Airborne Molecular Contamination (AMC) Control in Precision Optical Lens Manufacturing
Welcome to Particle Measuring Systems latest lithography blog series on mitigating defects caused by AMCs. Here, we look at the way in which we can control this contamination in functional areas.
How much Airborne Molecular Contamination (AMC) is too much?
Manufacturing DUV- and EUV-compatible optics and opto-mechanical assemblies requires a level of environmental control far beyond that of traditional particulate-based cleanrooms. Depending on the wavelength and fluence (energy per area) of the UV laser, different levels of molecular contamination control are required to prevent laser damage to the optical components. The table below shows the maximum advisable levels of organic and inorganic airborne molecular contamination (AMC) in air for manufacturing medium and high fluence DUV optics. Note that EUV litho areas implement the use of wavelengths well below 100 nm within EUV tools which hold the main exposure stage at vacuum. However, the reflective optics in this area of the stage must still be free of embedded AMC-related defects that could occur during optics manufacturing, and as such optics that are used in advanced litho areas should meet the control limits of 193 nm FAs.
Why havoc do AMCs wreak?
Higher airborne molecular contamination levels can lead to increased absorption and scattering of light and ultimately to laser induced damage, resulting in optical haze and overall decreased performance and lifetime. The effect of AMC on optical components is typically not observed prior to prolonged exposure to a UV laser or outgassing testing, so monitoring and control of AMC in the manufacturing environment is critical to prevent this failure mode.
Airborne Molecular Contamination Control
From an optical component and sub-system manufacturing standpoint, it is important to note that there is as of yet no practical method to detect the presence of AMC adsorbents on the surface of optical components prior to shipment to Metrology or Litho tool OEMs, thus the defect may emerge after the component is already installed and the defect is passed onto the consumer (OEM) rather than intercepted and remedied by the supplier during manufacturing. Real-time AMC monitoring in the optical component and sub-system manufacturing facility becomes a leading indicator of effective quality and reliability of the component and sub-system.
Thanks for joining us for this brief overview of AMC limits in lithography functional areas. Join us next time for the final blog in this series: AirSentry II Application in Precision Optical Component and Sub-System Manufacturing.