Global Node Optimization for Grating Structure Thickness
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Solution Overview
Problem
Accurately determining the thickness of binary layers in multiple layer grating structures on integrated circuit devices is challenging due to irregular edges and large local thickness variations, as existing methods like spectroscopic ellipsometry are inadequate for discontinuous films, and full diffraction theory requires excessive computational resources.
Innovation Solution
A global node optimization technique that approximates binary layers as continuous films, using a continuous film approximation and grating factors to minimize error in spectra fitting, allowing for the creation of a model that requires minimal computational resources and can be optimized using a design of experiment and in-die measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full diffraction theory is used to model grating structure, then measurement precision is improved, but computational resources required increase excessively
Solution Approach 1:
The patent segments the complex diffraction problem into two parts: (1) a simplified continuous film approximation model that provides quick initial thickness estimates, and (2) a grating factor correction term that accounts for the discontinuous nature of the grating structure. This segmentation allows the model to achieve high measurement precision without requiring full diffraction theory computations for every measurement.
Solution Approach 2:
The patent introduces grating factors as correction parameters that modify the continuous film model to account for grating effects. By changing the model parameters to include these correction terms rather than solving the full diffraction equations, the system achieves accurate thickness measurements with minimal computational resources.
2Ease of operation
If spectroscopic ellipsometry is used on discontinuous films, then measurement process is simplified, but measurement precision deteriorates due to inaccuracy for non-homogeneous layers
Solution Approach 1:
The patent introduces grating factors as intermediary correction terms that bridge the gap between the simple continuous film model and the complex discontinuous grating structure. These grating factors act as mediators that allow the ellipsometry measurement process to remain simple while accurately accounting for the non-homogeneous nature of the grating layers.
3Use of energy by moving object
If continuous film approximation is used for binary layers, then computational resources are minimized, but measurement precision deteriorates due to inability to account for irregular edges and thickness variations
Solution Approach 1:
The patent enhances the continuous film approximation by introducing grating factors as additional parameters. These parameters allow the model to account for irregular edges and local thickness variations while maintaining the computational efficiency of the continuous film approach. The grating factors effectively capture the deviations from ideal continuous film behavior without requiring full diffraction modeling.
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 enables accurate thickness estimation of grating structure layers while reducing computational requirements, providing a more efficient method for determining layer thicknesses and improving process control in chip fabrication.
Implementation Method 1
spectroscopic ellipsometry (SE) can measure the changes in the state of polarization of light upon reflection from a surface to determine the thicknesses of multiple continuous films
Data Source
AI summary
A global node optimization (GNO) technique can generate a model for a planar multiple layer film stack structure, e.g. a binary grating structure. In this technique, after obtaining spectra and target thicknesses from one or more wafers, a continuous film approximation (CFA) and a grating factor (GF) set are identified. A model using the CFA and the GF set is optimized by simultaneously fitting a plurality of the spectra while minimizing error compared to the target thicknesses. After simultaneously fitting all of the spectra, a GNO stack is created. A GNO recipe is then created using the GNO stack. Notably, a tool implementing the GNO technique uses minimal modeling capabilities and computational resources.