Across-Wafer Variation Reduction in Lithographic Exposure
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Solution Overview
Problem
Across-wafer variations in semiconductor manufacturing lead to errors in critical dimension measurements and OPC model calibration, due to non-uniform temperature distributions and other field-dependent variations, which existing methods struggle to accurately account for.
Innovation Solution
A method involving micro-stepped exposures and the use of a chrome frame to align test patterns, allowing for field-position dependent OPC model calibration, and a double exposure technique to characterize the illuminator's intensity distribution by superimposing exposures with varying doses and defocus conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single exposure methods are used, then the process is simple and fast, but measurement precision deteriorates due to across-wafer variations
Solution Approach 1:
The exposure process is divided into multiple discrete exposure fields that are sequentially exposed across the wafer. Each field is exposed independently with controlled overlap, allowing separate measurement and correction of across-wafer variations. This segmentation enables precise characterization of position-dependent effects while maintaining a manageable process structure.
Solution Approach 2:
The exposure fields are deliberately overlapped by a predetermined amount beyond what is strictly necessary for complete wafer coverage. This excessive exposure action ensures that regions affected by across-wafer variations are captured in multiple fields, enabling accurate measurement and correction of position-dependent measurement errors.
2Measurement precision
If micro-stepped exposures with overlapping fields are used, then measurement precision improves, but productivity decreases
Solution Approach 1:
Test patterns are pre-positioned in specific locations across the wafer before production exposure. These test patterns are exposed along with production fields, allowing simultaneous characterization of across-wafer variations and OPC model calibration without requiring separate measurement steps. This preliminary arrangement of test features enables efficient data collection during normal exposure operations.
Solution Approach 2:
The measurement of across-wafer variations and the production exposure process are merged into a single integrated operation. By incorporating test patterns into the production wafer and exposing them simultaneously with production fields, the system collects calibration data without sacrificing productivity. The overlapping exposure fields serve dual purposes: production patterning and variation characterization.
3Manufacturing precision
If across-wafer variations are not accounted for, then the process is simple, but manufacturing precision deteriorates
Solution Approach 1:
The system measures across-wafer variations using exposed test patterns and feeds this information back to correct OPC model parameters. The measured position-dependent variations are used to adjust the exposure model, which then compensates for these variations in subsequent exposures. This feedback loop continuously improves pattern transfer fidelity by adapting to actual wafer-specific variations.
Solution Approach 2:
The exposure system dynamically adjusts OPC model parameters based on measured across-wafer variations. By changing the model parameters to account for position-dependent effects such as focal plane curvature and illumination non-uniformity, the system maintains high manufacturing precision across the entire wafer surface without requiring hardware modifications.
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 minimizes measurement errors induced by across-wafer variations and provides accurate OPC model calibration and illuminator characterization, improving the fidelity of pattern transfer and imaging performance.
Implementation Method 1
Upon exposure to radiation chemical reactions are initiated within the resist that ultimately change the resist solubility in aqueous solutions
Data Source
AI summary
First and second exposures of a mask onto a wafer are performed such that the exposure field of the second exposure partially overlaps the exposure field of the first exposure. A characteristic of a set of features is determined, and a value of a parameter of an optical proximity correction model is determined. An alignment feature can be used to align a measurement tool. In yet another embodiment, pupil intensity distribution of an imaging system is measured by exposing an image field of a radiation detector with a bright feature, positioning the detector at a distance away from the image plane, and exposing the image field of the detector with a bright feature, resulting in a cumulative exposure of the image field of the detector from the two exposures. A characteristic of a spatial pattern in the cumulative exposure of the image field of the detector is then determined.