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Optical Proximity Correction (OPC) has been used for many years now in the semiconductor industry to provide through-pitch focus and dose matching across an entire mask field. By adding sub-resolution features, lines with large duty ratios can be made to have similar imaging properties as dense line patterns, reducing CD variation and increasing the flexibility of the design space. The subresolution features subtract zero-order diffraction energy which is the dominating determinate of how features are imaged in the resist. A binary chrome photomask with sub-resolution OPC features was designed at the Rochester Institute of Technology and fabricated by Photronics Inc. Austin, TX. The main features of mask are 1200nm (240nm on the wafer) with OPC features ranging from 300nm to 1200nm. Different scatter bar (parallel to main feature) configurations were implemented to gain a better understanding of when sub-resolution features start to print. Ladder bar (perpendicular to main feature) size and pitch was varied to observe the effect that the proximity of OPC features perpendicular to main features has on line edge roughness. The mask was printed on 6” wafers using a 248nm exposure tool (NAO.5, a”O.5). Shipley UVIII photoresist was coated to a thickness of 5000A and developed with CD26 developer. Printability data was collected through observation under a light microscope. To evaluate the effect of OPC features on minimizing CD variation, feature CDs were measured using a CDSEM. The CDSEM was also utilized to quantify the line edge roughness associated with ladder bars.

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