Wafer Focus Control via Selective Z-Stage Adjustment
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Solution Overview
Problem
As semiconductor devices miniaturize, finer patterns require effective automatic focus control to prevent and limit defocusing during visual inspection, but existing technologies struggle to accurately adjust focus based on varying light intensities and inspection areas.
Innovation Solution
An automatic focus controlling apparatus that includes a light detector, controller, focus error corrector, and stage driver, which generates driving signals to adjust the z-axis position of a wafer stage based on light intensity and area signals, ensuring focus control only at highly reflective areas and maintaining position at less reflective areas to prevent defocus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If automatic focus control is continuously performed across the entire wafer surface, then focus accuracy is improved, but defocus occurs at step structures due to z-axis position changes
Solution Approach 1:
The patent applies local quality by differentiating focus control behavior between different regions of the wafer. The controller determines whether the current inspection area is a step structure or a flat surface, and selectively applies focus control only to flat surfaces while maintaining fixed z-axis position over step structures. This regional differentiation resolves the contradiction by allowing high focus accuracy where needed without causing defocus at step structures.
2Measurement precision
If focus control is performed at all areas, then image clarity is improved, but inspection time increases due to continuous z-axis adjustments
Solution Approach 1:
The patent segments the wafer inspection area into different types: step structure areas and flat surface areas. By dividing the inspection space and applying different focus control strategies to each segment, the system achieves image clarity only where necessary (flat surfaces) while avoiding unnecessary z-axis adjustments over step structures, thereby reducing total inspection time.
Solution Approach 2:
The patent implements periodic action by using a predetermined pattern to identify step structure areas in advance. The controller periodically references this pattern during inspection to determine whether focus control should be applied at the current location, enabling selective and efficient focus adjustments that reduce overall inspection time while maintaining image clarity where needed.
3Measurement precision
If z-axis position is frequently adjusted for focus control, then focus precision is improved, but system stability deteriorates due to continuous position changes
Solution Approach 1:
The patent applies preliminary anti-action by using a predetermined pattern to identify step structure areas before inspection begins. This advance knowledge allows the controller to preemptively avoid making z-axis adjustments over step structures during inspection, preventing the instability that would result from frequent position changes while maintaining focus precision over flat surfaces where adjustments are necessary.
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
The apparatus effectively adjusts focus to maintain clear images by differentiating between highly reflective and less reflective areas, preventing defocus and ensuring accurate inspection, thereby enhancing the clarity and precision of semiconductor device inspections.
Implementation Method 1
a light detector configured to receive reflected light reflected by a surface of a wafer and generate a light reception signal based on the received light
Data Source
AI summary
An automatic focus control apparatus includes a light detector, which receives light reflected by a surface of a wafer and generates a light reception signal based on the received signal, a controller, which generates a driving signal, the driving signal being one of a first signal and a second signal, the driving signal indicating whether to perform automatic focus control based on the light reception signal, a focus error corrector, which generates a focus error correction signal based on the driving signal, and a stage driver, which displaces a wafer stage supporting the wafer by adjusting the z-axis position of the wafer stage based on the focus error correcting signal if the driving signal is the first signal, and maintains the z-axis position of the wafer stage based on the focus error correction signal if the driving signal is the second signal.