Front-End Wafer Geometry Metrics for In-Plane Distortion Screening
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Solution Overview
Problem
Conventional metrology tools only provide sufficient wafer geometry measurements after initial lithography, failing to predict overlay errors in semiconductor wafers due to elastic deformation during fabrication, leading to low back-end yield and increased costs from non-correctable errors.
Innovation Solution
The implementation of a Gapi wafer geometry metric, calculated from front-end processed wafer measurements, allows for early identification and correction of in-plane distortions, enabling efficient sorting and adjustment of wafers before irreversible processing steps, thereby improving back-end yield and reducing overlay error control needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional metrology tools are used to measure wafer geometry, then measurements can be obtained after initial lithography, but the tools fail to predict overlay errors due to elastic deformation during fabrication
Solution Approach 1:
The patent applies preliminary action by measuring wafer geometry at the front-end processing stage before lithography and fabrication steps occur. This early measurement captures the wafer's initial state, allowing prediction of overlay errors that will develop during subsequent processing due to elastic deformation. The Gapi metric is calculated from these preliminary measurements to identify wafers at risk of overlay errors before they occur.
Solution Approach 2:
The patent introduces the Gapi metric as an intermediary parameter that bridges the gap between front-end processed wafer geometry measurements and back-end overlay error prediction. The Gapi metric serves as a predictive indicator that correlates early wafer geometry characteristics with future overlay performance, enabling reliable prediction without requiring post-lithography measurements.
2Measurement precision
If high accuracy inspection tools are used to measure wafer distortions, then overlay errors can be detected between patterning steps, but the tools require polished surfaces and measurements can only be taken after fabrication has begun
Solution Approach 1:
The patent performs wafer geometry measurements at the front-end processing stage, before polishing and lithography begin. This preliminary measurement captures the wafer's initial geometry state, enabling early prediction of distortion patterns that will develop during fabrication. By measuring before processing begins, the system eliminates the time delay associated with waiting for polishing and fabrication steps to complete before measurement.
Solution Approach 2:
The patent creates a predictive model (Gapi metric) that copies the essential distortion characteristics from early front-end measurements and uses this model to predict future overlay errors. This copying approach allows the system to forecast distortion patterns without requiring physical presence of the wafer during later fabrication steps, effectively decoupling measurement timing from processing timing.
3Productivity
If wafers are processed without early distortion prediction, then the fabrication process can proceed without additional inspection steps, but non-correctable overlay errors occur resulting in low back-end yield
Solution Approach 1:
The patent implements preliminary action by calculating the Gapi metric from front-end processed wafer measurements before lithography begins. This early prediction identifies wafers that are likely to develop overlay errors during fabrication, allowing these wafers to be sorted out or reprocessed before irreversible processing steps occur. This maintains high back-end yield without requiring additional inspection steps during fabrication, as the prediction is made beforehand.
Solution Approach 2:
The patent implements feedback by using the Gapi metric to provide information about future overlay error risk based on current front-end wafer geometry. This feedback loop allows the system to make informed decisions about wafer processing and sorting before fabrication begins, enabling corrective actions to be taken on high-risk wafers while allowing low-risk wafers to proceed through the fabrication process without interruption.
Data Source
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AI summary
A method for processing semiconductor wafers includes obtaining measurement data from a surface of a semiconductor wafer processed by a front-end process tool. The method includes determining a center plane of the wafer based on the measurement data, generating raw shape profiles, and generating ideal shape profiles. The method further includes generating Gapi profiles based on the raw shape profiles and the ideal shape profiles, and calculating a Gapi value of the semiconductor wafer based on the Gapi profiles. The generated Gapi profiles and/or the calculated Gapi value may be used to tune the front-end process tool and/or sort the semiconductor wafer for polishing. Systems include at least a front-end process tool, a flatness measurement tool, and a computing device.