Electron Beam Drawing Cathode Current Control
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Solution Overview
Problem
In electron beam drawing apparatuses, controlling the emission current from the central portion of the cathode is challenging due to variations in the total emission current, which can adversely affect drawing accuracy as only the total emission current is typically controlled, not the individual currents from the central and peripheral portions.
Innovation Solution
An electron beam drawing apparatus with a controller that measures and controls the emission current from the central portion by calculating a coefficient based on the total and peripheral emission currents, ensuring the central emission current remains constant during pattern drawing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the total emission current is controlled to be held constant, then the overall electron beam stability is improved, but the emission current from the central portion of the cathode may vary adversely affecting drawing accuracy
Solution Approach 1:
The emission current measurement is segmented into two separate measurements: one for the central portion of the cathode and another for the outer peripheral portion. This segmentation allows independent monitoring and control of the central emission current, which is critical for drawing accuracy, while still maintaining overall beam stability through total current control.
Solution Approach 2:
The system implements feedback control by continuously monitoring the emission current from the central portion of the cathode and adjusting the total emission current accordingly. When the central emission current deviates from the target value, the feedback mechanism modifies the total current to compensate, ensuring the central current remains stable for high-precision drawing.
2Stability of the object's composition
If the emission current from the outer peripheral portion of the cathode varies, then the total emission current varies, but the emission current from the central portion remains constant
Solution Approach 1:
The system introduces an intermediary control mechanism that decouples the relationship between peripheral current variations and central current stability. By measuring and separately controlling the central emission current, the system acts as an intermediary that prevents peripheral variations from directly affecting the central beam quality, allowing total current to fluctuate without compromising central current stability.
3Device complexity
If only the total emission current is measured and controlled, then the control system remains simple, but the drawing accuracy deteriorates due to inability to independently control central emission current
Solution Approach 1:
The control system is segmented into multiple independent control loops: one for measuring total emission current and another for measuring central portion emission current. This segmentation enables sophisticated control of central current accuracy while maintaining relative simplicity in each individual control loop, avoiding the need for a completely complex unified control system.
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 stabilizes the electron beam emitted from the central portion, improving drawing accuracy by independently controlling the emission current from the central cathode portion, thereby maintaining consistent pattern formation.
Implementation Method 1
A thermionic-emission electron gun provided with a cathode serving as a heater is employed as an electron gun of an electron beam drawing apparatus. In such an electron gun, electrons are emitted by heating the cathode.
Implementation Method 2
The emitted electrons are accelerated with an acceleration voltage and are delivered in the form of an electron beam, which is applied to a sample.
Data Source
AI summary
In one embodiment, an electron beam drawing apparatus includes an electron gun including a cathode and an anode, a current control circuit controlling a total emission current, a first detector detecting a first emission current from an outer peripheral portion of the cathode, a second detector detecting a second emission current from an central portion of the cathode, and a controller that determines a coefficient, which is a ratio of an emission current from the outer peripheral portion of the cathode to the first emission current. During a period in which a pattern is drawn on the substrate, the controller estimates a value of the second emission current by subtracting a value, which is resulted by multiplying the first emission current by the coefficient, from the total emission current, and controls the current control circuit in a manner of holding the estimated value constant.