Sub Deflection Astigmatic Correction in Charged Beam Drawing
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Solution Overview
Problem
In electron beam and ion beam drawing apparatuses, the miniaturization of semiconductor integrated circuits leads to an increase in sub deflection astigmatic points, making it difficult to correct sub deflection astigmatic points due to the small sub deflection region, resulting in lowered drawing precision.
Innovation Solution
A charged beam drawing apparatus with a main/sub two-stage deflection system that includes a sub deflection astigmatic correction circuit and a sub deflection sensitivity correction circuit, which corrects deflection sensitivity and astigmatic points in parallel, using a sub deflection driving unit with an adder circuit to apply the necessary corrections to the sub deflector, allowing for high-speed operation and improved precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the sub deflection region is made small to reduce the number of sub deflection astigmatic points, then the influence of sub deflection points is reduced, but the drawing precision deteriorates due to the increased number of astigmatic points that cannot be neglected
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the sub deflection astigmatic correction values based on the shot position within the sub deflection region. The correction values are calculated using equations that incorporate positional parameters (x, y coordinates) to compensate for astigmatic effects that vary across different locations in the miniaturized deflection region, thereby maintaining drawing precision despite the small region size.
Solution Approach 2:
The patent implements preliminary action by pre-calculating and storing sub deflection astigmatic correction values for various shot positions before actual drawing operations. The correction values are computed in advance using measurement data from standard shots and stored in a lookup table, allowing the system to apply corrections without real-time calculation delays during high-speed drawing operations.
2Productivity
If high-speed operation is performed to correct sub deflection points in the main/sub two-stage deflection system, then correction can be made, but it becomes extremely difficult to correct sub deflection astigmatic points due to the complexity and time requirements
Solution Approach 1:
The patent performs preliminary calculation of sub deflection astigmatic correction values using measurement data from standard shots taken at specific positions. The correction values are computed in advance and stored, enabling high-speed retrieval and application during actual drawing operations without compromising correction accuracy or operational speed.
Solution Approach 2:
The patent uses a lookup table that stores pre-calculated correction values for different shot positions. During operation, the system copies the appropriate correction values from the lookup table based on the current shot position, avoiding the need for real-time calculation and enabling high-speed correction application while maintaining precision.
3Object-affected harmful factors
If conventional methods using alignment coil are used to reduce the number of sub deflection astigmatic points, then some reduction is achieved, but satisfactory correction cannot be attained
Solution Approach 1:
The patent changes the approach from physically reducing the number of astigmatic points using alignment coils to dynamically changing the correction parameters (correction values) based on shot position. By adjusting the correction parameters according to the specific position within the sub deflection region, the system achieves satisfactory correction without needing to physically alter the deflection system or reduce the number of astigmatic points.
Data Source
AI summary
There is provided a charged beam drawing apparatus which includes main/sub two-stage deflectors, divides a main deflection drawing region on a sample into sub deflection drawing regions determined by the deflection width of the sub deflector, selects one of the sub deflection drawing regions by use of the main deflector and draws shots in the selected sub deflection drawing region by use of the sub deflector. A sub deflection driving unit includes a sub deflection sensitivity correction circuit, a sub deflection astigmatic correction circuit, an adder circuit which adds an output of the sub deflection sensitivity correction circuit and an output of the sub deflection astigmatic correction circuit, and a deflection amplifier which additionally applies an output of the adder circuit to the sub deflector.