The Technical Principles of Acid Fumes Collection System and Practical Application
Introduction • Acidic, alkaline and organic gas fumes are many industrial production, including semiconductor and optoelectronics industry processes as unavoidable by-product, due to the extremely small particle size of smoke particles and enable it to cause lung disease through the upper respiratory tract of the human body; therefore, 2012.05.14 Taiwan EPA amended air quality standards, the fine particles (PM2.5) included in the regulation, refers to the fine particles suspended in the air, aerodynamic diameter less than or equal to 2.5 microns particles, the particle size is extremely small, easy to enter the body with the breath, the impact on health. Therefore, how to control the emission of smoke and sub-micron particles is one of the important direction of the air pollution control technology.
Particle diameter analysis of aerosols Diameter( μ m Φ ) Aerosol Clouds and fog < 2 Hydrochloric acid mist 1-3 Sulfuric acid mist 0.3-2 Ammonium chloride fume 0.05-1 Tobacco smoke 0.01-1
Particles size distribution of the aerosols from silane combustion from APCVD
Cause of acid gas fumes (white smoke) 1 • Acidic wet etching(heating) □ Aluminum: Acetic acid □ ITO Rework: Hydrochloric □ Aluminum oxide: Sulfuric acid and Phosphoric acid • Aqua regia(nitrohydrochloric) □ Hydrochloric • Metal cleaning □ Indium ball: Hydrochloric
Cause of acid gas fumes (white smoke) 2 • Plasma etching: □ Ammonium fluoride □ Silica particle • Plasma-Enhanced chemical vapor deposition (PECVD) □ Ammonium fluoride □ Silica particle • Wafer reclaim □ Ammonium fluoride
Cause of acid gas fumes (white smoke) 3 • Mixed acid-Base exhaust □ Ammonium fluoride □ Ammonium chloride □ Ammonium nitrate □ Ammonium sulfate
Introduction of the improved Venturi Scrubber system 1 Gas+particles
Principle of the improved Venturi Scrubber System 2 • The improved Quasi-Venturi Scrubbers are mechanical devices that rely on shearing and impaction forces to break water into fine droplets. The goal is to produce an evenly distributed regime of fine droplets at high density. The fine droplets are obtained by providing a nozzle just ahead of quasi-venture throat. Contaminant particles will impact on the droplets, enlarged through similar collisions and become inertially separated through application of centrifugal force.
Efficiency of the improved Venture Scrubber system 3
Introduction of acid gas deep filtration system 1 (SiO2/NH3/HCl/H2SO4)
Principle of acid gas fume deep filtration system 2 Gas f flow
Principle of acid gas fumes deep filtration system 3 • Filter construction ： The filters are typically constructed in vessel and consist of special panel(or cylinder type) mist eliminator densely packed between reinforcing screen. The filter material and material’s packing density determines the operating parameters of filter (such as pressure drop, collection rate and gas through-put etc … ). At the screen ends, plates and flanges are attached to permit a variety of mounting and draining methods.
DRE of acid gas fumes deep filtration for semiconductor fab. ITEM 01.SEX XX 01.SEX XX DRE (inlet) (outlet) (%) ug/m3 ppbv ug/m3 ppbv Chloride(Cl - ) 491 339 ND ND 100 Sulfate ion(SO4 2- ) 43.7 11.1 ND ND 100 Ammonium ion(NH4 - ) 320 435 0.867 1.18 99.73 Sampling date: 2016.06.22
Introduction of acid gas fume collection system 1 Venturi Scrubbing Deep Filtration
Introduction of acid gas fume collection system 2 (HCl/FeCl3)
Pictures of acid gas fume collection system 3 (HCl/FeCl3)
DRE of acid gas fume collection system 4 (HCl/H2SO4)
Layout DWG. of acid gas fume collection system 5 (HF/NH4/SiO2)
Picture of acid gas fume collection system 6 (NH4F/HF/H2O2/H2SO4)
Principle of acid gas fumes collection system 7 • Acid fumes are suspended liquid or solid particles ranging in diameter from the submicron range to the 3µm size. The acid fume removal system to collect submicron particulates which are hygroscopic using the principles of condensation scrubbing. Acid fumes as small as 0.3 microns in diameter pass through gas scrubbing stages and particle growth stage within the acid fume removal system before being collected by a final entrainment filtration stage.
Principle of Acid Gas Fumes Collection System 8 • Partcles Collection Mechanism ： Inertial impaction devices previously discussed give high efficiency on particles above 5 μm in size and often reasonable efficiency on particles above to 3 μm size at moderate pressure drops. However, this mechanism becomes ineffective for particle smaller than 3 μm because of the particle gaslike mobility. Only impaction devices having extremely high energy input such as venturi scrubbers or a flooded mesh pad can give high collection efficiency on fine particles, defined as 2.5 μm or 3 μm and smaller, including the submicron meter range.
Principle of acid gas fumes collection system 9 • Fine particles are subjected to brownian motion in gases, and diffusion deposition can be employed or their collection. Diffusion deposition becomes highly efficient as particles become smaller, especially below 0.2 μm to 0.3 μm . Randomly oriented filter having tortuous and narrow gas passages are suitable devices for utilizing this collection mechanism.
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