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Plasma chemical reaction in plasma cleaning machine

Plasma chemical reaction in plasma cleaning machine

The chemical reaction initiated by plasma of plasma cleaning machine can be described as the following three stages. Plasma production stage, in which a large number of electrons and ions with higher energy are produced; At the activation stage of reactive molecules, high-energy electrons in the plasma collide with reactive molecules, thus causing changes in the internal energy of reactive molecules and causing excitation, dissociation and ionization of reactive molecules. The stage of product formation, in which the reactive species produced by excitation, dissociation, and ionization of reactive molecules are unstable and various chemical reactions take place between them to produce reaction products. Chemical reactions in plasma can be divided into homogeneous reaction, polyphase reaction and photochemical reaction.

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Plasma etching machine process introduction

Plasma etching machine process introduction

Plasma etching machine etching can be divided into two processes: first, the chemical active components of the plasma, these active components react with solid material substances, produce volatile compounds, and diffuse to the surface, discharge. Take CF4 as an example, its dissociation F reacts with S to form SiF4 gas, forming micro-milling structure on the surface of Si material. Plasma etching refers to ion etching, sputtering etching and plasma ashing.   The modification depth of plasma etcher depends on the substrate temperature, treatment time and material diffusion characteristics, while the modification type depends on the substrate and process parameters. Plasmas can only be etched a few microns deep on the surface and the surface properties change, but the surface properties of most materials can be maintained. The technology can also be used for surface cleaning, curing, coarsening, changing hydrophilicity and adhesion, etc., as well as for the manufacture of semiconductor integrated circuits, where sample thinning can be observed under an electron microscope. Chemical reactions can produce volatile products by chemical sputtering. Common gases include Ar, He, O2, H2, H2O, CO2, Cl2, F2 and organic vapour. Inert ion sputtering is closer to the physical process than plasma sputtering with chemical reaction.   Plasma F etching Si is widely used in semiconductor equipment manufacturing. The three steps of etching reaction are as follows: Chemical adsorption: F2→F2 (ADS) →2F (ADS) Reaction: Si+4F (ADS) →SiF4 (ADS) Desorption: SiF4 (ADS) →SiF4 (GAS)   In the etching process, the high-density plasma source has many advantages, such as more accurate control of workpiece size, higher etching rate and better material selectivity. The high density plasma source can work under low voltage, so the oscillation of sheath can be weakened. In the process of chip etching, plasma source etching with high density is used, and independent rf source is needed to bias the wafer, so that energy and ions are independent of each other. Since the energy of ions is generally in the order of several electron volts, when ions enter the negative sheath, they will reach hundreds of electron volts through energy acceleration and have high directivity, thus making ion etching anisotropic.

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Conversion of low carbon alkane in plasma at atmospheric pressure

Conversion of low carbon alkane in plasma at atmospheric pressure

Low carbon alkanes (C1~C4) are very rich carbon hydrocarbon resources, widely exist in natural gas, oilfield gas, coalbed methane and catalytic cracking gas. With the depletion of petroleum resources in the world, it is particularly important to prepare high value-added chemical raw materials from natural gas, oilfield gas and coalbed methane. Due to low carbon alkane chemical inertness is stronger, in the early days of the low carbon alkane in olefins reaction adopts highly active oxidant O2 and N2O (such as 1982 Keller precursors of sex work oxidative coupling of methane to olefin response), these highly reactive oxidants in relatively high low carbon alkane conversion rate at the same time, also caused the product further oxidation, so difficult to achieve the desired purpose product selectivity. Since the 1990s, people began to explore plasma activation method and plasma-catalyzed co-activation method to carry out the conversion reaction of low carbon alkanes.   Methane conversion reaction in low-temperature plasma at atmospheric pressure:   Methane (CH4) is the main component of natural gas, accounting for more than 90% of total natural gas. Natural gas reserves are very rich. In 2015, the world's proven natural gas reserves were 1.97x10^21m3, and the recoverable natural gas reserves in China were 4.94x10^18m3. Broken less in recent years, with the oil resource, natural gas, for a total of considerable reserves become the 21st century is one of the promising substitute energy and chemical raw materials but at the moment, the effective utilization of natural gas is still quite low, the main reason is that the main components of the gas methane is very stable organic small molecule structure, four C - H average keys for 414 kj/mol, CH3 - H key in the key for 435 kj/mol, difficult to activate. How to convert methane into liquid fuel easily transported and chemical products with high added value is one of the research hotspots.

