Lock-in Thermography for Multi-Layer Hot Spot Localization
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Solution Overview
Problem
Existing methods for localizing hot spots in multi-layered semiconductor integrated circuits struggle to distinguish between hot spots that are spatially close or at different depth levels, often resulting in a single anomaly being misidentified when multiple anomalies are present, due to limitations in optical resolution and the ability to differentiate between overlapping thermal images.
Innovation Solution
The method employs lock-in thermography by applying test signals of multiple frequencies to excite hot spots in the DUT, imaging the top surface at timed intervals, and analyzing changes in hot spot images to determine the depth and separation of anomalies, using signal-to-noise ratio and phase shift analysis to differentiate between overlapping thermal responses and separate hot spots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical imaging methods are used to detect hot spots, then the detection process is simple and fast, but the optical resolution is insufficient to distinguish spatially close hot spots
Solution Approach 1:
The patent segments the detection process by applying test signals at multiple different frequencies to excite hot spots at different depth levels separately. By analyzing the frequency-dependent thermal response, the system segments overlapping hot spot signals that would otherwise be indistinguishable in conventional single-frequency imaging, thereby improving localization precision without requiring more complex hardware.
Solution Approach 2:
The patent adds the frequency dimension to the traditional spatial imaging approach. By incorporating frequency as an additional parameter for analyzing thermal responses, the system can differentiate hot spots based on their depth-related frequency characteristics, transforming a 2D spatial problem into a 3D problem (x, y, frequency) that resolves the resolution limitation.
2Measurement precision
If multiple test signals of different frequencies are applied to excite hot spots, then the depth localization accuracy improves, but the testing time and procedure complexity increase
Solution Approach 1:
The patent employs periodic test signals at multiple frequencies applied in a systematic sequence. Each frequency excites thermal responses at specific depth levels, and by periodically cycling through different frequencies and analyzing the cumulative thermal response, the system achieves accurate depth localization while managing total testing time through efficient signal sequencing.
Solution Approach 2:
The system uses feedback from the thermal response analysis to guide the testing process. By analyzing the frequency-dependent thermal responses and identifying which frequencies reveal which depth levels, the system can adaptively determine the minimum necessary frequency range and sequence, optimizing testing time while maintaining depth localization 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
This approach allows for precise localization of multiple hot spots at different depth levels, improving the accuracy of defect identification and enabling targeted further examination by distinguishing between hot spots that appear as a single anomaly, thereby enhancing the efficiency of testing and analysis procedures.
Implementation Method 1
imaging a top surface of the top layer of the DUT at timed intervals to obtain IR images of the DUT
Implementation Method 2
the images are in correlation to a propagation of heat from the hot spots in the DUT
Data Source
AI summary
Localizing hot spots in multi layered device under test (DUT) by using lock-in thermography (LIT) where plural hot spots of electrical circuits are buried in the DUT at different depth layers from a bottom layer to a top layer, comprises applying test signals of multiple frequencies to the electrical circuits of the DUT for exciting the hot spots; imaging a top surface of the top layer of the DUT at timed intervals to obtain IR images of the DUT while the test signal is applied to the electrical circuits wherein the images are in correlation to a propagation of heat from the hot spots in the DUT; detecting the thermal response signals at the timed intervals from the images taken from the DUT; and determining changes in the appearance of hot spot images on the top surface of the DUT in relation to the frequencies of the thermal response signals.