Extreme ultraviolet lithography (EUVL) is the most effective way to print sub-30 nm features. The roughness of both the
resist sidewall (line width roughness [LWR]) and resist top must be overcome soon for EUVL to be implemented.
Currently, LWR can vary by about 1 nm according to the recipe used. We have characterized two promising techniques
to improve LWR, an EUV rinse/TBAH process and an implant process, and demonstrated their efficacy. After cleaning
inspection (ACI), LWR was improved with both the rinse and implant processes. After development inspection (ADI),
LWR improved (0.12 nm, 2.4%) and ACI LWR improved (0.1 nm, 2.0% improvement) after using the EUV rinse
process. ADI and ACI LWR improvement (0.45 nm, 9.1%, and 0.3 nm, 6.9%, respectively) was demonstrated with the
EUV rinse/TBAH process. ADI LWR improvement (0.5 nm, 8.1%) and ACI LWR improvement (-0.5 nm, -16.9%) were
characterized with the implant process. Critical dimension (CD) showed similar changes through pitch after the EUV
rinse or TBAH process, but the degree of change depended on the initial pattern size giving CD difference of 2 nm
between 30 nm HP and 50 nm HP after the implant process. For this technique, the dependence of CD change on pattern
size must be minimized. Further extensive studies with rinse or implant are strongly encouraged for continued LWR
improvement and real process implementation in EUVL. Demonstrating <2.2 nm LWR after pattern transfer is important
in EUVL and needs to be pursued using various technical approaches.
Initial resist LWR is important in assessing LWR improvements with additional process techniques. An initial EUV
LWR < ~5.0 nm is required to properly assess the validity of the technique. Further study is required to improve ADI
LWR and maintain better LWR after etch with advanced EUV rinse materials. Defects also need to be confirmed
following the EUV rinse and TBAH developer. Further developing the implant process should focus on LWR
improvement at low frequencies and optimization of process conditions to maintain the EUV resist profile and resist
height. The dependence of CD change on pattern size likewise needs to be minimized.