Part 6 - 3D Surface PEC for greyscale lithography


Richard Bojko, Ulrich Hofmann - GenISys GmbH


  • Challenge in greyscale lithography
  • Resist process and contrast curve
  • Correction model and parameter
  • Challenges in exposure strategy
  • Application in laser lithography

Summary of the Webinar:

  • Binary (2D) PEC is adjusting the dose (or shape) for the same absorbed energy (D2C) at all feature edges. Greyscale (3D) lithography needs to adjust for different remaining resist thickness at any layout position, which is a more challenging task.
  • The proximity effect (backscatter) is corrected using the Monte-Carlo PSF like for 2D, for thick resist the use of 3D PSF to take care of PSF change over resist thickness is advisable
  • The resist process is highly important
    • Process is working at the falling edge of resist contrast curve, low contrast resist processes are preferred for better resolution of the resist thickness
    • The contrast curve needs to be measures with sufficient resolution
    • Using middle (linear) part of contrast curve is advisable
    • The lateral development to neighbors (form high dose to low dose) is a major effect to be corrected
  • Greyscale exposure are highly sensitive on dose non-uniformities
    • Field- / subfield stitching is showing up strongly in greyscale lithography. This can be mitigated by (dose sensitive) multi-pass strategies  
    • The Overlapped fracturing method (new in BEAMER 6.1.) may be another solution for some application
  • Greyscale laser lithography
    • The 3D-Surface PEC correction algorithm works also for laser by exchanging the (3D) PSF by laser intensity image over the resist thickness.
    • Major challenge is absorption and bleaching of the resist
    • Laser greyscale lithography enables thick resist (up to 100┬Ám) application, specifically optical elements such as lenses, blazed grating and DOE