Multi-Camera Die Tilt Inspection on Reflective Surfaces
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Solution Overview
Problem
Current inspection methods for semiconductor dies, such as three-dimensional illumination and White Light Scanning Interferometry, face challenges in accurately determining the tilt angle of semiconductor dies due to total reflection on reflective surfaces and difficulties in forming images when the die is tilted at specific angles, leading to inaccurate predictions of tilt degrees.
Innovation Solution
An apparatus and method utilizing multiple light sources and cameras to capture illumination and pattern images, processing these images to determine outlines, height values, and virtual planes, allowing for the precise calculation of tilt angles even when the surface is reflective or tilted at angles like 1.2 degrees or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three-dimensional illumination light is used to inspect semiconductor die, then the inspection coverage is improved, but the image quality deteriorates due to total reflection on the reflective upper surface
Solution Approach 1:
The patent segments the inspection task into two parts: using a first light source for general illumination to capture the overall die shape and position, and a second light source for pattern projection to capture surface topology. This segmentation allows each light source to perform its specific function without being hindered by the reflective surface, thereby maintaining both inspection coverage and image quality.
Solution Approach 2:
The patent introduces a patterned light source as an intermediary that projects specific patterns onto the die surface. This patterned light acts as a mediator that can penetrate or interact with the reflective surface in a controlled manner, enabling the capture of surface topology information that would otherwise be lost due to total reflection.
2Measurement precision
If White Light Scanning Interferometry is used to conduct tilt inspection, then the measurement capability is improved, but the image formation fails when the die is tilted at certain angles (e.g., 1.2 degrees or more)
Solution Approach 1:
The patent changes the lighting parameters by using multiple light sources with different illumination characteristics. Instead of relying on a single interferometry method that fails at certain tilt angles, the system uses a combination of general illumination and pattern projection, allowing reliable image formation and tilt measurement across a wider range of tilt angles.
Solution Approach 2:
The patent transitions from a single two-dimensional imaging approach to a multi-dimensional approach by combining images from multiple light sources and cameras. This dimensional expansion allows the system to reconstruct the die surface topology and determine tilt angles reliably even when the die is tilted, as the multi-angle illumination captures information that compensates for the tilt-induced image formation failure.
3Device complexity
If two-dimensional area inspection is used to derive tilt degree through parallelogram shape, then the simplicity is improved, but the measurement accuracy deteriorates when the upper surface is made of a reflector
Solution Approach 1:
The patent replaces the simple two-dimensional area inspection method with a more sophisticated optical measurement system that uses pattern projection and multi-camera imaging. This substitution allows the system to accurately measure tilt degrees by analyzing the distortion of projected patterns and the geometry of captured images, overcoming the limitations of reflector surfaces that prevent accurate parallelogram shape acquisition.
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
Enables accurate measurement of tilt angles and generation of virtual three-dimensional models, overcoming issues of total reflection and image clarity, and effectively determining tilt degrees in challenging inspection scenarios.
Implementation Method 1
one or more cameras configured to capture one or more illumination images generated by the illumination light reflected from the object
Data Source
AI summary
The present disclosure provides an apparatus. The apparatus according to the present disclosure comprises: at least one first light source configured to irradiate illumination light to an object on a reference surface; at least one second light source configured to irradiate pattern light to the object, a plurality of cameras configured to capture one or more illumination images and one or more pattern images; and one or more processors configured to determine a plurality of outlines indicating edges of the object based on two or more images captured in different directions among the one or more illumination images and the one or more pattern images; determine a virtual plane corresponding to an upper surface of the object based on the plurality of outlines; and determine an angle between the virtual plane and the reference plane.