The durability of deposition repairs of two different e-beam mask repair tools has been examined and compared in this work. To obtain this data, clear defects on production masks have been repaired with both tools. In between these repairs the mask was used for production and gathered exposure dose accordingly. The increase of transmission and hence the degradation of the deposition has been determined by AIMSTM. We could confirm that one tool/process shows better stability of the depositions than the other.
The era of EUV technology is approaching and use of EUV lithography in chip manufacturing process was reported. The EUV technology has still serious challenges to overcome, to which belong defectivity, source power and throughput of the exposure tool, to name the most obvious. Important part of the lithography, which differs significantly from previous optical technology, is the mask. The mask stack, especially the multilayer (ML) mirror surface and its protection is of high importance, determining the reflectivity of the mask. The ML mirror is protected by a thin Ru capping layer, which however is very sensitive to oxidation and damage during mask manufacturing processes and its use. Also estimation of the capping layer thickness is not trivial, and is unreliable by damage free analytical methods. In our work, we focus on the capping layer integrity and assess it as function of several applied cleaning processes. The integrity is examined via e-beam repair process and AFM measurement of the feature height. As identified in previous experiments, the UV exposure used in manufacturing processes has significant influence on the Ru layer at some conditions. However, there is good chance to find conditions at which the Ru layer is not attacked by the UV exposure, and removed by the subsequent wet process in which the products of Ru oxidization are diluted. Above mentioned procedure we intend to identify EUV mask manufacturing conditions, at which the capping layer is not impacted by the clean process. At the end of the manufacturing process, the EUV mask has to have a thick enough capping layer to perform the repair process and protect the ML mirror during the mask lifetime. Currently available processes allow us to manufacture EUV masks with a remaining capping layer up to five times thicker than required for the e-beam mask repair. This result confirms readiness of the mask manufacturing process for HVM from perspective of the mask health and integrity of the ML mirror and Ru capping layer.
The march toward tighter design rules, and thus smaller defects, implies stronger surface adhesion between defects and
the photomask surface compared to past generations, thereby resulting in increased difficulty in photomask cleaning.
Current state-of-the-art wet clean technologies utilize functional water and various energies in an attempt to produce
similar yield to the acid cleans of previous generations, but without some of the negative side effects. Still, wet cleans
have continued to be plagued with issues such as persistent particles and contaminations, SRAF and feature damages,
leaving contaminants behind that accelerate photo-induced defect growth, and others.
This paper details work done through a design of experiments (DOE) utilized to qualify an improved cryogenic cleaning
technology for production in the Advanced Mask Technology Center (AMTC) advanced production lines for 20 and 14
nm processing. All work was conducted at the AMTC facility in Dresden, Germany utilizing technology developed by
Eco-Snow Systems and RAVE LLC for their cryogenic local cleaning VC1200F platform. This system uses a newly
designed nozzle, improved gaseous CO2 delivery, extensive filtration to remove hydrocarbons and minimize particle
adders, and other process improvements to overcome the limitations of the previous generation local cleaning tool.
AMTC has successfully qualified this cryogenic cleaning technology and is currently using it regularly to enhance
production yields even at the most challenging technology nodes.