Fluorocarbon Plasma Etching Research Articles

3D modeling of feature-scale fluorocarbon plasma etching in silica

Fluorocarbon dry etching of vertical silica-based structures is essential to the fabrication of advanced complementary metal-oxide-semiconductor and dynamic random access memory devices. However, the development of etching technology is challenged by the lack of understanding of complex surface reaction mechanisms and by the intricacy of etchant flux distribution on the feature-scale. To study these effects, we present a three-dimensional, TCAD-compatible, feature-scale modeling methodology. The methodology combines a level-set topography engine, Langmuir kinetics surface reaction modeling, and a combination of reactant flux evaluation schemes. We calibrate and evaluate our model to a novel, highly selective, etching process of a mathrm {SiO_2} via and a textrm{Ru} hardmask by mathrm {CF_4/C_4F_8}. We adapt our surface reaction model to the novel stack of materials, and we are able to accurately reproduce the etch rates, topography, and critical dimensions of the reported experiments. Our methodology is therefore able to prototype and study novel etching processes and can be integrated into process-aware three-dimensional device simulation workflows.

Evolution of lithography-to-etch bias in multi-patterning processes

Quantitatively accurate, physics-based, computational modeling of etching and lithography processes is essential for modern semiconductor manufacturing. This paper presents lithography and etch models for a trilayer process in a back end of the line manufacturing vehicle. These models are calibrated and verified against top-down scanning electron microscope (SEM) and cross-sectional SEM measurements. Calibration errors are within 2 nm, while the maximum verification error is less than 3 nm. A fluorocarbon plasma etch of the spin-on-glass (SOG) layer accounts for most of the etch bias present in the process. The tapered profile in the SOG etch step is generated due to the polymerization process by fluorocarbon radicals generated in the plasma. The model predicts a strong correlation between the etch bias in the SOG etch step and the neutral-to-ion flux ratio in the plasma. The second etch step of the flow, which etches the spin-on-carbon (SOC) layer using an H2/N2 plasma, results in a negative etch bias (increase in CDs) for all measured features. The ratio of hydrogen to nitrogen radical fluxes effectively controls the etch bias in this step, with the model predicting an increase in the etch bias from negative to positive values as the H-to-N ratio decreases. The model also indicates an aspect ratio dependent etch rate in the SOG and SOC etch steps, as seen in the etch front evolution in a three-dimensional test feature. The third and final step of the process, SiO2-etch, generates an insignificant etch bias in all the test structures. Finally, the accuracy of the etch simulations is shown to be dependent on the accuracy of the incoming photoresist shapes. Models that consider only the top-down SEM measurement as input and do not account for an accurate photoresist profile, suffered significant errors in the post-etch CD predictions.

Passivation effect on the surface characteristics and corrosion properties of yttrium oxide films undergoing SF6 plasma treatment

This study investigates the structures, compositions and fluorocarbon-plasma etching behaviors of yttrium oxyfluoride (YOF) passivation films fabricated on sputter-deposited yttrium oxide (Y2O3) by high-density SF6 plasma irradiation. High-resolution transmission electron microscopy and nano-beam electron diffraction confirmed a YOF passivation film containing multiple phases of (104) and (006) crystal planes was formed on the fluorinated Y2O3 surface. X-ray photoelectron spectroscopy revealed few changes in the chemical compositions and surface roughness of the YOF passivation film after fluorocarbon plasma etching, confirming the chemical stability of the SF6 plasma-treated Y2O3 sample. The etching depth was ∼20% lower on the SF6 plasma-treated Y2O3 film than on the commercial Y2O3 coating. These results showed that the SF6 plasma-treated Y2O3 films have an excellent erosion resistance properties compared to the commercial Y2O3 coatings.

