Wafer Defect Review via Selective Reference Die Comparison
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Solution Overview
Problem
The current defect review process for wafers using scanning electron microscopes is time-consuming due to the small field of view and the need for mechanical movements and navigation between the wafer and electron optics, which slows down the inspection of suspected defects across multiple dice.
Innovation Solution
A system and method that utilize a memory unit to store defect locations, electron optics to obtain images of reference elements, and a processor to compare suspected defects to reference elements, selecting new reference elements based on evaluation results to optimize the review process, thereby reducing mechanical movements and accelerating the defect review.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the entire wafer is reviewed using SEM with high resolution, then defect detection quality is improved, but the review time increases due to small field of view and mechanical movements
Solution Approach 1:
The wafer is divided into multiple regions of interest (ROIs) based on suspected defect locations from optical inspection. Instead of reviewing the entire wafer, only these segmented regions are subjected to high-resolution SEM review, maintaining detection quality for critical areas while reducing overall review time.
Solution Approach 2:
Different review strategies are applied to different regions of the wafer. High-resolution SEM review is applied locally to suspected defect regions, while other areas use faster review methods or are skipped, optimizing the balance between quality and speed for each local area.
2Reliability
If mechanical movements and navigation are performed for each suspected defect, then comprehensive defect review is achieved, but productivity decreases due to time-consuming operations
Solution Approach 1:
Regions of interest are pre-identified using optical inspection before SEM review. This preliminary action creates a prioritized list of suspected defect locations, allowing the SEM to navigate directly to critical areas without exhaustive searching, thus maintaining comprehensive review of suspect regions while improving throughput.
Solution Approach 2:
The review process extracts and focuses only on suspected defect regions from the entire wafer. By taking out and isolating these specific areas for detailed SEM review, the system maintains comprehensive coverage of problematic regions while eliminating time spent on areas with no suspected defects.
3Measurement precision
If reference elements are obtained from multiple reference dice, then comparison accuracy is improved, but mechanical scan period increases due to additional acquisitions
Solution Approach 1:
Instead of obtaining reference elements from all possible reference dice, the system uses a partial set - specifically one or two reference dice that are most relevant to the suspected defect regions. This partial action provides sufficient comparison accuracy for the review task while significantly reducing the mechanical scan period.
Solution Approach 2:
Reference elements are selected from specific reference dice that are locally optimal for comparing with suspected defects in particular regions. The selection is based on proximity and process variation characteristics, ensuring high comparison accuracy for each local region without requiring comprehensive reference data from all dice.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the time required for defect review by limiting reference element acquisition to a single or few reference dice, resulting in faster mechanical scan periods and increased throughput, while maintaining quality, by strategically selecting reference dice based on process variations and timing constraints.
Implementation Method 1
electron optics that is configured to obtain images of reference elements
Data Source
AI summary
A system for reviewing a wafer, the system may include a memory unit that is configured to store information about locations of a set of suspected defects that are located at multiple dice of the wafer; electron optics that is configured to obtain images of reference elements, wherein the reference elements are located within a first reference die of the wafer; and a processor that is configured to: compare the first sub-set of suspected defects to a first sub-set of reference elements to provide a first evaluation result; and select, in response to the first evaluation result, a source of a second sub-set of reference elements. The electron optics is further configured to obtain images of a second sub-set of reference elements that are located within a second reference die of the wafer when it is determined that the second reference die is the source of the second sub-set of reference elements. The processor is further configured to compare the second sub-set of suspected defects to the second sub-set of reference elements to provide a second evaluation result.