Improving the performance of E-beam 2nd writing in mask alignment accuracy and pattern faultless for CPL technology

Abstract

The chromeless phase lithography (CPL ) is a potential technology for low kl optical image. For the CPL technology, we can control the local transmission rate to get optimized through pitch imaging performance. The CPL use zebra pattern to manipulate the pattern local transmission as a tri-tone structure in mask manufacturing. It needs the 2 nd level writing to create the zebra pattern. The zebra pattern must be small enough not to be printed out and the 2 nd writing overlay accuracy must keep within 40nm. The request is a challenge to E-beam 2 nd writing function, the focus of this paper is in how to improve the overlay accuracy and get a precise pattern to form accurate pattern transmission. To fulfill this work several items have been done. To check the possibility of contamination in E-Beam chamber by the conductive layer coating we monitor the particle count in the E-Beam chamber before and after the coated blank load-unload. The conductivity of our conductive layer has been checked to eliminate the charging effect by optimizing film thickness. The dimension of alignment mark has also been optimized through experimentation. And finally we checked the PR remain to ensure sufficient process window in our etching process. To verify the performance of our process we check the 3D SEM picture. Also we use AIMs to prove the resolution improvement capability in CPL compared to the traditional methods-Binary mask and Half Tone mask. The achieved overlay accuracy and process can provide promising approach for NGL reticle manufacturing of CPL technology.