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Conversion reaction of pure methane under plasma action

Conversion reaction of pure methane under plasma action

As early as the 1930s, Huels, a German company, began to study the pyrolysis of methane thermal plasma to produce acetylene. Methane is discharged in an electric field and transformed into black carbon, acetylene (C2H2), and hydrogen (H2). The key to this process is to make acetylene form and cool to the stable temperature of acetylene in a very short time. Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences has also carried out an amplification test of acetylene produced by natural gas plasma pyrolysis, with a production capacity of over 100T /a. Bao Weiren et al. used arc plasma to pyrolysis methane to produce acetylene, and obtained a small energy consumption of 9.68kW ·h/kg. The use of plasma low pressure cold plasmas for methane dehydrogenation to C2 hydrocarbon began in the early 1990s. Suib and Zerger applied microwave plasma technology to methane coupling reactions.   Methane can be converted to ethane (C2H6), ethylene (C2H4) and acetylene (C2H2) at system pressure of 4x102-6.7 x104Pa, plasma injection power of 40~ 80W, and gas flow rate of 50~500 mL /min. The conversion rate of methane was between 4% and 55%. The selectivity of ethane, ethylene and acetylene was 54%~ 75%, 13%~25% and 0~25%, respectively. Wang Baowei et al. from Tianjin University used asymmetric plasma technology to study the direct conversion of methane into C2 hydrocarbon (the mixture of C2H6, C2H4 and C2H2), and systematically investigated the influence of electrode structure, discharge voltage and reaction gas velocity on the reaction.   The atmospheric pressure DC pulse power supply USES the energy storage capacitor to discharge to the load through the rotating spark gap to generate the pulse high voltage, which has the characteristics of steep rising edge and narrow pulse width, so that the energy can be effectively injected into the reactor, and the energy consumption of the power supply is small. In the study of methane conversion reaction using pulsed corona discharge plasma, the main factors influencing methane conversion rate (Xcu4), C2 hydrocarbon selectivity (Sc2) and yield (Yc1) are plasma pulse peak voltage, electrode spacing and methane gas velocity.

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Influence of atmospheric pressure plasma pulse peak voltage electrode spacing

Influence of atmospheric pressure plasma pulse peak voltage electrode spacing

Influence of atmospheric pressure low temperature plasma pulse peak voltage:   When the pulse peak voltage varies from 12 to 16 kV, the methane conversion rate increases obviously with the constant increase of the pulse peak voltage. This is because the peak voltage reflects the energy injected into the reactor, which is equivalent to increasing the energy and number of high-energy electrons in the low-temperature plasma at atmospheric pressure, which is conducive to the improvement of methane activation and conversion rate. However, with the increase of peak voltage, the selectivity of C2 decreases and the yield of C2 does not change significantly. This is also because the increase of peak voltage leads to the increase of high-energy electrons, which leads to the continuous fracture of c-H bond of methane and the formation of carbon deposition, and the continuous decrease of C2 hydrocarbon selectivity.   Influence of low temperature plasma discharge electrode spacing at atmospheric pressure:   From the variation trend of methane conversion rate, C2 hydrocarbon selectivity and C2 hydrocarbon yield with discharge electrode spacing, it can be seen that the discharge electrode spacing increases, CH2 conversion rate decreases, C2 hydrocarbon selectivity increases, and C2 hydrocarbon yield slightly peaks. At the discharge spacing of 8mm, the yield of C2 was 19.8%. On the one hand, with the increase of electrode spacing, the discharge space increases, and the residence time of methane in the discharge space is prolonged. On the other hand, with the increase of discharge space, under the premise of constant input energy, the electric field intensity between electrodes decreases, and the average energy of high-energy electrons becomes weaker, that is, the energy transferred to a single methane molecule becomes weaker. Therefore, the increase of discharge distance reduces the average energy of high-energy electrons and increases the effective area of plasma. The two have different effects, but the reduction of the average energy of high-energy electrons has a more obvious effect on methane conversion, which shows a trend of decreasing methane conversion rate. The decrease of high-energy electron energy in plasma at atmospheric pressure is not conducive to the further fracture of C-H, which reduces carbon deposition and improves the selectivity of C2 hydrocarbon. The combined effect of the increase of discharge space and the decrease of the average energy of high-energy electrons was that the CH4 conversion rate decreased, the C2 hydrocarbon selectivity increased, and the C2 hydrocarbon yield did not change much.

