Deposited Silicon Nitride Films Research Articles

Permeation of oxygen and water into a plasma-enhanced chemical vapor deposited silicon nitride film as function of deposition pressure

In this work, we demonstrate that the permeability of a SiNx thin film (prepared by plasma-enhanced chemical vapor deposition) to water and oxygen is closely related to the deposition pressure. By dynamic secondary ion mass spectrometry, we confirmed that water penetration occurs into the SiNx film only in the oxidized layer. Furthermore, positron annihilation lifetime spectroscopy indicated that a SiNx film with a lower deposition pressure provides a smaller pore (free volume hole) radius, which is more effective in terms of blocking ambient molecular diffusion or penetration. The SiNx films were also applied as an encapsulation layer for organic light-emitting diodes; SiNx films with a lower deposition pressure exhibited higher encapsulation properties.

A Comparative Study on Self‐Aligned Top‐Gate Thin‐Film Transistors with Silicon Nitride as the Interlayer

Thin-film transistors (TFTs) with self-aligned top-gate structure are fabricated, in which the source/drain region is pretreated to be highly conductive during the deposition of silicon nitride as the interlayer. Without deteriorating the properties of the device's channel layer, the basic performance of TFTs can be simply controlled by altering the SiH4 flow rate during the deposition of silicon nitride film. Furthermore, the diffusion of hydrogen dissociated from SiH4 precursor, which can passivate the electron traps at the interface between the channel and dielectric layer or in the bulk of the dielectric layer, can significantly improve the positive bias temperature stress stability. The charge trapping mechanism is verified using the stretched-exponential model, and the rising values of the fitting parameters (ΔVth0 and τ) show that the TFTs stability improves as the flow rate of SiH4 rises. This approach can reduce the cost and simplify the manufacturing of thin-film transistors.

Selectively patterned Mg-doped GaN by SiNx-driven hydrogen injection

We demonstrate a method to achieve selectively patterned Mg-doped GaN layers using hydrogen drive-in through plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiNx) films. Activated Mg-doped GaN layers were selectively deactivated by patterned PECVD SiNx films with low-temperature annealing and showed high-resistive behavior. Spatially resolved photoluminescence measurements were used to optically verify the deactivation of Mg acceptors and showed distinct features corresponding to activated and deactivated Mg in GaN. The method suggested here provides a simple and effective method to achieve patterned Mg-doped GaN regions without thermal and plasma damage, which could cause degradation of device performance. The proposed method could provide a way to achieve future high-performance GaN lateral and vertical devices that rely on laterally patterned doping.

Effect of Hydrogen Plasma Treatment on Atomic Layer Deposited Silicon Nitride Film

Changes in the thin film properties of SiNx deposited via atomic layer deposition using remote N2 plasma were investigated based on the frequency of adding a hydrogen (H2) plasma treatment step during the process. The deposition rate decreased from 0.36 to 0.32 A cycle−1 when compared to SiNx deposited through the conventional deposition process for a thin film that was subjected to H2 treatment processes every 10th cycle, every 5th cycle, and every single cycle of SiNx deposition compared to the deposition process without H2 plasma at a temperature of 400 °C. As the hydrogen treatment process increased beyond a 5:1 ratio, the hydrogen content in the thin film increased based on secondary ion mass spectroscopy analysis, and a change in binding energy state was shown via X-ray photoelectron spectroscopy. The thin film deposited using the hydrogen plasma treatment process at a ratio of 10:1 showed similar characteristics to the SiNx thin film deposited through the conventional atomic layer deposition process and showed excellent etch resistance without an increase in the etch rate. The step coverage characteristics were increased by 16% compared to the deposition process without a H2 plasma treatment process.

Theoretical Study of Decomposition Kinetics and Thermochemistry of Bis(dimethylamino)silane-Formation of Methyleneimine and Silanimine Species.

