Segmented Mark Structure for E-Beam Alignment Accuracy
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Solution Overview
Problem
Conventional methods for measuring alignment accuracy between layers using box-in-box verniers and testkeys require large areas, are not accurate when embedded in products, and significantly impact throughput due to time-consuming electrical tests.
Innovation Solution
A mark structure with smaller area divisions that can be embedded in products, utilizing electron beam inspection to measure alignment accuracy by counting bright spots and deriving overlay errors and alignment margins, allowing for more precise and efficient measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If box-in-box vernier or testkey is used for alignment measurement, then alignment accuracy can be measured, but the area required is large (40×40 μm2)
Solution Approach 1:
The measurement structure is divided into multiple divisions, each containing multiple parts with patterns of former and latter layers. By segmenting the measurement into multiple smaller units with varying shift distances, the patent achieves comprehensive alignment measurement across the wafer while using a compact overall structure that fits within the product area.
2Measurement precision
If AA vernier is used for alignment measurement, then alignment accuracy can be derived, but the pattern cannot match the product pattern reducing accuracy
Solution Approach 1:
The measurement structure incorporates both product-like patterns and measurement-specific patterns in different regions. The first region contains patterns matching the product for accurate alignment measurement, while the second region contains test patterns for verifying measurement accuracy, allowing the structure to serve dual purposes.
3Measurement precision
If testkey with electrical test is used for alignment measurement, then alignment accuracy can be measured, but the measurement time is long reducing throughput
Solution Approach 1:
The patent replaces the electrical test method with an optical inspection method using bright spot detection. Instead of applying electrical probes to test pads, the system uses optical imaging to detect the presence and position of bright spots formed by aligned patterns, dramatically reducing measurement time while maintaining accuracy.
4Measurement precision
If AA vernier is used for alignment measurement, then alignment accuracy can be measured, but alignment margin cannot be derived
Solution Approach 1:
The measurement structure is designed with multiple divisions having predetermined shift distances before measurement. By pre-configuring divisions with known offset values, the system can directly determine alignment margin by comparing which divisions show bright spots, eliminating the need for additional measurement steps to extract margin information.
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 more accurate alignment measurements with reduced area requirements and faster processing times compared to conventional methods, improving throughput and accuracy.
Implementation Method 1
The respective divisions of the mark structure are irradiated by an electron beam (E-beam)
Data Source
AI summary
A mark structure for measuring the alignment accuracy between a former layer and a latter layer with electron beam inspection (EBI) is described. The mark structure includes multiple divisions, each of which includes at least one region that includes multiple parts each disposed with a pair of a pattern of the former layer and a pattern of the latter layer. In each region, all of the parts have the same distance in a direction between the pattern of the former layer and the pattern of the latter layer. The distance in the direction is varied over the regions of the divisions of the mark structure.