Principles and Control of Exhaust Gas Treatment in Semiconductor Manufacturing
Broadly speaking , the loss of electrons is an oxidation reaction, and the gain of electrons is a reduction reaction.
When organic matter reacts, the action of introducing oxygen or removing hydrogen to organic matter is called oxidation; on the contrary, the action of introducing hydrogen or losing oxygen is called reduction. For example: The oxidation that reacts slowly generates heat and does not emit light is called slow oxidation, such as metal rust, biological respiration, etc. Oxidation with intense light and heat is called combustion.
Oxidation in a narrow sense refers to the combination of substances and oxygen; reduction refers to the effect of substances losing oxygen. Oxidation value increases during oxidation; oxidation value decreases during reduction.
Control parameters, reaction principle and conditions of etching nitrogen-containing exhaust gas treatment
SUMMER
Etching exhaust gas composition:
Acid mist (hydrochloric acid HCL, sulfuric acid H2SO4, hydrofluoric acid HF, nitric acid HNO3): relatively large content;
Alkali gas (sodium hydroxide NaOH) : the content is small, and it is neutralized in the air duct;
NO, NO2, H2S, O2: The concentration of NO and NO2 is very high, and the main treatment objects; H2S also exists, but not much; if there is a large amount of H2S, the main reason is that the pH value of the second and third levels is not up to the standard;
Explanation: NaOH+HCl=NaCl+H2O This is the equation of acid-base neutralization. The essence of the neutralization reaction is: H+ and OH- combine to form water (H2O). Acid + alkali → salt + water) So as long as the acid-base reaction occurs, it is called neutralization, no matter how far it goes.
Nitrogen-containing exhaust treatment process:
Principles of chemical reactions at all levels of nitrogenous acid-base row
First-stage column chemical reaction:
The first type of reaction (mainly):
NaClO2+H2SO4=NaHSO4+HClO2
8HClO2=6ClO2+Cl2+4H2O
2ClO2+2NO=2NO2+Cl2+O2
The second type of reaction: 2NO+O2=2NO2
Second, third and fourth tower chemical reactions:
First class reaction:
2NO2+Na2S=S+2NaNO2
HNO3+NaOH=NaNO3+H2O
2NO2+H2O=2HNO3
Second type of reaction:
2NO2+2NaOH=NaNO3+NaNO2+H2O
The third type of reaction:
3Cl2+6NaOH+Na2S=6NaCl+Na2SO3+3H2O
The fourth type of reaction: chlorine gas is dissolved in water with a volume ratio of 2:1
Cl2+H2O=HCl+HClO (hypochlorous acid)
NaOH+HCl = NaCl+H2O
Notice:
1. NaNO2 is unstable and will be oxidized to NaNO3;
2. Na2SO3 is stable in neutral or alkaline environment;
Control parameters and reaction principles and conditions
Level 1:
1) Use H2SO4 and NaOH to control and adjust the pH. The range requirement is between 2 and 5. This range is the best pH range for the oxidation, treatment efficiency and economy of sodium chlorite NaCLO2;
2) Use NaCLO2 to adjust the ORP value, the appropriate range is between +600~+700 (this range is the control requirement adjusted according to the size and processing efficiency of our tower);
Second and third grades:
1) Use NaOH to control and adjust the pH, and the range requirement is between 11 and 13; this range can ensure that Na2S will not be hydrolyzed (S2-+H2O=OH-+H2S) to produce hydrogen sulfide after it is added;
2) Under the premise of alkaline, use Na2S to adjust the ORP value, the range is -600≤ORP≤-500 (this range is the control requirement adjusted according to the size and processing efficiency of our tower);
Level 4:
1) Use NaOH to control and adjust the pH, and the range requirement is between 10 and 11;
2) If you need to add Na2S, you need to refer to the second and third level dosing control requirements;
Control parameters, reaction principle and conditions of common acid exhaust gas treatment
SUMMER
Texturing, diffused general acid exhaust gas composition:
Acid mist (hydrochloric acid HCL, sulfuric acid H2SO4, hydrofluoric acid HF) : relatively large content;
Alkali gas (sodium hydroxide NaOH) : the content is small, and it is neutralized in the air duct;
Common acid discharge process:
Reaction principle: H+ and OH- combine to form water (H2O); this is also the essence of the neutralization reaction.
For example: NaOH+HCl=NaCl+H2O This is the equation for acid-base neutralization. The primary and secondary pH can be controlled between 9 and 12.
Silane exhaust gas treatment control parameters and reaction principle and conditions
SUMMER
Silane Exhaust Gas Composition:
Dust (Silicon Dioxide) : white powder with large content;
Unused special gas (phosphorus oxychloride TMA, trimethylaluminum, silane SiH4, ammonia NH3) : silane and ammonia are mainly processed on the roof;
Ammonia:
Features: It is a colorless gas with a strong pungent smell. At normal temperature and pressure, one volume of water can dissolve 700 volumes of ammonia, that is, 1:700. It can burn the skin, eyes, and mucous membranes of respiratory organs. If people inhale too much, it can cause lung swelling and even death. ;
Main application: Mainly used in the coating process of the workshop, and also produced in the waste gas exhaust silane exhaust;
Silane exhaust process:
Operating parameters and processing conditions
Combustor:
1) Use nitrogen N2 and compressed air CDA to burn the unused silane SiH4 in the treatment workshop. After burning, white silicon dioxide powder and water vapor will be produced: SiH4+2O2=SiO2+2H2O; The silane mixed with CDA reaches the flash point and explodes;
Dust collector (explosion-proof dust collector):
1) Use ø133*2500mm polyester needle-punched felt PTFE film, that is, filter bag, to filter silica dust; electromagnetic pulse backflush system, spray CDA to the outlet of the filter bag after a certain period of time (about 2s), and blow off the filter bag external dust;
2) Clean the dust collector at least once a week, and clean the combustion tube once every half a month;
3) The negative pressure in front of the dust collector is kept above 1200pa, and the tail exhaust wind speed of the coating vacuum pump in the workshop can guarantee 7m/s;
Scrubber:
1) Use H2SO4 (50%) to control and adjust the PH. The design range of the plant is required to be between 2 and 5. At present, according to the operation situation, in the case of overflow, it can be controlled at 2 to 11;
2) If the pressure difference of the washing tower is less than 500pa, it is considered that the washing tower is not blocked, otherwise it is recommended to clean or replace the packing;
Control parameters and reaction principle and conditions of organic waste gas treatment
SUMMER
Organic exhaust gas composition:
The drying process will produce: diethylene glycol monobutyl ether, diethylene glycol butyl ether, acetic acid-2-(2-butoxyethoxy) ethyl (alcohol) ester, etc.;
Solution:
Use activated carbon adsorption treatment: coal-based activated carbon 5# cylindrical shape, iodine value ≥ 800, hardness ≥ 90%;
