Spatial Weighting Maps for Wafer Dose, Focus, and Overlay Control
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Solution Overview
Problem
Current semiconductor manufacturing processes face challenges in accurately controlling overlay and critical dimension errors due to non-uniform stress and misalignment issues, which are exacerbated by shrinking ground rules and aggressive processes like multiple patterning and high aspect ratio etching.
Innovation Solution
A metrology system that generates a weighting map based on spatial process key performance indicators (KPIs) to create a modeled correction, which is used to control dose, focus, and overlay by weighing metrology measurements according to their position on the sample, allowing for feedback and feedforward control of process tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional uniform process control is used across the semiconductor wafer, then the manufacturing process is simple to implement, but overlay error and critical dimension error increase due to non-uniform stress and process variability
Solution Approach 1:
The patent divides the wafer surface into multiple spatial zones using a weighting map, where each zone has different weight values corresponding to different process variability characteristics. This segmentation allows the system to apply location-specific corrections rather than uniform control, directly addressing the non-uniform stress and process variability that cause overlay and critical dimension errors.
Solution Approach 2:
The weighting map assigns different weight values to different spatial locations on the wafer based on local process variability. Areas with higher process variability receive higher weights, allowing the process control system to prioritize corrections in those specific regions. This local quality approach enables precise control of overlay and critical dimension errors where they occur most frequently without unnecessarily complicating the entire process control system.
2Productivity
If aggressive semiconductor manufacturing processes like multiple patterning and high aspect ratio etching are used to maintain productivity, then manufacturing output is maintained, but non-uniformity and stress on the wafer increase leading to greater process variability
Solution Approach 1:
The system performs preliminary characterization of process variability across the wafer surface before manufacturing, creating a weighting map that predicts where non-uniformity will occur. This preliminary action allows the process control system to pre-compensate for expected variations from aggressive processes like multiple patterning and high aspect ratio etching, maintaining both high productivity and manufacturing precision.
Solution Approach 2:
The system uses measured overlay and critical dimension data from previous wafers to update and refine the weighting map for subsequent wafers. This feedback loop continuously improves the accuracy of the weighting map, allowing the system to better predict and compensate for non-uniformity introduced by aggressive manufacturing processes, thereby maintaining both productivity and precision over time.
3Measurement precision
If metrology measurements are taken at all positions on the wafer to achieve comprehensive process control, then measurement accuracy improves, but measurement time and system complexity increase
Solution Approach 1:
The system extracts and focuses metrology measurements only on critical regions of the wafer identified by the weighting map. Instead of measuring all positions uniformly, the system identifies areas with highest process variability and concentrates measurement resources there, achieving comprehensive process control for the most problematic regions while reducing overall measurement time.
Solution Approach 2:
The system performs measurements at a subset of wafer positions that are sufficient to characterize process variability, rather than measuring every possible location. The weighting map guides selection of measurement positions to achieve adequate process understanding with partial sampling, reducing measurement time while maintaining sufficient precision for effective process control.
Data Source
AI summary
A modeled correction may be generated based on metrology measurements and a weighting map. Residuals between the modeled correction and the metrology measurements may be weighted according to the weighting map. The modeled correction may be weighed via the weighting map according to a position at which the metrology measurements were generated on a sample. The modeled correction may include dose, focus, and overlay. A process tool may be controlled based on the modeled correction to control the dose, focus, and overlay.