Plasma Etching Behavior of YOF Coating Deposited by Suspension Plasma Spraying in Inductively Coupled CHF3/Ar Plasma

Dense yttrium oxyfluoride (YOF) coating was successfully deposited by suspension plasma spraying (SPS) with coaxial feeding. After deposition for 6 min at a plasma power of 105 kW, the thickness of the YOF coating was 55 ± 3.2 µm with a porosity of 0.15% ± 0.01% and the coating rate was ~9.2 µm/min. The crystalline structure of trigonal YOF was confirmed by X-ray diffractometry (XRD). The etching behavior of the YOF coating was studied using inductively coupled CHF3/Ar plasma in comparison with those of the Al2O3 bulk and Y2O3 coating. Crater-like erosion sites and cavities were formed on the whole surface of the Al2O3 bulk and Y2O3 coating. In contrast, the surface of the YOF coating showed no noticeable difference before and after exposure to the CHF3/Ar plasma. Such high resistance of the YOF coating to fluorocarbon plasma comes from the strongly fluorinated layer on the surface. The fluorination on the surface of materials was confirmed by X-ray photoelectron spectrum analysis (XPS). Depth profiles of the compositions of Al2O3, Y2O3, and YOF samples by XPS revealed that the fluorination layer of the YOF coating was much thicker than those of Al2O3 and Y2O3. These results indicate that if the inner wall of the semiconductor process chamber is coated by YOF using SPS, the generation of contamination particles would be minimized during the fluorocarbon plasma etching process.

Plasma Etching Behavior of SF6 Plasma Pre-Treatment Sputter-Deposited Yttrium Oxide Films

Yttrium oxyfluoride (YOF) protective materials were fabricated on sputter-deposited yttrium oxide (Y2O3) by high-density (sulfur fluoride) SF6 plasma irradiation. The structures, compositions, and fluorocarbon-plasma etching behaviors of these films were systematically characterized by various techniques. After exposure to SF6 plasma, the Y2O3 film surface was fluorinated significantly to form a YOF film with an approximate average thickness of 30 nm. X-ray photoelectron spectroscopy revealed few changes in the elemental and chemical compositions of the surface layer after fluorination, confirming the chemical stability of the YOF/Y2O3 sample. Transmission electron microscopy confirmed a complete lattice pattern on the YOF/Y2O3 structure after fluorocarbon plasma exposure. These results indicate that the SF6 plasma-treated Y2O3 film is more erosion resistant than the commercial Y2O3 coating, and thus accumulates fewer contamination particles.

A unified semi-global surface reaction model of polymer deposition and SiO2 etching in fluorocarbon plasma

We propose a semi-global surface reaction model to capture simultaneous polymer deposition and oxide etching in fluorocarbon plasma. The critical parameters of this model within reasonable ranges can be determined using predesigned experimental data with plasma diagnostics in inductively coupled fluorocarbon plasma. This model can describe the transition behavior from polymer deposition to oxide etch self-consistently without ad-hoc assumptions, providing better insight into abnormal etching behaviors in high aspect ratio contact hole etching, such as sidewall bowing and twisting toward next generation of memory devices in semiconductor industries.

Plasma etching properties of various transparent ceramics

The etching properties of four types of transparent ceramics: sapphire (a single crystalline α-Al2O3), γ-AlON (γ-aluminum oxynitride), Mg-spinel (MgAl2O4), and Y2O3, as well as a polycrystalline opaque Al2O3 were examined using an inductively coupled plasma etcher under an incident plasma power of 2,000 W for up to 3 h. The transparent γ-AlON and opaque Al2O3 showed significant surface morphological changes, whereas sapphire, Mg-spinel, and Y2O3 revealed a relatively smooth surface upon etching. However, direct correlation between the surface morphological change and the degree of etching could not be drawn because sapphire showed a uniform surface etching despite its significant mass loss. Even though Y2O3 was found to be more plasma-resistant than Al2O3, overall, Mg-spinel was the most feasible transparent material for monitoring window application in a semiconductor processing chamber because of its minimal degree of erosion (≤0.4g/m2) and the transmittance change (≤2%) upon 3 h of fluorocarbon (CF4) plasma etching.

