Overlay Metrology Optical Heads for Small-Area Layer Alignment
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Solution Overview
Problem
Current overlay metrology solutions in semiconductor manufacturing, primarily based on optics, struggle to provide sufficient resolution for measuring alignment errors between layers or patterns using product features, necessitating the use of larger dedicated overlay targets.
Innovation Solution
An overlay measuring apparatus is developed, comprising a stage and an imaging assembly with multiple optical heads and overlay marks. The apparatus captures images of semiconductor wafers using light reflected from the device and passing through overlay marks, allowing for precise determination of relative positions between patterned layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated overlay targets are used to measure alignment errors, then measurement accuracy is improved, but the measurement area increases beyond product features
Solution Approach 1:
The overlay mark is divided into multiple segments corresponding to different layers, with each segment containing pattern elements from a specific layer. This segmentation allows the measurement to be performed on distributed small features rather than requiring a single large dedicated target, thereby maintaining measurement accuracy while reducing the overall measurement area.
Solution Approach 2:
The overlay mark structure serves multiple functions: it contains pattern elements from multiple layers that need overlay measurement, provides reference marks for alignment, and enables measurement of relative positions between different layer patterns. This multi-functionality eliminates the need for separate dedicated targets for each layer pair, reducing total measurement area while maintaining accuracy.
2Area of stationary object
If product features are used for overlay measurement, then measurement area is reduced, but measurement precision is insufficient
Solution Approach 1:
The overlay mark acts as an intermediary structure that incorporates product feature patterns from multiple layers. Instead of measuring product features directly (which lacks precision) or using large dedicated targets (which increase area), the overlay mark provides a specialized measurement structure that maintains the small footprint of product features while achieving the precision of dedicated targets through its optimized pattern design and measurement methodology.
3Measurement precision
If overlay marks with micro-structures are used, then image resolution is improved, but device complexity increases
Solution Approach 1:
The overlay mark structure nests pattern elements from multiple layers within a single compact mark structure. Each layer's patterns are integrated into the same physical overlay mark, allowing simultaneous measurement of multiple layer pairs without requiring separate complex structures for each, thereby improving resolution while controlling overall device complexity.
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 solution enhances measurement accuracy by using overlay marks with micro-structures arranged in specific configurations, improving image resolution and enabling more precise calculations of relative displacements between layers, thus reducing misalignment issues in semiconductor devices.
Implementation Method 1
The relative positions of the two or more successive patterned layers of the device are determined using light reflected from the device and passing through the respective overlay mark mounted on the optical head
Data Source
AI summary
The present application provides an optical system and a method of operating an overlay measuring apparatus. The overlay measuring apparatus is adapted to determine relative positions of two or more successive patterned layers of a device. The overlay measuring apparatus includes a stage and an imaging assembly. The device is placed on the stage. The imaging assembly includes a plurality of optical heads and a plurality of overlay marks assembled on the optical heads. The relative positions of the two or more successive patterned layers of the device are determined using light reflected from the device and passing through the overlay mark mounted on the respective optical head.