Protective Layer Mill Rate Matching for SEM Metrology
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Solution Overview
Problem
The current methods for monitoring the width of small structures like write-head poles in semiconductor and data storage manufacturing face inaccuracies due to topographical variations caused by curtaining effects during charged particle beam milling, which obscure material boundaries and complicate edge recognition in SEM metrology.
Innovation Solution
The use of a protective layer with mill rates that closely approximate those of the substrate material at higher incidence angles, such as carbon overcoats for Permalloy structures, reduces topographical variations, allowing for more accurate SEM measurements by minimizing gray level variations and enhancing edge definition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is deposited over the structure before ion milling, then the structure is protected from damage during milling, but topographical variations and curtaining effects are introduced that obscure material boundaries and reduce measurement precision
Solution Approach 1:
The patent changes the material parameter of the protective layer from conventional materials (tungsten, platinum) to a material with specific properties (amorphous carbon) that has a milling rate closely matching the substrate material. This parameter change eliminates the curtaining effect by ensuring uniform material removal rates, thereby removing topographical variations that interfere with edge recognition while maintaining structure protection during ion milling.
2Reliability
If conventional protective layer materials (tungsten, platinum) are used, then the structure is well-protected during milling, but significant topographical variations occur that complicate SEM metrology
Solution Approach 1:
The patent changes the material parameter from conventional protective layer materials to amorphous carbon, which has a key property (milling rate) that closely matches the substrate material. This eliminates the mill rate mismatch that causes curtaining effects, allowing clear material boundary detection in SEM images while maintaining adequate structure protection during ion milling.
Solution Approach 2:
The patent achieves homogeneity in milling rates between the protective layer and substrate material by selecting amorphous carbon as the protective layer material. This homogeneous removal rate prevents the formation of topographical variations and curtaining effects, resulting in a planar cross-section that facilitates accurate material boundary detection and SEM metrology.
3Reliability
If the protective layer material has significantly different mill rates from the substrate, then the protective layer provides good protection, but curtaining effects are generated that reduce measurement accuracy
Solution Approach 1:
The patent changes the material parameter (milling rate) of the protective layer to closely match the substrate material by using amorphous carbon. This parameter matching eliminates the curtaining effect and produces a flat, planar cross-section surface, thereby improving manufacturing precision of the milled surface while maintaining protective layer effectiveness during ion milling.
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 results in a more planar cross-section face, improving the accuracy of metrology measurements and reducing the time required for critical dimension assessments, leading to more precise and robust process control.
Implementation Method 1
The protective layer may be formed by known deposition techniques such as physical vapor deposition (PVD)
Implementation Method 2
FIB systems are widely used in microscopic-scale manufacturing operations because of their ability to image, etch, mill, deposit, and analyze very small structures with great precision. FIB systems produce a narrow, focused beam of charged particles (hereinafter referred to as ions) that is typically scanned across the surface of a work piece
Data Source
AI summary
An improved method of controlling topographical variations when milling a cross-section of a structure, which can be used to reduce topographical variation on a cross-section of a write-head in order to improve the accuracy of metrology applications. Topographical variation is reduced by using a protective layer that comprises a material having mill rates at higher incidence angles that closely approximate the mill rates of the structure at those higher incidence angles. Topographical variation can be intentionally introduced by using a protective layer that comprises a material having mill rates at higher incidence angles that do not closely approximate the mill rates of the structure at those higher incidence angles.