Charged Particle Beam Focus Normalization via Reference Die Scanning
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Solution Overview
Problem
Existing focusing systems for charged particle beams, such as those used in scanning electron microscopes, face challenges in efficiently and accurately focusing on sites with different patterns and characteristics, leading to slower focusing processes.
Innovation Solution
A method involving a processor that uses a reference die to normalize focus scores by modulating the focal parameter of the primary charged particle beam, allowing for precise correction of the focusing parameter to achieve exact focus on sites with varying characteristics, utilizing phase and amplitude variations to determine optimal focus adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional focusing systems scan the beam over multiple sites to determine focus, then focus accuracy can be achieved, but the focusing process becomes slow and inefficient
Solution Approach 1:
The system performs preliminary scanning of a reference die to establish baseline focus scores before inspecting remaining dies. This preliminary action creates a reference pattern that enables faster subsequent focusing operations by eliminating the need to scan all sites on every die, thus resolving the contradiction between measurement precision and productivity.
Solution Approach 2:
The system creates a copy of the focus pattern from a reference die and uses this copied pattern to compare against remaining dies. By copying the reference focus scores and comparing normalized values, the system achieves accurate focusing without repeatedly scanning all sites, thereby improving focusing speed while maintaining accuracy.
2Measurement precision
If the system scans all dies individually to determine focus scores, then accurate focus determination is achieved, but the inspection time increases significantly
Solution Approach 1:
The system performs a preliminary scan of a reference die to establish baseline focus scores before inspecting remaining dies. This preliminary action creates a reference pattern that enables faster subsequent focusing operations by eliminating the need to scan all sites on every die, thus resolving the contradiction between measurement precision and productivity.
Solution Approach 2:
The system extracts the essential focus pattern information from a reference die and uses this extracted pattern to evaluate remaining dies through normalization comparison. By taking out only the critical reference information and comparing normalized focus scores rather than scanning all sites individually, the system reduces inspection time while maintaining focus determination accuracy.
3Device complexity
If the focusing system uses fixed focus parameters, then the system structure remains simple, but it cannot adapt to sites with different patterns and characteristics
Solution Approach 1:
The system dynamically adjusts focus parameters by comparing normalized focus scores from remaining dies against a reference die pattern. Instead of using fixed focus parameters, the system adapts the focus settings based on the specific pattern characteristics of each die being inspected, enabling versatility while maintaining relatively simple system architecture through software-based adaptation.
Solution Approach 2:
The system changes focus parameters based on normalized focus score comparisons with a reference die. By adjusting focal positions and parameters according to the specific pattern characteristics detected during inspection, the system achieves adaptability to different patterns without requiring complex hardware modifications, resolving the contradiction between device complexity and adaptability.
Data Source
AI summary
A method for focusing a scanning microscope, including scanning a primary charged particle beam across first sites of a reference die of a wafer, detecting a secondary beam emitted from the sites, and computing first focus scores for the sites based on the secondary beam. The method includes scanning the primary beam across second sites of a given die of the wafer while modulating a focal depth of the primary beam, the reference die and the given die having congruent layouts, the second sites corresponding vectorially in location with the first sites, and detecting the secondary beam emitted from the second sites in response to the primary beam. The method also includes computing second focus scores for the second sites based on the detected secondary beam emitted therefrom, and determining an exact focus of the primary beam for the second sites using the first and the second focus scores.