A catalytic device for purifying ozone tail gas

Abstract

This utility model discloses a catalytic device for purifying ozone exhaust gas, belonging to the field of environmental protection technology. Addressing the problems of low catalytic efficiency, easy catalyst deactivation, and unstable purification effects due to uneven airflow distribution in existing ozone decomposition equipment, this device includes a pretreatment unit and a catalytic reaction unit. The device solves the airflow deviation problem through an airflow uniform distribution network, and the catalyst coating increases the ozone decomposition rate to over 95%. The device can operate continuously for over 8000 hours. Furthermore, the device has a compact structure, small footprint, lower energy consumption than traditional equipment, and convenient operation and maintenance. It can be widely used in chemical, electronics, and indoor air purification fields, possessing significant environmental and economic value.

Description

Technical Field

[0001] This utility model belongs to the technical field of environmental pollution control and semiconductor manufacturing auxiliary equipment, specifically relating to a pipeline-type catalytic device for purifying ozone exhaust gas in semiconductor wafer cleaning, aiming to solve the problem of 100-500mg / m³ ozone concentrations during wafer cleaning. 3 High concentrations of ozone exhaust fumes pose health risks to personnel and corrode precision equipment. Background Technology

[0002] In semiconductor wafer cleaning processes, high-concentration ozone water or ozone gas is widely used to remove organic residues from wafer surfaces due to its strong oxidizing properties. However, the concentration of ozone exhaust gas emitted during the cleaning process is typically as high as 100-500 mg / m³. 3 It significantly exceeds the 0.3 mg / m³ limit specified in the "Occupational Exposure Limits for Hazardous Factors in the Workplace" (GBZ 2.1-2019). 3 The permissible concentration is calculated as an 8-hour time-weighted average. Prolonged exposure to such high concentrations of ozone can cause respiratory damage to operators, posing a clear occupational health risk. Furthermore, ozone can oxidize the optical coatings (such as magnesium fluoride coatings) on the surface of lithography machine lenses, causing a decrease in light transmittance and thus increasing equipment maintenance costs.

[0003] Among existing ozone decomposition methods, catalytic decomposition has become the mainstream technology due to its advantages such as low energy consumption, high efficiency, and wide applicability. Traditional ozone decomposition catalysts are mainly divided into noble metal catalysts and transition metal oxide catalysts. Although noble metal catalysts have high catalytic activity, their high cost and scarce resources limit their large-scale application. Transition metal oxide catalysts are relatively inexpensive, among which manganese-based catalysts are a more studied and superior class. However, in the high humidity environment of semiconductor wafer cleaning, their active sites are easily occupied by oxygen intermediates or water molecules generated during the reaction, resulting in a decrease in catalytic activity and stability under harsh conditions, making it difficult to meet the treatment requirements.

[0004] Furthermore, conventional ozone decomposition devices have significant technical drawbacks. Because wafer cleaning exhaust gases contain silicon powder with particle sizes between 0.1 and 5 micrometers, as well as residual impurities from cleaning agents such as isopropanol polymers, and existing single-stage filters typically have a filtration accuracy of only 5 micrometers or more, these fine particles easily penetrate the filter, infiltrate the catalyst pores, and accumulate as fouling. This is especially true when using porous carriers such as molecular sieves or activated carbon, whose pores are more prone to clogging, causing a rapid decrease in specific surface area in a short period, for example, a drop of over 40% within a month. Once clogging occurs, the system cannot perform online cleaning, requiring frequent shutdowns to replace the catalyst, thus shortening the catalyst's lifespan to only one to two months.

[0005] Therefore, developing an ozone decomposition device that is simple in structure, low in manufacturing cost, easy to scale up production, and can maintain high processing efficiency and stable operation under complex working conditions has important practical application value. Summary of the Invention

[0006] To address the problems existing in the prior art, this utility model provides a catalytic device for purifying ozone exhaust gas, comprising a pretreatment unit and a catalytic reaction unit. The pretreatment unit includes a housing I, which contains several composite filter layers to intercept wafer cleaning residue particles such as silicon powder and cleaning agent residue carried in the exhaust gas, achieving a filtration efficiency of up to 99.9% and preventing impurities from clogging the active sites of the catalyst. The composite filter layers consist of a wire mesh and a PTFE membrane disposed on the wire mesh. One end of the housing I has an air inlet I, and the other end has an air outlet I. A backwashing air inlet is also provided on the housing I. The catalytic reaction unit includes a housing II. The air outlet I of the pretreatment unit is connected to the air inlet II of the catalytic reaction unit via a pipe, and a valve is provided on the pipe. An airflow distribution mesh and a catalytic layer are alternately arranged inside the housing II. The catalytic layer consists of a porous honeycomb ceramic carrier and a catalyst coating disposed on the surface of the porous honeycomb ceramic carrier. An air outlet II is provided on the housing II opposite to the air inlet II.

