Overlay Target Assist Features for Edge Effect Reduction
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Solution Overview
Problem
Current micro-diffraction based overlay (μDBO) targets in semiconductor wafer metrology face challenges with edge effects and reduced available grating area, leading to poor reproducibility and accuracy in overlay measurements due to large edge intensities and contamination from optical crosstalk.
Innovation Solution
The introduction of metrology tool-driven optical proximity correction (MT-OPC) assist features at the periphery and between gratings, with smaller pitch than the gratings, to reduce measured intensity peaks and enhance pattern recognition, optimizing the target layout for improved metrology process response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If smaller target sizes are used to limit real-estate consumption on production wafers, then area efficiency is improved, but measurement precision deteriorates due to edge effects and reduced grating area
Solution Approach 1:
Assist features are introduced as intermediary elements between the measurement beam and the grating structures. These assist features modify the optical field distribution to reduce edge effects and enhance the measurement signal from the gratings, thereby improving measurement precision while maintaining small target sizes
Solution Approach 2:
The pitch of assist features is specifically designed to be smaller than the grating pitch, creating a parameter difference that allows the assist features to affect the optical measurement without interfering with the grating structure itself. This parameter optimization resolves the contradiction between small target size and measurement precision
2Measurement precision
If assist features with smaller pitch are introduced to reduce edge effects, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The target is segmented into distinct functional components: assist features for edge effect reduction and gratings for measurement. This segmentation allows each component to be optimized independently for its specific function, improving overall measurement precision while managing complexity through functional separation
3Reliability
If assist features are added to reduce intensity peaks and improve pattern recognition, then measurement reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The assist features are designed to automatically perform the function of reducing edge effects and improving pattern recognition through their geometric configuration and pitch relationships with the gratings. This self-service mechanism improves measurement reliability without requiring additional active control systems or complex manufacturing processes
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 reduces edge effects, increases the available grating area, and improves pattern recognition, leading to enhanced reproducibility and sensitivity of overlay measurements, allowing for more accurate and reliable detection of grating structures.
Implementation Method 1
introduction of metrology tool-driven optical proximity correction (MT-OPC) assist features
Implementation Method 2
A fast and non-invasive form of specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured
Implementation Method 3
properties of the scattered or reflected beam are measured
Data Source
AI summary
A method of devising a target arrangement, and associated target and reticle. The target includes a plurality of gratings, each grating having a plurality of substructures. The method includes: defining a target area; locating the substructures within the target area so as to form the gratings; and locating assist features at the periphery of the gratings, the assist features being configured to reduce measured intensity peaks at the periphery of the gratings. The method may include an optimization process including modelling a resultant image obtained by inspection of the target using a metrology process; and evaluating whether the target arrangement is optimized for detection using a metrology process.