Energy Ion Bombardment Research Articles

Fracture strain improving via structural austenitic stainless steel-coated 22MnB5 plates

A total of 316 austenitic stainless steel (ASS) coatings were deposited on 22MnB5 press-hardening steel plates by varying the substrate bias voltages using a magnetron sputtering technique and quenched in a flat mold with cooling water. The substrate bias current and ion-bombardment energy densities increased up to 0.5 mA/mm2 and 50 J/mm2 at a high voltage of −100 V, and, therefore, the variations in the coatings’ morphologies were owing to the increases in the ion bombardment. The porous bulk pattern appeared in the quenched ASS coating at −100 V, clearly different from the porous columnar structure of the others at −50 and −75 V. The γ-Fe and α-Fe phases were observed from the diffraction peaks, presented the ASS coating and 22MnB5 substrate, respectively. There was no intermetallic compound (IMC) peak detected. In addition, the diffusion layer of the quenched ASS-coated plate was observed, in which its morphology was different from the quenched martensite (M) plate, and proved to be the α-Fe microstructure by the very low α-Fe peak at the standard (110) position. The bright image of TEM and the select area electron diffraction pattern indicated the nanostructure of the quenched ASS coating. The nanohardness of the ASS coating, diffusion layer, and M plate (7.36, 3.60, and 6.25 GPa, respectively) was detected, indirectly proving an α-Fe structure of the diffusion layer. The fracture angles of the 316-coated plates significantly improved from 51.82° at −50 V, 53.77° at −75 V to 57.38° at −100 V, as the ASS structure changed to be porous bulk pattern. The clearance of IMC, coating’s porous bulk pattern, and the low hardness α-Fe diffusion layer benefited for the fracture strain by lengthening the pathway of the crack’s development and blocking the further crack’s propagation, respectively.

Deposition of hydrogenated amorphous carbon films by CH4/Ar capacitively coupled plasma using tailored voltage waveform discharges

We investigated the effects of tailored voltage waveform (TVW) discharges on the deposition of hydrogenated amorphous carbon (a-C:H) films in CH4/Ar capacitively coupled plasma. TVW discharges employ two driving radio frequencies (13.56 MHz and 27.12 MHz) and control their phase shifts to independently regulate ion bombardment energy (IBE) and ion flux. In this study, a-C:H films were deposited by changing DC-self bias with phase shift and constant applied voltage peak-to-peak. Additionally, we investigated phase-resolved optical emission spectroscopy (PROES) for plasma characterization. As a result, plasma-enhanced CVD (PECVD) for a-C:H films using TVW discharges realize control of film properties such as mass density, sp3 fraction, and H content, while keeping the deposition rate constant. Thus, it is suggested that TVW discharges realize the independent control of IBE and ion flux with high accuracy, highlighting its utility in a-C:H film depositions.

Planar deposition of Nb thin films by HiPIMS for superconducting radiofrequency applications

Cost efficiency and sustainability are critical challenges for future accelerator machines. Nb-coated Cu (Nb/Cu) superconducting radiofrequency (SRF) accelerating cavities, while requiring R&D to meet high acceleration gradient performance standards, show potential for addressing these challenges. Defects in the Nb layer responsible for the deterioration of cavity performance have been linked to the underlying Cu substrate. This study investigates a novel optimization method by mitigating the substrate surface’s impact on deposited Nb, using High Power Impulse Magnetron Sputtering alongside a DC substrate bias (from −50 to −300 V). Trenched silicon substrates are chosen to emulate substrates with exceptionally rugged surface characteristics. Film deposition is investigated both experimentally and through kinetic Monte Carlo simulations. Higher DC voltages are shown to eliminate self-shadowing during the coating process via improved incident ionic flux directionality, enhanced adatom mobility and increased re-sputtering rates, ultimately yielding flat and densely-packed films. The influence of the substrate’s shape on the film’s surface was found to decrease exponentially with increasing ion bombardment energies. Films sputtered under high DC bias conditions (−300 V) exhibited complete planarization with a 30% re-sputtering rate. Strategies for applying this technique to Nb/Cu SRF cavities, enhancing their viability for future particle accelerators, are also discussed.

