Overlay Error Determination via Asymmetry Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for determining overlay errors in lithographic processes are sensitive to target grating asymmetries, leading to measurement uncertainties and inefficiencies in recipe selection, particularly when the reference layer exhibits an asymmetrical profile, and do not effectively account for processing-induced asymmetries.
Innovation Solution
A method and apparatus that measure scattering properties of a target structure, construct a model of the structure, modify it to account for asymmetry, calculate asymmetry-induced overlay errors, and use these calculations to determine overlay errors in a second target, allowing for improved measurement robustness and recipe selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional scatterometer measurement methods are used, then measurement speed is maintained, but measurement precision deteriorates due to sensitivity to target grating asymmetries
Solution Approach 1:
The patent applies preliminary action by performing asymmetry correction calculations before final overlay error determination. The method pre-characterizes the asymmetry of the reference layer grating and uses this information to correct subsequent overlay measurements, thereby eliminating the adverse effect of asymmetry on measurement precision while maintaining measurement speed
Solution Approach 2:
The patent introduces an intermediary asymmetry correction factor that mediates between the measured scattering properties and the final overlay error calculation. This correction factor, derived from the asymmetry of the reference layer, acts as a mediator to compensate for asymmetry-induced errors and improve measurement precision without sacrificing reliability
2Measurement precision
If asymmetry correction calculations are performed, then overlay error determination accuracy is improved, but device complexity increases
Solution Approach 1:
The patent segments the overlay error determination process into distinct stages: (1) measuring scattering properties, (2) determining asymmetry of the reference layer, (3) calculating asymmetry correction factors, and (4) applying corrections to obtain final overlay errors. This segmentation allows each step to be optimized independently and simplifies the overall complex calculation process
Solution Approach 2:
The patent changes parameters by introducing asymmetry-related parameters (asymmetry factor, correction factor) that are derived from the scattering measurements. By expressing the correction in terms of these parameters, the complex physical problem of asymmetry compensation is transformed into a manageable mathematical correction that improves accuracy without excessive complexity
3Measurement precision
If conventional recipe selection based on TIS is used, then measurement efficiency is maintained, but measurement precision deteriorates when reference layer exhibits asymmetrical profile
Solution Approach 1:
The patent implements feedback by using the measured asymmetry of the reference layer to inform and adjust the overlay error measurement process. The asymmetry information feeds back into the calculation of correction factors, which then adjust subsequent measurements, creating a closed-loop system that maintains precision even with asymmetrical profiles while preserving measurement efficiency
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 processing variations and improves semiconductor manufacturing yield by accurately accounting for asymmetries and selecting optimal measurement recipes, leading to more precise overlay error determination and reduced measurement uncertainties.
Implementation Method 1
A fast and non-destructive 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
Data Source
AI summary
A method of determining an overlay error. Measuring an overlay target having process-induced asymmetry. Constructing a model of the target. Modifying the model, e.g., by moving one of the structures to compensate for the asymmetry. Calculating an asymmetry-induced overlay error using the modified model. Determining an overlay error in a production target by subtracting the asymmetry-induced overlay error from a measured overlay error. In one example, the model is modified by varying asymmetry p(n′), p(n″) and the calculating an asymmetry-induced overlay error is repeated for a plurality of scatterometer measurement recipes and the step of determining an overlay error in a production target uses the calculated asymmetry-induced overlay errors to select an optimum scatterometer measurement recipe used to measure the production target.