Substrate Edge Detection Using Inverted Sensor Arrangement
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Solution Overview
Problem
Conventional lithographic apparatuses face challenges in accurately aligning substrates due to limited space above the substrate, heat dissipation issues, and air downflow obstructions caused by radiation sources and cables, which affect the precision and reliability of pre-alignment.
Innovation Solution
A substrate handling system with a sensor system that includes a radiation source, imaging system, and reflective element arranged below the substrate, with the reflective element being the only component above the substrate, minimizing space usage and heat dissipation while providing accurate edge detection independent of substrate shape changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the radiation source and detector device are arranged above the substrate, then the sensor system can detect the substrate edge position, but the available space above the substrate is limited and heat dissipation and air downflow obstruction occur
Solution Approach 1:
The patent inverts the conventional arrangement by placing the radiation source and detector device below the substrate instead of above it. This inversion resolves the space occupation problem while maintaining detection functionality through the substrate's transparency to the radiation used.
Solution Approach 2:
The patent transitions from a two-dimensional arrangement (above/below the substrate plane) to utilizing the substrate's thickness dimension, allowing the radiation source and detector to be positioned in the opposite plane while still achieving edge detection through the substrate material.
2Measurement precision
If the radiation source is arranged above the substrate, then the sensor system can measure substrate position, but heat dissipation and ineffective radiation occur at undesirable locations
Solution Approach 1:
By inverting the radiation source position from above to below the substrate, the heat dissipation occurs in the opposite direction, away from the sensitive measurement area and substrate surface, thereby reducing thermal interference with the measurement process.
3Measurement precision
If cables and radiation source are arranged above the substrate, then the sensor system can function, but air downflow is obstructed on the substrate
Solution Approach 1:
Moving the radiation source and cables from above to below the substrate eliminates their obstruction of air downflow, as they are now positioned in the opposite direction where they do not interfere with the airflow pattern required for substrate cooling and contaminant removal.
4Measurement precision
If conventional sensor systems detect light reflected from the bottom surface, then substrate edge position can be determined, but shape differences near the edge change optical properties and reduce alignment reliability
Solution Approach 1:
The patent inverts the detection approach by illuminating from below and detecting light that passes through the substrate rather than reflecting from the bottom surface. This eliminates the interference from edge shape variations that affect bottom surface reflection, as the measurement now depends on the substrate's bulk optical properties which are more uniform.
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 system enhances alignment accuracy and reliability by reducing space occupation and heat-related issues, ensuring precise substrate positioning without obstructing air flow, and maintaining clear imaging of the substrate edge regardless of surface shape variations.
Implementation Method 1
a radiation source and a detector device, wherein the sensor and the detector device are arranged at opposite sides of the substrate
Implementation Method 2
a reflective element arranged at a second side of the substrate, opposite to the first side. The radiation source and the reflective element are positioned relative to each other such that an image of the substrate edge is comprised in the reflected first part and the reflected second part
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a sensor system (PSS) configured to determine a position of a substrate (W) having an edge (WE). The sensor system comprises a radiation source (LS) arranged to emit a radiation bundle (LB), a reflective element (RE), a detector device (DD) and a substrate table (PWT) having a supporting surface for supporting the substrate. The supporting surface is at least partly along a plane. The radiation source and the detector device are arranged on a first side of the plane. The reflective element is arranged on a second side of the plane other than the first side. The reflective element is arranged to create a reflected bundle by reflecting the radiation bundle. The reflective element is arranged to illuminate the edge with the reflected bundle. The detector device is arranged to receive the reflected bundle.