Effects of magnetic field gradient on capacitively coupled plasma driven by tailored voltage waveforms

This study utilized one-dimensional implicit particle-in-cell/Monte Carlo collision simulations to investigate the impact of different harmonic numbers and magnetic field strengths on capacitive-coupled argon plasma. Under the conditions of a pressure of 50 mTorr and a voltage of 100 V, simulations were conducted for magnetic field strengths of 0 and 100 G, magnetic field gradients of 10–40, 10–60, 10–80, 10–100, and 100–10 G, as well as discharge scenarios with harmonic numbers ranging from 1 to 5. Through in-depth analysis of the results, it was observed that the combined effect of positive magnetic field gradients and harmonic numbers can significantly enhance plasma density and self-bias properties to a greater extent. As the magnetic field gradient increases, the combined effect also increases, while an increase in harmonic numbers weakens the combined effect. Furthermore, this combined effect expands the range of control over ion bombardment energy. This provides a new research direction for improving control over ion energy and ion flux in capacitive-coupled plasmas.

Manipulating the thermal stability of the {111}-oriented nanotwinned Ag films by ion bombardment

Materials with nanotwinned structures have been known to possess high strength, high ductility, and low resistivity. Tailoring their mechanical and thermal stabilities has become a critical technique based on their practical applications in the electronic industry. In this study, we propose to manipulate the thermal stability of the nanotwinned Ag thin films with the assistance of ion bombardment. The {111}-oriented nanotwinned Ag films were fabricated on Si (100) substrate with 100 nm-thick Ti adhesion layer using different applied ion bombardment energies. We found that the thermal stability of highly {111}-oriented nanotwinned Ag films can be tailored by using different levels of ion bombardment during deposition. The sample with the highest ion bombardment energy exhibits exceptional thermal stability, which can sustain {111}-oriented nanotwinned structure and high mechanical strength after 450 °C annealing. On the other hand, the {111} to {100} texture transformation with large grain coarsening can be triggered at low temperature of 150 °C without introducing ion bombardment during the deposition. This study not only advances the fundamental understanding of the thermal stability of the nanotwinned Ag films after high-temperature annealing but also provides valuable insights into manipulating the thermal stability of sputtered nanostructured Ag films through ion bombardment based on the demands of their applications.

Investigations into penetration depth profiles of hydrogenic species in beryllium plasma-facing components via molecular dynamics simulations

During the operation of nuclear fusion reactors, plasma-facing components lining the reactor vessel are continually bombarded by plasma species. The penetration and subsequent trapping of these bombarding plasma ions has implications for component damage as well as in-vessel inventory. Accurately predicting the expected ion penetration depth profiles at a range of plasma ion and surface temperatures typical of fusion reactor operating conditions will inform the scrape-off layer design to limit particle radiation damage and tritium trapping in order to prolong the lifetime of the plasma-facing components and satisfy the DT fuel cycle requirements. By defining a statistical distribution for ion penetration depth and describing the evolution of its parameters across the fusion parameter space of interest, the expected ion deposition depth profiles can be calculated for any subset of ion and surface temperature ranges as needed. Molecular dynamics simulations were used to study the bombardment of beryllium lattices with surface temperatures of up to 1100 K by 5 eV–150 eV deuterium and tritium ions, and the resulting ion penetration depths were investigated. The distributions of two penetration depth quantities, considered from the perspectives of lattice damage and hydrogen retention are defined and their distribution parameter dependence on surface and ion temperature is identified. The expected positive correlation between penetration depth and ion temperature is observed, where the non-linear relationship between these quantities indicates the expected form of the velocity dependence of nuclear stopping power at low bombardment energies. Isotope effects on the distributions are also investigated, with results suggesting that heavier ions have comparably lower mobility within the sample and will generally accumulate closer to the surface. A short study on ion deposition rates is also performed; a non-linear increase of deposition rate with increasing bombarding ion energy has been observed, and evidence of a weak positive surface temperature correlation has been noted.