The gas-phase decomposition kinetics and thermochemistry of bis(dimethylamino)silane (BDMAS), a potential precursor in the chemical vapor deposition of silicon nitride and silicon carbonitride thin films, were systematically studied using ab initio calculations at the CCSD(T)/6-311 + G(2d,p)//B3LYP/6-311 + + G(d,p) level of theory. The reaction routes were mapped out, exploring both the concerted and stepwise reactions in three different zones with the initial cleavage of Si-N, N-Me (Me = CH3), and Si-H, respectively. It was found that the energy needed to break N-Me at 80.6 kcal·mol-1 is lower than the ones for Si-N and Si-H, both at 87.4 kcal·mol-1. When compared with tris(dimethylamino)silane (TrDMAS), it has been shown that the three bonds of N-Me, Si-N, and Si-H in BDMAS can be ruptured more easily, suggesting that BDMAS could be a more efficient precursor gas than TrDMAS. Upon decomposition, BDMAS tends to form methyleneimine and silanimine species, where four methyleneimine species and three silanimine species were produced. From the investigation of the effect of temperature on the kinetic and thermodynamic competition of different decomposition pathways, it has been demonstrated that the concerted formation of N-dimethylaminosilyl methyleneimine (H2C═N-SiH2NMe2) by the elimination of CH4 from BDMAS is the most kinetically and thermodynamically favored pathway in the whole temperature range from 0 K (ΔH0‡ = 62.7 kcal·mol-1 and ΔH0 = 7.7 kcal·mol-1) up to 2673 K. In addition, lower temperatures favor the production of N-methyl methyleneimime (H2C═NMe), whereas high temperatures promote the formation of N-methylsilanimine (H2Si = NMe) and 1-dimethylamino-N-methylsilanimine (Me2NSi = NMe).

Silicon nitride deposited by laser assisted plasma enhanced chemical vapor deposition for next generation organic electronic devices

Deposition of stoichiometric silicon nitride without damage and stress at low temperature using plasma enhanced chemical vapor deposition (PECVD) is an important issue in the application to various areas such as microelectronics, micro-electromechanical system (MEMS), etc. In this study, the effects of laser assistance during PECVD (LAPECVD) of silicon nitride on the physical and chemical characteristics of deposited Si3N4 film were investigated. The LAPECVD assisted by 193 nm laser at 80 °C showed higher deposition ratescompared to PECVD due to the enhanced dissociation of the reactant gases. In addition, the stoichiometric ratio of N/Si and the residual stress of the deposited silicon nitride film were improved. When the silicon nitride was directly deposited on the organic light emitting diode (OLED) for thin film passivation, no electrical damage was observed for LAPECVD possibly due to the coverage of a thin silicon nitride layer on the OLED surface by laser assisted deposition while conventional PECVD showed a damage of the device due to ion bombardment by direct exposure to plasma. We believe the LAPECVD system can be used for various next-generation microelectronic industries where high quality film deposition with minimized damage during PECVD at low temperature is required.

Surface kinetics and feature scale particle model of SixNy atomic layer deposition using Si2Cl6 precursor

One of the important steps in the fabrication of semiconductor memory devices is the deposition of ultrathin silicon nitride films with uniform film thickness and electrical properties. Such high-quality films have made atomic level control during deposition a necessity and can be achieved via atomic layer deposition (ALD) with excellent step coverage. While ALD has been studied experimentally by many authors, there exist significant gaps between their observations and the practical application of the ALD process in large-scale manufacturing. In this work, a computational model of thin film deposition for a silicon based ALD application was developed. The model includes a surface chemistry mechanism for the deposition of hexachlorodisilane (Si2Cl6) on a growing SixNy film. This mechanism quantifies the sticking probability of the Si2Cl6 precursor on the growth surface as well as an effective active reaction site density on these surfaces. This surface reaction chemistry was used in the context of a feature scale particle transport model to simulate ALD in 100 nm–1 μm critical dimension, ∼10–100 high aspect ratio holes. The model demonstrates the effects of hole size and aspect ratio dependence on the overall kinetics of the deposition process. An increase in the completion time for ALD processes with increasing hole aspect ratio and the increasing statistical nature of the deposition process with smaller critical dimension of the hole were predicted.

