On-axis Focus Sensor Using Beam Splitter for Semiconductor Inspection
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Solution Overview
Problem
High-resolution optical inspection systems face challenges in maintaining focus due to the complexity and expense of existing height sensors, which often require direct integration with the imaging system and can interfere with the imaging process, limiting flexibility and increasing costs.
Innovation Solution
A focus height sensor system that includes a sensor beam source, a reflector, and a sensor to measure the height of a semiconductor device within the field of view, allowing for precise positioning of the object plane without the need for complex mathematical transforms or specialized optical components, enabling efficient and cost-effective focus adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser triangulation sensor is used to measure height within the field of view, then measurement precision is improved, but device complexity and cost increase due to specialized optical components
Solution Approach 1:
A beam splitter is introduced as an intermediary component to separate the measurement beam path from the imaging beam path. The beam splitter directs the laser measurement beam to the substrate while allowing the imaging beam to pass through to the camera, enabling both functions to operate independently without requiring complex integrated optics
Solution Approach 2:
The optical system is segmented into separate measurement and imaging pathways. The measurement system uses a laser beam and beam splitter for height measurement, while the imaging system uses the main optical path for capture, allowing each subsystem to be optimized independently and reducing overall complexity
2Measurement precision
If a height sensor is integrated directly into the optical path, then measurement precision is improved, but the imaging process is interfered with and device complexity increases
Solution Approach 1:
The beam splitter acts as a mediator that separates the measurement and imaging optical paths. It reflects the laser measurement beam toward the substrate while transmitting the imaging beam to the camera, preventing interference between the two processes while maintaining measurement precision
Solution Approach 2:
The system uses temporal separation where the measurement beam is directed to the substrate during measurement cycles, and the imaging beam captures images during imaging cycles. This periodic operation allows both functions to share the optical path without continuous interference
3Measurement precision
If specialized objectives with integrated optical components are used, then measurement precision is improved, but adaptability decreases and cost increases
Solution Approach 1:
The beam splitter and measurement beam source are designed as universal components that can work with multiple different imaging objectives and camera systems. This allows the measurement system to remain constant while the imaging system can be adapted for different resolutions and applications, increasing overall system versatility
Solution Approach 2:
By separating the measurement optics from the imaging optics, the measurement system becomes an independent module that can be used with various imaging systems. This segmentation allows different objectives and cameras to be swapped for imaging purposes without affecting the measurement capability
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 provides a cost-effective, simple, and efficient method to maintain focus in high-resolution optical inspection systems, reducing interference and increasing flexibility by using a reflector and sensor to measure surface height directly within the optical path, ensuring high-quality images without the need for expensive modifications.
Implementation Method 1
A reflector receives the beam of electromagnetic radiation from the sensor beam source and directs the beam toward a surface of a semiconductor device positioned within a field of view of the optical system. The reflector is positioned to receive at least a portion of the beam back from the surface of the semiconductor device to direct the returned beam to a sensor.
Data Source
AI summary
A focus height sensor in an optical system for inspection of semiconductor devices includes a sensor beam source that emits a beam of electromagnetic radiation. A reflector receives the beam of electromagnetic radiation from the sensor beam source and directs the beam toward a surface of a semiconductor device positioned within a field of view of the optical system. The reflector is positioned to receive at least a portion of the beam back from the surface of the semiconductor device to direct the returned beam to a sensor. The sensor receives the returned beam and outputs a signal correlating to a position of the surface within the field of view along an optical axis of the optical system.