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Methodology and measurement results of resist acid diffusion

One of the important elements for imaging (sub-) 65nm dimensions involves diffusion of photo-generated acid in photo resists. Acid diffusion leads to blurring of the optical contrast, thereby affecting resolution capability, as well as photo speed (= dose) and line edge roughness (LER).

A previously developed methodology for lens characterisation was utilised, after some modifications, to determine this image blur. This allowed a good indication of the magnitude of acid diffusion lengths.

The method has been applied to various resist platforms, including 157nm photo resists, indicating that diffusion lengths in state-of-the-art 157nm resists are currently too large for imaging at the 65nm node.

Although the application for the acid diffusion measurement methodology has proven a valuable tool for 157nm resist status assessment, with the move away from 157nm technology it becomes unlikely that this approach will prove its value in this field. However, it has been demonstrated that the methodology is applicable also towards 193nm (immersion) resists as well as a valuable tool in the assessment of next generation Extreme Ultra-Violet Lithography (13.5nm) resists. Hence the benefits of the acid diffusion methodology development, partly developed through the UV2Litho project, will continue to prove its value and benefits in the coming years.

More information on the UV2LITHO project can be found at:

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Philips Innovative Technology Solutions
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