Raster Beam Dose Limiting With Ghost Exposure for Faster Lithography
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Solution Overview
Problem
In raster beam writing, particularly in multi-beam electron lithography, the writing time is prolonged due to the need to maintain high writing accuracy in main chip regions, while peripheral chip regions with lower accuracy requirements receive excessive doses, leading to reduced writing speed and potential pattern size reduction when both are written simultaneously.
Innovation Solution
A method and apparatus that calculates a normalized proximity effect-corrected dose, determines regions exceeding a threshold, and applies a ghost dose to compensate for insufficient doses in peripheral regions, ensuring accurate pattern size without extending writing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the dose is limited to the range used in the main chip region to reduce maximum dose and shorten writing time, then writing time is reduced, but the dose becomes insufficient in the peripheral chip region causing pattern size reduction
Solution Approach 1:
The patent applies preliminary action by performing ghost exposure before the main exposure. A first dose (ghost dose) is applied to the peripheral chip region in advance, and then a second dose (main dose) is applied during the main exposure. This preliminary dosing allows the main exposure to use a limited maximum dose for faster writing while still achieving sufficient total dose in the peripheral region to maintain pattern size.
2Productivity
If the writing speed is determined by the maximum dose in the peripheral chip region to enable simultaneous writing of main and peripheral regions, then writing time is reduced, but the writing speed in the main chip region decreases due to the maximum dose requirement
Solution Approach 1:
The patent applies local quality by differentiating the dosing strategy between main chip region and peripheral chip region. The main chip region receives only the main dose with limited maximum dose for high writing accuracy, while the peripheral chip region receives both ghost dose and main dose to achieve sufficient total dose despite the maximum dose limitation. This localized differentiation allows simultaneous writing of both regions without compromising the writing accuracy of the main chip.
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 reduced writing time in both main and peripheral chip regions while maintaining pattern accuracy by adjusting doses through ghost exposure, addressing the inefficiencies in existing methods.
Implementation Method 1
irradiating a position where a pattern is located (line pattern portion) with a beam having a dose that resolves a resist
Implementation Method 2
the beam is back scattered within the target object to cause electrons to be incident on the resist, thereby causing secondary resist exposure. As a result, a so-called proximity effect occurs
Data Source
AI summary
A raster beam writing method includes: calculating a ghost dose for ghost exposure for a small region having a proximity effect-corrected dose larger than the threshold value as a result of a determination; and for a plurality of irradiation unit regions to be irradiated with a charged particle beam obtained by dividing the writing region of the target object in a mesh shape, writing an irradiation unit region having a proximity effect-corrected dose larger than the threshold value with a charged particle beam having an incident dose obtained by adding the ghost dose to a dose based on a limited corrected dose more limited than a calculated proximity effect-corrected dose, and writing an irradiation unit region having a proximity effect-corrected dose not larger than the threshold value with a charged particle beam having an incident dose based on the calculated proximity effect-corrected dose without ghost exposure.