For years, industry experts have predicted the demise of Moore’s law, because with every successive node, the predicted doubling of transistors every two years has been taking longer and been costlier than expected. However, chip manufacturers have persevered in their efforts, and CMOS scaling has continued to 14nm and beyond. Achieving this has meant pushing the very limits of microlithography; a key technology in achieving smaller critical dimensions (CD) of devices.
Beyond 193nm, single-pattern lithography had become a bottleneck due to resolution limits. For more than 20 years, the industry has been exploring extreme ultraviolet (EUV) lithography to print smaller CD and pitch. While EUV technology is in active development today, it continues to be pushed further and further into the future. As a result, manufacturers have developed creative alternatives using other next-generation lithography processes like multiple patterning.
Self-aligned double patterning is one of the most used multiple-patterning processes by advanced semiconductor manufacturers. In advanced patterning processes, CD trimming is a critical step. Among the available CD trimming methods, etch trim is versatile and widely used, but it adds extra complexity and cost. Dow Electronic Materials has developed a novel spin-on chemical trim overcoat (CTO) formulation and process. Dow’s approach demonstrates a simplification of the advanced patterning process and can reduce cost of ownership.
At the 2016 SPIE Advanced Lithography Conference in San Jose, California, we reported on CTO in a paper titled “Chemical Trimming Overcoat: An Enhancing Composition and Process for 193nm Lithography,” showing how this extra step after lithography allows us to achieve smaller feature size and a better process window.
Figure 1: Typical CTO Process
In a typical process flow, CTO is coated over a positive-tone-developed ArF resist pattern. The wafer is then heated and developed. The process results in smaller feature size with pitch maintained. To demonstrate the performance of Dow’s new spin on CTO formulation, researchers compared the lithographic performance with and without CTO. The paper, available here for download, details the experiments that were performed, along with the results and conclusions drawn from this work that have resulted in a new product offering.
View the Paper
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Cong Liu; Kevin Rowell; Lori Joesten; Paul Baranowski; Irvinder Kaur; Wanyi Huang; JoAnne Leonard; Hae-Mi Jeong; Kwang-Hwyi Im; Tom Estelle; Charlotte Cutler; Gerd Pohlers; Wenyan Yin; Patricia Fallon; Mingqi Li; Hyun Jeon; Cheng Bai Xu and Pete Trefonas "Chemical trimming overcoat: an enhancing composition and process for 193nm lithography", Proc. SPIE 9779, Advances in Patterning Materials and Processes XXXIII, 97791Y (March 25, 2016); doi:10.1117/12.2219688; http://dx.doi.org/10.1117/12.2219688