Memory Array Inspection via Integer Pixel Imaging
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Solution Overview
Problem
Existing inspection methods for memory cell areas in integrated circuits face challenges in achieving high sensitivity for both memory cells and page breaks simultaneously, with current approaches either sacrificing sensitivity or requiring laborious definition of small care areas, leading to incomplete inspections and positional inaccuracy.
Innovation Solution
The method involves imaging memory arrays at a magnification where memory cell size is a whole integer pixel multiple, using image processing to automatically identify and separate memory cell and page break areas, allowing for pixel-level edge detection and comparison, thereby enabling simultaneous inspection of both areas without sacrificing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mixed mode inspection is used to inspect page breaks in random mode and memory cells in array mode, then both areas can be inspected, but the dynamic range required for imaging page breaks leaves memory cell areas with very low contrast and poor sensitivity
Solution Approach 1:
The inspection method segments the memory array into distinct memory cell areas and page break areas, applying different inspection modes to each segment. Memory cell areas are inspected using array mode with cell-to-cell comparison, while page break areas are inspected using random mode with die-to-die comparison. This segmentation allows each area to be inspected with the optimal mode for its characteristics, resolving the contradiction between coverage and sensitivity.
Solution Approach 2:
The patent applies different inspection qualities and parameters to different regions of the memory array. Care areas are defined with higher sensitivity thresholds specifically for memory cell regions, while page break regions use appropriate thresholds for their characteristics. This local differentiation of inspection quality ensures high sensitivity where needed without compromising overall inspection capability.
2Measurement precision
If small care areas are defined for memory cell areas to avoid page breaks, then inspection sensitivity can be maintained in those areas, but only a portion of memory cell pages can be inspected with array mode and border areas cannot be inspected at high sensitivity
Solution Approach 1:
The patent segments the inspection areas into memory cell care areas and page break areas, with clearly defined boundaries. By using automatic care area definition based on the integer pixel multiple imaging, the system can precisely delineate where high-sensitivity array mode inspection should be applied versus where random mode is appropriate, maximizing both sensitivity and coverage without manual intervention.
Solution Approach 2:
The inspection system automatically defines care areas based on the imaging parameters and detected pattern edges, eliminating the need for manual definition by users. The system self-determines the optimal care area boundaries by analyzing the integer pixel alignment and pattern repetition, thereby maximizing inspection coverage while maintaining sensitivity without requiring laborious user input.
3Measurement precision
If array mode inspection is used for memory cells, then high sensitivity can be achieved through cell to cell comparisons, but defects close to pattern edges cannot be detected due to care area borders excluded from inspection
Solution Approach 1:
The patent performs preliminary identification of pattern edges and care area boundaries before conducting the actual defect inspection. By using the integer pixel multiple imaging to pre-establish accurate care area definitions, the system can then extend inspection coverage to border areas that were previously excluded, detecting defects near edges with high confidence before the main inspection process begins.
Solution Approach 2:
The patent changes the imaging parameter to use an integer pixel multiple magnification, which fundamentally alters how care areas are defined and enables border area inspection. This parameter change allows the system to maintain the sensitivity of array mode inspection while extending coverage to previously problematic border regions, as the integer pixel alignment provides natural, precise boundaries for care area definition.
4Productivity
If page breaks are inspected using die to die comparisons in random mode, then page break areas can be inspected, but sensitivity degrades due to variation from die to die
Solution Approach 1:
The patent segments the inspection task by dedicating random mode die-to-die comparison specifically to page break areas, while reserving array mode cell-to-cell comparison for memory cell areas. This segmentation ensures that each inspection mode is applied where it is most effective, accepting the reduced sensitivity in page break inspection as an acceptable trade-off for achieving comprehensive coverage of these inherently variable regions.
Data Source
AI summary
A method of inspecting an array having memory blocks and page breaks. The array is imaged, and the image is divided into sections. Sections that include the memory blocks are selected into a candidate image. Pixels within a boundary horizontal line of pixels are inspected to determine horizontal edges of the memory blocks. Pixels within a boundary vertical line of pixels are inspected to determine vertical edges of the memory blocks. An image of a first memory block is compared to an image of a second memory block to determine differences. The differences are flagged as potential memory block defects. Images of the page breaks are compared to determine differences, and the differences are flagged as potential page break defects.