Defectivity issues in topcoatless photoresists

One method currently being employed to reduce the overall lithography process complexity and cost is the utilization of a topcoatless photoresist. The development of these materials administers an additive to create the same hydrophobic characteristics as those created by advanced topcoats. The main challenge for topcoatless resists is to increase the hydrophobicity without causing too much inhibition at the resist surface which leads to bridging or residue-type defects. The key to such a design lies in creating a balance between leaching control and dissolution characteristics of the resist without degrading lithography performance and increasing defectivity. The addition of these hydrophobic additives into existing ArF photoresist systems has been shown to increase both receding contact angle and advancing contact angle in water-based immersion lithography. In this work, the authors have demonstrated that the defectivity levels of topcoatless resist are equal to or better than the industry standard of topcoat systems. This was achieved by optimizing process conditions. This article will report the influences of the develop process, postcoat apply bake/postexposure bake (PAB/PEB) temperatures, and immersion specific rinses on defect performance of topcoatless resists. It was found that pattern collapse defects along nonexposed regions for some topcoatless material can be drastically reduced by PAB/PEB temperature optimization. Complete elimination of missing pattern defects achieved by use of de-ionized water immersion specific rinses for all materials tested. Finally, the impact of the PAB temperature on surface properties will be investigated.