Silicon Nitride and Carbonitride Films for Waveguide Structures Based on Strained Silicon

Waveguide microstructures based on strained silicon with the use of silicon carbonitride and silicon nitride films as cladding layers are created. A plasma-enhanced chemical vapor deposition technique is developed, which allows obtaining high values of intrinsic mechanical stresses in films (about 700 MPa). The strained waveguide structures are characterized by micro-Raman spectroscopy during a scanning procedure. It is demonstrated that deposition of silicon carbonitride and silicon nitride films induces compressive stresses in the silicon waveguide, which is proved by the shift of the maximum of the main peak of scattering on LO-phonons of silicon toward higher wave numbers. The compressive stresses in the silicon waveguide clad with silicon nitride and carbonitride layers are estimated as 350 and 250 MPa, respectively, which is sufficient for the emergence of nonlinear optical properties of silicon (Pockels effect).

SiNx Deposition at Low Temperature Using UV-Irradiated NH3

We developed a low-temperature silicon nitride (SiNx) film deposition technique using ultraviolet (UV)-irradiated ammonia (NH3) as the reactant gas. In this work, to determine the effect of UV-irradiated NH3, we deposited SiNx films using the developed chemical vapor deposition technique and then evaluated their characteristics. The energy of UV light was only used to excite NH3. Disilane (Si2H6) without UV irradiation was used as the precursor gas. The results demonstrated that using UV-irradiated NH3 as the reactant gas enabled deposition of SiNx films at 30 and 450°C. The N/Si ratio of the SiNx film deposited at 450°C was close to 1.33.

Effect of Laser Beam Dimension on Laser-Assisted Chemical Vapor Deposition of Silicon Nitride Thin Films.

Laser assisted chemical vapor deposition based on the ultraviolet laser illuminated in parallel to sample surface has been examined as a useful means to deposit thin films without sample heating or damage. In this study, we investigate the effect of enlarged laser beam towards silicon nitride film deposition on larger sample area, relying on Argon Fluoride excimer laser beam of 193 nm wavelength to induce photolysis in SiH4/NH3 mixture. Advantages and mechanisms of enlarged beam are presented, and further parametric trends including the influences of reactant gas and laser parameters, and substrate temperature are reported.

Low Temperature Thermal ALD of Silicon Nitride Utilizing a Novel High Purity Hydrazine Source