A study of the formation of fuzzy tungsten in a HiPIMS plasma system

Nanostructured ‘fuzzy’ tungsten has been grown for the first time in a high-power impulse magnetron sputtering high power-impulse magnetron sputtering-(HiPIMS) system. The fuzzy layers were formed over range of surface temperatures T s, from 1025 to 1150 K, for helium ion fluences of 5.02 × 1024 m−2, and mean ion bombardment energy of 55 eV. The time-evolution of the helium ion flux (ΓHe) and incident energy (E He) were determined during the HiPIMS pulse (of width of 150 μs) using a planar Langmuir probe. The micrographic findings revealed that, the thickness of HiPIMS-grown nano-tendrill layers increased by 83% (from 274 to 501 nm) for only a 125 K rise in T s. This result is explained by the fact that higher surface temperatures led to larger helium bubbles which ultimately produce a thicker nanostructured layer. The growth rate of fuzzy tungsten layers in HiPIMS conditions is approximately 50% lower than those observed for DC magnetron operation.

Clean SiO2 atomic layer etching based on physisorption of high boiling point perfluorocarbon.

This study aimed to evaluate the SiO2 atomic layer etching (ALE) process that is selective to Si3N4 based on the physisorption of high boiling point perfluorocarbons (HBP PFCs; C5F8, C7F14, C6F6, and C7F8 have boiling points above room temperature). The lowering of the substrate temperature from 20 °C to -20 °C not only increased SiO2 etch depth per cycle (EPC) but also increased etch selectivity of SiO2/Si3N4 to near infinity. Due to the differences in fluorocarbon adsorption at a temperature during the physisorption depending on boiling points of PFCs, the desorption time and ion bombardment energy during the desorption step needed to be optimized, and higher ion bombardment energy and longer desorption time were required for higher HBP PFCs. Even though near infinity etch selectivity of SiO2/Si3N4 was obtained, for the SiO2 etching masked with Si3N4 patterns, due to the adsorption of PFC on the sidewall of the Si3N4 layer, the difficulty in anisotropic etching could be observed. By adding an O2 descumming step in ALE processes, an anisotropic SiO2 etch profile could be obtained with no adsorption of fluorocarbon on the chamber wall. Therefore, it is believed that the HBP ALE processes can be applicable for achieving high selective SiO2/Si3N4 with more stability and reliability.

Analysis of internal material characteristics of cathode crater of micro-cathodic arc thruster

In this study, the material loss relationship between the electrodes of a micro-cathodic arc thruster was investigated by adjusting the input voltage. The crater morphology of the micro-cathodic arc thruster was observed with a scanning electron microscope. The internal crater material was analyzed with an energy spectrum analyzer. On this basis, the arc path is obtained and the material loss of the structure between the electrodes of the micro-cathodic arc thruster was studied through further numerical simulation. The experimental and simulation results show that with a change in the Power processing unit (PPU) input voltage of the micro-cathodic arc thruster, the material distribution in the cathode crater and the discharge channel between the electrodes changed, affecting the bombardment of ions between the electrodes of the thruster on the insulating structure and conductive coating. In engineering applications, regulation of the arc breakdown path can effectively reduce the total energy of ion bombardment on the wall.

Characterization of SiO2 Plasma Etching with Perfluorocarbon (C4F8 and C6F6) and Hydrofluorocarbon (CHF3 and C4H2F6) Precursors for the Greenhouse Gas Emissions Reduction.

This paper proposes the use of environmentally friendly alternatives, C6F6 and C4H2F6, as perfluorocarbon (PFC) and hydrofluorocarbon (HFC) precursors, respectively, for SiO2 plasma etching, instead of conventional precursors C4F8 and CHF3. The study employs scanning electron microscopy for etch profile analysis and quadrupole mass spectrometry for plasma diagnosis. Ion bombardment energy at the etching conditions is determined through self-bias voltage measurements, while densities of radical species are obtained using quadrupole mass spectroscopy. The obtained results compare the etch performance, including etch rate and selectivity, between C4F8 and C6F6, as well as between CHF3 and C4H2F6. Furthermore, greenhouse gas (GHG) emissions are evaluated using a million metric ton of carbon dioxide equivalent, indicating significantly lower emissions when replacing conventional precursors with the proposed alternatives. The results suggest that a significant GHG emissions reduction can be achieved from the investigated alternatives without a deterioration in SiO2 etching characteristics. This research contributes to the development of alternative precursors for reducing global warming impacts.