Analytical study of polymer deposition distribution for two-dimensional trench sidewall in low-k fluorocarbon plasma etching process

In this study, a new polymer deposition distribution model for a two-dimensional low-k porous SiOCH trench structure during the fluorocarbon plasma etching process is described so as to investigate the bowing effect in a nanoscale trench. The model consists of three processes, namely, (1) polymer reflection, (2) ion-assisted polymer deposition, and (3) ion-assisted polymer emission. To calculate the distribution of the polymer, the polymer flux arrived at the surface points of the trench was calculated based on the model. To estimate the profile of the trench, the flux of the etchants at the point of the trench surface was also considered. The simulated etching process is based on a simple flux model, which takes into account angular distributions for ions and radicals from the sheath edge to the trench. Simulation results show that the lower section of the sidewall had a larger number of polymer particles than the other positions of the sidewall did. According to the simulated results, the sidewall bowing amount was estimated to be about 2.9 nm and the bowing position was approximately 29.8 nm at a trench depth of about 148.5 nm. With the proposed polymer distribution model, the bowing effect during fluorocarbon plasma etching can be further understood for a nanoscale process.

Benefits of plasma treatments on critical dimension control and line width roughness transfer during gate patterning

The present work focuses on the line width roughness (LWR) transfer and the critical dimension control during a typical gate stack patterning and shows the benefits of introducing 193 nm photoresist treatments before pattern transfer into the gate stack to improve process performance. The two investigated treatments (HBr plasma and vacuum ultra violet (VUV) plasma radiation) have been tested on both blanket photoresist films and resist patterns to highlight the etching and roughening mechanisms of cured resists. Both treatments reinforce the etch resistance of the photoresist exposed to fluorocarbon plasma etching process used to open the Si-ARC (silicon antireflective coating) layer. The etch resistance improvement of cured resists is attributed to both the decrease in oxygen content within the resist and the crosslinking phenomena caused by VUV radiation during the treatment. As the magnitude of the surface roughness is directly correlated to the etched thickness, cured resists, which are etched less rapidly, will develop a lower surface roughness for the same processing time compared to reference resists. The LWR evolution along the pattern sidewalls has been studied by critical dimension atomic force microscopy during the Si-ARC plasma etching step. The study shows that the LWR is degraded at the top of the resist pattern and propagates along the pattern sidewalls. However, as long as the degradation does not reach the interface between resist and Si-ARC, the LWR decreases during the Si-ARC etching step. As resist pretreatments reinforce the resist etch resistance during Si-ARC etching, the LWR degradation along the sidewalls is limited leading to minimized LWR transfer. The LWR decrease observed after plasma etching has been explained thanks to a spectral analysis of the LWR performed by critical dimension scanning electron microscopy combined with the power spectral density fitting method. The study shows that the high and medium frequency components of the roughness (periodicity below 200 nm) are not totally transferred during the gate patterning allowing a LWR decrease at each plasma step.

Surface morphology and structural analysis of fluorocarbon nano-rings formation through EBL and SiO2 plasma etching

This paper reports the formation of nano-scale ring-shaped fluorocarbon macromolecules during silicon dioxide SiO2 reactive ion etching (RIE). This nanostructure was created on a SiO2 substrate with poly methyl methacrylate (PMMA) mask during the RIE process, using trifluoromethane (CHF3) and oxygen etchants. Variation in etching time results in the creation of square, double concentric, and flower-shaped nano-rings around SiO2 micro-pits. In addition, increasing the etching times leads to an increase in ring width. The formation of these nano-rings is shown by a deposition of passivation layer, consisting of silicon oxide, SixOy and fluorocarbon, CxFy, on sidewalls during SiO2 etching in fluorocarbon plasma. Field Emission Scanning Electron Microscopy (FESEM) and Energy-dispersive X-ray (EDX) were utilized to investigate the morphology and the structure of the nano-rings. Results show that the flower-shaped nano-rings were created on the surface of silicon for 8 min of etching time. These fluorocarbon nano-rings could be used as nano-scale templates.

