SiO2 Etch Rate Research Articles

Effect of RF Powers and O2 Flow Rates on Etch Rate of SiO2 with Reactive Ion Etching System

Effect of RF Powers and O2 Flow Rates on Etch Rate of SiO2 with Reactive Ion Etching System

Etching selectivity of SiO2 to SiN using HF and methanol at higher pressures up to 900 Pa

Isotropic gas-phase etching of SiO2 was examined using HF and methanol vapor while changing the pressure from 300 to 900 Pa. The temperature dependence of the etching rate of SiO2 showed a broad maximum around –30 °C, and the rate increased with increasing pressure. The etching rate of plasma-enhanced CVD (PE-CVD) SiO2 was more than 60 nm min−1 at 900 Pa and –30 °C. When the pressure was increased from 300 to 900 Pa, the temperature range that indicates SiO2 etching was shifted to a higher temperature. The etching of SiO2, which did not proceed at 300 Pa, was found to proceed even at 0 °C at 900 Pa. The etching rate of PE-CVD SiN was also found to increase slightly with pressure. At the higher pressure of 900 Pa, the formation of ammonium hexafluorosilicate, which is a by-product of SiN, was found to increase. As a result, a high selectivity of more than 20 was obtained at a lower pressure of less than 600 Pa and a lower temperature of less than –40 °C.

Pseudo-Wet Plasma Mechanism Enabling High-Throughput Dry Etching of SiO2 by Cryogenic-Assisted Surface Reactions.

Manufacturing semiconductor devices requires advanced patterning technologies, including reactive ion etching (RIE) based on the synergistic interactions between ions and etch gas. However, these interactions weaken as devices continuously scale down to sub-nanoscale, primarily attributed to the diminished transport of radicals and ions into the small features. This leads to a significant decrease in etch rate (ER). Here, a novel synergistic interaction involving ions, surface-adsorbed chemistries, and materials at cryogenic temperatures is found to exhibit a significant increase in the ER of SiO2 using CF4/H2 plasmas. The ER increases twofold when plasma with H2/(CF4 + H2) = 33% is used and the substrate temperature is lowered from 20 to -60°C. The adsorption of HF and H2O on the SiO2 surface at cryogenic temperatures is confirmed using in situ Fourier transform infrared spectroscopy. The synergistic interactions of the surface-adsorbed HF/H2O as etching catalysts and plasma species result in the ER enhancement. Therefore, a mechanism called "pseudo-wet plasma etching" is proposed to explain the cryogenic etching process. This synergy demonstrates that the enhanced etch process is determined by the surface interactions between ions, surface-adsorbed chemistry, and the material being etched, rather than interactions between ion and gas phase, as observed in the conventional RIE.

High-rate etching of silicon oxide and nitride using narrow-gap high-pressure (3.3 kPa) hydrogen plasma

We investigated the etching behavior of silicon oxide (SiO x ) and silicon nitride (SiN x ) in narrow-gap, high-pressure (3.3 kPa) hydrogen (H2) plasma under various etching conditions. Maximum etching rates of 940 and 240 nm min−1 for SiO x and SiN x , respectively, were obtained by optimizing the H2 gas flow rate. The dependence of the etching rate on gas flow rate implied that effective elimination of etching products is important for achieving high etching rates because it prevents redeposition. The sample surfaces, especially the oxide surfaces, were roughened and contained numerous asperities after etching. Etching rates of both SiO x and SiN x decreased as the temperature was raised. This suggests that atomic H adsorption, rather than H-ion bombardment, is an important step in the etching process. X-ray photoelectron spectroscopy revealed that the etched nitride surface was enriched in silicon (Si), suggesting that the rate-limiting process in high-pressure H2 plasma etching is Si etching rather than nitrogen abstraction. The etching rate of SiO x was three times higher than that of SiN x despite the higher stability of Si–O bonds than Si–N ones. One reason for the etching difference may be the difference between the bond densities of SiO x and SiN x . This study presents a relatively non-toxic, low-cost, and eco-friendly dry etching process for Si-based dielectrics using only H2 gas in comparison with the conventional F-based plasma etching methods.