On mechanisms to control SiO2 etching kinetics in low-power reactive-ion etching process using CF4 + C4F8 + Ar + He plasma

This work discusses effects of gas mixing ratios and bias power (at 13.56 MHz and 2 MHz) on both gas-phase characteristics and etching kinetics of SiO2 in the CF4 + C4F8 + Ar + He plasma. The subject was the low input power regime (∼0.05 W/cm3). The substitution of C4F8 for CF4 exhibits no principal influence on electrons- and ions-related plasma parameters, produces weakly increasing F atom density as well as causes a comparable increase in the etching rate. The latter is provided by the chemical etching pathway with the nearly constant reaction probability. The substitution of Ar for He sufficiently affects plasma parameters, reduces the F atom density, but accelerates the etching process due to increasing reaction probability. Probably, the latter traces decreasing surface passivation by fluorocarbon radicals. Bias parameters do not disturb bulk plasma, but do influence the etching kinetics through the ion bombardment energy. The growth of etching rate vs. bias power mainly appears due to increasing efficiency of chemical etching pathway. The 2 MHz bias frequency produces lower etching rates in spite of higher ion bombardment energies. This effect is probably due to higher desorption rate and lower sticking probability for F atoms. It was found that most effective parameters to control etching profile are Ar/He mixing ratio and bias frequency.

Influence of magnetic field gradient on the capacitive argon discharge at 8 MHz and 40 MHz

A one-dimensional implicit particle-in-cell/Monte Carlo collision model is used to study the effects of magnetic field gradients on the capacitively coupled argon plasma at 8 MHz and 40 MHz. The magnetic field strength at the powered electrode is fixed at 10 G, while varies from 30 to 100 G at the grounded electrode. The simulations show that the magnetic field with variable gradient can produce controllable asymmetry in the plasma density and ion flux profiles to each electrode. Increasing the magnetic field gradient will generate a significant dc self-bias, which results in a large ion bombardment energy at the powered electrode. The magnetic field gradients have been demonstrated to be an approach to create the dc self-bias and also effectively improve the plasma density. It is also found that at a higher frequency of 40 MHz, the dc self-bias voltage decreases, due to the fact that high collision rate of electrons with background gas will disturb the cyclotron motion of electrons, so the effect of the magnetic field is weakened. As a result, the ability to independently control ion energy and flux is weakened.

Electron-assisted PR etching in oxygen inductively coupled plasma via a low-energy electron beam

In this study, electron-assisted photoresist (PR) etching is conducted using oxygen inductively coupled plasma at a pressure of 3 mTorr. During the PR etching, a low-energy electron beam is generated and is controlled by varying the acceleration voltage (0–40 V) on the grid to assist with the PR etching. When a low acceleration voltage (<20 V) is applied, no electron beam is generated, and PR etching is assisted by the accelerated ions. However, the acceleration voltage is increased (about 20–25 V), an electron beam is generated, and PR etching is assisted by the electron beam. At high acceleration voltages (>25 V), the etch rate increases, and the ion bombardment energy decreases with increasing electron beam energy. The electron energy probability function is measured to verify the relation between the etch rate and acceleration voltage with respect to the sheath thickness on the grid. Furthermore, low contribution of the O radical to the etch rate increment is observed via optical emission spectroscopy measurements.

Effect of charge-up of surfaces of sintered Y2O3 and yttrium oxyfluoride on their erosion rates due to ion bombardment

The erosion rate of sintered Y2O3 and yttrium oxyfluoride (Y-O-F) due to Ar ion bombardment was investigated for use in the plasma process chamber. The Ar ion bombardment was performed by irradiations of Ar plasma and Ar ion beam. In addition, charge-up behavior of these ceramics was investigated by two methods. One was the measurement of the surface voltage during the plasma irradiation (the so-called self-bias voltage), and the other was the measurement of the surface voltage generated due to the accumulation of static electricity in the clean room air. It was found that the negative self-bias voltage of the Y2O3 surface was smaller than that of Y-O-F. It was also found that Y2O3 was easily positively charged by the accumulation of the static electricity compared to Y-O-F, which was consistent with the observed relationship of the self-bias voltages between Y2O3 and Y-O-F. For the evaluation of the erosion rate due to Ar ion bombardment, it was found that the material and setting of masks to make the erosion step for evaluating the rate greatly affected the results. When electrically conductive masks with electrically connecting to a substrate were used, the erosion rate of Y-O-F was smaller than that of Y2O3. The results suggested that the intrinsic ion-bombardment-induced erosion rate of Y-O-F was smaller than that of Y2O3, because the ion bombardment energy was expected to be almost the same due to the existence of the conductive masks. On the other hand, when insulating masks were used, the rates of Y2O3 and Y-O-F were almost the same level. Considering the aforementioned charge-up behavior, the results suggested that a relatively larger positive charge-up of the Y2O3 surface during the ion bombardment decelerated injecting ions, resulting in the decrease in ion bombardment energy and, thus, the erosion rate.

