Binary Light Pattern Projection for 3D Surface Profile Reconstruction
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Solution Overview
Problem
Current three-dimensional inspection technologies for small, highly specular, and textureless surfaces such as wafer bumps in IC packaging are limited by slow speed, low resolution, brightness saturation, and noise sensitivity, making them inefficient for accurate defect detection.
Innovation Solution
A method using a binary light pattern projection system where a binary string of '1's and '0's is projected onto the surface, with the pattern shifted multiple times to capture images, allowing for the calculation of surface heights relative to a reference plane, thereby overcoming issues of image brightness saturation and noise sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional inspection technologies (laser triangulation, confocal microscopy) are used for wafer bumps, then three-dimensional measurement capability is achieved, but inspection speed is slow and resolution is limited
Solution Approach 1:
The continuous light pattern is segmented into discrete binary patterns (0 and 1 states), allowing parallel processing of multiple surface points simultaneously. This segmentation enables the system to capture three-dimensional information across the entire wafer bump surface in a single exposure rather than scanning point-by-point, thereby dramatically increasing inspection speed while maintaining measurement precision.
Solution Approach 2:
The system employs periodic switching between binary light patterns (on/off states) to encode depth information. By projecting a sequence of binary patterns with different spatial frequencies and analyzing the phase shift of reflected light, the system achieves accurate three-dimensional reconstruction at high speed without mechanical movement, resolving the contradiction between measurement precision and inspection speed.
2Measurement precision
If gray-level pattern projection is used for surface inspection, then three-dimensional reconstruction is achieved, but the system suffers from brightness saturation and high noise sensitivity
Solution Approach 1:
The gray-level intensity information is segmented into binary states (0 and 1), eliminating the problems of brightness saturation and noise sensitivity associated with continuous gray-level patterns. Each binary pattern provides unambiguous depth encoding without the dynamic range limitations of analog gray-level systems, improving reliability while maintaining three-dimensional reconstruction accuracy.
Solution Approach 2:
The system changes the parameter of light intensity from continuous gray-level values to discrete binary states. This parameter transformation converts a noisy, saturation-prone analog measurement into a robust digital measurement, where each binary state clearly indicates the presence or absence of surface features, thereby eliminating brightness saturation and reducing noise sensitivity.
3Measurement precision
If continuous grating patterns are used for phase displacement measurement, then surface profile reconstruction is achieved, but the system experiences multi-reflection interference and gray-level brightness disturbance
Solution Approach 1:
The continuous grating pattern is segmented into discrete binary patterns, which eliminate multi-reflection interference by providing clear on/off states that are insensitive to reflected light intensity variations. The binary segmentation allows unambiguous phase determination even in the presence of specular reflections from highly reflective wafer bump surfaces, removing the harmful effects of multi-reflection and gray-level disturbance.
Solution Approach 2:
The system uses disposable binary patterns (simple on/off light states) instead of complex continuous gratings. These binary patterns are computationally simple and robust against environmental disturbances, effectively discarding the complexity of continuous gratings that are susceptible to multi-reflection and noise, thereby achieving reliable phase displacement measurement.
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 enables fast and efficient three-dimensional reconstruction of surface profiles with reduced noise, improving the accuracy of defect detection on small IC packaging components like wafer bumps.
Implementation Method 1
projecting a binary pattern of light onto the surface of the object... obtaining an image of the binary pattern illuminating the surface
Data Source
AI summary
A system for three-dimensional reconstruction of a surface profile of a surface of an object is provided that utilizes a binary pattern projected onto the surface of the object. A binary string consisting of a series of “1”s and “0”s is first created, and a binary pattern of light that is constructed in accordance with the binary string such that bright and dark bands of light of equal widths correspond to “1”s and “0”s from the binary string respectively is projected onto the surface. The binary pattern is shifted with respect to the surface multiple times, during which an image of the binary pattern illuminating the surface is obtained at each position of the binary pattern. Thereafter, a height of each predetermined point on the surface is calculated relative to a reference plane based upon the images cumulatively obtained at said predetermined point.