Understanding the contributions of F–, HF, and HF2– to the etching of SiO2 and unveiling the reaction kinetics to represent etching behavior of SiO2 up to pH 5

Understanding of the silicon dioxide (SiO2) etching mechanism in hydrofluoric acid (HF) solutions is important in semiconductor manufacturing processes. A study on the previous SiO2 etching mechanism claimed that only difluoride (HF2–) participated in SiO2 etching. However, in this study, it was observed that the etching of SiO2 occurred in the HF solution, where difluoride barely existed. Hence, a new SiO2 etching mechanism and reaction rate were proposed. Various concentrations of HF and ammonium fluoride (NH4F) under varying pH conditions were used to etch SiO2, leading to an SiO2 etching rate of 510[F–] + 610[HF] + 2890[HF2–] (Å/min). HF2– was the primary contributor to SiO2 etching; however, unlike the previous SiO2 etching mechanism, the effects of F– and HF on the etching of SiO2 were included in the rate of SiO2 etching. The SiO2 etching rate, considering the reactions between various fluorine species with varying SiO2 surface states, effectively represented the SiO2 etching behavior under various conditions over a broader pH range, up to pH 5. Controlling the ratio of the fluorine species, F–, HF, and HF2–, our etching model could also be extended to the selective etching of SiO2.

Necking Reduction at Low Temperature in Aspect Ratio Etching of SiO2 at CF4/H2/Ar Plasma.

This study investigated the effect of temperature on the aspect-ratio etching of SiO2 in CF4/H2/Ar plasma using patterned samples of a 200 nm trench in a low-temperature reactive-ion etching system. Lower temperatures resulted in higher etch rates and aspect ratios for SiO2. However, the plasma property was constant with the chuck temperature, indicated by the line intensity ratio from optical emission spectroscopy monitoring of the plasma. The variables obtained from the characterization of the etched profile for the 200 nm trench after etching were analyzed as a function of temperature. A reduction in the necking ratio affected the etch rate and aspect ratio of SiO2. The etching mechanism of the aspect ratio etching of SiO2 was discussed based on the results of the surface composition at necking via energy-dispersive X-ray spectroscopy with temperature. The results suggested that the neutral species reaching the etch front of SiO2 had a low sticking coefficient. The bowing ratio decreased with lowering temperature, indicating the presence of directional ions during etching. Therefore, a lower temperature for the aspect ratio etching of SiO2 could achieve a faster etch rate and a higher aspect ratio of SiO2 via the reduction of necking than higher temperatures.

Atomic Layer Etching of GaN and AlGaN Using CH4/H2, H2 and HCl Chemistry

Modern microelectronic components for high-power and high-frequency applications require reliability and reproducibility of the production processes. Atomic layer etching (ALE) represents a key technology for achieving these requirements.An ALE sequence is characterized by a chemical modification step that affects only the top atomic layer of the surface (adhesion) and an ion assisted non-reactive inert gas etching step that removes only this chemically modified area due to creation of volatile byproducts. These two steps are separated by inert gas purge. This grants the etching of single atomic layers. The etching step can be triggered by thermal energy or kinetic energy by impinging particles (e.g. ion bombardment by a plasma). The low energy required for ALE guarantees low-damage etching.In literature ALE processes using Cl2 are often reported. In this work, the results of plasma-enhanced ALE of GaN and AlGaN using different chemistries of CH4/H2, H2 and HCl as etch gases are presented. The experiments were performed with a highly customized etch facility equipped with a capacitively coupled plasma source (CCP, 60 MHz) and a substrate bias generator (RF, 2 MHz). The investigations were carried out on epitaxially deposited GaN on sapphire with masks of protective resist and SiO2 as well as GaN-AlGaN heterostructures with patterned SiO2 maskings. For process analysis optical emission spectroscopy (OES) was carried out. The etching rate and roughness were determined by ellipsometry and atomic force microscopy (AFM) as well as scanning electron microscopy (SEM).Observations by OES indicate a successful excitation and dissociation of the etching molecules. With rising plasma powers physical sputtering effects were revealed. At the beginning of the process development continuous etching processes were examined. With CH4/H2 chemistry using GaN samples it was found that the etching behavior is strongly influenced by the type of masking material. Protective resist resulted in a low etch rate of 7.5 nm/min and significant damage of the masking material. The cause of this behavior is assumed to be redeposition of material by interaction of methane, resist, and plasma. With the change to a hard mask of SiO2 etch rates of 45 to 72 nm/min were achieved, increasing with RF-power and CH4/H2 ratio. Adding methane led to detrimental side effects such as dendrite growth and wall formation on the transient region of unmasked to former masked sample areas. In the further development of the ALE process an etch chemistry using only hydrogen as the chemical etchant was used resulting in an etch per cycle (EPC) of about 3 Å for GaN samples. Further investigations of ALE with hydrogen etch chemistry on GaN-AlGaN samples revealed that AlGaN, in contrast to pure GaN, could not be etched successfully with this chemistry.Substituting CH4/H2 or H2 to HCl enables the etch of AlGaN. The investigations carried out indicate that this etching process is also a self-limiting ALE. AFM measurements revealed an EPC of 1.2 Å for lower RF-powers (50 W). Increasing the RF power to 150 W only slightly enhance the EPC to 2.0 Å. The surface roughness tends to decrease with rising RF-power from 50 to 300 W.

