Electron Beam Scan Control Unit for Semiconductor Wafer Testing
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Solution Overview
Problem
The increasing diameter of semiconductor wafers and decreasing size of circuit patterns demand higher throughput in test apparatuses using electron beams, but these systems face challenges due to the charge-up phenomenon, which distorts images and reduces precision.
Innovation Solution
A test apparatus with a scan control unit that utilizes two-dimensional coordinate transformation using small-capacity and large-capacity lookup tables to perform high-speed scan control, allowing for arbitrary direction scanning and efficient coordinate transformation, thereby addressing the charge-up issue and improving throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the electron beam scanning speed is increased to improve throughput, then productivity increases, but the charge-up phenomenon becomes more severe causing image distortion and reducing measurement precision
Solution Approach 1:
The patent applies preliminary action by pre-charging the sample surface with a low-energy electron beam before performing the actual high-speed imaging with the primary electron beam. This preliminary charging creates a controlled potential distribution that compensates for the charge-up effects that would otherwise occur during rapid scanning, thereby maintaining image precision while enabling high throughput
2Productivity
If the electron beam scanning speed is increased to improve throughput, then productivity increases, but image distortion occurs due to charge-up phenomena
Solution Approach 1:
The patent applies preliminary action by pre-charging the sample surface with a low-energy electron beam before performing the actual high-speed imaging with the primary electron beam. This preliminary charging creates a controlled potential distribution that compensates for the charge-up effects that would otherwise occur during rapid scanning, thereby maintaining image precision while enabling high throughput
3Measurement precision
If two accelerating voltages are used to prevent charge-up, then image precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies local quality by using two different electron beams with different accelerating voltages for different purposes: a low-energy beam (1-5 keV) for preliminary surface charging and a high-energy beam (10-30 keV) for primary imaging. Each beam is optimized for its specific function, allowing precise control of charge-up effects without requiring complex switching mechanisms or dual-voltage accelerators
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 solution enables high-speed scan control and image processing, reducing the influence of charge-up phenomena and enhancing the precision of image acquisition, making it compatible with multiple scan types and improving overall throughput.
Implementation Method 1
an electron beam is emitted with a predetermined accelerating voltage along plural scan lines to scan an area to be tested on a semiconductor wafer. Secondary electrons generated are detected to obtain image information of the area to be tested
Implementation Method 2
When the sample is a non-conductive sample, the electrons remain in the sample and charging occurs. When charging occurs, the electron beam is bent due to repulsion of the charges remained at the time of emitting the electron beam to the sample and is deviated from an intended irradiation position
Data Source
AI summary
A scan control unit for generating two-dimensional coordinates for performing a scan with an electron beam of an electron scanning microscope is provided with first and second transforming units for transforming coordinates in the horizontal (X) direction and the vertical (V) direction. An area to be tested in a sample is scanned with an electron beam in an arbitrary direction. As the first and second transforming units, small-capacity transformation tables (LUTs) capable of operating at high speed in each of the horizontal (X) direction and the vertical (Y) direction are used. By also using a large-capacity transformation table (LUT) that stores coordinate transformation data corresponding to plural scan types, a test apparatus compatible with the plural scan types, having multiple functions, and capable of performing high-speed scan control is realized.