Hybrid simulation of instabilities in capacitively coupled RF CF4/Ar plasmas

Radio frequency capacitively coupled plasmas (RF CCPs) sustained in fluorocarbon gases or their mixtures with argon are widely used in plasma-enhanced etching. In this work, we conduct studies on instabilities in a capacitive CF4/Ar (1:9) plasma driven at 13.56 MHz at a pressure of 150 mTorr, by using a one-dimensional fluid/Monte-Carlo (MC) hybrid model. Fluctuations are observed in densities and fluxes of charged particles, electric field, as well as electron impact reaction rates, especially in the bulk. As the gap distance between the electrodes increases from 2.8 cm to 3.8 cm, the fluctuation amplitudes become smaller gradually and the instability period gets longer, as the driving power density ranges from 250 to 300 W/m2. The instabilities are on a time scale of 16-20 RF periods, much shorter than those millisecond periodic instabilities observed experimentally owing to attachment/detachment in electronegative plasmas. At smaller electrode gap, a positive feedback to the instability generation is induced by the enhanced bulk electric field in the highly electronegative mode, by which the electron temperature keeps strongly oscillating. Electrons at high energy are mostly consumed by ionization rather than attachment process, making the electron density increase and overshoot to a much higher value. And then, the discharge becomes weakly electronegative and the bulk electric field becomes weak gradually, resulting in the continuous decrease of the electron density as the electron temperature keeps at a much lower mean value. Until the electron density attains its minimum value again, the instability cycle is formed. The ionization of Ar metastables and dissociative attachment of CF4 are noticed to play minor roles compared with the Ar ionization and excitation at this stage in this mixture discharge. The variations of electron outflow from and negative ion inflow to the discharge center need to be taken into account in the electron density fluctuations, apart from the corresponding electron impact reaction rates. We also notice more than 20% change of the Ar+ ion flux to the powered electrode and about 16% difference in the etching rate due to the instabilities in the case of 2.8 cm gap distance, which is worthy of more attention for improvement of etching technology.

A Review: Inductively Coupled Plasma Reactive Ion Etching of Silicon Carbide

The inductively coupled plasma reactive ion etching (ICP-RIE) is a selective dry etching method used in fabrication technology of various semiconductor devices. The etching is used to form non-planar microstructures—trenches or mesa structures, and tilted sidewalls with a controlled angle. The ICP-RIE method combining a high finishing accuracy and reproducibility is excellent for etching hard materials, such as SiC, GaN or diamond. The paper presents a review of silicon carbide etching—principles of the ICP-RIE method, the results of SiC etching and undesired phenomena of the ICP-RIE process are presented. The article includes SEM photos and experimental results obtained from different ICP-RIE processes. The influence of O2 addition to the SF6 plasma as well as the change of both RIE and ICP power on the etching rate of the Cr mask used in processes and on the selectivity of SiC/Cr etching are reported for the first time. SiC is an attractive semiconductor with many excellent properties, that can bring huge potential benefits thorough advances in submicron semiconductor processing technology. Recently, there has been an interest in SiC due to its potential wide application in power electronics, in particular in automotive, renewable energy and rail transport.

Considerations on the kinetic correlation between SiC nitridation and etching at the 4H-SiC(0001)/SiO2 interface in N2 and N2/H2 ambient

Kinetics of SiC surface nitridation process of high-temperature N2 annealing was investigated with 4H-SiC(0001)/SiO2 structure based on the correlation between the rates of N incorporation and SiC consumption induced by SiC etching. During the early stage of the annealing process, the rate-limiting step for N incorporation would be the removal of the topmost C atoms in the slow-etching case, while it would be another reaction step, probably the activation process of nitrogen in the fast-etching case. The SiO2 layer thickness and the annealing ambient which serve as the parameters to affect the SiC etching rate, would determine the N incorporation rate according to the kinetic correlation between the N incorporation and SiC etching. The SiC consumption observed during high-temperature annealing in N2 or N2/H2 ambient would be induced by the active oxidation by residual O2 or H2O in the ambient, which would lead to the SiC surface roughening.

Metal-Assisted Chemical Etching for Anisotropic Deep Trenching of GaN Array

Realizing the anisotropic deep trenching of GaN without surface damage is essential for the fabrication of GaN-based devices. However, traditional dry etching technologies introduce irreversible damage to GaN and degrade the performance of the device. In this paper, we demonstrate a damage-free, rapid metal-assisted chemical etching (MacEtch) method and perform an anisotropic, deep trenching of a GaN array. Regular GaN microarrays are fabricated based on the proposed method, in which CuSO4 and HF are adopted as etchants while ultraviolet light and Ni/Ag mask are applied to catalyze the etching process of GaN, reaching an etching rate of 100 nm/min. We comprehensively explore the etching mechanism by adopting three different patterns, comparing a Ni/Ag mask with a SiN mask, and adjusting the etchant proportion. Under the catalytic role of Ni/Ag, the GaN etching rate nearby the metal mask is much faster than that of other parts, which contributes to the formation of deep trenches. Furthermore, an optimized etchant is studied to restrain the disorder accumulation of excessive Cu particles and guarantee a continuous etching result. Notably, our work presents a novel low-cost MacEtch method to achieve GaN deep etching at room temperature, which may promote the evolution of GaN-based device fabrication.

