CHEMICAL FILTER
The problem of corrosion and odor contamination in industrial environment at manyfactories. it is not caused by a single factor and can not be resolved by a single solution.
SEMl standard F21-95 provides a method of classifying microelectronic cleanrooms withrespect to Airbore Molecular Contamination(AMC)levels. This is for gas phasecontaminants,analogous to Federal standard 209E for particulate contamination.SEMstandard F21-95 classifies a cleanroom based upon the category of the gas-phasecontaminant,and the allowable concentration level for each category.
The four categories of gas-phase contaminants:
1.Acids(category A):
Corrosive gases which react chemically as acids (an electronacceptor)
2.Bases(category B):Corrosive qasses which react chemically as bases (an electron donor)
3.Condensables (category C):Contaminants whose boiling point are typically above room temperature and arecapable of condensing on the wafer surface.
4.Dopants (category D):
Contaminants that modify the electrical properties of semiconductor material.
The SEMl F21-95 classification is identified by the letter “M",followed by the categorydesignator,then the allowable contaminant concentration in part per trilion(ppt).Folexample,a classification of MA-10is interpretedas having a maximum allowableconcentration of 10 ppt of all acid gases in the room air.
Classification of Airborne Molecular Contaminants
| Material Category | 1 ppt | 10 ppt | 100 ppt | 1,000 ppt | 10,000 ppt |
| Acids | MA-1 | MA-10 | MA-100 | MA-1000 | MA-10,000 |
| Bases | MB-1 | MB-10 | MB-100 | MB-1000 | MB-10,000 |
| Condensables | MC-1 | MC-10 | MC-100 | MC-1000 | MC-10,000 |
| Dopants | MD-1 | MD-10 | MD-100 | MD-1000 | MD-10,000 |
"SEMlF21-95:Classification of Airborne Molecular Contaminant Levels in CleanEnvironments".1 ppb=1,000 ppt,and 1ppm=1,000,000 ppt.
The allowable AMC (airborne molecular contaminants) concentration depends uponthe class of cleanroom,the process used,and the equipment employed.
Projected AMC limits for the 0.25 um Process
|
|
|
|
|
|
| Process Step | MAX Sit Time | MA(ppt) | MB (ppt) | MC (ppt) | MD (ppt) |
| Pre-gateoxidation | 4 hrs | 13,000 | 13,000 | 1,000 | 0.1 |
| Salicidation | 1 hrs | 180 | 13,000 | 35,000 | 1,000 |
| Contact Formation | 24 hrs | 5 | 13,000 | 2,000 | 100,000 |
| DUV Photorithagraphy | 2 hrs | 10,000 | 1,000 | 100,000 | 10,000 |
Typical Contaminants and Concentrations in Cleanroom
| Category | Contaminants | Concentrationrangr,ppt Low High |
Acids | Hydrochloric Acid | 20,000 | 400，000 |
| Hydrofluoric Acid | 40,000 | 250,000 |
| Nitric Acid | 20,000 | 250,000 |
| Sulfuric acid | 10,000 | 300,000 |
| Phosphoric acid | 10,000 | 400,000 |
| Acetic acid | 10,000 | 250,000 |
| Nitrogen dioxide | 30,000 | 300,000 |
| Sulfur dioxide | 10,000 | 150,000 |
Bases | Ammonia | 10,000 | 200,000 |
| NMP | 20,000 | 300,000 |
Condensables | Acetone | 20,000 | 500,000 |
| Toluene | 10,000 | 250,000 |
Dopants | Boric acid | ND | 200,000 |
| Phosphor ous | ND | 5,000 |
| Arsine | ND | 50,000 |
Four main techniques for controlling odor and gas contaminants:masking,combustion,.ventilation and removal.Media pellets are used to control gas contaminants by adsorp-tion and oxidation.Chemical filter can be removed molecular contaminants by adsorbingand absorbing principles.
To purify air by elimianting particulate material,gaseous and vaporous compoundParticulate filters do not have the effective on undesirable gases and vapors.
When gaseous or liquid molecules reach the surface of an adsorbent and remain withoutany chemical reaction,the phenomenon is called physical adsorption or physisorption.
The carbon can be impregnated with other chemicals to improve certain gases of lowadsorptive capacity by untreated carbon.These chemicals react with the gases to reducethe contaminant concentration.
Another way to delete specific gases is to catch and react with them.This process is calledchemisorption.
Many adsorptive materials are available;each of them with special affinity for certainvapors.
The surface area increased when the dimensions of carbon are getting smaller.The particlesize can be very small,even though it just becomes carbon dust.lt also creates problems ofescaping into the air steam,or packing tightly caused high pressure drop. The optimal sizemust be determined by experimentation.
In molecular contaminant system,initial contaminant removal efficiency doesn' t depend onweight,carbon particle size,and carbon activity,Total surface area and surface chemistry aretwo important parameters for determining initial efficiency.
If air pollution is very humid (like on a rainy day),the moisture can be adsorbed competitivelywith targeted contaminated gases for carbon capacity,However.f the reaction ischemisorbed,moisture can increase reaction rapidly.
Temperature also can affect the rate of adsorption when temperature is gettinghigher.it is harder to attract the contaminants to the carbon.
Three types of filter systems are available which offer some level of AMC removalCarbon slurry coated type,Carbon tray and Carbon loaded web in pleated form.
Carbon slurry coated type(Polysorb Activated Carbon Media):are typically coated powder carbon with adhesive into foam or nonwoven.
Carbon tray type:usually loaded larger pellets of carbon in 1-3 inch deep trays.
Cabon loaded web in pleated torm:smaller granulated carbon is physically boundin pleated non-woven media.
