of ∼2 nm/min) and low leakage current density (∼10−8 A/cm2) were obtained. The step coverage, examined by transmission electron microscopy, was about 80% on a trench with an aspect ratio of 4.5.

Reaction Mechanisms of Halogenated Silanes on N-Rich Surfaces during Atomic Layer Deposition of Silicon Nitride

Atomic layer deposition (ALD) has recently received increasing attention for the growth of high-conformity silicon nitride (SiN) thin films. In particular, plasma enhanced ALD (PEALD) allows SiN deposition at substantially lower temperatures (< 400 °C) with better film properties, compared to thermal ALD. These advantages make PEALD more attractive for ultra large scale integrated circuit (ULSI) device fabrication where the growth of aspect ratio independent and high-quality conformal thin dielectric films is tremendously important. The PEALD of SiN films involves a repetitive two-step process: (1) adsorption and decomposition of silicon-containing precursors and ii) nitridation of the Si-rich surface by active N species emanating from the plasma. Halogenated silanes such as hexachlorodisilane, bis(tertiary-butyl-amino)- silane, and dicholorosilane (DCS, SiH2Cl2) have been utilized as Si precursors. Despite previous studies, the underlying reaction mechanisms of these Si precursors with a N-rich SiN surface during PEALD still remain uncertain. Parameters controlling the rate of growth and uniformity have been demonstrated experimentally, but without knowledge of the reaction mechanisms, direct contributions of specific process conditions cannot be explained. Using first-principles density functional theory (DFT) calculations combined with experimental characterization, we have examined and identified a novel mechanism for the adsorption and decomposition of DCS on a N-rich SiN surface. Our study predicts that the DCS adsorption and dissociation can occur by overcoming a moderate barrier (~ 0.3 eV), far lower than the prohibitively large barriers predicted for previously proposed mechanisms. Through a detailed electronic structure analysis of the reaction intermediates, we have also elucidated the principles underlying the reaction mechanism, notably the hypervalent nature of Si which permits the facile reaction of molecularly adsorbed DCS with primary and secondary amines on the surface, followed by simultaneous Cl release and deportation steps and subsequent HCl formation and desorption. We have examined the same mechanism utilizing alternative precursors and the predicted trends are found to be corroborated with the important properties of the system. Understanding these principles allows us to develop guidelines for processing conditions, such as the importance of maintaining the proper surface composition to facilitate Si precursor adsorption and dissociation. Our study provides insight into the SiN ALD process via chlorosilanes and guidelines to control the deposition for high-quality SiN films and provides a framework for future theoretical studies of surface reactions during ALD.

Theoretical evaluation of thermal decomposition of dichlorosilane for plasma-enhanced atomic layer deposition of silicon nitride: the important role of surface hydrogen.

Silicon nitride (SiN) thin films have been widely employed for various applications including microelectronics, but their deposition presents a challenge especially when highly conformal layers are necessary on nanoscale features with high aspect ratios. Plasma-enhanced atomic layer deposition (PEALD) has been demonstrated to be a promising technique for controlled growth of SiN thin films at relatively low temperatures (<400 °C), in which thermal decomposition of Si-containing precursors on a N-rich surface is a critical step. Based on periodic density functional theory calculations, we present potential underlying mechanisms leading to facile thermal decomposition of dichlorosilane (DCS, SiH2Cl2) on the N-rich β-Si3N4(0001) surface. Our study highlights the importance of high hydrogen content on the N-rich surface, rendering primary and secondary amine groups. When the N-rich β-Si3N4(0001) surface is fully hydrogenated, the molecular adsorption of DCS is predicted to be exothermic by 0.6 eV. In this case, DCS decomposition appears to be initiated by nucleophilic attack by an amine lone-pair on the electrophilic Si, leading to the formation of a DCS-amine adduct intermediate followed by release of a Cl- anion and a proton. The predicted activation barrier for the DCS decomposition reaction is only 0.3 eV or less, depending on its adsorption configuration. We also discuss the formation and desorption of HCl, the subsequent formation and nature of Si-N bonds, and the interaction between adsorbed DCS molecules. While clearly demonstrating the advantageous features of DCS as a Si precursor, this work suggests that the thermal decomposition of Si precursors, and in turn the ALD kinetics and resulting film quality, can be strongly influenced by surface functional groups, in addition to product accumulation and precursor coverage.