Depth Profile Analysis of the Modified Layer of Poly(vinyltrimethylsilane) Films Treated by Direct-Current Discharge

Previously, we found that modification of the membrane surface from polyvinyltrimethylsilane (PVTMS) by treatment with low-temperature plasma induced by low pressure DC discharge leads to a significant increase in gas separation characteristics. To understand the mechanism of this phenomenon, in this article XPS combined with precision etching 10 keV beam of Ar2500+ clusters was used for depth profiling of PVTMS spin-coated films before and after DC discharge treatment. The etching craters depths were measured by stylus surface profiler. The average etching rate of the untreated PVTMS film by Ar2500+ clusters was defined (230 nm/min). It was found that the low temperature plasma treatment of PVTMS leads to a sharp increase in the oxygen concentration on a surface with a simultaneous decrease in the carbon content. The experimental data obtained indicate also that the treatment of PVTMS film by plasma leads not only to a change in the chemical structure of the surface, but also to the formation of a gradient subsurface layer with a thickness of about 50 nm.

FEATURES OF PLASMA CHEMICAL ETCHING OF LITHIUM TANTALATE SUBSTRATE (LiTaO3)

The results of researches of plasma chemical treatment of lithium monocrystalline tantalate (LiTaO3) from gas type, bias voltage (energy of chemically active ions) and from current of additional bias generator are given. A closed-loop electron drift plasma chemical reactor and gas mixtures containing Ar, Ar + ClС4, and Ar + SF6 were used for the experiments. It was found that the etching rate of LiTaO3 for the discharge in the gas mixture Ar + CCl4 is 14 times higher than all other mixtures that were used. It is shown that the proposed idea and approaches of LiTaO3 processing can be effectively applied for the production of optical systems with a minimum core thickness of about 2…3 μm.

Characterization of m-GaN and a-GaN Crystallographic Planes after Being Chemically Etched in TMAH Solution

This paper proposes a new technique to engineer the Fin channel in vertical GaN FinFET toward a straight and smooth channel sidewall. Consequently, the GaN wet etching in the TMAH solution is detailed; we found that the m-GaN plane has lower surface roughness than crystallographic planes with other orientations, including the a-GaN plane. The grooves and slope (Cuboids) at the channel base are also investigated. The agitation does not assist in Cuboid removal or crystallographic planes etching rate enhancement. Finally, the impact of UV light on m and a-GaN crystal plane etching rates in TMAH has been studied with and without UV light. Accordingly, it is found that the m-GaN plane etching rate is enhanced from 0.69 to 1.09 nm/min with UV light; in the case of a-GaN plane etching, UV light enhances the etching rate from 2.94 to 4.69 nm/min.

Surface Texturing Behavior of Nano-copper Particles under Various Copper Salts System during Copper-assisted Chemical Etching

In this work, the effects of different copper salts on the etching behavior of n-type monocrystalline silicon wafers were detailedly studied by Cu-assisted chemical etching method. Firstly, the inverted pyramid, inverted pyramid-like and oval pit texturing structures were obtained by HF/H2O2/Cu(NO3)2, HF/H2O2/CuSO4 and HF/H2O2/CuCl2 etching systems. Then, the evolution of copper particles deposition behavior was studied to reveal the influencing mechanism of different anion species, the textured wafer surfaces were characterized by scanning electron microscopy (SEM) and ultraviolet-visible (UV) spectrophotometer, the etching rate, silicon wafer thinning and the deposition amount of copper particle was systematically analyzed. We conclude that the binding force between anion and cation, the oxidation of anions and the formation of complex groups [CuCl2]− lead to great difference in the deposition behavior of copper, resulting in different etching morphology and etching rate. The moderate size copper particles deposited from HF/H2O2/Cu(NO3)2 system make that the etching process is mild and the anisotropic etching ability can fully demonstrated, and the regular inverted pyramid structures can be formed under low thinning of silicon wafers. This work will provide guidance for controllable preparation of inverted pyramid structure and future application in high efficiency solar cells.

Comparison of Structure Stability of Graphene and Mxene by Peak Force Tapping Mode of Atomic Force Microscope

In this paper, the structural stability of graphene and Mexene was compared by peak force tapping mode of AFM. When in-situ scanning of two-dimensional material of reduced graphene oxide (rGO), the morphology of rGO did not change with time, which indicated that peak force tapping mode had no damage effect on the stable structure surface; while when in-situ scanning of two-dimensional material V2C, nano-etching occurred on the surface of V2C, and the morphology surface area decreased with scanning time. The data processing software was used to analyze the area change and calculate the nano etching rate. It was found that the average nano-etching rate increased with the increase of the peak force, and the etching rate in the atmospheric environment was higher than that in the glove box (Ar atmosphere, the H2O and O2 content was less than 1 ppm), which indicated that the moisture in the atmosphere had an impact on the stability of the material and would accelerate the nano-etching. This study shows that the peak force tapping mode of AFM can be used to qualitatively characterize the stability of two-dimensional materials

Dry Etching of Germanium with Laser Induced Reactive Micro Plasma

High-quality, ultra-precise processing of surfaces is of high importance for high-tech industry and requires a good depth control of processing, a low roughness of the machined surface and as little as possible surface and subsurface damage but cannot be realized by laser ablation processes. Contrary, electron/ion beam, plasma processes and dry etching are utilized in microelectronics, optics and photonics. Here, we have demonstrated a laser-induced plasma (LIP) etching of single crystalline germanium by an optically pumped reactive plasma, resulting in high quality etching. A Ti:Sapphire laser (λ = 775 nm, EPulse/max. = 1 mJ, t = 150 fs, frep. = 1 kHz) has been used, after focusing with a 60 mm lens, for igniting a temporary plasma in a CF4/O2 gas at near atmospheric pressure. Typical etching rate of approximately ~ 100 nm / min and a surface roughness of less than 11 nm rms were found. The etching results were studied in dependence on laser pulse energy, etching time, and plasma – surface distance. The mechanism of the etching process is expected to be of chemical nature by the formation of volatile products from the chemical reaction of laser plasma activated species with the germanium surface. This proposed laser etching process can provide new processing capabilities of materials for ultra—high precision laser machining of semiconducting materials as can applied for infrared optics machining.