Height Triangulation Using Spatially Incoherent Illumination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical triangulation systems face excessive errors when measuring small wafer bumps due to shape-errors and surface defects, which are not adequately addressed by averaging methods, especially in led-free manufacturing processes.
Innovation Solution
A spatially incoherent illumination method with a unique optical configuration using a narrow strip of light and non-circular aperture stops to maintain a long depth of focus and define illumination and imaging angles, allowing for accurate height measurement of small features by illuminating and imaging with large numerical apertures along the strip and small apertures perpendicular to it, and employing a symmetrical configuration for averaging results from multiple angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser line triangulation is used to measure small wafer bumps, then measurement capability is provided, but excessive shape-error occurs due to the narrow illumination strip width
Solution Approach 1:
The illumination is divided into multiple independent point sources arranged along the illumination direction, creating a spatially incoherent composite illumination pattern. This segmentation allows each point source to illuminate a different portion of the bump, and the combined effect provides comprehensive coverage that eliminates shape-error while maintaining measurement precision.
2Measurement precision
If averaging along the scanning axis is used to reduce shape-error, then measurement accuracy improves for smooth surfaces, but measurement fails completely when surface defects are present
Solution Approach 1:
The illumination is segmented into multiple independent point sources that simultaneously illuminate different portions of the bump from different angles. This creates a spatially incoherent composite pattern that provides redundant measurement paths, allowing the system to tolerate surface defects and maintain both accuracy and reliability without requiring averaging operations.
Solution Approach 2:
The spatially incoherent composite illumination acts as an intermediary that transforms the interaction between light and the bump surface. By creating a multi-component illumination pattern, it enables measurement through surface defects that would otherwise block single-point laser illumination, thereby improving reliability while maintaining accuracy.
3Illumination intensity
If a narrow strip of light is used for illumination, then illumination intensity is high and spatial coherence is good, but the measurable section of the bump is limited
Solution Approach 1:
The illumination strip is segmented into multiple independent point sources distributed along the illumination direction. While each individual point source provides high intensity and spatial coherence, the composite pattern of all point sources simultaneously covers a larger measurable section of the bump, resolving the contradiction between intensity and coverage area.
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
This approach significantly reduces noise from surface roughness and defects, enabling precise height measurement of small wafer bumps by extending the measurable section and averaging errors in a single scan, thereby improving accuracy and reliability.
Implementation Method 1
illuminating the object from a known angle with a narrow strip of light being spatially incoherent, having a large numerical aperture along the light strip and a small numerical aperture perpendicular to the light strip
Implementation Method 2
imaging the object with a large numerical aperture along the light strip and a small numerical aperture perpendicular to the light strip
Data Source
AI summary
A method for height triangulation measurement particularly for measuring the height of an object on a surface, the method includes: a) illuminating said object from a known angle with a narrow strip of light, having a large numerical aperture along said light strip and a small numerical aperture perpendicular to said light strip; b) imaging said object from a known angle having a large numerical aperture along said light strip and a small numerical aperture perpendicular to said light strip, having an image of said object illuminated by said light strip; and c) calculating the height of said object from the location of said light strip on said image.