Numerical Simulation Method for Plasma-Induced Damage Profile in SiO2 Etching

We developed a numerical simulation method for the depth profiles of plasma-induced physical damage to SiO2 and Si layers during fluorocarbon plasma etching. In the proposed method, the surface layer is assumed to consist of two layers: a C–F polymer layer and a reactive layer. Physical and chemical reactions in the reactive layer divided into several thin slabs and in the deposited C–F polymer layer, which depend on etching parameters, such as etching time, gas flow rate, gas pressure, and ion energy (Vpp), are considered in detail. We used our simulation method to calculate the SiO2 etch rate, the thickness of the C–F polymer layer (TC–F), and the selectivity of SiO2 to Si during C4F8/O2/Ar plasma etching. We confirmed that the calculated absolute values and their behavior are consistent with experimental data. We also successfully predicted depth profiles of physical damage to the Si and SiO2 layers introducing our re-gridding method. We found that much Si damage is generated in the pre- and early stages of the overetching step of SiO2/Si layer etching despite the high selectivity. These simulation results suggest that the TC–F value and the overetching time must be carefully controlled by process parameters to reduce damage during fluorocarbon plasma etching. The results have also provided us with useful knowledge for controlling the etching process.

Surface and near-surface modifications of ultralow dielectric constant materials exposed to plasmas under sidewall-like conditions

The authors describe the temporal evolution of the surface and near-surface regions of a porous SiCOH ultralow k (ULK) dielectric during exposure under sidewall-like exposure conditions to various plasma processing environments. The authors studied the exposure of the ULK material to Ar plasma, C4F8/Ar-based etching plasma, and O2 or CO2 ashing plasmas, as well as various sequences of these processes. Real-time monitoring of the ULK surfaces during plasma processing was performed by in situ ellipsometry employing a novel gap structure. Additionally, changes in ULK surface properties were characterized by x-ray photoelectron spectroscopy and selective dilute hydrofluoric acid wet etching in combination with ex situ ellipsometry measurements. Pristine ULK material exposed to O2 plasma without ion bombardment shows the formation of a near-surface porous layer. For exposure of the ULK to CO2 plasma operated at comparable plasma operation conditions, the modification depth for a given exposure time is reduced relative to O2, but otherwise an identical ellipsometric trajectory is followed. This is indicative of a similar ULK damage mechanism for the two discharges, although at different rates. Energetic (∼400 eV) ion bombardment on the surface of ULK with line-of-sight Ar plasma exposure introduced a ∼12 nm thick SiO2-like densified layer on the ULK surface meanwhile sputtering off the ULK material. The sidewall-like modifications of ULK due to metastable Ar, if present, were too subtle to be measurable in this article. For ULK exposed under sidewall-like geometry to C4F8/Ar-based etching plasma, fluorocarbon quickly permeated into the subsurface region and showed saturation at a mixed layer thickness of about 14 nm. For additional exposure to O2 or CO2 discharges, a strong decrease of the CO2 plasma induced ULK surface modifications with increasing fluorocarbon (FC) film thickness was found, indicative of surface protection by FC surface deposition along with pore-sealing by the FC material. Attempts to increase the protective nature of the FC film by additional plasma processing, e.g., by exposure to Ar or He plasma after FC plasma etching, did not reduce CO2 plasma induced ULK surface modifications further.

Ultrahydrophobic and Microporous Electrodes Fabricated by Fluorocarbon Plasma Etching of Carbon Fiber

The ultrahydrophobic, conductive, and porous properties of microporous electrodes (MPEs) are successfully deposited by a reactive ion etcher with the plasma treatment. The electrodes fabricated with plasma exhibit a good water-repellent behavior due to hydrophobic groups such as and groups and the ultrahydrophobic properties are achieved when the water contact angle is greater than 130°. The proton exchange membrane fuel cell performance, related to surface properties of Teflon-like MPEs, is studied by fuel cell system and X-ray photoelectron spectroscopy. The ratio of fluorine-based precursor is the main parameter to adjust the conductivity, porosity, and ultrahydrophobicity of the electrodes. When the electrodes are fabricated with a ratio of fluorine-based precursor of 1.5, it has a much more stable output density, with an optimal power output of corresponding to a current density of , than that fabricated with a ratio of fluorine-based precursor of 4 during the long-duration test.