Oxygen-Based Reactive Ion Etching of Ruthenium Thin Film

Copper (Cu) is a popular interconnect material in ICs and other microelectronics. As the technology node is reduced, the performance of copper interconnect lines becomes challenging due to the CMP limitation and the reliability concern [1,2]. It has been suggested that Ruthenium (Ru) can replace Cu in the sub 10 nm node for better conductivity and reliability [3]. An effective plasma etching method for Ru is needed to meet the demand of the industry [4,5].O2 can be utilized in the plasma etch of Ru as it can form volatile RuO3 and RuO4 in the process [5-9]. However, the solid RuO2 can also be formed on the Ru surface, which decreases the overall etch rate of the film [9]. Gases, such as N2, Cl2, and CF4, can be added to the O2 plasma to enhance the removal of RuO2 [6,7]. In this study, authors investigated the RIE etch of Ru using the O2/Ar and O2/N2 feed gases.The TiW (10nm)/Ru (280 nm) stack was sputter deposited on a silicon dioxide (SiO2) coated silicon (Si) wafer [10]. TiW served as a barrier layer similar to the Cu case [10]. The etching experiment was done in a parallel reactor system (PlasmaTherm 700) under the RIE mode with a constant flow rate of 25 sccm at various O2/Ar and O2/ N2 ratios, 450W to 600W power, and 50 mTorr and 70 mTorr pressure. The photoresist and Ru etch rates were determined from the thickness change before and after the etch.Figure 1 (a) shows the Ru etch rate as a function of the Ar concentration in the Ar + O2 feed stream. As the increase of Ar concentration in the feed stream, the overall etch rate decreased, unlike in previous studies, where the addition of additive gases with an O2 mixture improved the etch rate of the thin films [5-7]. However, this phenomenon can be explained by changes in the ion bombardment energy and plasma phase chemistry, as shown in Fig. 1 (b) and (c).Fig. 1 (b) shows the slight change of the cathode self-bias voltage -Vdc with the increase of the Ar concentration in the feed stream over a large range of plasma power. Since ion bombardment enhances the removal of the reaction product, the very small change of the -Vdc indicates that the change of the etch rate is very slightly contributed by the removal of the RuOx product.Fig. 1(c) shows changes in two major radical components, i.e., O 777.5 nm and Ar 751 nm, with the increase of the Ar concentration in the feed stream. With the addition of Ar in the feed stream, the O radical concentration is reduced while the Ar radical concentration is increased. This result indicates that the Ru etch is more influenced by the O radical etchant concentration than the ion bombardment [5,7].A minimum ion bombardment energy may still be needed for the etch process, which will be discussed in the presentation. In addition, the influence of N2 on the Ru etch rate will be discussed with respect to the plasma phase chemistry and ion bombardment energy.[1] S. Paolillo, et al., J. Vac. Sci. Technol. B, 36(3), E103 (2018).[2] R. Chang, et al., IEEE TED, 51, 1577 (2004).[3] L. G. Wen, et al., ACS Appl. Mater. Int., 8(39), 26119 (2016).[4] SIA Roadmap for Semiconductors (2003).[5] C. C. Hsu, et al., J. Vac. Sci. Technol. A, 24(1), 1 (6006).[6] W. Pan and S. B. Desu, J. Vac. Sci. Technol. B, 12(6), 3208 (1994).[7] E. J. Lee, et al., Jpn. J. Appl. Phys., 37(5R), 2634 (1998).[8] S. M. Hwang, et al., Thin Solid Films, 587, 28 (2015).[9] M. Nakahara, et al., J. Vac. Sci. Technol. B, 19(6), 2133 (2001).[10] Y. Kuo, M. Li, J. Q. Su, ECS Transactions., 92(5), 9 (2019). Figure 1