Comparison of distributions of etching rate and calculated plasma parameters in dual-frequency capacitively coupled plasma

Abstract We measured the etching rates of SiO2 and Si in dual-frequency excited CF4 plasma and compared the etching rates with the radical species distribution calculated by plasma simulation. The etching rates of SiO2 and Si at the wafer edge became higher than those at the wafer center, and the etching rate of Si distributed uniformly without bias voltage. In the simulation, the calculation model was calibrated on the basis of the measured (electron density). Assuming that CF3 + contributes to SiO2 and Si etching, and F contributes to Si etching without bias voltage, the radical fluxes flowing into the wafer were calculated by plasma simulation. The fluxes of CF3 + and CF2 became higher at the edge, and the F flux distribution was uniform without the bias voltage. It was shown that the distributions of the etching rate in the experiment and radical flux that contributes to etching in the simulation were in agreement.

Controlling Bowing and Narrowing in SiO2 Contact-Hole Etch Profiles Using Heptafluoropropyl Methyl Ether as an Etchant with Low Global Warming Potential

Heptafluoropropyl methyl ether (HFE-347mcc3), as a lower-GWP (global warming potential) alternative to PFCs (perfluorocarbons), was used to etch SiO2 contact holes. The etch profiles of the SiO2 contact holes in HFE-347mcc3/O2/Ar plasmas showed more bowing at lower flow rate ratios of HFE-347mcc3 to Ar, whereas more narrowing occurred at higher ratios. The measurements of the angular dependences of the deposition rates of fluorocarbon films on the surface of SiO2 and the etch rates of SiO2 showed that the shape evolution of contact-hole etch profiles at different HFE-347mcc3/Ar ratios was attributed to an increase in etch resistance and a decrease in etch ability of the sidewalls of the contact hole with the increasing HFE-347mcc3/Ar ratio. This resulted in determining the optimum ratio of HFE-347mcc3 to Ar to achieve the maximum anisotropy of the contact hole etched in HFE-347mcc3/O2/Ar plasmas. By carefully selecting the specific flow rates of HFE-347mcc3/O2/Ar (9/2/19 sccm), a highly anisotropic and bowing-free SiO2 contact hole, with a 100 nm diameter and an aspect ratio of 24, was successfully achieved.

Methods for Uniform Wet Etching in Narrow Trenches and Vias

Abstract. Advanced semiconductor technology features complicated three-dimensional nanostructures and nanoconfined spaces such as nanosheets, supervias, deep contact holes and nanocavities. Uniform wet etching of such nanoconfined spaces across different feature sizes or critical dimensions (CD) is extremely challenging. Typically, etch rate decreases with decrease in CD size. In this paper we report methods to achieve uniform wet etch rate (ER) of SiO2 across different CD sizes by mixing organic solvents in the etching solution. We also report a reversal of etch rate trend where SiO2 structure of smaller CD etches faster than a larger CD, by tuning the ratio of organic to water solvents in the etching solution. We also investigate the impact of parameters such as solvent type, wall material, surface tension and ionic strength on ER. Our data suggests, while surface tension and ionic strength show no impact, the type of wall material, surface potential and organic solvent amount in the etching solution show a strong influence on SiO2 ER. Also, zeta potential could explain most of our results but not all, suggesting that surface potential is not the only factor impacting CD dependent ER in a nanoconfined spaces.

