Views: 0 Author: Site Editor Publish Time: 2025-04-20 Origin: Site
The core mission of the Cleanroom, the ‘sterile greenhouse’ of semiconductor manufacturing, is to control airborne contaminant concentrations at the parts per trillion (ppb) or even parts per trillion (ppt) level.
According to ISO 14644-1, Cleanroom contaminants can be classified into four main categories: solid particles, gaseous chemical contaminants, molecular-level film contaminants, and microbiological contaminants.
Technical Principle: According to Stokes' Law, the settling velocity of particles in air is proportional to the square of the particle size. 0.1μm particles can take up to 2 hours to settle in static air, while 10μm particles take only 3 minutes. The main sources of particle pollution are:
1. Personnel movements: 10^4 particles ≥ 0.5 μm per minute (in normal clean suits).
2. equipment friction: Metal particles (Fe, Ni 65%) generated by vacuum pump bearing wear.
3. process by-products: Silica abrasive particles (particle size 0.2-1μm) generated during the CMP process.
Technology principle: According to Langmuir adsorption theory, gaseous molecules (e.g. SO2, NOx) will be adsorbed on the surface of silicon wafers through van der Waals forces, forming a monomolecular layer of contamination.
The main sources of pollutants are: Acid gases, alkaline gases, organic gases, metal vapours.
Principle of the technology: Hydroxyl groups (-OH) on the wafer surface easily adsorb polar molecules, forming a contamination layer with a thickness of 1-5nm. For example:
Water vapour adsorption: When the relative humidity is > 40%, more than 3 layers of hydrated film are formed on the wafer surface.
Silicone contamination: Si-O-Si polymer is formed after condensation of vacuum pump oil vapour, resulting in a 25% decrease in photoresist adhesion.
Specificity: Bacterial spores (0.5-5μm diameter) can be removed by HEPA Filtration, but metabolites (e.g. endotoxins) may release volatile organic compounds (VOCs). ISO 14644-6 requires microbiological concentrations in Class 100 Cleanrooms to be ≤5 CFU/m³, and pathogens such as Staphylococcus aureus must not be detected.