Band gap engineering of the top layer of mica by organized defect formation

We report the narrowing of bandgap of the topmost layer of muscovite mica by low energy Ar+ ion beam induced defect formation. Variation of sputtering rate of the constituent elements of mica leads to organized defects creation. The first principle (DFT) calculation shows a bandgap of 4.63 eV for a single layer of muscovite mica, whereas the absence of specified atoms in that layer results in a reduction of bandgap to 1.3 eV. To examine the change of bandgap of a single mica layer, the top most layer of the muscovite mica is selected, and controlled atomic vacancies are created by low energy Ar+ ion sputtering at glancing angle. The bombarding ion energy and incidence angle are chosen by Monte Carlo Simulation (SRIM) to create the desired defects on the top most layer. Removal of the constituent atoms is probed by X-ray photoelectron spectroscopy and the change in bandgap is experimentally estimated by UV-Vis reflectance spectroscopy and conducting Atomic Force Microscopy (c-AFM). The experimental measurements of bandgap change are found to be consistent with the first principle calculation. The key features of bandgap alteration of the top layer of muscovite mica by ion induced sputtering are discussed.

Ion energy analysis of a bipolar HiPIMS discharge using a retarding field energy analyser

The time evolution of the positive ion energy distribution functions (IEDF’s) at the substrate position in an asymmetric bipolar high-power impulse magnetron sputtering (HiPIMS) system was determined using a gridded energy analyser. This was done for a range of operating conditions, namely the positive voltage U rev and ‘on-time’ negative pulse duration τ neg. The magnetron sputtering discharge was equipped with a Nb target. Based on the knowledge of the IEDF’s, the bombarding ion flux density Γi and energy flux density Q i to a grounded surface were calculated. Time-resolved IEDF measurements showed that ions with energies approaching the equivalent of the positive pulse voltage U rev were generated as the reverse positive voltage phase developed. On time-average, we observed that increasing the set U rev value (from 0 to 100 V), resulted in a marginal decrease in the ion flux density Γi to the analyser. However, this is accompanied by a five-fold increase in the ion energy flux density Q i compared to the unipolar, U rev = 0 V case. Reducing the negative HiPIMS pulse duration τ neg (from 130 to 40 μs) at a constant discharge power leads to a modest increase in Γi, but a four-fold increase in Q i. The results reveal the benefit of the bipolar HiPIMS technique, in which it is possible to control and enhance the power density of ions bombarding a grounded (or fixed bias) substrate, for potentially better tailoring of thin film properties.

PLASMA COMPOSITION AND SiO2 ETCHING KINETICS IN CF4/C4F8/Ar/He MIXTURE: EFFECTS OF CF4/C4F8 MIXING RATIO AND BIAS POWER

Gas-phase characteristics as well as reactive-ion etching kinetics of silicon dioxide in CF4/C4F8/Ar/He plasma with variable CF4/C4F8 mixing ratio and bias potential were investigated under conditions of low (~ 0.05 W/cm3) input power regime. The interest to such regime is due to the possibility to obtain higher etching anisotropy with lower surface damages. The research scheme included plasma diagnostics by Langmuir probes and optical emission spectroscopy in the internal (with no use of standard additives) actinometry approach. It was shown that the substitution of C4F8 for CF4 does not produce sufficient changes in both electrons- and ions-related plasma parameters, but causes a weak increase in fluorine atom density. On the contrary, an increase in the bias power (and thus, in the bias potential) does not disturb plasma composition, but is characterized by proportional changes in the ion bombardment energy. As such, selected variable parameters represent somewhat classical “chemical” and “physical” factors influencing heterogeneous stages of the etching process. It was found that the dominant contribution to the SiO2 etching process belongs to its chemical component while bias powers above 400 W provide no dependence of Si(s.) + xF → SiFx (where index (s.) points out the particle situated on the surface) reaction probability on the efficiency of ion-induced production of adsorption sites for fluorine atoms, as SiOx(s.) → Si(s.) + xO. At lower bias powers, the presence of such dependence is confirmed by similar changes of effective reaction probability and ion bombardment intensity, traced by the multiplication of ion flux on square root of ion energy. Some suggestions concerning peculiarities of both gas-phase and heterogeneous process kinetics at low plasma densities were made.