Chamber in-situ estimation during etching process by SiF4 monitoring using laser absorption spectroscopy

The behavior of the partial pressure of SiF4, a byproduct of fluorine-based plasma etching, has been measured in real-time using a method based on Laser Absorption Spectroscopy (LAS). The partial pressure of SiF4 is highly correlated with the etch rate of SiO2 (R 2 = 0.999). Etch endpoints were clearly observed from the signal transitions, whose period indicate the etch rate uniformity. In addition, integrating the partial pressure of SiF4 with respect to time is correlated with the number of Si atoms etched regardless of the composition of the etched materials. Specifically, Si, SiO2 and Si3N4 were examined in this work. Based on the strong relationship between the measured SiF4 partial pressure and the etching profiles, real-time monitoring by LAS is useful for the prediction of etch profiles.

ON THE COMPARISON OF REACTIVE-ION ETCHING MECHANISMS FOR SiO2 AND Si3N4 IN HBr + Ar PLASMA

This work investigated the influence of component ratio in the HBr + Ar gas mixture on electro-physical plasma parameters, steady-state densities of active species and reactive-ion etching (RIE) kinetics for SiO2 and Si3N4 under conditions of inductive RF (13.56 MHz) discharge. The combination of plasma diagnostics by Langmuir probes and plasma modeling indicated that an increase in Ar content at constant gas pressure and input power a) caused an increase in electron temperature and densities of charged species; b) results in increasing ion bombardment intensity; and c) leads to the nearly proportional decrease in Br atoms density and flux. It was found that variations of SiO2 and Si3N4 etching rates vs. mixture composition are qualitatively similar while the maximum difference in corresponding absolute values takes place in pure HBr plasma. The analysis of RIE mechanisms was carried out using model-predicted data on fluxes of ions and bromine atoms. It was found that the dominant SiO2 etching mechanism is the ion-assisted chemical reaction which is characterized by the nearly-constant rate in the range of 0–80% Ar due to an increase in the effective reaction probability. That is why the noticeable intensification of physical sputtering with increasing Ar fraction in a feed gas causes the only weak growth of obtained SiO2 RIE rate. Oppositely, the Si3N4 etching process is mainly contributed by the physical sputtering while the efficiency of ion-stimulated chemical reaction is limited by the low reaction probability. This provides both slower etching process (especially in Ar-poor plasmas) and stronger sensitivity of etching rate to the change in mixture composition. For citation: Efremov A.M., Betelin V.B., Kwon K.-H. On the comparison of reactive-ion etching mechanisms for SiO2 and Si3N4 in HBr + Ar plasma. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 37-45. DOI: 10.6060/ivkkt.20236606.6786.

Highly selective isotropic gas-phase etching of SiO2 using HF and methanol at temperatures –30 °C and lower

The gas-phase etching of SiO2 was examined using HF and methanol vapor at temperatures below 0 °C and at low pressure. The etching rate of SiO2 increased with decreasing temperature and showed a maximum around –30 °C. The obtained etching rate was a maximum of 40 nm min−1 at plasma-enhanced chemical vapor deposition SiO2. The etching rate of SiN examined for comparison was more than ten times smaller than that of SiO2 under the same condition. As a result, the etching selectivity of SiO2 to SiN was found to be over 20 at –40 °C. When utilizing a low temperature of less than –30 °C, gas-phase etching of SiO2 showing a high etching rate and selectivity was achieved.

