Full chip correction of EUV design

Abstract

Extreme Ultraviolet Lithography (EUVL) is currently the most promising technology for advanced manufacturing nodes: it recently demonstrated the feasibility of 32nm and 22nm node devices, and pre-production tools are expected to be delivered by 2010. Generally speaking, EUVL is less in need of Optical Proximity Correction (OPC) as compared to 193nm lithography, and the device feasibility studies were indeed carried out with limited or no correction. However, a rigorous optical correction strategy and an appropriate Electronic Design Automation (EDA) infrastructure is critical to face the challenges of the 22nm node and beyond, and EUV-specific effects such as flare and shadowing have to be fully integrated in the correction flow and properly tested. This study aims to assess in detail the quality of a full chip optical correction for a EUV design, as well to discuss the available approaches to compensate for EUV-specific effects. Extensive data sets have been collected on the ASML EUV Alpha-Demo Tool (ADT) using the latest IMEC baseline resist Shin-Etsu SEVR59. In total about 1300 CD measurements at wafer level and 700 at mask level were used as input for model calibration and validation. The smallest feature size in the data set was 32nm. Both one-dimensional and twodimensional structures through CD and pitch were measured. The mask used in this calibration exercise allowed the authors to modulate flare by varying tiling densities within the range expected in the final design. The OPC model was fitted and validated against the CD data collected on the EUV ADT. The shadowing effect was modeled by means of a single bias correction throughout the design. Horizontal and vertical features of different type through pitch and CD were used to calibrate the shadowing correction, and the extent of the validity of the single bias approach is discussed. In addition, the quality of the generated full-chip flare maps has been tested against experimental results, and the model has been validated in the full flare range available within the mask. The model calibration yielded an RMS of about 1nm, and a EUV mask fully corrected for OPC, flare and shadowing was finally fabricated and qualified.

Extending a 193 nm mask inspector for 22 nm HP EUV mask inspection

“…Flare correction as applied to EUV masks, to compensate for optical irregularities in the scanner, will inhibit the ability of a mask inspector to perform a die-to-die or cell-to-cell type inspection because of the non-uniform correction 3 . The magnitude and density of this correction factor are still under study, as is the global correction vs. local correction application.…”

Gradient-based inverse extreme ultraviolet lithography

“…In the past, a set of approaches were developed to resolve the imaging degradation attributed to flare [13][14][15], while some other methods were used to compensate the effect of shadowing or off-axis incidence [16][17][18][19]. Recently, comprehensive OPC methods incorporating OPE, flare, photoresist, and mask shadowing models in the optimization flow have been proposed so as to jointly consider these effects [5,[20][21][22][23][24][25]. However, most of these EUV OPC approaches are edge-based, which only move the segments of mask edges to optimize the imaging performance.…”

Impact of Process-Effect Correction Strategies on Variability of Critical Dimension and Electrical Characteristics in Extreme Ultraviolet Lithography

“…Applying a standard model-based OPC to compensate for proximity effects has been attempted. [16][17][18][19][20][21][22] A modelbased correction was preliminarily studied using rigorous 3D mask simulation for an oblique angle of incidence. 16,17) For further extension of previous studies, a strategy of combining model-based and rule-based corrections was proposed.…”

“…16,17) For further extension of previous studies, a strategy of combining model-based and rule-based corrections was proposed. [18][19][20][21][22] This conventional correction strategy is accomplished by incorporating independent corrections in which rule-based corrections are used to compensate for EUV-specific imaging effects such as mask shadowing at oblique incidence, and a model-based correction is used to compensate for proximity effects at normal incidence. It was stated that the benefits of using the model-based correction at normal incidence are shorter calculation time and direct use of a traditional OPC algorithm 23) developed for DUV lithography.…”

“…However, because most rule-based corrections for mask shadowing effects are empirically developed by using simple Manhattan patterns, some of the simplified approximation approaches would not be applicable in a circuit layout with complicated geometric patterns, such as non-Manhattan patterns. 20) These kinds of approximation approaches can lead to ineffective corrections of EUVspecific imaging effects, resulting in inaccurate patterns printed on a wafer which will significantly alter the electrical characteristics of fabricated circuits.…”