Inductively Coupled Plasma System Research Articles

Remote inductively coupled plasmas in Ar/N2 mixtures and implications for plasma enhanced ALD

Plasma enhanced atomic layer deposition (PEALD) is a cyclic atomic layer deposition (ALD) process that incorporates plasma-generated species into one of the cycle substeps. The addition of plasma is advantageous as it generally provides unique reactants and a substantially reduced growth temperature compared to thermal approaches. However, the inclusion of plasma, coupled with the increasing variety of plasma sources used in PEALD, can make these systems challenging to understand and control. This work focuses on the use of plasma diagnostics to examine the plasma characteristics of a remote inductively coupled plasma (ICP) source, a type of plasma source that is commonly used for PEALD. Ultraviolet to near-infrared spectroscopy and spatially resolved Langmuir probe measurements are employed to characterize a remote ICP system using nitrogen-based gas chemistries typical for III-nitride growth processes. Spectroscopy is used to characterize the relative concentrations of important reactive and energetic neutral species generated in the remote ICP as a function of gas flow rate, Ar/N2 flow fraction, and gas pressure. In addition, the plasma potential and plasma density for the same process parameters are examined using an RF compensated Langmuir probe downstream from the ICP source. The results are also discussed in terms of their impact on materials growth.

Sub-nanometer finishing of polycrystalline tin by inductively coupled plasma-assisted cutting

Polycrystalline tin is an ideal excitation material for extreme ultraviolet light sources. However, the existence of grain boundary (GB) limits the surface roughness of polycrystalline tin after single-point diamond turning (SPDT). In this work, a novel method termed inductively coupled plasma (ICP)-assisted cutting was developed for the sub-nanometer finishing of polycrystalline tin. The relationship between ICP power, processing time, and modification depth was established by thermodynamic simulation, and the fitted heat transfer coefficient of polycrystalline tin was 540 W/(m2·K). The effects of large-thermal-gradient ICP treatment on the microstructure of polycrystalline tin were studied. After 0.9 kW ICP processing for 3.0 s, corresponding to the temperature gradient of 0.30 K/µm, the grain size of polycrystalline tin was expanded from a size of approximately 20–80 µm to a millimeter scale. The Taguchi method was used to investigate the effects of rotational speed, depth of cut, and feed rate on SPDT. Experiments conducted based on the ICP system indicated that the plasma-assisted cutting method promoted the reduction of the influence of GB steps on the finishing of polycrystalline tin, thereby achieving a surface finish from 8.53 to 0.80 nm in Sa. The results of residual stress release demonstrated that the residual stress of plasma-assisted turning processing after 504 h stress release was 10.7 MPa, while that of the turning process without the ICP treatment was 41.6 MPa.

Capacitively coupled nonthermal plasma synthesis of aluminum nanocrystals for enhanced yield and size control

Uniform-size, non-native oxide-passivated metallic aluminum nanoparticles (Al NPs) have desirable properties for fuel applications, battery components, plasmonics, and hydrogen catalysis. Nonthermal plasma-assisted synthesis of Al NPs was previously achieved with an inductively coupled plasma (ICP) reactor, but the low production rate and limited tunability of particle size were key barriers to the applications of this material. This work focuses on the application of capacitively coupled plasma (CCP) to achieve improved control over Al NP size and a ten-fold increase in yield. In contrast with many other materials, where NP size is controlled via the gas residence time in the reactor, the Al NP size appeared to depend on the power input to the CCP system. The results indicate that the CCP reactor assembly, with a hydrogen-rich argon/hydrogen plasma, was able to produce Al NPs with diameters that were tunable between 8 and 21 nm at a rate up ∼ 100 mg h−1. X-ray diffraction indicates that a hydrogen-rich environment results in crystalline metal Al particles. The improved synthesis control of the CCP system compared to the ICP system is interpreted in terms of the CCP’s lower plasma density, as determined by double Langmuir probe measurements, leading to reduced NP heating in the CCP that is more amenable to NP nucleation and growth.

Characteristics of segmented dielectric window inductively coupled plasma

In this study, a novel inductively coupled plasma (ICP) system is proposed. It comprises a segmented dielectric window and a metal frame. For the proposed ICP system, a thin window can be designed, thereby compensating for the power loss caused by the metal frame. The proposed ICP system has two potential advantages: it can enhance the controllability of the gas flow field and it can reduce the capacitive power coupling. These characteristics enable the superior uniformity and reliable operation of ICP systems for semiconductor processes. The characteristics of the proposed ICP system are investigated using three-dimensional fluid self-consistent plasma simulations and experiments. The proposed ICP system exhibits performance similar to that of the conventional ICP system currently used in etching and deposition processes.

