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

Aerosol Diameter(μmΦ)

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 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

(inlet)

01.SEX XX

(outlet)

DRE

(%)

ug/m3 ppbv ug/m3 ppbv

Chloride(Cl-) 491 339 ND ND 100

Sulfate ion(SO42-) 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 5μm in size and often reasonable

efficiency on particles above to 3μm size at moderate pressure

drops.

However, this mechanism becomes ineffective for particle

smaller than 3μm 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 2.5μm or 3μm

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 0.2μm to 0.3μm. Randomly

oriented filter having tortuous and narrow gas passages are

suitable devices for utilizing this collection mechanism.