Enabling EUV pattern transfer by optimized underlayer

摘要

For extreme ultraviolet lithography (EUVL), resist mask pattern height is limited by resist line pattern collapse. High aspect ratio patterns improve resist roughness performance and provide more etch resistance to allow a wider margin of etch transfer. However, the high aspect ratio patterns tend to induce pattern collapse easily. In the past, many works have focused on the reduction of capillary force to mitigate pattern collapse. These methods employ low surface tension rinse and optimization of developer process. However, other factors can also influence pattern collapse. Another important parameter causing pattern collapse is the low adhesion force between the resist and underlayer. In this work, we investigate the adhesion properties between resist and underlayer materials. Materials screened were spin-on SiARC, organic BARC, SiC as well as CVD SiON. In addition, two adhesion treatments were used for the underlayers to change the surface properties. Each underlayer material was evaluated on a criteria of pattern collapse limit CD and process window. Adhesion between resist and underlayer is discussed by using adhesive work. The adhesive work was calculated from surface free energy and found to have good correlation with pattern collapse limiting CD. As an application of the improved adhesive work, a resist film thickness was increased to achieve higher aspect ratio (AR) patterns. While the reference pattern was limited by collapse at an AR of 1.2, with the improved adhesion, an AR of 2.1 was achieved. The knowledge gained in this work will be especially useful for 5 nm and smaller nodes.