In semiconductor manufacturing, Chemical Mechanical Polishing (CMP) is an essential process to planarize the wafer surface. However, CMP is not a perfect process and often causes two major defects: Dishing and Erosion. In this article, we will delve into the causes and mechanisms of these phenomena, and introduce metrology solutions to control them.
📌 What Are Dishing & Erosion?
🔹 Dishing
Dishing refers to the phenomenon where metal (e.g., copper, tungsten) is removed more than the surrounding dielectric (e.g., SiO₂) during the CMP process, resulting in a concave pattern inside the metal areas. This occurs because the metal has a higher contact area with the polishing pad, especially in wide patterns, leading to more removal.
- Common Locations: Wide metal pattern areas such as power lines and wide interconnects
- Causes:
- Hardness difference between metal and dielectric → different removal rates
- Non-linear polishing characteristics of the pad and slurry
- Wider metal patterns lead to lower local pressure and deeper removal
- Impact:
- Focusing issues in subsequent photolithography processes
- Step height between interconnects leads to signal delay and capacitance imbalance
- Potential vertical alignment errors in stacked structures
Dishing is especially problematic in 3D NAND, HBM, and TSV structures where vertical alignment and electrical connectivity are critical.
🔹 Erosion
Erosion refers to the excessive removal of dielectric materials during CMP, typically in high-density interconnect regions. It occurs when the alternating layout of metals and dielectrics causes the surrounding dielectric to be polished more than metal.
- Common Locations: Dense pattern areas with high wiring density
- Causes:
- High pattern density → localized pressure concentration
- Uneven slurry flow due to step height → localized accelerated polishing
- Combined effect of chemical reactivity and mechanical abrasion
- Impact:
- Poor surface planarity → uneven resist coating
- Critical dimension (CD) variation in fine patterning
- Dielectric thinning → increased electrical crosstalk
Erosion affects overlay precision and circuit reliability, especially in highly integrated processes.
🔍 Why Is This a Problem?
Dishing and Erosion are not mere surface imperfections. They lead to patterning accuracy degradation, layer misalignment, leakage current, signal delay, and other severe reliability issues.
📉 In advanced packaging and 3D stacking processes, even a 100nm-level step can cause issues in step coverage, thin film deposition, or laser cutting alignment, directly impacting yield.
🛠 Strategies to Prevent and Optimize Dishing & Erosion
✅ Design Stage
- Dummy fill insertion → Balance metal density
- Use a metal density map to insert dummy patterns evenly
- Maintain pattern density uniformity → Improve CMP predictability
- Reduce differences between high and low density regions
✅ CMP Process Optimization
- Adjust pressure and speed → Control local pressure variations
- Modify slurry composition (control chemical reactivity)
- Prevent excessive metal removal by tuning metal selectivity
- Apply multi-step CMP (soft + hard steps)
- Address dishing and erosion with stepwise polishing
✅ Metrology Equipment Utilization
Dishing and erosion can be monitored in real time using high-precision 3D metrology systems
🔎 Recommended Metrology Tools
- White Light Interferometer (WLI)
- Nano- to micron-level surface height analysis
- Depth mapping of dishing/erosion areas
- High-resolution topography imaging
- Ideal for feedback loops and process control
- 3D Optical Profiler
- Quantitative step height comparison (Step height, Peak-to-Valley analysis)
- Fast scanning and area-based profiling for large-scale inspection
- TTV/Bow/Warp Measurement Tools
- Measure overall wafer flatness variation
- Analyze cumulative effects of multiple processes
- Essential for optimizing continuous processing
🧭 Conclusion
Dishing and Erosion are fundamental challenges in CMP processes. However, through proper design, process tuning, and metrology implementation, they can be effectively managed, leading to higher yield and improved product reliability.
📌 Our WLI-based 3D surface metrology solution offers real-time monitoring and optimization for dishing & erosion issues.
Precision metrology is the key to process quality.
Make the smartest choice for your CMP process— Discover it now with our metrology tools.