Porous SiOCH, SiCH and SiO2 Etching in High Density Fluorocarbon Plasma with a Pulsed Bias

AbstractThe effect of radio frequency bias pulsing on porous SiOCH, SiCH and SiO2 etching using inductively coupled fluorocarbon plasmas was investigated. It was found that pulse frequency had only a small influence on material etch rates. However, pulse duty cycle, defined as the time during which a bias is applied over the total period, clearly modified etch rates and selectivities. Indeed, etch selectivities between porous SiOCH and SiCH or SiO2 were considerably improved when the duty cycle was decreased. This enhancement was associated with relatively high porous SiOCH etch rates, and pattern transfers under low duty cycle conditions proved to be successful. To better understand the pulse process, surface analysis was also realised. According to XPS analysis, the material surface structure was found to be similar after etching in continuous or in pulsed mode. However, fluorocarbon species on material surfaces were fluorine richer after etching in the pulsed mode.magnified image

High density fluorocarbon plasma etching of methylsilsesquioxane SiOC(H) low-k material and SiC(H) etch stop layer: surface analyses and investigation of etch mechanisms

This paper focuses on plasma etching and XPS surface analyses of new dielectric materials used in integrated circuits. We investigate by XPS surface modifications of methylsilsesquioxane low-k polymer (SiOC(H)) and amorphous hydrogenated silicon carbide (SiC(H)) when exposed to Ar, SF6 and C2F6-based high density plasmas. Ar and SF6 plasmas remove the carbonaceous groups from the surface leading to the formation of fluorinated top layers (SiOF and SiF-like layers) in SF6 plasma. In the case of C2F6-based mixtures, the surface structure fits well with a two-layer model, consisting of a fluorocarbon top layer above a fluorinated interaction layer (SiOF or SiF) on the bulk materials (SiOC(H) or SiC(H)). Determination of top layer thicknesses from XPS data is discussed. We show that material etch rate is not correlated with the total modified thickness, in contrast to the top fluorocarbon layer thickness which is in good correlation with etch rates. Etch yields (etch rates divided by the ion flux) are calculated and are studied in order to draw material etch mechanisms in C2F6 based mixtures. We conclude that for both materials, etching mechanisms in C2F6/H2 mixtures, and to a lesser extent in C2F6/Ar mixtures, are close to those of silicon in fluorocarbon plasmas and different from those of the conventional interlevel dielectric material SiO2. On the contrary etching mechanisms in C2F6/O2 mixtures are similar to those of silicon dioxide in fluorocarbon plasmas.

Anisotropic fluorocarbon plasma etching of Si∕SiGe heterostructures

Fluorocarbon plasma etching of Si∕SiGe heterostructures is demonstrated as a method for fabrication of quantum devices with vertical sidewalls. The heterostructures consist of layers of Si and SiGe, and anisotropic etching of the heterostructures using plasmas to isolate device elements is an attractive approach to fabricating devices. A challenge that has limited the use of fluorocarbon etching is the difference in Si and SiGe etch rates under comparative conditions. Preferential etching of SiGe can lead to undercutting beneath the top Si layer, causing a reduction in critical device dimensions of unknown magnitude. By using fluorocarbon etch gases with high carbon content, fluorocarbon sidewall passivation improves the anisotropy of etched feature profiles by preventing lateral etching of SiGe. Etch results with a C4F8∕Ar∕N2 gas mixture show a straight sidewall profile through the layers of the heterostructure.