[0007] The pore size of the PTFE (polytetrafluoroethylene) membrane is 0.3-0.6 μm.

[0008] The catalyst in the catalyst coating is a commercially available catalyst for decomposing ozone, such as a carbonaceous manganese-based metal oxide composite supported oxidation catalyst coating or a manganese-copper-cerium metal oxide silicon-aluminum-based catalyst coating. The coating thickness is 5-15 μm, which can ensure the catalyst loading and maximize the contact area between the gas and the active sites, thus ensuring mass transfer efficiency.

[0009] A gas monitor is installed on the gas outlet II of the catalytic reaction unit.

[0010] The backwash air inlet is equipped with a valve for precisely controlling the airflow and flow rate between the two units, as well as for backwashing the pretreatment unit.

[0011] When this device is in use, ozone exhaust gas enters from the pretreatment unit inlet I, the valve on the backwash inlet is closed, and after being filtered to remove larger particles, it enters the catalytic reaction unit and is discharged from the outlet II after being completely catalyzed.

[0012] The airflow distribution network ensures that the airflow flows evenly through each catalytic component, avoiding differences in reaction efficiency caused by excessively strong or weak local airflow.

[0013] The gas monitoring device can collect the outlet gas in real time and detect the ozone concentration therein. This not only allows operators to intuitively grasp the catalytic reaction effect, but also enables them to adjust process parameters in a timely manner to ensure overall operational stability.

[0014] The backwashing operation is an automatic pulse backflushing every 8 hours. The backwashing air enters from the air outlet I of the pretreatment unit. A control valve is provided between the two units to close the air. The dust blown into the dust collection bag installed on the air inlet I to avoid secondary pollution.

[0015] Advantages and technical effects of this utility model: This device addresses the issue of impurities such as silicon powder and cleaning agent residue in semiconductor wafer cleaning exhaust gases penetrating the catalyst channels and causing fouling. This is especially problematic when using porous supports such as molecular sieves and activated carbon, where the channels are easily clogged, leading to a sharp drop in specific surface area. Furthermore, once clogged, these materials cannot be cleaned online, requiring frequent shutdowns to replace the catalyst. Additionally, the high humidity environment of semiconductor wafer cleaning presents further challenges to catalyst performance: some active sites are preferentially occupied by oxygen intermediates or water molecules generated during the reaction, resulting in a significant decrease in catalytic activity and stability under these harsh conditions, ultimately failing to meet the requirements for efficient purification of wafer cleaning exhaust gases. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the catalytic device of this utility model; In the diagram: 1-Shell I, 2-Composite filter layer, 3-Inlet I, 4-Outlet II, 5-Backwash inlet, 6-Airflow distribution mesh, 7-Catalyst layer, 8-Shell II. Detailed Implementation

[0017] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the content described.

[0018] Example 1: As Figure 1As shown, the catalytic device for purifying ozone exhaust gas includes a pretreatment unit and a catalytic reaction unit. The pretreatment unit includes a shell I1, which contains several composite filter layers 2. The composite filter layers 2 consist of a wire mesh and a PTFE membrane attached to the wire mesh. The PTFE membrane has a pore size of 0.5 μm. One end of the shell I has an air inlet I3, and the other end has an air outlet I. A backwashing air inlet 5 is provided on the shell I. The catalytic reaction unit includes a shell II8. The air outlet I of the pretreatment unit is connected to the air inlet II of the catalytic reaction unit through a pipe. An airflow distribution mesh 6 and a catalytic layer 7 are alternately arranged inside the shell II. The catalytic layer consists of a porous honeycomb ceramic plate and a carbonaceous manganese-based metal oxide composite supported oxidation catalyst (model OC-Q315, purchased from Pingdingshan Tanernuo New Materials Co., Ltd.) coating attached to the porous honeycomb ceramic plate. The coating thickness is 10 μm. An air outlet II4 is provided on the shell II opposite to the air inlet II. A valve is provided on the backwashing air inlet 5.

[0019] Example 2: The device in this example is the same as in Example 1, except that a gas monitor is installed on the gas outlet II4 of the catalytic reaction unit.

