Contact size will continue to shrink aggressively for future technology nodes. The high costs and uncertainties associated with 193 nm lithography have made extension of DUV the mainstream approach for the semiconductor industry. Phase shift masks have successfully achieved deep sub-wavelength printing, pushing k1 well below 0.5, but with accompanying high mask-making costs. We have examined the practical limits of 248 nm lithography for contact printing utilizing cost-effective methods. Using a single binary mask, the IDEAL-Smile resolution enhancement technique (RET), in combination with aggressive photoresist technology and post-develop processing, we have demonstrated contact printing capability suitable for the 45 nm generation. A variety of DUV photoresist chemistries and processing techniques are available for imaging small contacts. We have examined state of the art ESCAP and hybrid-acetal photoresists as well as a silicon-containing bi-layer material for their direct printing capability and post-develop thermal processing properties. A photoresist with the best combination of optical, thermal, and mechanical properties was selected. This photoresist was then used to produce sub-50nm contacts. For the numerical aperture used in this study (0.73) this equates to a k1 factor near 0.15.
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