Optical Wafer Inspection via Diluted Scanning
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Solution Overview
Problem
Optical wafer inspection is time-consuming, especially at high magnification, limiting throughput to a few wafers per hour, and partial scanning risks missing defects if not all areas are inspected.
Innovation Solution
Implementing improved partial scanning techniques that reduce slice transitions and increase scanning velocity by scanning fewer slices or frames, while maintaining statistical data relevance and accuracy through dilution methods that image some but not all areas, parallel and perpendicular to the scanning axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full wafer scanning is performed, then defect detection accuracy is improved, but inspection time increases
Solution Approach 1:
The patent applies partial action by performing diluted scanning where only a subset of slices or frames are inspected. The system scans fewer slices than the total available slices, or scans fewer frames within slices, thereby reducing inspection time while maintaining statistically valid defect detection through representative sampling of the wafer surface.
Solution Approach 2:
The patent segments the wafer inspection process into discrete slices and frames, allowing selective scanning of specific segments. By dividing the wafer into manageable units (slices perpendicular to scanning axis, frames within slices), the system can strategically select which segments to inspect, reducing overall inspection time while preserving detection accuracy through proper segment selection.
2Productivity
If scanning velocity is increased, then productivity is improved, but measurement precision deteriorates
Solution Approach 1:
The patent enables higher scanning velocities by inspecting only a diluted subset of wafer areas. By reducing the total number of slices or frames scanned, the system can operate at higher speeds without compromising overall inspection quality, as the reduced scan volume compensates for the lower per-unit inspection thoroughness.
3Loss of time
If partial scanning is performed, then inspection time is reduced, but reliability of defect detection deteriorates
Solution Approach 1:
The patent maintains detection reliability through systematic segmentation and strategic selection of slices and frames for inspection. By dividing the wafer into structured segments and selecting representative samples according to defined criteria, the system ensures that partial scanning still provides statistically valid and reliable defect detection coverage.
Solution Approach 2:
The patent adjusts inspection parameters (number of slices scanned, number of frames per slice, dilution factors) to optimize the balance between inspection time and reliability. By dynamically changing these parameters based on wafer characteristics and inspection requirements, the system maintains reliable defect detection while minimizing inspection time.
Data Source
AI summary
Inspection of objects, such as semiconductor wafers, can be performed using a diluted scan wherein not all of an inspected area is actually imaged. Instead, a dilution plan can be devised based on the desired amount of area to be skipped and the particular parameters of the inspection, such as the size of each unit area to be imaged or not imaged and the distribution features of the wafer. When the same area is inspected in multiple wafers, the wafers can be inspected in sets using a dilution plan whereby a wafer (or inspected area) can be statistically inspected using diluted scans of the set of wafers. Similarly a die or group of dies of a specified type can be statistically inspected using diluted scans of a set of dies (or group of dies). When statistical inspection is used, the end results of such inspections, such as defect densities and distributions, can be corrected to account for inaccuracies that may be introduced when certain portions are imaged more often than others due to the dilution plan.