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Introduction to plasma etching machine

Introduction to plasma etching machine

There are many kinds of plasma etching machines, and the designs of different etching machine manufacturers are also different. Since plasma maintains the plasma shape of etched gas through external energy input, different energy input modes and the design of machine structure will have great influence on the performance and application of plasma. The following is a description of several Plasma etching machines that are frequently used in vLSI production. They are Capacitively CoupledPlasma (CCP), Inductively CoupledPlasma (ICP& TransformerCoupled Plasma (TCP), and Electron Cyclotron Resonance Plasma (Electron Cyclotron Resonance), ECR, Remote Plasma and Plasma BevelEtch. The first three etching machines are named after the way of plasma generation, while the last two machines achieve different etching effects mainly through special structural design. The remote plasma etching machine filters out the charged particles of plasma and etches the materials to be etched with free radicals. This reaction is pure chemical reaction and belongs to isotropic etching. The plasma edge etching machine is specially designed to clean and etch the edge area of the wafer only through the reaction chamber structure, which has a very good effect on reducing the number of defects and improving the yield.   1. Capacitive coupling plasma machine: High-frequency electric fields were applied to two parallel plate capacitors. The initial electrons in the reaction chamber obtained energy under the action of rf electric fields, and the etching gas was ionized by bombardment, generating more electrons, ions and neutral free radical particles to form a dynamically balanced low-temperature plasma. Under the action of the radio frequency electric field, the self-bias voltage perpendicular to the direction of the wafer will be formed, which enables the ions to obtain relatively large bombardment energy. In the initial development stage of capacitance-coupled plasma machine, there is only one RF power supply, and the variation of RF power will affect both plasma density and ion bombardment energy, so the controllability of single-frequency capacitance-coupled plasma is not satisfactory.   Multi-frequency capacitive Coupled Plasma makes the performance of capacitive Coupled Plasma Etchers greatly improved by introducing multi-frequency external power source. For multi-frequency applied electric field, high frequency electric field mainly plays the role of controlling plasma density, and low frequency electric field mainly plays the role of controlling ion surface strike energy. At present, the mainstream capacitively coupled plasma etching machines in semiconductor industry are all dual-frequency and multi-frequency capacitively coupled plasma etching machines. Another characteristic of capacitive coupled etching machines is that the two electrical areas are different. For capacitor-coupled plasmas, the electrode with smaller area will get higher potential difference due to self-bias.   2. Inductively coupled plasma machine: Inductively coupled plasma machine is a method by applying rf voltage to the electromagnetic coil outside the reaction chamber. In the reaction chamber, the rapidly changing induced magnetic field will generate an induced electric field in the chamber, so that the initial electrons can obtain energy and then generate a low-temperature plasma. The electrons in the inductively coupled plasma revolve around the magnetic field lines, and the free path is larger than that in capacitive coupled plasma, and the plasma can be excited at lower pressure. The plasma density is about two orders of magnitude higher than that of capacitive coupling plasma, and the ionization rate can reach 1% ~ 5%. The direct current potential and ion bombardment energy of plasma is about 20 ~ 40V. Compared with capacitive coupled plasma; The ion flux and energy of inductively coupled plasma can be controlled independently. To better control ion bombardment energy, another RF power supply is typically capacitively coupled to a substrate wafer. In the process of inductive discharge, the coil and the capacitive driven substrate will generate capacitive coupling components, that is, in the process of plasma generation, the voltage difference will be generated by the external power supply. This is not conducive to independent control of plasma density and energy. Therefore, a layer of electrostatic shielding is generally added between the coil and the plasma to filter out the capacitive coupling components of the coil without affecting the inductive coupling. The coil layout has a great influence on the performance of the machine, and the design of induction coils from different manufacturers often varies greatly. The main coil layout structure has the aromatic structure and the cylindrical structure.   3. Electron cyclotron resonance plasma machine: Electron cyclotron resonance plasma etching machi

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