Plasma Parameters and Kinetics of Reactive Ion Etching of SiO2 and Si3N4 in an HBr/Cl2/Ar Mixture

The parameters of the gas phase and the kinetics of reactive ion etching of SiO2 and Si3N4 under conditions of an induction RF (13.56 MHz) discharge with a varying HBr/Cl2 ratio is studied. The study includes plasma diagnostics using Langmuir probes, plasma modeling to find stationary concentrations of active particles, measuring velocities, and analyzing etching mechanisms in the effective interaction prob-ability approximation. It is found that the substitution of HBr by Cl2 at a constant argon content (a) is accompanied by a noticeable change in the electrical parameters of the plasma; (b) leads to a weak increase in the intensity of ion bombardment of the treated surface; and (c) causes a significant increase in the total concentration and flux density of reactive particles. It is shown that the etching rates of SiO2 and Si3N4 increase monotonically as the proportion of Cl2 increases in a mixture, while the main etching mechanism is an ion-stimulated chemical reaction. The model description of the kinetics of such a reaction in the first approximation assumes (a) the additive contribution of bromine and chlorine atoms and (b) the direct pro-portional dependence of their effective interaction probabilities on the intensity of ion bombardment. The existence of an additional channel of heterogeneous interaction with the participation of HCl molecules is proposed.

SiO2 etching and surface evolution using combined exposure to CF4/O2 remote plasma and electron beam

Electron-based surface activation of surfaces functionalized by remote plasma appears like a flexible and novel approach to atomic scale etching and deposition. Relative to plasma-based dry etching that uses ion bombardment of a substrate to achieve controlled material removal, electron beam-induced etching (EBIE) is expected to reduce surface damage, including atom displacement, surface roughness, and undesired material removal. One of the issues with EBIE is the limited number of chemical precursors that can be used to functionalize material surfaces. In this work, we demonstrate a new configuration that was designed to leverage flexible surface functionalization using a remote plasma source, and, by combining with electron beam bombardment to remove the chemically reacted surface layer through plasma-assisted electron beam-induced etching, achieve highly controlled etching. This article describes the experimental configuration used for this demonstration that consists of a remote plasma source and an electron flood gun for enabling electron beam-induced etching of SiO2 with Ar/CF4/O2 precursors. We evaluated the parametric dependence of SiO2 etching rate on processing parameters of the flood gun, including electron energy and emission current, and of the remote plasma source, including radiofrequency source power and flow rate of CF4/O2, respectively. Additionally, two prototypical processing cases were demonstrated by temporally combining or separating remote plasma treatment and electron beam irradiation. The results validate the performance of this approach for etching applications, including photomask repair and atomic layer etching of SiO2. Surface characterization results that provide mechanistic insights into these processes are also presented and discussed.

Passivation of poly-Si surface using vinyl and epoxy group additives for selective Si3N4 etching in H3PO4 solution

This work investigates the mechanism of polycrystalline silicon (poly-Si) dissolution in H3PO4. The etching rate of poly-Si was more rapid than that of silicon dioxide (SiO2) in H3PO4 solution, because poly-Si surface possesses unstable Si1+, Si2+, and Si3+ states – rather than Si4+, which is more stable. Additives such as epichlorohydrin, 1,2-epoxy-3-phenoxypropane, vinyl bromide, and phenyl vinyl ether with epoxy or vinyl groups were introduced into the H3PO4 to passivate the poly-Si surface. This significantly increased the presence of the Si4+ state and provided hydrophobic functional groups on the poly-Si surface to reduce the wettability of the poly-Si surface. The introduction of these additives significantly reduced the etching rate of poly-Si. 3-glycidyloxypropyl trimethoxysilane, 3-glycidyloxypropyl dimethoxymethylsilane, allyltrimethoxysilane, and vinyltrimethoxysilane with Si–O bonds, as well as epoxy or vinyl groups in their molecular structures, were demonstrated to suppress the etching rate of both SiO2 and poly-Si. The introduction of these additives to H3PO4 promoted the selective removal of silicon nitride (Si3N4) layers from multi-layered Si3N4/SiO2 trench structures without the loss of either poly-Si or SiO2.

