Perfluorocompound Emissions Research Articles

Thermal Abatement of Perfluorocompounds with plasma torches

Perfluorocompounds (PFCs) have long lifetimes and high global-warming potentials. PFCs include CF4, C2F6, C3F8, CHF3, SF6, NF3, etc., which are widely used in the electronic industries. Although the atmospheric concentrations of PFCs are currently much lower than CO2, the annually increasing rate of CF4 and SF6 are 3.3 and 12 times higher than CO2, respectively. A thermal plasma torch can offer an extremely high temperature stream for thermal decomposition of PFCs, and is regarded as a state-of-the-art technology for PFC emission control. In the study a thermal plasma torch is designed and experimentally tested for PFC abatements. Results show that PFC abatements are mainly determined by the plasma power, gas flow rate, and PFC’s concentration. The effects of operational parameters are further evaluated by the multiple regressions and the sensitivity analysis. For CF4, the most significant factor to the removal efficiency is the plasma power, and the flow rate plays a negative role. In addition, the most sensitive factor to the energy efficiency goes to the CF4 concentration. There is a trade-off between abatement efficiency and the energy efficiency. Thermal plasma torches can easily achieve high PFCs abatement efficiencies by an increase of plasma power. From an energy viewpoint, a thermal PFCs abatement system is better operated for streams with higher PFC concentrations. Therefore, installation of a PFCs concentrated unit in front of thermal plasma torch should be a good option in viewpoint of both abatement efficiency and energy efficiency.

Perfluorocompounds emission reduction by the semiconductor industry

The semiconductor industry uses a number of gases classified as perfluorocompounds (PFCs) in both silicon and dielectric layer etching and chamber cleaning in wafer fabrication equipment. The use of PFC gases in these processes is crucial to the production of semiconductor devices, as there are no effective substitutes that can be utilized. Although PFC emissions caused by the semiconductor industry are a tiny fraction of all industry greenhouse gases emissions, the world's semiconductor manufacturers, assembled in the World Semiconductor Council (WSC) and its affiliated associations, have officially agreed to voluntarily reduce atmospheric emissions of PFCs to 10% below baseline levels in 2010. The WSC has established a reporting program to track PFC emissions by the present five semiconductor manufacturing associations (USA, Europe, Japan, Taiwan, Korea). Data released by the WSC today show that the 2008 PFC emissions in most regions are already below the target set for 2010. This cooperative effort by the members of the WSC to reduce PFC emissions is an excellent example of what can be accomplished by collaboration. Because the PFC emission reduction program is considered to be pre-competitive, members freely share information on techniques and strategies. One of the key success factors has also been the strong involvement of equipment and gas suppliers to the semiconductor industry. Key measures that have contributed to substantially reduce PFC emissions are, among others, installation of dedicated post process tool PFC abatement, and application of NF3 gas in combination with so-called remote plasma in chamber cleans. The latter affords a highly efficient process alternative for the semiconductor industry with minimal PFC emission footprint, since the NF3 is utilized with better than 98% conversion efficiency. A gradual trend is visible, i.e. more advanced tools and facilities with relatively low emissions are supplanting relatively old tools and facilities with relatively high emission profiles. Presently, the global semiconductor industry is considering whether and how PFC emissions can be further reduced post-2010. A new global agreement should include other relevant regions with substantial semiconductor production, such as China and Singapore. Such discussions have already commenced. One of the key elements in a new agreement is harmonization of regional reporting. Moreover, it should be emphasized that semiconductor manufacture is no longer the sole or even the largest industry that makes use of PFCs. In this respect, the production of Liquid Crystal Displays (LCDs) and the manufacture of photovoltaic cells are likely to become major players.

Exploring the operating efficiency of semiconductor industry by a sustainable development approach

This study attempts to characterise performance in terms of a simple indicator (revenue) to a multi-dimensional systems perspective, which includes the development of eco-efficiency and the sustainable development indicator. The influence of Perfluorocompounds (PFCs) on the operating performance of the semiconductor industry is studied by using data envelopment analysis (DEA), which inherently recognises tradeoffs among various measures. Samples used in this study included 14 global semiconductor firms, each of which was treated as a decision making units (DMUs) under DEA analysis. The empirical result reveals that the overall technical inefficiencies of the firms are due primarily to pure technical inefficiencies rather than the scale inefficiencies. In addition, the results in this study indicate that the operating efficiency ranking changes when the amount of PFCs emission is considered in the analysis.

