Part 2 – Dose PEC Algorithm and Parameter


Ulrich Hofmann, Nikola Belic - GenISys GmbH


  • Why PEC?
  • Dose PEC with Edge Equalization Algorithm (“Optimum Contrast”)
  • Dose range, accuracy, fracturing
  • Long-, Mid-, Short range Correction
  • What is the “Base Dose” & “Effective Short-Range Blur”
  • Strength & Weaknesses of “Optimum Contrast”, “Uniform Clearing” and “Mixed Mode”

Summary of the Webinar:

  • Always use PEC
    • Avoids dose matrices by adjusting all layouts (small - large, dense – coarse, …) to one specific base dose
    • Improves litho-quality and minimizes beam-on time (improves throughput) by adjusting local doses to optimum, avoiding overdosing
    • Opens / enlarges process window (more stable process)
  • “Edge-Equalization” is a stable and robust PEC method
    • Adjusts all layout edges to the same absorbed dose (dose-to-clear)
    • “Iso-focal” (not sensitive to blur change) provides best CD control over field position (corner / edges), blur change over time
  • Proximity influence ranges
    • Pixel based algorithm for long range is fast and stable for long-range (backscatter)
    • For short-range local (shape based) algorithm couple with DRC to determine the shapes requiring SR correction is a better choice
    • Mid-range is included into short- or/and long-range if feasible. For high midrange energies a separate pixel-based correction with a finer grid is performed.
  • The basic PEC parameters are pretty simple
    • Point Spread Function (PSF) from Monte Carlo simulation
    • Based dose can be determined by exposing dose matrix of a PEC’ed typical pattern
    • Effective Blur can be estimated from dose variation of isolated line around dose-to-size
  • Absorbed energy and resist contour at threshold can be simulated by convolution of the layout with the PSF
  • For low contrast resists on dense material the “Mixed-Mode” between Optimum Contrast (Edge-Equalization) and Uniform clearing (Surface-Equalization) may be an alternative