High‐aspect‐ratio oxide etching using CF4/C6F12O plasma in an inductively coupled plasma etching system with low‐frequency bias power

AbstractHigh‐aspect‐ratio (HAR) etch of SiO2 films was attempted using a low‐frequency (2 MHz) bias power in an inductively coupled plasma (ICP) system using heptafluoroisopropyl pentafluoroethyl ketone (C6F12O) gas, which has a lower global warming potential (GWP). Etching characteristics of the oxide film according to changes such as the CF4/C6F12O mixing ratio, source power (13.56 MHz), and bias power were derived. To understand the etching characteristics and mechanism, optical emission spectroscopy (OES), double Langmuir probe (DLP) measurement, and X‐ray photoelectron spectroscopy (XPS) analysis were performed. We observed the vertically etched profile of the 100 nm etched line pattern with a scanning electron microscope (SEM) and at first suggested that the HAR oxide etching process is feasible using the ICP system.

Fabrication of black GaAs by maskless inductively coupled plasma etching in Cl2/BCl3/O2/Ar chemistry

Textured GaAs surfaces with near-zero reflectance are promising for the antireflective application of photovoltaic and optoelectronic devices. Such surfaces can be described as “black GaAs” attributing to their superior light-trapping capability. In this paper, black GaAs with grasslike nanowire bunches was fabricated in a maskless inductively coupled plasma (ICP) etching manner. Cl2/BCl3/O2/Ar chemistry was selected as the feed gas in the ICP system. Undoped black GaAs with solar-weighted reflectance (SWR) of 1.01% and doped black GaAs with SWR of 2.56% were obtained. In the study, the surface morphology and antireflection behavior of the textured GaAs were found to vary at different etching time, power conditions, and O2 contents. Combined with the surface element analyses, the etching mechanism of the maskless process was proposed. It is considered as a competing mechanism for the removal of the GaAs material by Cl-based gases and the passivation of the surface by O radicals. This maskless texturing method has the advantages of simplicity, scalability, and efficiency. The black GaAs of such patterns has prospects in photodetectors, solar cells, and flexible devices.

Investigation of SiO2 Etch Characteristics by C6F6/Ar/O2 Plasmas Generated Using Inductively Coupled Plasma and Capacitively Coupled Plasma.

The etching properties of C6F6/Ar/O2 in both an inductively coupled plasma (ICP) system and a capacitively coupled plasma (CCP) system were evaluated to investigate the effects of high C/F ratio of perfluorocarbon (PFC) gas on the etch characteristics of SiO2. When the SiO2 masked with ACL was etched with C6F6, for the CCP system, even though the etch selectivity was very high (20 ~ infinite), due to the heavy-ion bombardment possibly caused by the less dissociated high-mass ions from C6F6, tapered SiO2 etch profiles were observed. In the case of the ICP system, due to the higher dissociation of C6F6 and O2 compared to the CCP system, the etching of SiO2 required a much lower ratio of O2/C6F6 (~1.0) while showing a higher maximum SiO2 etch rate (~400 nm/min) and a lower etch selectivity (~6.5) compared with the CCP system. For the ICP etching, even though the etch selectivity was much lower than that by the CCP etching, due to less heavy-mass-ion bombardment in addition to an adequate fluorocarbon layer formation on the substrate caused by heavily dissociated species, highly anisotropic SiO2 etch profiles could be obtained at the optimized condition of the O2/C6F6 ratio (~1.0).

Influence of Plasma Ultraviolet/Vacuum Ultraviolet Irradiation Damage on Silicon Metal-Oxide-Semiconductor Capacitor During Etching.

In this study, we evaluate the defects and charges caused by the ultraviolet (UV)/vacuum ultraviolet (VUV) irradiation in the high-k/metal gate stack structure, especially in HfO₂ layer and at Si/HfO₂ interface. First, we measured the photons irradiating to the surface in the neutral beam etching (NBE) system and in the conventional inductively coupled plasma (ICP) system through optical emission spectroscopy (OES), respectively. By using this method, we evaluate the ability of reducing UV/VUV irradiation damage in the NBE system. As a result, photon intensity detected in the ICP system shows larger magnitude as compared to the NBE system, which indicates the UV/VUV irradiation is more severe in the ICP system. Moreover, in order to understand the twisting of electrical characteristics caused by UV/VUV irradiation, we set the prefabricated metal-oxide-semiconductor (MOS) capacitors in both systems to absorb the irradiation of UV/VUV photons respectively. The electrical characteristics of the etched MOS capacitors and its related plasma-induced damage model are discussed. The result of the devices exposed in the ICP system reveals a greater electrical characteristics shift compared to the devices in NBE such as the interface trap density (Dit) in case of NBE is 3.55621×1012 cm-2eV-1 and in case of ICP is higher i.e., 4.19961×1012 cm-2eV-1.