Analysis Technique for Exhaust Gas Including PFCs from Microelectronics Manufacturing Processes

In the manufacturing processes of Semiconductor and the Liquid Crystal Display (LCD), Perfluorocompounds (PFCs), Sulfurhexafluoride (SF6) and Nitrogenfluoride (NF3), which have high Green house effect,are used in large quantities. As emission reduction of these gases, the following countermeasures are taken. 1. Opimization of PFCs usage 2. Utilization of alternative gas 3. Instllation of Scrubber for exhaust gas treatment To inspect the effect of countermeasure that are introduced for these PFCs emission reduction, it is necessary to analyze PFCs in exhaust gas. In this report, we will discribe about analysis technique for exhaust gas including PFCs from microelectornics manufacturing processes.

High-Efficiency PFC Abatement System Utilizing Plasma Decomposition and Ca(OH)$_{2}$/CaO Immobilization

In order to minimize contributions to global warming, it is important to develop a perfluorocompound (PFC) abatement system that can remove PFCs effectively with low electric power. We have developed a new PFC abatement system consisting mainly of a 2-MHz ICP plasma source and two Ca(OH)2/CaO columns operated under a decompression pressure. Reactive fluorinated compounds including SiF4 are immobilized in the Ca(OH)2/CaO columns without a water scrubber. Stable compounds such as CF4 are excited by the 2-MHz ICP plasma. When the emissions from an Si oxidation film etching process chamber were treated by this abatement system, F2 equivalent removal efficiency was 99.6%, which was about one order of magnitude larger than that of a conventional abatement system. But the CO2 equivalent removal efficiency was calculated to be 91.4% because over 95% of CO2 equivalent emissions were caused by the plasma source power consumption of 2.4 kWh. It means that minimization of the plasma source power consumption, depending on PFC emissions, is a very effective method of minimizing contributions to global warming in a manner similar to improving the PFC removal efficiency.

Plasma Kinetic Study of Silicon-Dioxide Removal with Fluorocompounds in a Plasma-Enhanced Chemical Vapor Deposition Chamber

Plasma kinetics of silicon dioxide plasma cleaning is investigated with C2F6 and CF3CF2OCF=CF2 (perfluoroethyl vinyl ether, PEVE) in this work. Perfluorocompounds (PFCs) are widely used in the semiconductor industry, and they are known to have long atmospheric lifetimes and high global warming potentials (GWP) due to their chemical stability and large cross sections for infrared radiation absorption. The silicon dioxide (SiO2) cleaning process in a plasmaenhanced chemical vapor deposition (PECVD) chamber is known to be the largest PFC emission source for the semiconductor industry. Silicon-dioxide removal rates by surface reactions in plasmas were measured in the temperature range from room temperature to 400 C by using laser interferometry, and the fluorine density was determined by using an optical emission spectroscopy (OES) actinometry technique. The ion density and the ion energy were determined by using an impedance analysis and an equivalent circuit model. The activation energy was determined from Arrehenius plot to be 0.163 eV and 0.169 eV for C2F6 and PEVE plasmas, respectively, in the PECVD chamber cleaning condition. It is shown here that silicon-dioxide removal rate is linearly proportional to the fluorine concentration for the PECVD chamber cleaning condition of 300 400 C and that the removal rate depends on the ion flux and the ion energy below 100 C. The combined etch rate model is suggested to explain this temperature dependence in this work. From this plasma kinetic study, we can conclude that the atomic fluorine concentration is the dominant factor in silicon-dioxide removal for the PECVD chamber cleaning condition.

Evaluation Method on Destruction and Removal Efficiency of Perfluorocompounds from Semiconductor and Display Manufacturing

Recently, the semiconductor and display industries have tried to reduce the emissions of perfluorocompounds (PFCs) from the globally environmental regulation. Total amount of PFC emission can be calculated from the flow rate and the partial pressures of PFCs. For the precise measurement of PFC emission amount, the mass flow controlled helium gas was continuously injected into the equipment of which scrubber efficiency is being measured. The partial pressures of PFCs and helium were accurately measured using a mass spectrometer in each sample extracted from inlet and outlet of the scrubber system. The flow rates are calculated from the partial pressures of helium and also, PFC destruction and removal efficiency (DRE) of the scrubber is calculated from the partial pressure of PFC and the flow rate. Under this method, the relative expanded uncertainties of the flow rate and the partial pressures of PFCs are ± 2% (k = 2) in case the concentrations of NF3 and SF6 are as low as 100 μmol/mol.

