Bump Height Metrology With Virtual Penetration Error Correction
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Solution Overview
Problem
Visual light based triangulation methods fail to accurately measure the height difference between the top of bumps and the upper surface of partially transparent top layers due to virtual penetration depth errors, as they measure a virtual reflection plane instead of the actual surface, leading to unreliable height measurements.
Innovation Solution
A method and system that combines white light triangulation with reflectometry or chromatic confocal measurements to determine the height difference by correcting for virtual penetration depth errors using the refraction index of the top layer, allowing concurrent or partially overlapping execution of measurements to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If visual light based triangulation is used to measure bump height, then the measurement process is simple and fast, but the measurement precision deteriorates due to virtual penetration errors caused by the partially transparent top layer
Solution Approach 1:
The patent introduces a second measurement system (reflectometry or chromatic confocal) as an intermediary to measure the virtual penetration depth. This intermediary measurement allows correction of the first measurement errors without requiring a complete redesign of the measurement approach, thus resolving the contradiction between speed and precision.
Solution Approach 2:
The patent implements a feedback mechanism where the second measurement system provides correction data to adjust the first measurement results. The processing unit uses the virtual penetration depth information from the second system to correct the height measurements from the first system, continuously improving measurement accuracy while maintaining the original fast measurement capability.
2Difficulty of detecting and measuring
If the top layer is made partially transparent for optical measurements, then optical penetration allows depth measurement, but measurement reliability deteriorates due to inability to accurately determine the upper surface position
Solution Approach 1:
The patent uses the virtual penetration depth measurement as an intermediary parameter to bridge the gap between optical penetration capability and reliable surface position measurement. By measuring how deep the optical signal effectively penetrates, the system can correct the apparent surface position to determine the actual upper surface location reliably.
Solution Approach 2:
The patent changes the measurement parameter from direct surface position detection to virtual penetration depth measurement. This parameter transformation allows the system to work with the partially transparent property of the top layer while achieving reliable measurement results through mathematical correction based on the measured penetration depth.
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 reliable and accurate estimation of the height difference between bump tops and the upper surface of transparent layers by compensating for measurement errors, ensuring precise measurements across multiple bumps on a wafer.
Implementation Method 1
Visual light based triangulation may scan the bumps and the top layer to provide height measurements
Implementation Method 2
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. While the light is reflected by the top surface of the base layer
Implementation Method 3
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 4
The performing of the second measurements may include performing reflectometry
Implementation Method 5
The performing of the second measurements may include performing chromatic confocal measurements
Data Source
AI summary
A method that 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 resulting from a virtual penetration of the first illumination into the layer; wherein each bump has a corresponding area that is proximate to the bump; preforming second measurements of thickness of the layer at the corresponding areas; wherein at least some of the first measurements are executed in parallel to an executing of at least some of the second measurements; determining first measurement errors, based on the second measurements; and determining the height differences between the bumps and the corresponding areas based on the first measurements and the first measurements errors.