The demand for faster, smaller and more energy efficient logic devices as well as higher density, higher speed, and increased reliability for advanced memory devices has led to numerous challenges in Semiconductor device manufacturing. Novel metal materials, 3D architecture and increasing High-aspect-ratio (HAR) structures are being used to address these challenges, however this has placed additional constraints on film deposition methods. CVD and ALD of SiN are used in several applications including, gates, spacers, etch stops, liners, encapsulation layers as well as passivation layers.1 Recently PEALD of SiN is taking on an increasingly important role due to new temperature constraints of <400°C. However, several challenges remain on HAR and 3D structures in applications where plasma approaches may not meet conformality requirements. In addition, thermal ALD with NH3 may not be feasible due to the high temperature requirement (500°C-700°C) of these reactions.2 Our approach involves the development and use of a novel hydrazine delivery system in order to develop methods for thermal ALD of SiN at <400°C. The resulting films must meet requirements of high growth rate, high density, and low wet etch rate similar to materials grown by thermal ammonia ALD at 600°C, or Ammonia PEALD at 400°C or less. In addition, the methods developed must show promise for highly uniform growth on 3D and HAR structures where PEALD methods currently have difficulties. A hydrazine delivery system was developed to provide a stable flow of ultra-dry hydrazine gas from a liquid source in a sealed vaporizer. The liquid source combines anhydrous hydrazine and a proprietary solvent that acts as a stabilizer. The solvent is highly non-volatile, where high purity hydrazine gas may be generated in-situ and delivered to the deposition chamber while the solvent remains in the vaporizer. Testing confirms that hydrazine vapor pressure is maintained at levels viable for ALD (12-14 torr) even in the presence of the solvent used to dilute the liquid source to safe handling levels. Previous studies with hydrazine were plagued by oxygen contamination.3 This study demonstrates high purity hydrazine delivery at <800ppb water contamination in the gas phase. Delivery system safety and optimization versus conventional hydrazine will be addressed. A study of silicon nitride deposition was conducted using hexacholorodisilane (HCDS) and hydrazine on a Si-H substrate. A custom made thermal ALD reactor was used to deposit silicon nitride films from 250-400°C. Film growth per cycle (GPC) with hydrazine was 0.4-0.5 Å/cycle at 400°C with refractive index of 1.813. Film stoichiometry was confirmed with X-ray photoelectron spectroscopy. SiN films with low impurities were achieved for oxygen (<2%) and chlorine (<1%). Highly uniform films were obtained across a 4 inch wafer for 200 as well as 400 cycles. Results were similar to films deposited using PEALD at 360°C with HCDS and NH3. Film growth and resulting properties at 350°C closely resemble those grown thermally at 400°C for hexachlorodisilane and hydrazine. Some discrete differences in film density and composition start to become apparent at a growth temperature of 325°C. Specifically, film density decreases and wet etch rate increases. The presentation will compare growth rates, film density, refractive index and wet etch rate results at different temperatures for hydrogen terminated silicon. Initial growth studies with the use of Hydrazine and Organosilicon Amide precursors will also be discussed.

Characteristic Study of Silicon Nitride Films Deposited by LPCVD and PECVD

This paper analyzes and compares the characteristics of silicon nitride films deposited by low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD), with special attention to the hydrogenation and chemical composition of silicon nitride films. Three different LPCVD processes at various DCS and NH3 gas flow rates and deposition temperatures, together with PECVD using SiH4 and NH3 and ICP CVD using SiH4 and N2, were compared. The silicon nitride film deposition rate decreases with an increasing NH3/DCS ratio in LPCVD, which also leads to an increase in the refractive index and a decrease in the residual stress in the film. There is nearly no hydrogen incorporated in the LPCVD films, which differs from PECVD and ICP CVD that show significant Si-H and N-H bonds. The chemical composition of silicon nitride films is mostly Si-rich, except for the LPCVD process at high NH3/DCS ratio with near stoichiometric chemistry.

Novel plasma enhanced chemical vapor deposition of highly conformal SiN films and their barrier properties

A novel plasma-enhanced chemical vapor deposition technique was used to fabricate highly conformal silicon nitride (SiN) films and study their barrier properties. Trisilylamine was used as the main precursor and was introduced into the reaction chamber in 0.3-s pulses while the plasma was excited. The deposited SiN film exhibited good conformality (91%) and an aspect ratio of ∼4.2 (a width of 70 nm and a depth of 300 nm). The film growth rate was 2.0 Å/cycle. The k-value and leakage current were 7.1–6.66 and lower than 1.0 × 10−8 A/cm2, respectively, at a 1 MV charge (8.5 × 10−10–3.5 × 10−8 A/cm2) in the temperature range of 200–400 °C. The wet etch rates of the SiN deposition at 200 and 400 °C were 32.1 and 11.1 nm/min, respectively. The wet etch rate of the films was evaluated in a dilute hydrogen fluoride (HF) solution (H2O:HF = 100:1). The 5.0-nm thick SiN films deposited at 200 and 400 °C exhibited excellent abilities to prevent moisture from entering. By modifying the supply method of the Si precursor, the step coverage improved to the plasma enhanced atomic layer deposition level and the moisture barrier property was maintained even at thicknesses of less than 10 nm.