Moth-eye structured mold using sputtered glassy carbon layer for large-scale applications

Surface reflection is a problem in applications such as solar panels, smartphones, and tablet computers. To prevent such reflection, we previously developed a moth-eye structure that can be fabricated with a single film. This antireflection structure (ARS) suppresses reflection over a wide range of light wavelengths and incident angles. The production of large-area ARS films, which can be achieved using ultraviolet nanoimprint lithography (UV-NIL), is required for solar panels and displays. In our previous study, a moth-eye structure was fabricated by irradiating a glassy carbon (GC) substrate with an oxygen ion beam. However, it is difficult to fabricate a large GC substrate because GC is made using powder metallurgy. To overcome this problem, we used a sputtered GC layer as the ARS master mold material. In this study, we demonstrate that a moth-eye structure can be formed by irradiating sputtered GC with an oxygen ion beam using an inductively coupled plasma (ICP) system. We formed a moth-eye structure on sputtered GC using two-step ICP etching. The fabricated moth-eye structured mold had a reflectance of approximately 0.1% in the visible-light region. In addition, a moth-eye film transferred using UV-NIL with the fabricated moth-eye structured mold had a low reflectance of approximately 0.4% in the visible-light region. • A GC layer was formed uniformly on the glass substrate with sputter-coated titanium. • A moth-eye structured mold was fabricated by irradiating the sputtered GC layer with an oxygen ion beam using an ICP system. • An optimized moth-eye structure was formed on the sputtered GC layer using two-step ICP etching. • A transparent moth-eye film with low reflectance was fabricated using UV-NIL from the fabricated moth-eye structured mold.

Porous Desiccant Wheel Produced Using Inductively Coupled Plasma Technique

In this study, the adsorption material is fabricated from the aluminum residues using inductively coupled plasma (ICP) technique and applied as a raw material to manufacture porous solid desiccant wheel. An ICP system is developed to refine aluminum hydroxide extracted from aluminum residues into activated alumina by utilizing its high energy densities. A six-turn induction coil is suitable for our match box to produce alternating electromagnetic field, to sustain space discharge, and to have well reaction zone. The ICP generator power is set at 800 W, and the batch of aluminum residues is purified to generate activated alumina with a BET surface area of 122 m2/g. The porous desiccant wheel is manufactured using activated alumina with a 3-D random porous structure and applied to adsorb moisture from the air. The equilibrium time for the solid desiccant wheel and humidity are determined by observed kinetics in the adsorption experiment. The adsorption equilibrium time of the desiccant wheel (60 pores per inch) with 15-cm diameter and 5-cm thickness is 12 minutes. The maximum adsorption capacity is 51.4 g (at 12 min) and per gram of the desiccant wheel can adsorb 0.184-g water.

Computational Fluid Dynamics (CFD) Simulations and Experimental Measurements in an Inductively-Coupled Plasma Generator Operating at Atmospheric Pressure: Performance Analysis and Parametric Study

In this article, electrical characteristics of a high-power inductively-coupled plasma (ICP) torch operating at 3 MHz are determined by direct measurement of radio-frequency (RF) current and voltage together with energy balance in the system. The variation of impedance with two parameters, namely the input power and the sheath gas flow rate for a 50 kW ICP is studied. The ICP torch system is operated at near atmospheric pressure with argon as plasma gas. It is observed that the plasma resistance increases with an increase in the RF-power. Further, the torch inductance decreases with an increase in the RF-power. In addition, plasma resistance and torch inductance decrease with an increase in the sheath gas flow rate. The oscillator efficiency of the ICP system ranges from 40% to 80% with the variation of the Direct current (DC) powers. ICP has also been numerically simulated using Computational Fluid Dynamics (CFD) to predict the impedance profile. A good agreement was found between the CFD predictions and the impedance experimental data published in the literature.

