Angularly Resolved Scatterometer Focus Determination
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Solution Overview
Problem
Current methods for measuring focus and detecting micro-loading and process effects in lithographic processes are limited by the size of metrology targets, sensitivity, and the need for additional measurement techniques, which can be time-consuming and destructive, and do not provide comprehensive information about profile asymmetries and variations.
Innovation Solution
A method using an angularly resolved scatterometer that forms and detects images using non-zero order diffracted radiation, excluding zero order radiation, to determine focus and process-induced variations by analyzing intensity variations across the diffraction spectrum, allowing for smaller target sizes and more sensitive measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If traditional scatterometer methods are used to measure focus and process effects, then measurements can be obtained, but the target size must be large which consumes valuable substrate real estate
Solution Approach 1:
The patent extracts and analyzes only the non-zero order diffracted radiation components, excluding the zero order radiation. This selective extraction enables precise focus determination and detection of micro-loading effects using significantly smaller target structures, thereby reducing the area consumed on the substrate while maintaining or improving measurement sensitivity.
Solution Approach 2:
The patent applies different analysis methods to different components of the diffracted radiation. By specifically analyzing the intensity variations in non-zero order diffracted radiation and excluding zero order radiation, the method achieves local optimization of measurement sensitivity for focus and process effect detection, enabling smaller target sizes without sacrificing measurement quality.
2Loss of information
If additional measurement techniques are used to detect process effects, then comprehensive information can be obtained, but the process becomes time-consuming and destructive
Solution Approach 1:
The patent makes the scatterometer measurement method multi-functional by enabling it to simultaneously determine focus, detect micro-loading effects, and measure profile asymmetries all through a single measurement process using non-zero order diffracted radiation. This eliminates the need for multiple separate measurement techniques, reducing measurement time and avoiding destructive sampling while maintaining comprehensive information acquisition.
Solution Approach 2:
The patent changes the measurement parameters by selecting specific non-zero order diffracted radiation components for analysis and excluding zero order radiation. This parameter change enables a single measurement to provide comprehensive information about focus, process effects, and profile asymmetries, making the method both faster and less destructive while maintaining information completeness.
3Use of energy by moving object
If zero order diffracted radiation is included in measurements, then more signal strength is available, but focus determination and process effect detection sensitivity are reduced
Solution Approach 1:
The patent extracts and utilizes only the non-zero order diffracted radiation components while deliberately excluding the zero order radiation. This selective extraction may reduce overall signal strength but dramatically improves focus determination sensitivity and process effect detection by eliminating the dominant zero order component that masks the subtle variations needed for precise measurements.
Solution Approach 2:
The patent applies selective analysis to different radiation orders, treating non-zero order diffracted radiation differently from zero order radiation. By focusing measurement energy and analysis on the non-zero order components, the method achieves local optimization of measurement precision for focus and process effects, even though the total energy utilized is reduced.
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
Enables precise focus determination and detection of micro-loading and process effects with improved sensitivity and speed, reducing real estate consumption and avoiding the need for additional measurement tools, while providing comprehensive 2D information over the wafer field.
Implementation Method 1
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
Implementation Method 3
A first measurement step comprising forming and detecting a first image of the periodic structure while illuminating the structure with a first beam of radiation, the first image being formed using a first part of non-zero order diffracted radiation
Data Source
AI summary
In a method of determining the focus of a lithographic apparatus used in a lithographic process on a substrate, the lithographic process is used to form a structure on the substrate, the structure having at least one feature which has an asymmetry in the printed profile which varies as a function of the focus of the lithographic apparatus on the substrate. A first image of the periodic structure is formed and detected while illuminating the structure with a first beam of radiation. The first image is formed using a first part of non-zero order diffracted radiation. A second image of the periodic structure is formed and detected while illuminating the structure with a second beam of radiation. The second image is formed using a second part of the non-zero order diffracted radiation which is symmetrically opposite to the first part in a diffraction spectrum. The ratio of the intensities of the measured first and second portions of the spectra is determined and used to determine the asymmetry in the profile of the periodic structure and/or to provide an indication of the focus on the substrate. In the same instrument, an intensity variation across the detected portion is determined as a measure of process-induced variation across the structure. A region of the structure with unwanted process variation can be identified and excluded from a measurement of the structure.