Kinetic Modeling of the NF3 Decomposition via Dielectric Barrier Discharges in N2/NF3 Mixtures

AbstractSummary: Emission of PFCs (perfluorocompound) has attracted much attention in recent years due to its relatively high contribution to the global warming. Non‐thermal plasma is one of the most promising technologies to effectively control the PFC emissions. In this study, a cylindrical DBD (dielectric barrier discharge) reactor is adopted for the treatment of NF3‐containing streams. Besides the experimental work, a numerical model is also developed for better understanding of the reaction mechanism of NF3 abatement in N2/NF3 mixtures. Good agreement is observed between the experimental data and the simulation results. Simulation results indicate that the electrons and the N atoms are the major active species responsible for the NF3 decomposition. In addition, N2(A3Σ) metastables plays a significant role in the NF3 abatement. A simplified mechanism for the NF3 decomposition in the N2 – NF3 plasmas is proposed as well.Reaction mechanisms for the decomposition of NF3 in a N2 – NF3 plasma.imageReaction mechanisms for the decomposition of NF3 in a N2 – NF3 plasma.

Reduction of semiconductor process emissions by reactive gas optimization

Tailoring the chemical environment in plasmas by addition of reactive gases to affect byproduct formation has been demonstrated to reduce perfluorocompound (PFC) emissions. Perfluorocompound emissions from dielectric etch processes are reduced by oxygen addition, which reduces polymerization and increases etch rates, primarily by affecting the fluorine or carbon in the plasma, and secondarily, by affecting resist erosion. Oxygen or water vapor introduced upstream of plasma abatement devices reduces PFC reformation by preferentially combining with carbon and fluorine-containing radicals to form thermodynamically favorable byproducts that are non- or low-global warming. Introducing oxygen to low-k chemical vapor deposition (CVD) chamber clean processes also reduces PFC emissions, primarily by reducing CF/sub 4/ by forming thermodynamically stable CO and CO/sub 2/. Analogously, adjusting the fuel or the oxidizer flow in fuel-fired abatement devices provides a higher flame temperature where thermal cracking of higher molecular weight low-k CVD organosilicon precursors can more readily occur, allowing the carbon-rich precursors to more completely oxidize.

Reduction of PFC emissions to the environment through advances in CVD and etch processes

One the most focused environmental health and safety (EHS) goals for the semiconductor industry has been to reduce perfluorocompound (PFC) emissions because of their high global warming potentials and long residence times in the atmosphere. During the last decade, significant achievements have been reached in attaining this goal. Chemical vapor deposition (CVD) chamber cleaning and plasma etch are two processes that use PFCs in which studies have been conducted to reduce emissions. Two successful strategies for reducing PFC emissions and enhancing process performance are described.

Reduced PFC Emissions and Gas Consumption Using a c-C<tex>$_4$</tex>F<tex>$_8$</tex>-Based PECVD Chamber Clean Chemistry

Perfluorocompounds (PFCs) used in semiconductor manufacturing are potential contributors to greenhouse gas-driven climate change. PFCs emitted from plasma enhanced chemical vapor deposition (PECVD) chamber cleans can be a significant portion of the total PFC emissions for a typical semiconductor fabrication facility. Previous work adopting octafluorocyclobutane (c-C/sub 4/F/sub 8/) clean chemistries to reduce gas consumption and PFC emissions have been reported on applied materials and novellus PECVD tools. In this study, c-C/sub 4/F/sub 8/ was evaluated as an alternative chamber clean gas on Mattson ASPEN II PECVD tools. A statistical design of experiment (DOE) methodology and tool emission analysis by Fourier transform infrared spectrometry were used to develop a low gas consumption and low PFC emission process. This c-C/sub 4/F/sub 8/ process reduced the clean gas consumption by 65% and PFC emission by 78%, compared to our current C/sub 2/F/sub 6/ clean with no impact on deposited film properties or process repeatability.

Process Optimization and PFC Emission Reduction Using a c-C<tex>$_4$</tex>F<tex>$_8$</tex>Chamber Cleaning Process on a Novellus Concept 1 Dielectric PECVD Tool

While the new generation of chemical vapor deposition (CVD) tools adapts NF/sub 3/ as a chamber clean gas to reduce perfluorocompound (PFC) reductions, process optimization (C/sub 2/F/sub 6/) and alternative C/sub x/F/sub y/ clean chemistries are options for the installed-base tools. From a previous study comparing the various C/sub x/F/sub y/ chamber clean chemistries, we further conducted a production test in a 150-mm wafer fabrication facility comparing the best alternative C/sub x/F/sub y/ clean chemistry (C/sub 4/F/sub 8/ clean) with an optimized C/sub 2/F/sub 6/ clean process on a Novellus Concept 1 Dielectric tool running TEOS-based SiO/sub 2/ CVD. Gas flow rates, chamber pressure, and oxygen volume percentages were studied as variables to develop an optimal c-C/sub 4/F/sub 8/ process recipe for maintaining or improving cleaning efficiency while reducing gas consumption and PFC emissions compared to the optimized C/sub 2/F/sub 6/ process. After the initial experimental matrix was completed, several single-variable experiments were run to fine tune the recipe. Based on the data analysis and the model results from the design of experiment, two optimal C/sub 4/F/sub 8/ cleaning processes were identified. Both processes significantly lowered gas consumption and PFC emissions. Marathon process testing showed no adverse impact on film properties or device yield.

