Confocal Inspection for Vertical Stack Memory Defect Depth
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Solution Overview
Problem
Current semiconductor wafer inspection systems are inadequate for detecting defects in vertical semiconductor devices like 3D or VNAND memory, as they struggle with depth localization and material classification due to limitations in lithography and process steps, leading to increased costs and reduced manufacturing efficiency.
Innovation Solution
A confocal inspection method that focuses an illumination beam at multiple depths using a wavelength range of 700 nm to 950 nm, inhibiting out-of-focus light to generate in-focus images, allowing for accurate defect localization and material classification within vertical stacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional wafer inspection systems are used, then manufacturing costs are reduced, but depth localization and material classification accuracy deteriorate in vertical semiconductor devices
Solution Approach 1:
The patent transitions from conventional 2D planar inspection to 3D vertical inspection by implementing multiple focal planes at different depths (e.g., 0 μm, 2 μm, 4 μm, 6 μm). This dimensional extension enables depth localization of defects within vertical stacks, allowing the system to determine which focal plane contains the defect based on where the defect appears in focus across multiple images.
Solution Approach 2:
The inspection process is segmented into multiple discrete focal planes rather than attempting to inspect the entire vertical stack in a single plane. The system captures images at different depths separately, then processes these segmented images to determine defect depth and material classification, making the complex 3D inspection problem manageable through systematic division.
2Measurement precision
If multiple focal planes are used for depth localization, then measurement precision improves, but inspection time increases
Solution Approach 1:
The system employs periodic scanning through multiple focal planes in a systematic sequence (e.g., 0 μm, 2 μm, 4 μm, 6 μm). By periodically cycling through these predetermined depth levels and capturing images at each, the system efficiently locates defects at specific depths without requiring continuous or exhaustive scanning of all possible positions.
Solution Approach 2:
The inspection methodology performs preliminary actions by first capturing images at multiple focal planes to identify which plane contains the defect. This preliminary depth localization step enables subsequent focused analysis only at the relevant depth level, avoiding the need to analyze all focal planes in detail and thereby reducing overall inspection time.
3Measurement precision
If out-of-focus light is inhibited, then measurement precision improves, but device complexity increases
Solution Approach 1:
The system introduces an intermediary optical element (such as a confocal pinhole or aperture) positioned at the focal plane to selectively transmit in-focus light while blocking out-of-focus light. This intermediary component acts as a spatial filter that enables high-contrast imaging at each focal plane without requiring complex post-processing or additional sensors.
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 enables precise detection of defects at various depths within thick vertical stacks, improving manufacturing yields and reducing costs by enhancing the accuracy and efficiency of defect identification in 3D semiconductor structures.
Implementation Method 1
repeatedly focusing an illumination beam at a plurality of focus planes at a plurality of different depths of a first vertical stack
Implementation Method 2
out-of-focus light is inhibited from reaching the detector of the confocal system and inhibited from contributing to generation of the in-focus images
Data Source
AI summary
Disclosed are methods and apparatus for inspecting a vertical semiconductor stack of a plurality of layers is disclosed. The method includes (a) on a confocal tool, repeatedly focusing an illumination beam at a plurality of focus planes at a plurality of different depths of a first vertical stack, wherein a defect is located at an unknown one of the different depths and the illumination beam has a wavelength range between about 700 nm and about 950 nm, (b) generating a plurality of in-focus images for the different depths based on in-focus output light detected from the first vertical stack at the different depths, wherein out-of-focus output light is inhibited from reaching the detector of the confocal system and inhibited from contributing to generation of the in-focus images, and (c) determining which one of the different depths at which the defect is located in the first vertical stack based on the in-focus images.