Silicon nitride films fabricated by a plasma-enhanced chemical vapor deposition method for coatings of the laser interferometer gravitational wave detector

Silicon is a potential substrate material for the large-areal-size mirrors of the next-generation laser interferometer gravitational wave detector operated in cryogenics. Silicon nitride thin films uniformly deposited by a chemical vapor deposition method on large-size silicon wafers is a common practice in the silicon integrated circuit industry. We used plasma-enhanced chemical vapor deposition to deposit silicon nitride films on silicon and studied the physical properties of the films that are pertinent to application of mirror coatings for laser interferometer gravitational wave detectors. We measured and analyzed the structure, optical properties, stress, Young's modulus, and mechanical loss of the films, at both room and cryogenic temperatures. Optical extinction coefficients of the films were in the ${10}^{\ensuremath{-}5}$ range at 1550-nm wavelength. Room-temperature mechanical loss of the films varied in the range from low ${10}^{\ensuremath{-}4}$ to low ${10}^{\ensuremath{-}5}$ within the frequency range of interest. The existence of a cryogenic mechanical loss peak depended on the composition of the films. We measured the bond concentrations of $\mathrm{N}─\mathrm{H}$, $\mathrm{Si}─\mathrm{H}$, $\mathrm{Si}─\mathrm{N}$, and $\mathrm{Si}─\mathrm{Si}$ bonds in the films and analyzed the correlations between bond concentrations and cryogenic mechanical losses. We proposed three possible two-level systems associated with the $\mathrm{N}─\mathrm{H}$, $\mathrm{Si}─\mathrm{H}$, and $\mathrm{Si}─\mathrm{N}$ bonds in the film. We inferred that the dominant source of the cryogenic mechanical loss for the silicon nitride films is the two-level system of exchanging position between a ${\mathrm{H}}^{+}$ and electron lone pair associated with the $\mathrm{N}─\mathrm{H}$ bond. Under our deposition conditions, superior properties in terms of high refractive index with a large adjustable range, low optical absorption, and low mechanical loss were achieved for films with lower nitrogen content and lower $\mathrm{N}─\mathrm{H}$ bond concentration. Possible pairing of the silicon nitride films with other materials in the quarter-wave stack is discussed.

New Compact Electron Cyclotron Resonance Plasma Source for Silicon Nitride Film Formation in Minimal Fab System

A compact magnetic-mirror confined electron cyclotron resonance plasma source for low-damage plasma processings was developed, especially aiming for the realization of high-quality silicon nitride film formation for the sub-micron complementary metal-oxide semiconductor device processes in the minimal fab system. The developed plasma source was installed in the minimal tool, and deposition of silicon nitride film was performed. The magnetic mirror confinement method worked well to excite the high-density plasma with low plasma excitation power of 10 W or less. By adopting the substrate position slightly apart from the core plasma region with the pressure range of 25 Pa, the silicon nitride film having the similar N/Si ratio to the ideal value of Si3N4 could be obtained in the room-temperature deposition. Under this condition, impurity concentration of oxygen in the film could be suppressed less than 1%, which was even smaller than that in the controlled low-pressure chemical-vapor deposited film at 750 °C.

Improved PECVD SixNy film as a mask layer for deep wet etching of the silicon

Although plasma enhanced chemical vapor deposition (PECVD) silicon nitride (SixNy) films have been extensively investigated by many researchers, requirements of film properties vary from device to device. For some applications utilizing SixNy film as the mask Layer for deep wet etching of the silicon, it is very desirable to obtain a high quality film. In this study, SixNy films were deposited on silicon substrates by PECVD technique from the mixtures of NH3 and 5% SiH4 diluted in Ar. The deposition temperature and RF power were fixed at 400 °C and 20 W, respectively. By adjusting the SiH4/NH3 flow ratio, SixNy films of different compositions were deposited on silicon wafers. The stoichiometry, residual stress, etch rate in 1:50 HF, BHF solution and 40% KOH solution of deposited SixNy films were measured. The experimental results show that the optimum SiH4/NH3 flow ratio at which deposited SixNy films can perfectly protect the polysilicon resistors on the front side of wafers during KOH etching is between 1.63 and 2.24 under the given temperature and RF power. Polysilicon resistors protected by the SixNy films can withstand 6 h 40% KOH double-side etching at 80 °C. At the range of SiH4/NH3 flow ratios, the Si/N atom ratio of films ranges from 0.645 to 0.702, which slightly deviate the ideal stoichiometric ratio of LPCVD Si3N4 film. In addition, the silicon nitride films with the best protection effect are not the films of minimum etch rate in KOH solution.

