Hyung-ho Ko

Damage/organic free ozonated DI water cleaning on EUVL Ru capping layer

The adaption of EUVL requires the development of new cleaning method for the removal of new contaminant without surface damage. One of the harsh contaminants is the carbon contamination generated during EUV exposure. This highly dense organic contaminant is hardly removed by conventional SPM solution on Ru capped Mo/Si multilayer. The hopeful candidate for this removal is ozonated water (DIO3), which is not only well-known strong oxidizer but also environmentally friendly solution. However, this solution might cause some damage to the Ru capping layer mostly depending on its concentration. For these reasons, DIO3 cleaning solutions, which are generated with various additive gases, were characterized to understand the correlation between DIO3 concentration and damages on 2.5 nm thick ruthenium (Ru) surface. An optimized DIO3 generation method and cleaning condition were developed with reduced surface damage. These phenomena were explained by electrochemical reaction.

Effect of EUV exposure upon surface residual chemicals on EUV mask surface

Photo-induced defect for optic mask mainly depends on the surface residual ions coming from cleaning process, pellicle outgassing, or storage environments. Similar defect for EUV mask triggered by accumulated photon energy during photolithography process has drawn interest recently but this defect is somewhat different from normal photo-induced defect for optic mask. The photo-induced defect for EUV mask is known to be created by the chemical deposition of Carbon atoms originating from cracking of hydrocarbons by EUV light and secondary electrons on capping layer. It is very likely that Carbon contamination would be dominant under normal EUV exposure condition. On the other hand, it is expected that another kind of photo-induced defects would rise to surface under controlled environment where Carbon contamination growth is severely suppressed. We may have to understand the behavior of surface residual ions under EUV light in order to cope with another probable EUV photo-induced defect. In this paper, we will investigate whether surface ions remaining after cleaning process like sulfate or ammonium ions would create printable defects or decompose into evaporable species under EUV light. In case they create certain defects on mask surface, their effect on EUV reflectivity and absorber pattern CD variation will be also examined. Finally, improved cleaning process to impede photo-induced defect creation on EUV mask will be introduced.

Durability of Ru-based EUV masks and the improvement

In EUV Lithography, an absence of promising candidate of EUV pellicle demands new requirements of EUV mask cleaning which satisfy the cleaning durability and removal efficiency of the various contaminations from accumulated EUV exposure. It is known that the cleaning with UV radiation is effective method of variety of contaminants from surface, while it reduces durability of Ru capping layer. To meet the expectation of EUV mask lifetime, it is essential to understand the mechanism of Ru damage. In this paper, we investigate dominant source of Ru damage using cleaning method with UV radiation. Based on the mechanism, we investigate several candidates of capping to increase the tolerance from the cycled UV cleaning. In addition, we study durability difference depending on the deposition method of Ru capping. From these studies, it enables to suggest proper capping material, stack and cleaning process.