Tight-pitch contact-hole patterns in EUV lithography

One of the key steps in the pattern formation chain of Extreme Ultraviolet (EUV) lithography is the development process to resolve the resist pattern after EUV exposure. The traditional development process might be insufficient to clear the hydrophilic holes in Contact Hole (CH) patterns and often causes missing hole defects and a high Local CD Uniformity (LCDU). The aim of this paper is to establish a process to achieve a low LCDU, a low defectivity, a low EUV dose for tight-pitch CH patterns. A novel development method has been introduced to improve the performance of CH patterns with Metal Oxide-Resists (MOR). This is made possible thanks to the capability of the new development that can effectively remove the scums (resist residues) inside CH to extend the missing hole defect margins. The high development contrast of the new development technique results also in a much higher exposure latitude and a lower LCDU. Using 0.33 NA EUV scanners on 36-nm, 34-nm, and 32-nm pitch hexagonal patterns, the novel development produced a lower LCDU, a higher EUV sensitivity, a higher exposure latitude (EL), and a wider failure free dose range. If compared to the data by conventional development, using the new development on 34-nm pitch CH patterns, the EL was increased from 12% to 26%, and the failure free dose range was extended from 9% to 56% at ADI. The 34-nm CH patterns developed by the novel development were also nicely transferred to a TiN layer with the failure free dose range was extended to 60% from almost 0% if using traditional development. With all the advantages of having a high EUV sensitivity, a low defectivity, and a low LCDU, the new development method, which has a high removal capability of hydrophilic region, can help the tight-pitch CH patterning with negative tone MOR more realistic.