Equi-resistant probe distribution for wafer-level voltage measurements
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Solution Overview
Problem
The accuracy of parametric measurements in semiconductor devices, particularly high-current devices like power MOSFETs, is compromised due to variations in resistance between multiple probe needles contacting the same pad, affecting the measurement of ON resistance.
Innovation Solution
The positioning of probe needles is optimized to create equi-resistant paths between force and sense needles, reducing variations in resistance and improving measurement accuracy by averaging voltages across different contact points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple probe needles are used to deliver test current to high-current devices, then the current capacity is sufficient, but the measurement accuracy deteriorates due to resistance variations between needles
Solution Approach 1:
The patent segments the measurement function by separating force needles (delivering current) from sense needles (measuring voltage). This segmentation allows multiple needles to share current delivery while dedicated sense needles provide accurate voltage measurements, resolving the contradiction between current capacity and measurement accuracy.
Solution Approach 2:
The patent introduces sense needles as intermediary elements that mediate between the force needles and the measurement system. These sense needles provide a dedicated path for accurate voltage measurement, isolating the measurement function from the resistance variations inherent in current-delivering force needles.
2Power
If multiple probe needles contact the same pad, then the current delivery capability increases, but the resistance variations between needle paths increase
Solution Approach 1:
The patent segments the needle functions into force needles for current delivery and sense needles for voltage measurement. This segmentation ensures that multiple needles can contact the same pad for current delivery while dedicated sense needles provide stable reference points, reducing the impact of resistance variations.
Solution Approach 2:
The patent applies local quality by positioning sense needles at specific locations on the pad where they contact points with low and stable resistance. This localized optimization ensures that while force needles may have varying resistance paths, the sense needles maintain consistent contact quality at their specific positions.
3Area of stationary object
If probe needles are positioned closer together, then the contact area is reduced, but the resistance variation between paths increases
Solution Approach 1:
The patent resolves this contradiction by transitioning from a one-dimensional consideration (needle spacing) to a two-dimensional arrangement. Force needles and sense needles are positioned in different spatial relationships on the pad surface, with sense needles strategically placed to minimize resistance path variations while maintaining adequate contact area.
Solution Approach 2:
The patent optimizes local contact quality by positioning sense needles at specific locations on the pad where the contact resistance is minimized and most stable. This localized optimization allows for reduced overall contact area while maintaining low resistance variation through strategic sense needle placement.
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 enhances the accuracy of ON resistance measurements for semiconductor devices with low ON resistance, such as 1 milliohm or less, and high-current devices exceeding 10 A, by compensating for contact resistance variations and averaging voltages effectively.
Implementation Method 1
the tips of the plurality of first needles are positioned so as to provide equi-resistant paths between tips of the first needles to a nearest tip of a needle of the at least one second needle
Data Source
AI summary
A test system and test techniques for accurate high-current parametric testing of semiconductor devices. In operation, the test system supplies a current to the semiconductor device and measures a voltage on the device. The testing system may use the measured voltage to compute an ON resistance for the high-current semiconductor device. In one technique, multiple force needles contact a pad in positions that provide equi-resistant paths to one or more sense needles contacting the same pad. In another technique, current flow through the force needles is regulated such that voltage at the pad of the device under test is representative of the ON resistance of the device and independent of contact resistance of the force needle. Another technique entails generating an alarm indication when the contact resistance of a force needle exceeds a threshold.