Overlay Error Measurement Model for Lithographic Apparatus
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Solution Overview
Problem
Current methods for determining overlay error in lithographic processes are inaccurate due to variations in illumination mode, polarization, and aberrations, as well as differences in geometry and surrounding structures between dedicated targets and features of interest.
Innovation Solution
A method involving measuring the overlay error of a target and using a model to determine the overlay error of a feature, which accounts for relative differences in illumination, position, and feature characteristics, based on lithographic apparatus metrology inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If overlay error is measured using dedicated targets in scribe lane, then measurement can be performed, but measurement precision deteriorates due to differences in illumination mode, polarization, and aberrations between targets and features
Solution Approach 1:
The patent segments the overlay error determination process into two independent components: (1) measuring the overlay error of the dedicated target using scatterometry, and (2) separately determining the relative overlay error between the target and feature using a model that accounts for illumination mode, polarization, and aberrations. This segmentation allows each component to be optimized independently, resolving the contradiction between measurability and accuracy.
Solution Approach 2:
The patent introduces a model as an intermediary that bridges the gap between the measured target overlay error and the actual feature overlay error. This model incorporates lithographic apparatus metrology inputs to account for differences in illumination mode, polarization, and aberrations, enabling accurate determination of feature overlay error without requiring direct measurement of the feature itself.
2Ease of manufacture
If dedicated targets are used for overlay measurement, then measurement process is simplified, but measurement precision deteriorates due to different geometry and surrounding structures compared to features of interest
Solution Approach 1:
The model serves as an intermediary that compensates for the geometric and structural differences between dedicated targets and features. By incorporating lithographic apparatus metrology inputs, the model translates the simplified target measurement into an accurate feature overlay error determination, maintaining both ease of manufacture and measurement precision.
Solution Approach 2:
The patent changes the parameters used in the analysis by separately modeling the effects of illumination mode, polarization, and aberrations. This allows the system to account for geometric and structural differences through parameter adjustments in the model, rather than requiring identical target and feature geometries.
3Ease of operation
If overlay error of target is assumed to be the same as feature overlay error, then determination is straightforward, but measurement precision deteriorates due to position-dependent variations and process dependencies
Solution Approach 1:
The patent segments the overlay error determination into two parts: the measured target overlay error and the modeled relative difference. This segmentation replaces the simplistic assumption with a structured approach that maintains ease of operation through automated modeling while improving precision by accounting for position-dependent variations and process dependencies.
Solution Approach 2:
The model incorporates lithographic apparatus metrology inputs that provide feedback about the actual illumination conditions, polarization state, and aberrations present during exposure. This feedback enables the model to accurately predict the relative overlay error between target and feature, improving precision without complicating the overall determination process.
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 provides a more accurate determination of overlay error by accounting for various factors affecting the feature, improving precision in lithographic processes.
Implementation Method 1
One 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 2
properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate
Data Source
AI summary
A lithographic apparatus including an inspection apparatus can measure the overlay error of a target in a scribelane is measured. The overlay error of the required feature in the chip area may differ from this due to, for example, different responses to the exposure process. A model is used to simulate these differences and thus a more accurate measurement of the overlay error of the feature determined.