Role of Trimethylaluminum in Low Temperature Atomic Layer Deposition of Silicon Nitride

Aminosilanes are attractive precursors for atomic layer deposition of silicon oxides and nitrides because they are halide-free and more reactive than chlorosilanes. However, the deposition of silicon nitride on oxide substrates still requires relatively high temperatures. We show here that for a process involving disec-butylaminosilane and hydrazine, the insertion of Al from trimethyl aluminum allows the deposition of silicon nitride films at relatively low temperatures (250 °C). First-principles calculations reveal that the presence of Al increases the binding of molecular hydrazine, thereby effectively enhancing the reactivity of hydrazine with the silicon precursor during the atomic layer deposition process, which leads to nitrogen incorporation into silicon. However, the range of this enhancement is limited to ∼1 nm, requiring additional trimethylaluminum exposures to continue the Si3N4 deposition.

Surface reaction of silicon chlorides during atomic layer deposition of silicon nitride

The reaction of precursor with surface active site is the critical step in atomic layer deposition (ALD) process. We performed the density functional theory calculation with DFT-D correction to study the surface reaction of different silicon chloride precursors during the first half cycle of ALD process. SiCl4, SiH2Cl2, Si2Cl6 and Si3Cl8 were considered as the silicon precursors, and an NH/SiNH2*-terminated silicon nitride surface was constructed to model the thermal ALD processes using NH3 as well as the PEALD processes using NH3 plasma. The total energies of the system were calculated for the geometry-optimized structures of physisorption, chemisorption, and transition state. The order of silicon precursors in energy barrier, from lowest to highest, is Si3Cl8 (0.92eV), Si2Cl6 (3.22eV), SiH2Cl2 (3.93eV) and SiCl4 (4.49eV). Silicon precursor with lower energy barrier in DFT calculation showed lower saturation dose in literature for both thermal and plasma-enhanced ALD of silicon nitride. Therefore, DFT calculation is a promising tool in predicting the reactivity of precursor during ALD process.

Feature profile simulation of silicon nitride atomic layer deposition

We perform feature-scale numerical simulations with the FPS3D software package to model the atomic layer deposition of silicon nitride using cycles of hexachlorodisilane and hydrazine. Whenever available, the results of simulations are compared with the published experimental data. These simulations emphasize the power of a feature-scale approach, which is effective even for atomic layer deposition, a delicate method of materials processing. We demonstrate reasonably good agreement with the results of experiments. Based on simulations, we suggest some explanations of important phenomena such as the increase in surface roughness as the number of processing cycles increases, the rounded corners of deposited film, the small amount of impurities in the film comprised of elements of the processing gases, and the observation that typically less than a full monolayer of film is deposited per cycle.

Atomic Layer Deposition of Silicon Nitride from Bis(tertiary-butyl-amino)silane and N2 Plasma Studied by in Situ Gas Phase and Surface Infrared Spectroscopy

The atomic layer deposition process (ALD) of silicon nitride (SiNx), employing bis(tertiary-butyl-amino)silane (SiH2(NHtBu)2, BTBAS) and N2 plasma, was investigated by means of Fourier transform infrared (FT-IR) spectroscopy. In situ gas phase, film, and surface infrared measurements have been performed during different stages of the ALD process. From gas phase IR measurements it can be concluded that tert-butylamine is the main reaction product released during precursor exposure. Infrared measurements performed on the deposited SiNx films revealed the incorporation of C in the form of CN and SiC, where more C is incorporated at a deposition temperature of 85 °C compared to 155 or 275 °C. Surface IR measurements, employing a four-axes sample manipulator, showed the formation of SiH- and NH-groups on the surface and revealed that most of the H is incorporated during the precursor exposure step. Furthermore, after the N2 plasma step a vibrational mode around 2090 cm–1 was observed. This mode could be attrib...

Reactivity of different surface sites with silicon chlorides during atomic layer deposition of silicon nitride

The reactivity of surface sites plays a very important role to determine the thermodynamics and kinetics of ALD processes.

Role of Surface Termination in Atomic Layer Deposition of Silicon Nitride.

There is an urgent need to deposit uniform, high-quality, conformal SiN(x) thin films at a low-temperature. Conforming to these constraints, we recently developed a plasma enhanced atomic layer deposition (ALD) process with bis(tertiary-butyl-amino)silane (BTBAS) as the silicon precursor. However, deposition of high quality SiNx thin films at reasonable growth rates occurs only when N2 plasma is used as the coreactant; strongly reduced growth rates are observed when other coreactants like NH3 plasma, or N2-H2 plasma are used. Experiments reported in this Letter reveal that NH(x)- or H- containing plasmas suppress film deposition by terminating reactive surface sites with H and NH(x) groups and inhibiting precursor adsorption. To understand the role of these surface groups on precursor adsorption, we carried out first-principles calculations of precursor adsorption on the β-Si3N4(0001) surface with different surface terminations. They show that adsorption of the precursor is strong on surfaces with undercoordinated surface sites. In contrast, on surfaces with H, NH2 groups, or both, steric hindrance leads to weak precursor adsorption. Experimental and first-principles results together show that using an N2 plasma to generate reactive undercoordinated surface sites allows strong adsorption of the silicon precursor and, hence, is key to successful deposition of silicon nitride by ALD.

