Focus-Sensitive Metrology Target for EUV Overlay Error Correction
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Solution Overview
Problem
Existing focus control methods in extreme ultraviolet lithography are inefficient due to high measurement acquisition times and incompatibility with focus and overlay metrology using a single target, particularly when dealing with focus-induced overlay metrology errors.
Innovation Solution
A focus-sensitive metrology target system that includes segmented pattern elements on multiple layers, allowing for simultaneous focus control and overlay measurement, with a controller system to determine focus-offset values and provide corrections to fabrication tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing focus control methods are used, then focus measurement can be obtained, but measurement acquisition time is excessive
Solution Approach 1:
The metrology target is divided into multiple segmented pattern elements (first pattern elements and second pattern elements) with different geometries. Each segment responds differently to focus variations, enabling parallel measurement of multiple focus parameters simultaneously, thereby reducing total measurement acquisition time while maintaining precision
Solution Approach 2:
The metrology target structure is designed to serve multiple functions: it enables both focus measurement and overlay measurement using a single target. The different pattern elements respond to different measurement modes, allowing the same physical structure to provide multiple measurement outputs without requiring separate measurement systems
2Adaptability or versatility
If existing focus control methods are used, then focus measurement is possible, but focus and overlay metrology cannot be performed using a single target
Solution Approach 1:
The metrology target incorporates multiple pattern elements with different geometries that respond to both focus variations and overlay misalignment. By designing the target structure to contain elements sensitive to different parameters, a single target can simultaneously provide focus measurement data and overlay measurement data, eliminating the need for separate measurement systems
Solution Approach 2:
The patent utilizes the vertical dimension by forming pattern elements on different layers (first layer and second layer) of the substrate. This multi-layer structure enables differentiation between focus effects (which affect all layers) and overlay effects (which affect relative positioning between layers), allowing both measurements to be extracted from a single target structure
3Productivity
If focus control is not properly implemented, then manufacturing process can proceed, but focus-induced overlay metrology errors occur
Solution Approach 1:
The system measures focus and overlay parameters using the segmented metrology target, determines focus-offset values from these measurements, and provides feedback corrections to the fabrication tool. This closed-loop feedback mechanism enables real-time correction of focus drift and overlay errors, maintaining manufacturing precision without sacrificing productivity
Solution Approach 2:
The metrology target is formed as part of the manufacturing process itself, allowing focus and overlay measurements to be taken at the appropriate stage in the fabrication sequence. By integrating the measurement function into the manufacturing flow rather than adding separate measurement steps, the system maintains both productivity and precision
Data Source
AI summary
A focus-sensitive metrology target may be formed and read-out by a fabrication tool. A resulting overlay signal may be translated into a focus offset by comparison to a previously-determined calibration curve. One or more translated signals may be fed back to the fabrication tool for focus correction or used for prediction of on-device overlay (correction of overlay metrology results). In one embodiment, focus and overlay may be measured using a single target, where one portion of the target is formed on a first layer and includes a focus-sensitive design, and where another portion of the target is formed on a second layer and includes a relatively less focus-sensitive design. In some embodiments, a relative difference in focus response may be used to estimate an impact of focus error on device overlay and calculate non-zero offset contributions.