Scanning Electron Beam Device Focus Adjustment
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Solution Overview
Problem
Scanning electron beam devices face challenges in measuring the dimensions of deep holes and grooves with high aspect ratios, as increasing the acceleration voltage to detect bottom portions leads to issues such as deteriorated resolution, inability to determine magnification due to hysteresis, and magnetic saturation of the objective lens, making precise dimension measurement difficult.
Innovation Solution
The device employs a stage that can be raised or lowered to adjust the working distance, allowing for rough focus adjustment and maintaining constant lens strength, thereby reducing the need for frequent excitation current changes and avoiding magnetic saturation, enabling precise measurement of both top and bottom portions of high-aspect-ratio features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the acceleration voltage is increased to detect bottom portions of deep holes and grooves, then the measurement capability for bottom portions is improved, but the resolution deteriorates and magnetic saturation occurs
Solution Approach 1:
The patent dynamically adjusts the working distance based on the acceleration voltage being used. When high acceleration voltage is applied to enable bottom portion detection, the working distance is automatically extended to prevent magnetic saturation and maintain resolution. This dynamic parameter adjustment resolves the contradiction between measurement capability and resolution.
2Ease of operation
If the excitation current for the objective lens is increased to converge the electron beam, then the beam convergence is improved, but magnetic saturation of the lens occurs
Solution Approach 1:
The patent changes the working distance parameter in response to acceleration voltage changes. By extending the working distance when high voltage is used, the system achieves beam convergence without requiring excessive excitation current, thereby avoiding magnetic saturation of the objective lens.
3Reliability
If the working distance is extended to avoid magnetic saturation, then the lens reliability is improved, but the resolution deteriorates
Solution Approach 1:
The system dynamically adjusts the working distance based on the acceleration voltage. The working distance is extended only when high acceleration voltage is applied, which is necessary for bottom portion detection. This conditional dynamic adjustment maintains resolution by keeping the working distance short during low-voltage top portion measurement while ensuring lens reliability during high-voltage operation.
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 allows for high-precision dimension measurement of both top and bottom portions of deep holes and grooves, improving the accuracy and throughput of semiconductor wafer production by maintaining focus and preventing magnetic saturation across a wide range of acceleration voltages.
Implementation Method 1
electrons emitted from an electron source are accelerated
Implementation Method 2
converged by an objective lens to which an excitation current is applied
Implementation Method 3
Through the irradiation of the electron beam, secondary electrons are generated from the wafer
Implementation Method 4
the electron beam is scanned on the wafer surface through electromagnetic deflection
Data Source
AI summary
A scanning electron beam device having: a deflector (5) for deflecting an electron beam (17) emitted from an electron source (1); an objective lens (7) for causing the electron beam to converge; a retarding electrode; a stage (9) for placing a wafer (16); and a controller (15); wherein the stage can be raised and lowered. In the low acceleration voltage region, the controller performs rough adjustment and fine adjustment of the focus in relation to the variation in the height of the wafer using electromagnetic focusing performed through excitation current adjustment of the objective lens. In the high acceleration voltage region, the controller performs rough adjustment of the focus in relation to the variation in the height of the wafer by mechanical focusing performed through raising and lowering of the stage, and performs fine adjustment by electrostatic focusing performed through adjustment of the retarding voltage. It thereby becomes possible to provide a scanning electron beam device that measures, in a highly accurate manner, both the upper part and the bottom part of a groove or a hole having a high aspect ratio.