CMP Dummy Metal Fill & Pattern Density: CAM Vector Prepress Guide

Learn how to generate rule-compliant dummy metal fill patterns for Chemical Mechanical Planarization (CMP). Eliminate dielectric erosion, copper dishing, and thickness variations across multi-layer semiconductor and MCM interconnects.

1. Chemical Mechanical Planarization (CMP) Overview

Chemical Mechanical Planarization (CMP) combines chemical slurry etching with mechanical abrasive polishing to achieve global and local planarity across multi-layer semiconductor wafers and advanced multi-chip packaging. In modern sub-micron processes, severe non-uniformities in metal pattern density cause localized over-polishing (copper dishing) and dielectric erosion.

2. Preston's Polishing Law & Pattern Density Dishing

Preston's Law:
  MRR = K_p * P * V   [nm/min]

Where:
  K_p = Preston material removal coefficient
  P   = Polishing downforce pressure (psi)
  V   = Relative linear sliding velocity (m/s)

3. Dummy Fill Algorithm Guidelines & CAM Vector Prepress

• Density Window: Design rules mandate that metal density within any sliding window ($20\,\mu\text{m} \times 20\,\mu\text{m}$ to $100\,\mu\text{m} \times 100\,\mu\text{m}$) must remain between $35\%$ and $65\%$.
• Floating vs Grounded Tiles: Floating dummy tiles reduce parasitic capacitance, whereas grounded/shielded dummy grids provide power return paths and noise isolation for sensitive analog/RF circuits.