Environment, health, and safety performance plays a vital role in sustaining the growth of the semiconductor industry

Rapid technology advances and rapid growth have historically been the basis for the success of the semiconductor industry. Over the last 25 years the industry has enjoyed a growth rate (∼15%) which far exceeds the growth rate of the U.S. economy overall (3%–4%). To ensure that this rapid growth rate can be sustained into the future, it is important that the industry makes efficient use of natural resources, minimizes any impact on the environment, and ensures the protection of its workers and the communities in which it operates. It has been repeatedly shown that resource efficiency is linked to lower operating costs and better environmental performance. International SEMATECH’s Environment, Safety and Health (ESH) division is engaged in several projects that are aimed at enabling continued, sustainable growth for the industry. These include energy and water conservation, perfluorocompound (PFC) emissions reduction as well as early ESH assessment of the multitude of new chemicals and materials being considered for 157 nm photolithography, low-k dielectrics, and advanced gate stacks. The timely assessment of any potential ESH impacts associated with these materials is essential to ensure that they are used in a safe and environmentally sound manner through cost-efficient ESH solutions and controls. This paper will describe the approach and results of International SEMATECH’s efforts in the areas of resource conservation, PFC emissions reduction, and early identification of potential ESH impacts associated with the next generation semiconductor chemicals and materials.

Reduction of perfluorocompound emissions by microwave plasma-torch

Perfluorocompounds (PFCs), which have long lifetimes and serious global warming implications, are widely used during plasma etching and plasma-assisted chamber cleaning processes in metal and dielectric film, by chemical vapor deposition (CVD) systems. Surface cleanings are performed within a reduced pressure chamber by making use of PFC gases. These contaminant gases are emitted with nitrogen gas, which are used for vacuum pump purges. In order to destroy all of the global warming gases including PFCs, we have developed a plasma abatement device, an electrodeless atmospheric microwave plasma-torch, which can easily generate plasma at a given atmospheric pressure. The plasma abatement device is attached to the vacuum pump, which discharges the nitrogen gas with contaminants. The abatement was carried out using oxygen and air as additive gases. Destruction and removal efficiency (DRE) of more than 98% was achieved for tetrafluoromethane (CF 4).

Evaluation of Octafluorocyclobutane as a Chamber Clean Gas in a Plasma-Enhanced Silicon Dioxide Chemical Vapor Deposition Reactor

The evaluation of octafluorocyclobutane, as a new chemistry for plasma-enhanced chemical vapor deposition (PECVD) tool chamber cleaning is reported. Using a statistical design of experiments, the cleaning time and perfluorocompound emissions were measured in a Novellus Concept One 200, a widely used commercial PECVD tool. By mass spectrometry of the process exhaust, the effect of flow rate, feed-gas ratio, and pressure effects on cleaning time and perfluorocompound (PFC) emissions were determined. Experimental results and neural network analysis indicate that high oxygen levels (75-90 vol %) and pressure (4.0 Torr) achieve reductions in process clean times of 20%, reduce gas requirements and PFC emissions greater than 80% relative to the standard -based cleans. These process advantages, combined with the similar physical and discharge properties of and suggest good potential for this new chemistry as a drop-in gas replacement for current chamber cleaning applications. © 2003 The Electrochemical Society. All rights reserved.

Infrared Study of Process Emissions during C 3 F 8 / O 2 Plasma Cleaning of Plasma Enhanced Chemical Vapor Deposition Chambers

In this work, Fourier transform infrared spectroscopy (FTIR) is used to monitor perfluorocompound process emissions during in situ cleaning of a plasma enhanced chemical vapor deposition chamber. Gas mixtures containing , and are identified and quantified simultaneously using FTIR. The results of this study show that the lower flow rate and higher utilization of etch gas during a chamber cleaning process can contribute to reductions in net perfluorocompound emissions relative to a cleaning process of similar duration. This work also demonstrates that FTIR spectroscopy can provide information which is necessary to support the development of alternative chamber cleaning chemistry. In this way, monitoring methods based on FTIR spectroscopy are valuable to the semiconductor industry's perfluorocompound emission reduction objectives.