Multi-beam Lithography Pattern Reshaping for Dose Uniformity
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Solution Overview
Problem
Charged-particle multi-beam writing apparatuses face limitations in maximizing exposure dose and throughput due to constraints in current density and dose manipulation techniques, leading to issues with pattern quality and accuracy, particularly with overdosing or underdosing in scanning stripe exposure methods.
Innovation Solution
A method to re-calculate patterns by reshaping pattern elements with assigned doses deviating from a nominal dose, using a predefined dose slope function to offset boundary segments and assign the nominal dose, allowing for improved dose distribution and feature size correction without significant throughput loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the maximum exposure dose is increased to improve pattern quality, then the lithography quality improves, but the productivity decreases due to reduced scanning velocity
Solution Approach 1:
The patent applies local quality by differentiating between pattern elements that require dose manipulation and those that do not. Only specific pattern elements with assigned doses deviating from the nominal dose are reshaped, while other elements maintain their original geometry and dose assignment. This selective approach ensures that productivity is maintained for the majority of pattern elements while achieving the required lithography quality only where dose variations are necessary.
Solution Approach 2:
The patent implements preliminary action by performing dose-related feature reshaping during the data preparation stage before the actual exposure process. The pattern data is pre-processed to calculate and apply the necessary geometric modifications based on the dose slope function, so that during exposure, the system can write the reshaped patterns at nominal dose without requiring real-time dose adjustments or velocity changes.
2Measurement precision
If dose manipulation techniques are used to correct feature sizes, then the placement accuracy improves, but non-linear effects increase affecting pattern accuracy
Solution Approach 1:
The patent applies the inversion principle by reversing the conventional approach to dose manipulation. Instead of adjusting the exposure dose to achieve the desired feature size, the method adjusts the feature geometry (reshaping) to achieve the desired feature size at a constant nominal dose. This inversion eliminates the non-linear effects associated with variable dose exposure while maintaining placement accuracy through geometric correction.
3Use of energy by moving object
If the scanning velocity is reduced to increase exposure dose, then the exposure dose increases, but the throughput decreases
Solution Approach 1:
The patent applies parameter changes by transforming the dose requirement into a geometric parameter modification. The dose slope function relates the assigned dose to the required feature size adjustment, allowing the system to compensate for dose variations through geometric reshaping rather than by changing the scanning velocity or exposure dose parameters. This maintains constant scanning velocity and nominal dose while achieving the required feature dimensions.
4Manufacturing precision
If feature reshaping is applied to all pattern elements, then dose distribution uniformity improves, but the processing complexity increases
Solution Approach 1:
The patent applies local quality by selectively reshaping only those pattern elements that have assigned doses deviating from the nominal dose. The processing system identifies and processes only the necessary subset of pattern elements, leaving other elements unchanged. This reduces processing complexity compared to universal reshaping while still achieving dose distribution uniformity where it is actually needed.
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 enhances productivity and lithography quality by reducing dose variations, improving placement accuracy, and minimizing non-linear effects, while maintaining or improving critical dimension uniformity across the exposure region.
Implementation Method 1
a 50 keV electron multi-beam writer which allows to realize leading-edge complex photomasks
Data Source
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Figure 3~4
AI summary
A method for re-calculating a pattern to be exposed on a target by means of a charged-particle multi-beam writing apparatus is presented. The pattern elements (t1, t2, t3) of a pattern, initially associated with a respective assigned dose (D1, D2, D3), are recalculated in view of obtaining reshaped pattern elements (rt1, rt2, rt3) which have a nominal dose (Dl) as assigned dose. The nominal dose (Dl) represents a predefined standard value of exposure dose to be exposed for pixels during a scanning stripe exposure within the multi-beam apparatus. For the pattern elements (t2, t3) associated with an assigned dose (D2, D3) deviating from the nominal dose (Dl), the pattern element is reshaped by (i) determining a reshape distance (f2, f3) from the value of the assigned dose (D2, D3) using a predefined dose slope function (fDS), (ii) forming a reshaped pattern element (rt2, rt3), whose boundary is offset with regard to boundary of the initial pattern element (t2, t3) by an offset distance equaling said reshape distance, (iii) assigning the nominal dose (Dl) to the reshaped pattern element, and (iv) replacing the pattern element (t2, t3) by the reshaped pattern element (rt2, rt3).