Application of Stochastic Modeling to Resist Optimization Problems John J. Biafore, Mark D. Smith KLA-Tencor, FINLE Division, 8843 North Capital of Texas Highway, Austin, TX 78759
BACKGROUND: Modifying specific resist properties or isolating a particular resist response can be difficult or impossible in experiments. At EUV, tool time is limited and expensive, complicating access to experimental data. Computer modeling can help to mitigate these difficulties, allowing researchers to reduce or better focus the nature of actual experiments. METHODS: We apply stochastic simulation to the study of chemically-amplified resists at EUV. The model is calibrated to experimental data; the agreement between data and simulation are compared using RLS triangles. Using the calibrated model as a representation of the initial condition, we attempt to improve virtual resist performance by decreasing acid diffusivity rate, increasing quencher loading and by replacing conventional quencher with photo-decomposable base (PDB). The effect of PDB upon the virtual resist is further investigated. RESULTS: Virtual resist performance improved by lowering acid diffusivity, by increasing quencher loading and by replacing conventional quencher with photo-decomposable base (PDB). The net improvements observed are a 17% increase in EL and a 13% reduction in LER compared to the initial condition. PDB may offer a path to reduce resist roughness up to 20%, by allowing higher loading density than conventional quenchers and relaxing the acidic quantum yield required to achieve acceptable roughness. Using the simulator to isolate a specific response, PDB acts to improve the chemical contrast and reduce the chemical noise in the blocked polymer concentration after PEB. Keywords: Stochastic modeling, EUV photoresist, RLS, photodecomposable base, PDB, line-edge roughness, line-width roughness, LER, LWR I.
INTRODUCTION
The semiconductor industry has maintained Moore’s law by using a either an increase in numerical aperture (NA) or a reduction in wavelength (λ). The next planned technology change is a reduction in wavelength from ArF (193 nm) to EUV (13.5 nm). The dramatic reduction in wavelength combined with a reduction in NA to ca. 0.25 has obvious advantages for resolution and depth of focus, but it also leads to optical and physical effects that were practically insignificant in ArF tools. For example, there are new manufacturing challenges for EUV, including throughput, CD uniformity (CDU), line-width and line-edge roughness (LWR, LER). These problems are all closely tied to the power that can be supplied by the EUV source, because lower power means either a lower scan rate (which is detrimental to throughput) or a lower exposure dose (which leads to poor CDU and LWR due to the effects of photon shot noise). Photoresist vendors are working directly on this problem, as they try to determine the right compromise between resolution, exposure latitude, roughness and sizing dose. With all of these new optical and physical effects, photolithography simulation is an invaluable tool for the researcher. Under normal circumstances, much of the learning needed to build a viable resist system can be obtained by a large, extensive set of Edisonian experiments. For EUV, it is not practical to rely upon experiments alone because there are so many new effects and experimental data are currently difficult and expensive to obtain. Simulation can help to mitigate these difficulties, allowing researchers to guide, reduce the number of or better focus actual experiments. In this work, we apply the stochastic resist model (SRM) in PROLITH version X4.1 to study the refinement of chemically-amplified resists at EUV. The model is calibrated to experimental data 1; the agreement between data and simulation are compared using RLS triangles. Using the calibrated model as a representation of the
Advances in Resist Materials and Processing Technology XXIX, edited by Mark H. Somervell, Thomas I. Wallow, Proc. of SPIE Vol. 8325,83250H © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.916518 Proc. of SPIE Vol. 8325 83250H-1 Downloaded from SPIE Digital Library on 14 Mar 2012 to 192.146.1.12. Terms of Use: http://spiedl.org/terms