Challenges with Industrialization of Atomic Layer Deposition of Silicon Nitride

Scaling of next generation logic and memory semiconductor devices requires conformal thin films on high aspect ratio features at low deposition temperatures (<500ºC). Atomic layer deposition (ALD) is an ideal method for depositing these films and is currently being used in high volume manufacturing (HVM) to deposit high-k dielectric materials (HfO2, ZrO2, etc.) as well as the more traditional dielectrics silicon oxide (SiO2) and silicon nitride (SiNx). With the notable exception of silicon nitride, all of these films can be deposited at sufficiently low temperatures to satisfy the integration requirements while maintaining reasonable throughput and cost. In the HVM environment, silicon nitride ALD has historically been deposited in large furnaces operating at high temperatures, and although both plasma and thermal deposition of silicon nitride have been reported at low temperatures1-2, translation of these low temperature R&D films into HVM films has been challenging.In this presentation, we discuss some of the challenges faced with addressing the requirements associated with bringing low temperature ALD SiNx into HVM, which include achieving high wafer throughput and low per wafer cost, while simultaneously keeping the resistance of the film to multiple downstream etches and cleans, which may include exposure to hydrofluoric acid (HF). Generic to all ALD processes is the high cost of the precursors relative to traditional chemical vapor deposition (CVD); in the case of SiNx, this is exacerbated by the relative low “reactivity to cost ratio” of available silicon precursors. Cost can partially be addressed with chlorosilane precursors, but the chlorine byproducts create challenges with deposition chamber materials and effluent management. Low reactivity of the silicon precursors poses challenges with respect to process design; the choice of spatial ALD vs. temporal ALD and isobaric vs. non-isobaric deposition sequences affects the final cost and throughput. Lastly, the use of plasmas in ALD poses challenges for achieving isotropic film properties over the complex topography on today’s semiconductor substrates.

A study of vapor-phase deposition of silicon nitride layers by ammonolysis of dichlorosilane at lowered pressure

Deposition kinetics of silicon nitride layers at lowered reactor pressures of 10–130 Pa and temperatures in the range 973–1073 K has been studied. The equilibrium constant of the bimolecular reaction of dichlorosilane with ammonia has been calculated. The apparent activation energies calculated taking into account the experimental growth rate nearly coincide with the experimental data. Recommendations for improving the quality of silicon nitride layers are made.

Passivation and etching of fine-grained polycrystalline silicon films by hydrogen treatment

Abstract Here we investigated the effects of hydrogen treatment on highly defected polycrystalline silicon solar cells in terms of defects passivation and surface etching. The poly-Si films were formed by high-temperature chemical vapour deposition. The hydrogen treatment was carried out through deposition of a-SiN x :H layer followed by a thermal treatment or by direct hydrogen plasma. The deposition of silicon nitride layers on polysilicon cells led to a slight increase in the open-circuit voltage without damage to the surface. In contrast, after plasma hydrogenation, the results revealed an etching process of the emitter simultaneously with an important increase of the measured open-circuit voltage by a factor 2, reaching 420 mV.

Bulk and surface passivation of silicon solar cells accomplished by silicon nitride deposited on industrial scale by microwave PECVD

Bulk and surface passivation by silicon nitride has become an indispensable element in industrial production of multicrystalline silicon (mc-Si) solar cells. Microwave PECVD is a very effective method for high-throughput deposition of silicon nitride layers with the required properties for bulk and surface passivation. In this paper an analysis is presented of the relation between deposition parameters of microwave PECVD and material properties of silicon nitride. By tuning the process conditions (substrate temperature, gas flows, working pressure) we have been able to fabricate silicon nitride layers which fulfill almost ideally the four major requirements for mc-Si solar cells: (1) good anti-reflection coating (refractive index tunable between 2·0 and 2·3); (2) good surface passivation on p-type FZ wafers (Seff<30 cm/s); (3) good bulk passivation (improvement of IQE at 1000 nm by 30% after short thermal anneal); (4) long-term stability (no observable degradation after several years of exposure to sunlight). By implementing this silicon nitride deposition in an inline production process of mc-Si solar cells we have been able to produce cells with an efficiency of 16·5%. Finally, we established that the continuous deposition process could be maintained for at least 20 h without interruption for maintenance. On this timescale we did not observe any significant changes in layer properties or cell properties. This shows the robustness of microwave PECVD for industrial production. Copyright © 2005 John Wiley & Sons, Ltd.

