Bump Height Metrology Using Triangulation and Interferometry
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Solution Overview
Problem
Existing visual light-based triangulation methods fail to accurately measure the height difference between the top of bumps and the upper surface of a partially transparent top layer due to the unknown virtual penetration depth, leading to unreliable measurements.
Innovation Solution
A method and system that combines white light triangulation with interferometry to measure the height difference, using first and second radiation to account for measurement errors, where the second radiation does not penetrate the top layer, and employs extrapolation to correct for errors in the first measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If visual light based triangulation is used to measure bump height, then measurement speed is improved, but measurement precision deteriorates due to unknown virtual penetration depth
Solution Approach 1:
The measurement process is divided into two distinct phases: a first measurement phase using white light triangulation for rapid scanning of all bumps, and a second measurement phase using interferometry for precise measurement of a subgroup. This segmentation allows each method to operate in its optimal regime, combining speed and precision throughout the measurement process.
Solution Approach 2:
A correction factor is introduced as an intermediary element that bridges the two measurement methods. The correction factor, derived from comparing the fast but imprecise triangulation measurements with the slow but precise interferometry measurements, is then applied to all triangulation measurements to compensate for the virtual penetration depth effect, enabling both speed and precision.
2Measurement precision
If interferometry is used to measure bump height, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The measurement process is divided into two distinct phases: a first measurement phase using white light triangulation for rapid scanning of all bumps, and a second measurement phase using interferometry for precise measurement of a subgroup. This segmentation allows each method to operate in its optimal regime, combining speed and precision throughout the measurement process.
Solution Approach 2:
The fast white light triangulation measurements serve a dual purpose: they provide rapid initial data for all bumps and simultaneously serve as a reference to calculate the correction factor when compared with the interferometry measurements. This self-service approach allows the faster method to contribute to improving the accuracy of the slower method without requiring separate calibration procedures.
3Area of stationary object
If white light triangulation is used for height measurement, then measurement coverage is improved, but measurement accuracy deteriorates due to virtual penetration depth
Solution Approach 1:
The measurement process is divided into two distinct phases: a first measurement phase using white light triangulation for rapid scanning of all bumps, and a second measurement phase using interferometry for precise measurement of a subgroup. This segmentation allows each method to operate in its optimal regime, combining speed and precision throughout the measurement process.
Solution Approach 2:
The system uses feedback from the interferometry measurements to correct the triangulation measurements. By comparing the two measurement methods and calculating a correction factor based on the known relationship between them, the system continuously refines the height measurements, ensuring both comprehensive coverage and high accuracy.
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
Provides accurate and reliable height difference measurements between bumps and the top layer surface by minimizing measurement errors through a combination of triangulation and interferometry, offering a trade-off between accuracy and time efficiency.
Implementation Method 1
The light changes its propagation angle when entering the top layer—due to a difference between the refraction index of the air and the refraction index of the top layer
Implementation Method 2
While the light is reflected by the top surface of the base layer
Implementation Method 3
performing second measurements of height differences between a subgroup of the bumps and a subgroup of the corresponding areas, by illuminating the subgroup of the bumps and the subgroup of the corresponding areas with second radiation that does not penetrate the layer
Data Source
AI summary
A method for measuring height differences between tops of multiple bumps of an upper surface of a layer, the method may include performing first measurements of the height differences between the bumps and the corresponding areas, by illuminating the bumps and the corresponding areas with first radiation; wherein the first measurements are subjected to first measurement errors; and determining the height differences between the bumps and the corresponding areas based on the first measurements and the first measurements errors.