Semiconductor Mfg.: Techs & Apps of Ultra - clean Air Filtration Sys.

In the field of advanced semiconductor manufacturing, air cleanliness control has evolved from an auxiliary process to a core technical element that determines the chip yield rate. As the process node enters the era below 3nm, the number of 0.1μm-level particulate matters allowed per cubic meter of space needs to be controlled at a single-digit level, which poses unprecedented technical challenges to the air filtration system.

I. Classification of Semiconductor Cleanrooms and Technical Standard System

According to the ISO 14644-1 international standard, the core areas of a wafer fabrication plant generally require an ISO Class 1-3 cleanliness level. Its core parameters include:

• - Particle Size Distribution Control: Establish a multi-stage interception model for the Most Penetrating Particle Size (MPPS) of 0.1-0.3μm.

• - Airborne Molecular Contamination (AMC) Control: Cover eight major categories of gaseous pollutants such as acids/bases/organics/dopants, etc. 

• - Temperature and Humidity Precision: Control the temperature fluctuation within ±0.1℃ and maintain the humidity stability within ±1%RH. In the 7nm process, the AMC concentration needs to be controlled below 1ppb. In the era of the GAA transistor architecture, the limits of specific metal pollutants (such as Na+ and K+) have been reduced to the 0.1ppt level.

II. Architecture of the Air Filtration System and Technological Innovations

• 1. Three-stage Filtration System - Primary Filtration Layer: Use G4/F7-grade glass fiber filter media to intercept large particles larger than 5μm. - Medium-efficiency Filtration Module: Configure H13-grade HEPA filters, with a collection efficiency of ≥99.97% for 0.3μm particles. - Terminal Treatment Layer: ULPA U15-U17-grade filters, with a filtration efficiency of 99.9995% for 0.12μm particles.

• 2. Breakthroughs in Anti-static Technology Reduce the surface resistance of the filter media to 10^6-10^8Ω through a nanoscale conductive coating (such as ITO doping) to effectively prevent electrostatic adsorption pollution of 300mm wafers. The dedicated filtration module for ASML EUV lithography machines even adopts radioactive neutralization technology to control the electrostatic voltage within ±5V.

• 3. Innovations in Chemical Filtration - Acidic Gas Treatment: Multi-layer impregnated activated carbon (modified with phosphates) achieves an adsorption rate of >99.9% for gases such as HCl and HF. - Alkaline Gas Capture: The molecular sieve modified with sulfuric acid has a removal efficiency of 99.99% for NH3. - VOC Treatment: The honeycomb activated carbon-zeolite composite structure has an adsorption capacity of >35wt% for benzene series compounds.

III. Analysis of Application Scenarios in Key Process Steps

• 1. Environmental Control in the Lithography Area - Immersion lithography machines need to be equipped with 0.05μm ULPA filters to ensure that there are ≤1 particle per cubic meter in the path of the laser beam. - AMC control requirements in the photoresist coating area: DOP vapor < 0.1μg/m3, SOx < 0.5ppb.

• 2. The Thin Film Deposition Area - The intake system of the CVD reaction chamber is equipped with a ceramic membrane filter with a pore size of 0.05μm and a temperature resistance of 800℃. - The ALD precursor delivery uses a nickel-based sintered metal filter, with the metal ion precipitation amount < 0.01μg/m3.

• 3. The Ion Implantation Process - A 0.03μm PTFE membrane is set at the entrance of the Mass Filter, with an interception rate of 99.9999%. - The helium leak detection system is equipped with a catalytic oxidation device, with the hydrocarbon residue < 1ppb.

IV. Technical Challenges and Solutions

• 1.Nanoscale Particle Capture - Develop a gradient-structured nanofiber membrane (with a fiber diameter of 100-300nm). - Apply acoustic agglomeration technology to make 0.01μm particles aggregate into clusters larger than 1μm.

• 2. Optimization of Pressure Drop and Energy Consumption - Optimize the flow channel design through Computational Fluid Dynamics (CFD) simulation, reducing the pressure drop by 40%. - The intelligent variable frequency control system dynamically adjusts the air volume according to the process requirements, saving 30% of energy.

• 3. Online Monitoring Technology - The Laser Particle Counter (LPC) realizes real-time monitoring of 0.05μm particles. - The FTIR spectrometer conducts ppb-level online analysis of AMC.

V. Future Development Trends

• - Two-dimensional Material Filter Membrane: Graphene/boron nitride composite membranes achieve atomic-level filtration precision.

• - Self-cleaning Technology: The photocatalytic decomposition of pollutants technology will extend the maintenance cycle to 5 years.

• - Digital Twin System: Predict the life of the filter element based on big data, with an accuracy of ±3%.

As semiconductor devices develop towards a three-dimensional stacking architecture, the air filtration system is shifting from passive protection to active control, and its technological breakthroughs directly determine the sustainability of Moore's Law. In the next five years, advanced filtration technologies will drive a 25% reduction in the energy consumption of wafer fabrication plants, and the defect rate control will enter a new era with 0.01 particles per square centimeter.