Surface reaction mechanisms for atomic layer deposition of silicon nitride

We use density functional theory to investigate atomic layer deposition of silicon nitride using silane and ammonia as precursors. Cluster models are used to represent the reactive sites on the surface of silicon nitride. We have simulated surface reactions on as-deposited Si 3N 4 as well as the initial Si 3N 4 growth on Si(1 0 0). We have calculated the kinetics and mechanisms for the reactions of SiH 4 and NH 3 on Si–H ∗ and N–H ∗ surface sites. We find that reactions of NH 3 and SiH 4 with the Si–H ∗ surface sites of as-deposited Si 3N 4 have activation barriers of 40 and 80 kcal/mol, respectively. On the other hand, SiH 4 and NH 3 react on the N–H ∗ surface sites of as–deposited Si 3N 4 with activation barriers of 52 and 114 kcal/mol, respectively. The low activation barriers for forming Si–N bonds relative to the barriers for reactions that form Si–Si and N–N bonds lead to the properties of selectivity and self-limiting reaction required for ALD. The barrier for formation of Si–Si bonds is significantly below the barrier for formation of N–N bonds explaining the tendency for CVD grown Si 3N 4 films using SiH 4 and NH 3 to be Si rich.

Growth process and properties of silicon nitride deposited by hot-wire chemical vapor deposition

Hot-wire chemical vapor deposition (HWCVD) is a promising technique for the deposition of silicon nitride layers (a-SiNx:H) at low temperatures. In contrast to the commonly used plasma-enhanced chemical vapor deposition, no ion bombardment is present in HWCVD, which makes it particularly attractive for the deposition of passivation layers on structures that are sensitive to the impact of energetic ions. We deposit hot-wire a-SiNx:H from a mixture of silane and ammonia at substrate temperatures in the range of 300–500 °C. Layers deposited with an ammonia/silane gas-flow ratio of R=30 are close to stoichiometry (N/Si=1.33) with a hydrogen content around 10 at. %. Such films have been implemented in hot-wire a-Si:H thin-film transistors. Deposition with R&amp;gt;30 did not result in an increase of the N content, but led to more porous films. Infrared spectroscopy revealed that moisture penetrates these layers and that oxygen is incorporated in the network under air exposure. Cross-sectional transmission electron microscopy images show that these layers contain spherical voids with diameters of several nanometers. In contrast, films deposited with a lower gas-flow ratio (R&amp;lt;30) are inert and do not contain these voids. Both types of films show columnar growth. To better understand the deposition process, we used deuterated silane (SiD4) as a source gas. We found that no deuterium was incorporated in the films. This gives rise to the assumption that SiH4(SiD4) is cracked effectively at the filaments. We infer that the ammonia species are scarcely dissociated at the filaments but rather in the gas phase by the atomic hydrogen (deuterium) originating from the dissociated silane. The abundance of atomic hydrogen in the gas phase is crucial for the breakup of ammonia and the incorporation of N in the film.

Fabrication of Twin Nano Silicon Wires Based on Arsenic Dopant Effect

This paper reports a simple fabrication process of Si “twin nano wires” based on As dopant effect which gives rise to a significant increase of the oxidation rate at the peak concentration of As. The processing procedures consist of As doping, deposition of silicon nitride layer, electron beam lithography, reactive ion etching, wet oxide and deposition of polysilicon. The resulting Si “twin nano wires” have a small top wire with a dimension of 10 nm and a triangular channel wire with a height of 250 nm. A possible application of the “twin nano wires” to a future single-electron memory device on silicon on insulator (SOI) wafer is also discussed.

Investigation of charge carrier injection in silicon nitride/silicon junctions

Contactless measurements of the conductance of silicon wafers with silicon nitride top layers are presented. The deposition of silicon nitride layers leads to an increase of the conductance, both for p-Si and n-Si. This is attributed to the increase of the number of electrons in the Si wafer, in an inversion layer in p-Si, and in an accumulation layer in n-Si. Comparison of the increase of the conductance with the fixed charge density in the nitride layer points to a strongly reduced electron mobility in these layers. It is shown that the change of the conductance increases with growing thickness of the nitride layer up to a thickness of 20 nm, whereafter a constant value is attained.