Pump-Probe Thermo-Reflectance for Void Detection in Interconnects
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Solution Overview
Problem
The detection of voids in metal interconnects during the deposition process in integrated circuit devices is difficult due to their optical opacity, making current optical metrology and destructive techniques unsuitable for in-line monitoring.
Innovation Solution
A non-destructive pump-probe technique using modulated pump and probe lasers to measure thermo-reflectance changes, allowing for the detection of voids and abnormalities in metal interconnects by analyzing the thermal response through optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical metrology techniques are used to monitor the deposition process, then the detection speed and non-destructive measurement are improved, but the detection capability is worsened due to optical opacity of metal interconnects
Solution Approach 1:
The patent introduces an intermediary substance (liquid crystal material) that mediates between the optical measurement system and the metal interconnect. This liquid crystal material is applied to the sample surface and exhibits optical anisotropy that changes in response to thermal fields generated by the metal interconnect, thereby enabling optical detection of otherwise optically opaque metal structures through thermal field mapping
Solution Approach 2:
The patent replaces direct optical interaction with metal interconnects (which fails due to opacity) with a thermal field-based detection mechanism. By using the liquid crystal's thermal response to indirect thermal fields from the metal, the system substitutes direct optical-mechanical interaction with a thermal-optical indirect measurement approach
2Measurement precision
If cross-section SEM or transmissive TEM are used to detect voids, then the measurement precision is improved, but the productivity is worsened due to destructive and slow nature of these techniques
Solution Approach 1:
The liquid crystal material applied to the sample surface serves multiple functions simultaneously: it acts as a thermal field sensor, an optical contrast enhancer, and a non-destructive interface layer. The material's inherent optical anisotropy and thermal response properties enable it to self-generate the necessary optical contrast for void detection without requiring additional processing or destruction of the underlying metal interconnect structure
Solution Approach 2:
The patent exploits the color/optical property changes of liquid crystal materials in response to thermal fields. The liquid crystal exhibits different optical orientations and colors based on local thermal variations caused by voids in the metal interconnect, allowing visual or optical detection of defects through color/orientation changes rather than direct structural imaging
3Reliability
If in-line monitoring is implemented during deposition, then the process control is improved, but the measurement technique is worsened by the optical opacity of metal interconnects
Solution Approach 1:
The liquid crystal material is applied to the sample surface before or during the deposition process to enable real-time monitoring. This preliminary application of the sensing material allows the thermal field mapping capability to be in place before metal interconnects are formed, enabling continuous in-line monitoring throughout the deposition process rather than post-processing inspection
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
Enables fast and accurate in-line detection of voids and other structural abnormalities in metal interconnects, improving process control and device performance by providing non-contact, non-destructive measurement of thermal conductivity.
Implementation Method 1
a pump probe measurement comprises: illuminating the sample by a laser pump beam that is modulated by a modulation frequency... determining, based on the detected radiation, thermo-reflectance information regarding a sample region located at a depth of the sample; thermo-reflectance information comprises information about an oscillatory component of a thermal response of the sample
Implementation Method 2
illuminating the sample by a laser probe beam; detecting radiation resulting from the illumination of the sample; determining, based on the detected radiation, thermo-reflectance information regarding a sample region
Data Source
AI summary
A method for evaluating a sample, the method includes performing one or more pump probe measurements, wherein a pump probe measurement includes (i) illuminating the sample by a laser pump beam that is modulated by a modulation frequency; (ii) illuminating the sample by a laser probe beam; (iii) detecting radiation resulting from the illumination of the sample; (iv) determining, based on the detected radiation, thermo-reflectance information regarding a sample region located at a depth of the sample; wherein the thermo-reflectance information comprises information about an oscillatory component of a thermal response of the sample measured during the pump probe measurement; and (v) determining a presence of one or more sample abnormalities based on the analysis results.