Grafting of amine functions on cellulose acetate fibers by plasma processing

The aim of this study was to graft the amine functions on the surface of cellulose acetate (CA) fibers by two kind of plasma processing; namely, inductively coupled plasma (ICP) and radiofrequency plasma, using either NH3/He or mixture of N2/H2 gases. Optical emission spectroscopy was used to examine the various chemical species of the N2/H2 ICP system. Due to the entangled morphology of the CA fibers, only X-ray photoelectron spectroscopy (XPS) was used to characterize the surface. The effects of the different experimental conditions on the grafting efficiency have been studied. The results showed that in all cases NH2 groups were successfully grafted onto the surface of the CA fibers, and it seems that the ICP process is more effective for the amine grafting than low pressure radiofrequency plasma. Ageing tests carried out under laboratory conditions on the plasma-treated CA tow showed that the density of grafted amines was almost stable over a period of 60 days.

Diamond-like amorphous carbon layer film by an inductively coupled plasma system for next generation etching hard mask

Amorphous carbon layer (ACL) deposited by the capacitively coupled plasma (CCP), plasma-enhanced chemical vapor deposition (PE-CVD) is widely used in etching hard masks in the semiconductor industry. As the feature size of semiconductor devices decreased below 30 nm, a carbon hard mask film with high etching selectivity and high transparency is required. However, it is very difficult to deposit the amorphous carbon film with both high etching selectivity and high transparency by CCP type PE-CVD. In this study, ACL films were deposited by an inductively coupled plasma (ICP) type deposition system. We selected the ICP deposition method because it allows independent control of the plasma density and ion impingement energy. The ACL films deposited by the ICP system had higher film density than the density of ACL films deposited by PE-CVD system. Moreover, Raman spectroscopy analysis of the ICP-made ACL films showed diamond-like properties with a high ratio of sp3 bonding, which could be due to the optimal bias power in ICP during deposition. The dry-etching selectivity of ACL films linearly increased with the density of the film. These studies confirmed that ICP is an effective method for the deposition of carbon hard masks with high etching selectivity.

Numerical Analysis on the Electrical and Thermal Flow Characteristics of Ar-N2 Inductively Coupled Plasma Torch System

Numerical analysis on the electrical and thermal flow characteristics of Ar-N2 inductively coupled plasma (ICP) were carried out for N2 content from 0 to 50 mol% at plasma power level of 50 kW. Firstly, the computational results of thermal flow fields revealed that the addition of N2 could reduce the radiation heat loss, together with increasing the exit enthalpy. For example, the radiation heat loss of Ar-N2 ICP with N2 content of 20 mol% is reduced by ∼ 33%, compared with that of Ar-only ICP, which are essential for the safe operation of an ICP system at the high power level of 50 kW. In addition, the increase of N2 content was also found to increase the load resistance of a tank circuit for a vacuum tube oscillator. Equivalent circuit analysis using the numerical results shows that this increase of the load resistance comes from the increasing equivalent resistance and the decreasing equivalent inductance of Ar-N2 ICP, corresponding to the changes of thermal flow fields with the increase of N2 content. For a tank circuit consisting of a capacitor and an inductor with a capacitance of 6,500 pF, and an equivalent inductance of 0.84 μH, the load resistance was calculated to be increased from 81 Ω for Ar only ICP to 130 Ω for Ar-N2 ICP with N2 content of 20 mol%. Considering the internal resistances of high power vacuum tubes higher than 130 Ω, this increase of load resistance clearly shows that N2 addition can improve the impedance mismatching of an ICP torch system with a vacuum tube oscillator having no variable part to tune the load resistance. By providing these basic data for the calculation of load resistance and thermal flow characteristics, the numerical analysis combined with equivalent circuit analysis used in this work can help in designing and operating a high-powered ICP torch system with a vacuum tube oscillator.

Overcoming Etch Challenges on a 6″ Hg1−x Cd x Te MBE on Si Wafer

The effect of increasing photoresist (PR) thickness on the inductively coupled plasma (ICP) dry etched characteristics of a 6″ (c.15 cm) molecular beam epitaxy Hg1−x Cd x Te/Si wafer is investigated. It is determined that the Hg1−x Cd x Te etch rate (ER) does not vary significantly with a change in the PR thickness. Also, the vertical ER of the PR is seen to be independent of the PR thickness, but the lateral ER is seen to reduce significantly with increased PR thickness. Indeed, very little reduction in the pixel mesa area post-dry etch is seen for the thicker PR. Consequently, the trench sidewall angle is also seen to vary as a function of the PR thickness. Since ICP is the more attractive choice for dry etching Hg1−x Cd x Te, this simple, cost-effective way to extend the capabilities of dry etching (larger mesa top area post-dry etch, ability to create tailor-made trench sidewall angles for optimal conformal passivation deposition, and potential for reduced dry etch damage) described here would allow for the fabrication of next generation infrared detectors with increased yield and reduced cost. Although similar results have been presented using the electron cyclotron resonance system to dry etch Hg1−x Cd x Te, to the best of our knowledge, this is the first time that such results have been presented using an ICP system.