Molecular dynamics simulation of Si trench etching with SiO2 hard masks

Molecular dynamics simulations were performed to demonstrate nanometer-scale silicon (Si) trench etching with silicon dioxide (SiO2) hard masks by chlorine (Cl+) ion beams possibly with low-energy chlorine (Cl) radicals. Although the sputtering yield of SiO2 is typically much lower than that of Si, the etch rates of SiO2 and Si can be comparable because of the lower Si atomic density of SiO2. This implies that the erosion of the mask can significantly affect etched structures. This study has demonstrated that although the fluxes of incident ions and radicals are uniform in space and constant in time, the individuality of incident ions and radicals causes atomic-scale surface roughness, which cannot be neglected for nanometer-scale etched structures. Furthermore, some transient effects of surface etching, such as initial swelling of the Si surface due to incorporation of Cl atoms and preferential sputtering of oxygen, can affect the profiles of etched structures. The insufficiency of the local mechanical strengths of nanometer-scale materials also enhances their erosion, leading to the formation of nanometer-scale roughness on the sidewalls of masks and etched structures.

Correlation of SiO2 etch rate in CF4 plasma with electrical circuit parameter obtained from VI probe in inductively coupled plasma etcher

The plasma etch process has become more difficult and longer than other processes and the etch process engineers have tried to confirm whether the results of etch process were normal by monitoring the equipment. However, it is difficult for the engineers unfamiliar with plasma to discover the parameter correlated to the real etch results, so the intuitive parameter to easily estimate the etch results is required. In this study, we focused on analyzing the correlation of the etch rates of SiO2 in CF4 plasma with electrical circuit parameters closely related to genuine plasma, which were obtained by chamber modeling and VI probe. We also introduced the intuitive parameter by combining several electrical circuit parameters to estimate the etch rate more precisely. The proposed parameter was strongly correlated to the etch rates and the coefficient of determination between the etch rates and the proposed parameter was over 0.94. We expect that using the proposed parameter can contribute to maintaining the stability of etch process.

Purgeless atomic layer etching of SiO2

Atomic layer etching (ALE) typically proceeds through four sequential steps of surface modification, purging, removal of the modified surface, and a second purging. This serial process is repeated to achieve atomic-scale precision etching by removing material layer by layer. However, it is is challenging for ALE to play a bigger role in semiconductor fabrication due to its low productivity. Among various obstacles, the time-consuming purging steps between the surface modification and removal steps of the ALE cycle have been a major hurdle hindering the ALE process. In this work, we experimentally demonstrate a purgeless SiO2 ALE methodology in which the surface modification and removal steps are controlled solely by pulsed C4F8 injection into continuous Ar plasma. The working principle of this simple approach is based on the conventional fluorocarbon (FC) plasma SiO2 etching mechanism, where the SiO2 etch rate decreases to zero when the thickness of an FC film on the SiO2 is above a certain level. Here, a thick FC film is considered to act as a protective layer against residual FC radicals in the surface removal step, allowing the purging step between the surface modification and removal steps to be omitted. The proposed approach is expected to facilitate the improvement of ALE equipment costs and potentially lead to wider employment of ALE technology in semiconductor manufacturing.

Effect of hydrofluorocarbon structure of C3H2F6 isomers on high aspect ratio etching of silicon oxide

In this study, using three isomers (1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,2,2,3,3-hexafluoropropane (HFC-236ca)) having the same chemical composition of C3H2F6, effects of chemical branch structure of three C3H2F6 isomers on the plasma characteristics and etch characteristics of high aspect ratio ACL patterned SiO2 were investigated. During the etching of SiO2 and amorphous carbon layer (ACL) using the three isomers mixed with oxygen, different etch characteristics and plasma characteristics were observed. In the plasmas, more CF2 and H but, less F were related to the formation of a fluorocarbon polymer layer on the surface, while lower high mass ion species such as C3HF4+ and, C3H2F5+ were related to the ion bombardment in the order of HFC-236fa, HFC-236ea, and HFC-236ca consequently leading to a lower SiO2 etch rate. Therefore, when C3H2F6 was used, even with the same chemical composition, the chemical branch structure of the compound affected the plasma properties and etch characteristics significantly depending on chemical branches in the compound. We believe that, for other hydrofluorocarbon compounds mixed with a critical oxygen flow rate, plasma properties and SiO2 etch characteristics can be estimated through properties of chemical branches attached in these compounds.