Mechanical and Optical Properties of Amorphous SiN-Based Films Prepared By ECR PECVD and CCP PECVD

Hydrogenated amorphous silicon nitride (a-SiN:H) and silicon carbonitride (a-SiCN:H) films grown by plasma enhanced chemical vapor deposition (PECVD) are widely investigated for their interesting optical and electrical properties [1]. In this work, we discuss the effect of the deposition power on SiN-based films during plasma deposition. The influence on the optical and mechanical properties of the films was investigated. In order to study this issue on a broader basis, two types of plasmas were applied to deposit 0.5 to 1.5 μm a-SiN:H and a-SiCN:H films. First, a-SiN:H and a-SiCN:H films were deposited by electron cyclotron resonance (ECR) PECVD using the same deposition parameters for all films. During the deposition process, the carbon content in the a-SiCN:H thin films was introduced into the chamber through a pure CH4 gas source to avoid any perturbation on the deposition pressure. Second, a-SiN:H films were deposited by a capacitively coupled plasma reactor CCP PECVD using a SiH4/NH3/N2/Ar precursor mixture. In both deposition processes, the ion bombardment energy was tuned only by the deposition power. The mechanical properties of the films were determined ex-situ by profilometry to evaluate the residual stress using the wafer curvature method and by nanoindentation to determine Young’s modulus and hardness of the films. The thickness and the refractive index were measured by variable angle spectroscopic ellipsometry (VASE). It was observed that the evolution of the residual stress according to the deposition power in the ECR PECVD was different from the CCP PECVD. Besides, we notice a slight increase in the refractive index when the residual stress becomes more compressive as illustrated in figure 1 for a-SiN:H and a-SiCN:H films. Through this discussion, we try to have a better understanding of the different interactions taking place when the deposition power increases in terms of ion bombardment energy. Then, we will study the effect of ion bombardment on the film structure based on the composition and structure of the films and the hydrogen bond concentration measured by Fourier transmission infrared spectroscopy (FTIR). In addition, we have also investigated the influence of carbon incorporation on a-SiN:H thin film properties. We notice a decrease in the refractive index and an increase in the compressive residual stress caused by the carbon incorporation.[1] A. Abdelal, Z. Khatami, and P. Mascher, “Optical and Electrical Properties of ECR-PECVD Grown SiCN Thin Films,” ECS Meet. Abstr., vol. MA2018-01, no. 17, p. 1189, Apr. 2018, doi: 10.1149/ma2018-01/17/1189. Figure 1

Characteristics of silicon nitride deposited by very high frequency (162 MHz)-plasma enhanced atomic layer deposition using bis(diethylamino)silane

Silicon nitrides, deposited by capacitively coupled plasma (CCP)-type plasma enhanced atomic layer deposition (PEALD), are generally applied to today’s nanoscale semiconductor devices, and are currently being investigated in terms of their potential applications in the context of flexible displays, etc. During the PEALD process, 13.56 MHz rf power is generally employed for the generation of reactive gas plasma. In this study, the effects of a higher plasma generation frequency of 162 MHz on both plasma and silicon nitride film characteristics are investigated for the purpose of silicon nitride PEALD, using bis(diethylamino)silane (BDEAS) as the silicon precursor, and N2 plasma as the reactant gas. The PEALD silicon nitride film deposited using the 162 MHz CCP exhibited improved film characteristics, such as reduced surface roughness, a lower carbon percentage, a higher N/Si ratio, a lower wet etch rate in a diluted HF solution, lower leakage current, and higher electric breakdown field, and more uniform step coverage of the silicon nitride film deposited in a high aspect ratio trench, as compared to silicon nitride PEALD using 13.56 MHz CCP. These improved PEALD silicon nitride film characteristics are believed to be related to the higher ion density, higher reactive gas dissociation, and lower ion bombardment energy to the substrate observed in N2 plasma with a 162 MHz CCP.