[0020] When using the above-mentioned device, the backwash inlet 5 of the pretreatment unit remains closed; the control valve between the pretreatment unit and the catalytic reaction unit is in the normally open state, and the ozone tail gas (100mg / m³) is adjusted accordingly. 3 The actual concentration of ozone is determined by adjusting the valve opening to the process setting (maintaining a mass hourly space velocity of 500 L / g·h). The ozone exhaust gas to be treated is continuously introduced from the inlet I3 of the pretreatment unit, entering the internal cavity of the shell I of the pretreatment unit. The ozone exhaust gas flows through the composite filter layer, with a filtration efficiency of ≥99.9%, which can effectively intercept wafer cleaning residue particles carried in the exhaust gas, achieving preliminary purification of the gas and preventing impurities from entering the subsequent catalytic reaction unit and clogging the active sites of the catalyst. The clean gas filtered by the composite filter layer enters the shell II of the catalytic reaction unit stably through the control valve, flowing sequentially through the layered airflow distribution network 6 and the catalytic layer 7 inside the shell. Ozone molecules are efficiently catalyzed and decomposed during contact with the active coating. The gas that has completed catalytic decomposition is discharged from the outlet II at the right end of the catalytic reaction unit. At the same time, the gas monitor at the outlet II collects the discharged gas in real time to detect the ozone concentration. Operators can intuitively grasp the catalytic reaction effect through monitoring data. If the ozone concentration is consistently lower than the emission standard limit, the current process parameters will be maintained to ensure continuous and efficient removal of ozone exhaust gas. The ozone decomposition rate can reach more than 95%. When the composite filter layer of the pretreatment unit experiences increased filtration resistance due to long-term impurity trapping, a backwashing procedure must be initiated. Upon reaching the preset backwashing cycle (automatically triggered every 8 hours, or manually initiated by the operator), the normal ozone exhaust gas treatment process is first suspended. The control valve between the pretreatment unit and the catalytic reaction unit is closed, cutting off the airflow channel from the pretreatment unit to the catalytic reaction unit. The backwash inlet of the pretreatment unit is then opened, introducing clean backwash gas into the housing I cavity. This allows the airflow to pass through the composite filter layer in the opposite direction to normal filtration. The dust blown off moves downward with the reverse airflow and enters the dust collection bag pre-connected to inlet I, ensuring effective dust collection and preventing its re-diffusion or re-entry into the catalytic reaction unit, thus avoiding secondary pollution.

Claims

1. A catalytic device for purifying ozone exhaust gas, characterized in that: It includes a pretreatment unit and a catalytic reaction unit. The pretreatment unit includes a shell I (1). Several composite filter layers (2) are provided inside the shell I. The composite filter layers (2) are composed of a wire mesh and a PTFE membrane set on the wire mesh. One end of the shell I has an air inlet I (3) and the other end has an air outlet I. A backwashing air inlet (5) is provided on the shell I. The catalytic reaction unit includes a shell II. The outlet I of the pretreatment unit is connected to the inlet II of the catalytic reaction unit through a pipe and a valve is provided on the pipe. An airflow distribution net (6) and a catalytic layer (7) are alternately arranged inside the shell II. The catalytic layer consists of a porous honeycomb ceramic carrier and a catalyst coating on the surface of the porous honeycomb ceramic carrier. An outlet II (4) is provided on one end of the shell II opposite to the inlet II.

2. The catalytic device for purifying ozone exhaust gas according to claim 1, characterized in that: A gas monitor is installed on the gas outlet II of the catalytic reaction unit.

3. The catalytic device for purifying ozone exhaust gas according to claim 1, characterized in that: The pore size of the PTFE membrane is 0.3-0.6 μm.

4. The catalytic device for purifying ozone exhaust gas according to claim 1, characterized in that: The catalyst in the catalyst coating is used to decompose ozone, and the coating thickness is 5-15 μm.

5. The catalytic device for purifying ozone exhaust gas according to claim 4, characterized in that: The catalyst coating is a carbonaceous manganese-based metal oxide composite supported oxidation catalyst coating or a manganese-copper-cerium metal oxide silicon-aluminum-based catalyst coating.

6. The catalytic device for purifying ozone exhaust gas according to claim 1, characterized in that: A valve is installed on the backwash air inlet (5).

7. The catalytic device for purifying ozone exhaust gas according to claim 1, characterized in that: When backwashing the pretreatment unit, a dust collection bag is installed on the air inlet I (3).

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