Robust Cu Dual Damascene Interconnects With Porous SiOCH Films Fabricated by Low-Damage Multi-Hard-Mask Etching Technology

Low-damage hard-mask (HM) plasma-etching technology for porous SiOCH film (k=2.6) has been developed for robust 65-nm-node Cu dual damascene interconnects (DDIs). No damage is introduced by fluorocarbon plasma etching irrespective of whether rigid (k=2.9) or porous (k=2.6) SiOCH films are used, due to the protective CF-polymer layer deposited on the etched sidewall. The etching selectivity of the SiOCH films to the inorganic HMs is kept high by controlling the radical ratio of carbon relative to oxygen in the etching plasma gas. However, oxidation damage penetrates the films from the sidewalls due to the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma used for photoresist ashing. This damage is increased by the porous structure. As a result, we developed a via-first multi-hard-mask process for the DD structure in porous SiOCH film with no exposure to O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -ashing plasma, and we controlled the via-taper angle by RF bias during etching. We fabricated robust Cu DDIs with tapered vias in porous SiOCH film that can be applied to 65-nm-node ULSIs and beyond

Modeling dual inlaid feature construction

Dual inlaid construction of copper interconnect structures involves a sequence of tightly coupled plasma processes with subtle variations in one process impacting subsequent processes. An integrated plasma reactor/feature physics based modeling suite has been applied to three-dimensional (3D) dual inlaid (DI) feature construction. Specifically, the goal of this article is to understand process interdependencies during DI construction. The DI feature is used in inlaid copper interconnects to define metal lines and their connection to the metal layer below. One advantage of the DI feature is only one metallization step (barrier deposition/seed deposition/electroplating/chemical mechanical polish) is required to deposit metal into both the metal lines and the via connections to the metal layer below. Discussed will be the 3D feature modeling of fluorocarbon plasma etching of vias and trenches in SiO2 to construct dual inlaid features. The model includes 11 steps in the dual inlaid construction process. Papaya, the feature model, applies the many mask, etch, and deposition process steps as characterized by reactor models onto an evolving feature. The model thus allows for an integrated study of the dual inlaid feature construction including the cumulative effect of prior etch steps on subsequent etch steps. Polymer build up can shield a surface from enchants and plays a role in etch selectivity. The amount of polymer in the via and trench etch is shown to affect the amount of bowing in the feature as decreased passivation from less polymer leads to more chemical etching on the via and trench sidewalls. The height of the “slug” used to protect the via in a via first trench last (VFTL) DI integration controls the fencing or notching seen at the via opening. As the slug to dielectric etch ratio is increased the etching at the via opening is enhanced leading to notching at the via opening as well as widened and sloped vias. A larger trench width versus via diameter leads to larger via openings and more flared vias. Also, bilayer resist VFTL and trench first via last (TFVL) DI integration schemes have been modeled. TFVL DI integration is shown not to suffer issues at the via opening (fencing, notching, and flare) as seen in the VFTL DI integration scheme.

Structure of surface reaction layer of poly-Si etched by fluorocarbon plasma

A structure of surface reaction layer of poly-Si substrate during fluorocarbon plasma etching was studied by using a plasma beam irradiation apparatus and a quasi-in situ x-ray photoelectron spectroscopy. A fluorinated silicon (SiF) layer was formed under a fluorocarbon (CF) layer. It was found that the thickness of the SiF layer linearly increased with the etch yield of poly-Si regardless of the change of the CF layer thickness. The average ratio of the number of Si to that of F in the SiF layer did not strongly depend on the etch yield. The carbon-rich region of the CF layer was formed just above the SiF layer due to the consumption of fluorine for the formation of SiF layer.

Reactive ion etching of glass for biochip applications: Composition effects and surface damages

Due to its insulating properties, transparency, and well known surface chemistry, glass represents an interesting alternative to silicon or polymers for biochip processing. However, high aspect-ratio posts for DNA electrophoresis have only been reported in expensive quartz substrates. Therefore, we investigate here metal mask transfer by fluorocarbon plasma etching in nine silica or glasses of different grades. With increasing amounts of non-SiO 2/non-B 2O 3 oxides in the material, the etch rate decreases and, in some cases, strong surface roughening appears. Furthermore, even for fused silica, surface damages such as cone-like defects were observed. Consequently, soda-lime slides coated with silica by plasma enhanced chemical vapor deposition (PECVD) were used as a good compromise between etching quality and cost. Electrophoresis chips with features down to 100 nm and aspect-ratio up to 10 could then be fabricated.