BSE Detector Layout for Deep-Hole Charged Particle Beam Inspection
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Solution Overview
Problem
Existing BSE detectors in charged particle beam devices face challenges in achieving high detection efficiency and response speed due to the size constraints of the scintillator and SiPM, leading to increased parasitic capacitance and circuit noise, which hinders the detection of backscattered electrons from deep holes or grooves with high aspect ratios.
Innovation Solution
A BSE detector design incorporating a scintillator with a larger light receiving surface than the SiPM, connected via a light guide, allows for efficient light transmission while minimizing optical loss and parasitic capacitance, enabling high detection quantum efficiency and response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light receiving surface of the SiPM is increased to increase the scintillator size and prevent decrease in detection efficiency, then the detection efficiency is improved, but the output parasitic capacitance of the SiPM increases leading to increased circuit noise and response delay
Solution Approach 1:
The patent divides the light receiving surface into two distinct areas: a first light receiving surface area for receiving light from the scintillator, and a second light receiving surface area for receiving light from an external light source. This segmentation allows the SiPM to simultaneously achieve large area for high detection efficiency while managing parasitic capacitance through selective activation of different regions.
Solution Approach 2:
The patent changes the operational parameters of the SiPM by selectively activating different light receiving surface areas based on measurement conditions. The control unit adjusts which area is active, effectively changing the operational capacitance and sensitivity parameters to match the specific measurement requirements, thereby optimizing both detection efficiency and noise performance.
2Ease of operation
If a BSE detector is disposed between the objective lens and the sample under severe spatial constraint, then the detector can be positioned for BSE detection, but the scintillator size is constrained by the SiPM size limiting detection efficiency
Solution Approach 1:
The patent transitions from a direct coupling configuration to a separated configuration using optical coupling. By introducing optical coupling means, the scintillator can be positioned in the constrained space between the objective lens and sample, while the SiPM can be located in a more favorable position with less spatial constraint, effectively solving the positioning problem while maintaining large scintillator area for high detection efficiency.
3Loss of energy
If the scintillator and SiPM are brought into direct contact for efficient light propagation, then light transmission efficiency is improved, but the scintillator size is limited by SiPM size reducing BSE detection efficiency
Solution Approach 1:
The patent introduces optical coupling means as an intermediary between the scintillator and SiPM. This intermediary component enables efficient light transmission from the scintillator to the SiPM while allowing the scintillator to have a larger area than the SiPM's first light receiving surface, thereby resolving the contradiction between light transmission efficiency and scintillator size for BSE detection.
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
The design provides stable detection characteristics and improved signal-to-noise ratio, suitable for observing deep holes or grooves with high aspect ratios, enhancing throughput in semiconductor inspection and measurement devices.
Implementation Method 1
a scintillator 107, a light guide 106, a silicon photomultiplier (SiPM, a solid-state photomultiplier tube, or a multi-pixel photon counter (MPPC)) 104
Implementation Method 2
a light guide 106 provided between the scintillator and the solid-state photomultiplier tube
Implementation Method 3
a silicon photomultiplier (SiPM, a solid-state photomultiplier tube, or a multi-pixel photon counter (MPPC)) 104
Data Source
AI summary
A charged particle beam device includes: a stage 124 on which a sample 108 is to be placed; a charged particle optical system including a charged particle source 113 and an objective lens 121 that focuses a charged particle beam from the charged particle source onto the sample; and a detector 123 disposed between the objective lens and the stage and configured to detect electrons 109 emitted by an interaction between the charged particle beam and the sample. The stage, the charged particle optical system, and the detector are housed in a vacuum housing 112, and the detector includes a scintillator 107, a solid-state photomultiplier tube 104, and a light guide 106 provided between the scintillator and the solid-state photomultiplier tube, and an area of a light receiving surface of the scintillator is larger than an area of a light receiving surface of the solid-state photomultiplier tube.