Inductively Coupled Plasma etching of amorphous silicon nanostructures over nanotopography using C4F8/SF6 chemistry

Inductively Coupled Plasma (ICP) etching of amorphous silicon (a-Si) nanostructures using a continuous C4F8/SF6 plasma over nanotopography in silicon dioxide (SiO2) is investigated. The coil power of the ICP system is used to tune the a-Si etch rate from 20 to 125 nm/min. The etch rates of a-Si, SiO2 and electroresist are measured depending on the SF6 ratio, platen power and chamber pressure and used to optimize the a-Si:SiO2 etch selectivity. The results on nanostructures show that the presence of an insulating etch-stop layer affects the passivation ratio required to achieve vertical sidewalls. A low pressure is also necessary in order to etch the silicon nanostructure embedded into the oxide nanotrenches to form a highly conformable a-Si nanowire. We argue that both of these behaviors could be explained by surface charging effects. Finally, etching of 20 nm a-Si nanowires that cross 15 nm trenches in oxide with vertical sidewalls and a 4.3:1 a-Si:SiO2 etch selectivity is demonstrated. This etching process can be used in applications where nanotopography is present such as single electron transistors or multigate transistors.

The effects of neutral gas heating on H mode transition and maintenance currents in a 13.56 MHz planar coil inductively coupled plasma reactor

The H mode transition and maintenance currents in a 13.56 MHz laboratory 6 turn planar coil inductively coupled plasma (ICP) reactor are simulated for low pressure argon discharge range of 0.02–0.3 mbar with neutral gas heating and at ambient temperature. An experimentally fitted 3D power evolution plot for 0.02 mbar argon pressure is also shown to visualize the effects of hysteresis in the system. Comparisons between simulation and experimental measurements show good agreement in the pressure range of 0.02–0.3 mbar for transition currents and 0.02–0.1 mbar for maintenance currents only when neutral gas heating is considered. This suggests that neutral gas heating plays a non-negligible role in determining the mode transition points of a rf ICP system.

Amorphous/crystalline silicon heterojunction solar cells via remote inductively coupled plasma processing

Low-frequency inductively coupled plasma (ICP) has been widely used to deposit amorphous or microcrystalline Si thin films, but the intrinsic drawback namely ion bombardment effect limits its application in Si heterojunction solar cells. In this letter, we redesigned typical ICP and realized a remote plasma deposition with suppressed ion bombardment effect. This remote ICP system enables the synthesis of high quality amorphous Si layers with a compact network and a high hydrogen content (10.5%). By using this remote ICP system, we achieved amorphous/crystalline silicon heterojunction solar cells with an efficiency of 14.1% without any back surface field or textures.

Low cost high-efficiency amorphous silicon solar cells with improved light-soaking stability

We investigate the performance of amorphous Si (a-Si) solar cells fabricated with Inductively Coupled Plasma (ICP) deposition technique. The ICP system produces a-Si films with low defect density (3×1015cm−3), resulting in a conversion efficiency of 9.6%. Deep level transient spectroscopy (DLTS) reveals that hole carriers trapped at defects near the valence band edge delocalize at 130K; while trapped electrons can only be emitted into the conduction band near room temperature. Spectrally resolved DLTS study further indicates that light soaking enhances the emission rate of the tapped electrons near the conduction band edge while reduces the transition moments from the hole-trapping defect levels to the conduction band. The combined effects and light soaking-induced defects are responsible for the degradation of a thin film solar cell by light soaking.

SiO2 shallow nanostructures ICP etching using ZEP electroresist

We propose an inductively coupled plasma (ICP) process to etch nanometer scale patterns defined by electron beam lithography in ZEP520A. The nanoscale patterns have been successfully transferred in thermal SiO2 using a CF4 based etching chemistry and a resist post-bake after development. Firstly, we show that platen temperature have a significant effect on line edge roughness (LER). We also present the effect of coil and platen RF power and pressure on sidewall angle, oxide to resist selectivity and LER. We demonstrate that 20nm deep trenches with sidewall angles of 86° and LER of less than 1nm can be etched in an ICP system with a platen temperature of −20°C using an electroresist mask.