Pre-Bond Optical Inspection Using SLM Pattern Suppression
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Solution Overview
Problem
Existing pre-bonding inspection systems struggle to effectively detect small point defects such as particles, chips, cracks, or excessive topographical variations on chiplets and substrates due to optical signals from large geometrical patterns obscuring the detection of smaller defects, leading to post-bonding defects and costly wastage.
Innovation Solution
An optical inspection system using a spatial light modulator (SLM) to block optical signals from large periodic patterns while enhancing signals from small defects, allowing for precise defect detection and location mapping, followed by corrective actions before bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If optical inspection is performed on substrates with large geometrical patterns, then the inspection coverage is improved, but the detection precision of small point defects deteriorates due to signal obscuration
Solution Approach 1:
The optical signal from the substrate surface is segmented into different spatial frequency components. Large geometrical patterns produce low spatial frequency signals that are separated and blocked by the spatial light modulator, while small point defects produce high spatial frequency signals that pass through to the detector, enabling selective detection
Solution Approach 2:
A spatial light modulator is introduced as an intermediary component between the sample and the detector. This intermediary selectively modulates the optical signals based on their spatial characteristics, blocking signals from large patterns while transmitting signals from small defects, thereby resolving the signal obscuration problem
2Productivity
If the substrate size is increased to host multiple chiplets, then the productivity is improved, but the loss of substance increases due to post-bonding defects from undetected point defects
Solution Approach 1:
The inspection system performs preliminary detection of point defects on substrates before the bonding process. By identifying and flagging substrates with critical defects prior to bonding, the system enables corrective actions to be taken, preventing post-bonding failures and reducing wastage of expensive chiplets and large substrates
3Device complexity
If conventional optical inspection methods are used, then the device complexity is kept low, but the measurement precision deteriorates due to inability to separate defect signals from pattern signals
Solution Approach 1:
A spatial light modulator is introduced as an intermediary component between the sample and the detector. This intermediary selectively modulates the optical signals based on their spatial characteristics, blocking signals from large patterns while transmitting signals from small defects, thereby resolving the signal obscuration problem
Solution Approach 2:
The system changes the spatial frequency parameter of the optical signals by using the spatial light modulator to selectively block low spatial frequency components (from large patterns) while transmitting high spatial frequency components (from small defects), achieving signal separation without complex mechanical systems
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
Enhances detection of small defects, reducing post-bonding defects and improving yield by enabling corrective processes during the chip-to-substrate hybrid bonding process.
Implementation Method 1
optical signals from small point defects is buried in large optical signals from features (e.g., metallic interconnects) in certain geometrical patterns
Implementation Method 2
optical signals from small point defects is buried in large optical signals from features
Implementation Method 3
a measurement lens configured to transmit a beam of light transmitted through the transmissive SLM
Implementation Method 4
an optical fiber, a transmissive spatial light modulator (SLM)... and a measuring beam path through which a beam of light from the optical fiber is incident on and reflected at the surface of the sample
Data Source
AI summary
An optical inspection system for pre-bonding inspection includes a stage having a surface on which a sample to be inspected is placed, the surface of the sample having a two dimensional (2D) periodic pattern and defects, an optical fiber, a transmissive spatial light modulator (SLM), a measurement lens configured to transmit a beam of light transmitted through the transmissive SLM, a camera configured to detect the transmitted beam of light from the measurement lens, and a measuring beam path through which a beam of light from the optical fiber is incident on and reflected at the surface of the sample on the stage, and transmitted to the transmissive SLM, wherein the transmissive SLM is configured to block the beam of light reflected by the 2D periodic pattern on the surface of the sample.