Characterization and modeling of CD performance with thin PBS

Robert L. Dean; Charles A. Sauer

doi:10.1117/12.301212

12 February 1997 Characterization and modeling of CD performance with thin PBS

Robert L. Dean, Charles A. Sauer

Proceedings Volume 3236, 17th Annual BACUS Symposium on Photomask Technology and Management; (1997) https://doi.org/10.1117/12.301212
Event: 17th Annual BACUS Photomask Technology and Management, 1997, Redwood City, CA, United States

Abstract

As requirements for critical dimension (CD) control tighten, continuing advances in processing techniques are necessary. Mask blanks with reduced film thickness, good control of film thickness uniformity, and resistance to pinholes are now commercially available. The reduction in the amount of forward scattering with these reduced film stacks is primarily responsible for improvements in CD uniformity and CD linearity. CD uniformity, CD linearity, and CD control (mean to target) were measured using 6' by 0.25' PBS substrates and exposing them with MERES^R 4500 and 4500S machines. Both thick and thin resists were studied. The thin PBS process was modified by changing developer solvents. This was done to keep the development time in the desired range for the best CD control. Both processes use puddle develop with a reduced temperature postbake and exposure at 2.0 (mu) C/cm². Blanks from two vendors were examined and compared. Results show a significant improvement (greater than 30%) in CD uniformity over a 132 mm² array. In addition, an improvement in CD linearity and in the ability to maintain mean-to-target CD control were also noted. Modeling and experimental results were compared. We conclude that adoption of a thin resist process has significant advantages in commercial maskmaking. The lithographic properties of thin (200 nm) and standard (400 nm) PBS were modeled using ProBEAM/3D. ProBEAM/3D uses a Monte Carlo model to predict the energy deposited in the resist during exposure and a development rate model to predict the resist profile and CD size after development. Results from modeling were compared to experimental results. As expected, modeling confirms the hypothesis that reduced forward scatter is the dominant mechanism to improve CD performance.

Citation Download Citation

Robert L. Dean and Charles A. Sauer "Characterization and modeling of CD performance with thin PBS", Proc. SPIE 3236, 17th Annual BACUS Symposium on Photomask Technology and Management, (12 February 1997); https://doi.org/10.1117/12.301212

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