The comparison of three types of chemical filters is as follows.
| PerformanceParameter | Carbon Slurry CoatedFilter
| Carbon Tray | Carbon loadedWeb in pleated form |
| Low Pressure Drop | + | - | + |
| Carbon Weight | - | + + | + + + |
| 0ptimal Carbon Size | + | - | + + + + |
| 0verallAdsorptionPerformance | - - - | + | + + + |
Low Dust
| + | - - | + + |
| Ability of Pleated | + | N/A | + + + + |
| Easy Replacement | + | - - | + |
Carbon slurry coated type:(Polysorb Activated Carbon Media)
AIR FLOW VS.RESISTANCE
Carbon Slurry Coated Type Performance Data
Custom sizes available
Tray type Chemical Filter
(Media Type)
MM-1000 is composed of activated aluminum(Al₂O₃)impregnated with potassiumpermanganate (KMnO₄).The aluminum adsorbs moisture and odor. For example:H₂S+KMnO₄:+H₂O→K₂SO₄+KOH+MnO₂,+H₂O·K₂SO₄, KOH,and MnO₂ are solids and exist inpellet.
MM-3000 consists of activated carbon,physical adsorption removes the gas moleculesActivated carbon is used for removing wide range of contaminants with higher affinity tospecific gases.
MM-7000 consists of activated carbon impregnated with phosphoric acid.lt enhancesefficiecy and capacity for base type molecular contaminants.After adsorption,thecontaminants are neutralized by chemical reaction.
MM-9000 consists of activated carbon impregnated with potassium hydroxide. it en.hances efficiency and capacity for acid type molecular contaminants.After adsorptioncontaminants are neutralized by chemical reaction.
MM-1000
MM-9000
| Type | MM-1000 | MM-3000 | MM-7000 | MM-9000 |
Ingredient of Material | 4% Potassium Permanganate+Aluminum Oxide | Activated Carbon | 10% Phosphoric Acid + Carbon | 5-10%Potassium Hydroxide +Carbon |
| Moisture(wt%) | 15 | 2 | 15 | 15 |
| Crush Test(wt%) | 32 | - | - | - |
| Hardness(wt%) | - | 95 | 95 | 95 |
| Particle Diameter(mm) | 3.5（6 mesh) | 3 | 4 | 3 |
| Substrate Surface Area (m²/g) | 250 | 1000 | 1000 | 1000 |
| Shape | Spherical Pellet | Pellet | Pellet | Pellet |
| Apparent Density(g/cc) | 0.8(50 lb/ft⊃3;) | (30 lb/ft⊃3;) | 0.8(50 lb/ft⊃3;) | 0.55((35lb/ft⊃3;) |
H₂S Capacity(min)
| 0.1g H₂S/cc | - | 0.05g NH₃/cc | 0.15g H₂S/cc |
| Substrate CTC(wt%） | - | 60 | 60 | 60 |
| Pressure Drop@50fpm | 1.0“w.g./ft of bed | 1.7“w.g./ft of bed | 1.8“w.g./ft of bed | 1.7“w.g./ft of bed |
The comparison of various adsorbents for removing various gases and vapors
A:Regular activated carbon
B:Potassium permanganate plus based material
C:Activated carbon coated with potassium hydroxide
| A | B | C |
| VOC | 8
| 2 | 6 |
| Ozone | 10 | 2 | 10 |
| Nitrogen dioxide | 6 | 4 | 9 |
| Nitric acid | 6 | 6 | 9 |
| Acid /corrosive gases(HCI,HF, chlorine) | 0 | 0 | 8 |
| H,S(odor and corrosive gas) | 1 | 8 | 10 |
| S0,(odor and corrosive gas) | 7 | 8 | 9 |
| Organic Sulfur (odor and corrosive vapor) | 5 | 8 | 9 |
Tray:
Standard trays are in cold rolled steel black baked finished, optional stainless steel orepoxy coated trays.
Standard Tray Size
| SIZE | Weight of Chemisorbant |
| 24*24*1" | 4kg |
| 24*24*2" | 8.5kg |
| 12*24*2" | 2kg |
| 12*24*2" | 4kg |
Flow Rate vs.Pressure Drop
Single tray
Flow Rate（CFM)
Side Access Adsorbent Tray Housing :
It's similar to the housing of particulate filters,except it contains a series of offset tracksthe trays are installed into the tracks in horizontal position to form the V shape.it's alsostructure included a 2 inch deep W-Pre disposable pleated filter to provide someprotection from particulate contamination.
CAPACITY INDEX CHART
The capacity index has the following meaning:
4 High capacity for all materials in this cat-egory. One pound takes up about 20% to50% of its own weight-average about 1/3(33-1/3%).This category includes mostof the odor causing substances.
3 Satisfactory capacity for all items in this ca-tegory.These constitute goods applic-ations but the capacity is not as high as forcategory 4.Absorbs about 10 to 25% of itsweight-average about 1/6(16.7%)
2 Includes substances which are not high-ly adsorbed but which might be taken upsufficiently to give good service underthe particular conditions of operation. Theserequire individual checking.
1 Adsorption capacity is low for these ma-terials. Activated chacoal cannot be satisfactorily used to remove them underordinary circumstances.
* For the asterisked compounds,retreated carbon orMM-1000,MM-7000,MM-9000 will greatly increasethe adsorption ability.
DSX is a professional manufacturer of chemical filters, specializing in the production of composite filters that effectively eliminate corrosive gases and unpleasant odors in various environments. Our cutting-edge technology and expertise enable us to provide tailored solutions for a wide range of filtration needs. We take pride in offering top-notch technical support to ensure the success of our customers. Contact us today for all your filtration requirements.
