EUV telecentricity and shadowing errors impact on process margins

Monte Carlo simulations are used in the semiconductor industry to evaluate variability limits in design rule generation, commonly for interaction between different layers. The variability of the geometry analyzed is determined mainly by the lithography, process and OPC used. Monte Carlo methods for design rule evaluation can provide the requisite level of accuracy, and are suitable for two or more layer interactions because the variations on one can be assumed to be independent of variations on the other(s). The variability parameters and budget utilized in optical Monte Carlo simulations is well-established. With the upcoming implementation of EUV lithography the variability budget will be impacted. EUV has an off-axis illumination angle that complicates the lithography process by causing telecentricity and shadowing errors. Telecentricity errors manifest as a printed feature being shifted relative to the design. The amount the feature is shifted is a function of the pattern density and design. Shadowing is caused by the 3D nature of the mask combined with EUV reflective mask technology. A shadow occurs at feature edges, where the source does not fully illuminate. Telecentricity and shadowing errors, although small at the 10 nm node, will increase in relative size compared to the features printed beyond the 7 nm node. Telecentricity and shadowing errors are complex in nature and can't be compensated for with a flat bias. These errors unique to EUV are incorporated into Monte Carlo simulations and evaluated against the standard cell design layers. The effect of these variability parameters is evaluated on critical 7 nm node layout clips.