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.

Gettering of interstitial iron in silicon by plasma-enhanced chemical vapour deposited silicon nitride films

It is known that the interstitial iron concentration in silicon is reduced after annealing silicon wafers coated with plasma-enhanced chemical vapour deposited (PECVD) silicon nitride films. The underlying mechanism for the significant iron reduction has remained unclear and is investigated in this work. Secondary ion mass spectrometry (SIMS) depth profiling of iron is performed on annealed iron-contaminated single-crystalline silicon wafers passivated with PECVD silicon nitride films. SIMS measurements reveal a high concentration of iron uniformly distributed in the annealed silicon nitride films. This accumulation of iron in the silicon nitride film matches the interstitial iron loss in the silicon bulk. This finding conclusively shows that the interstitial iron is gettered by the silicon nitride films during annealing over a wide temperature range from 250 °C to 900 °C, via a segregation gettering effect. Further experimental evidence is presented to support this finding. Deep-level transient spectroscopy analysis shows that no new electrically active defects are formed in the silicon bulk after annealing iron-containing silicon with silicon nitride films, confirming that the interstitial iron loss is not due to a change in the chemical structure of iron related defects in the silicon bulk. In addition, once the annealed silicon nitride films are removed, subsequent high temperature processes do not result in any reappearance of iron. Finally, the experimentally measured iron decay kinetics are shown to agree with a model of iron diffusion to the surface gettering sites, indicating a diffusion-limited iron gettering process for temperatures below 700 °C. The gettering process is found to become reaction-limited at higher temperatures.

Finite Element Analysis of Fabrication- and Operation-Induced Mechanical Stress in AlGaN/GaN Transistors

Mechanical stress is an important factor influencing the performance and reliability of GaN-based devices. In highly piezoelectric materials like AlGaN/GaN, mechanical stress directly influences the piezoelectric polarization, and hence the charge density of the 2-D electron gas. Fabrication processes for devices as well as device operating conditions can change the mechanical stress in AlGaN/GaN transistors. In this paper, the mechanical stress resulting from fabrication and operation of AlGaN/GaN transistors has been modeled using a finite element analysis approach. Specifically, the stress induced in AlGaN/GaN by chemical vapor deposition of silicon nitride films is discussed. Furthermore, the temperature-induced mechanical stress during on-state device operation is computed and the effect of source field plates and substrate materials has been investigated. Finally, the above-mentioned stress components are compared with those due to lattice mismatch, epi growth, and inverse piezoelectric effect. The potential impact of mechanical stress on device reliability is also discussed.

Silicon Nitride Thickness Profile Tuning to Reduce Shallow Trench Isolation Variability in Planar CMOS

A method for low pressure chemical vapor deposition of silicon nitride that utilizes thermal ramping during multiple deposition steps is demonstrated in a 300 mm vertical batch reactor. Temperature ramp rates in each heater zone are optimized to deposit silicon nitride films with edge-thin (or dome-shape) thickness profiles across the length of the reactor. This process is compatible with real-time automated tuning schemes commonly used to control thickness across all reactor zones. No significant film degradation or interface formation is detected in silicon nitride films deposited using the multi-deposition technique. This technique is applied to deposit pad silicon nitride with an edge-thin thickness profile, and is incorporated into a planar CMOS shallow trench isolation integration scheme to improve post-CMP oxide step height uniformity.