Compensating Defective Beamlets in Charged-Particle Lithography
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Solution Overview
Problem
In particle-beam exposure tools, defective apertures in the blanking aperture array can introduce errors in the dose distribution, particularly affecting the DTC line, which are challenging to correct using existing methods, especially when the defective aperture is near or at the DTC line, requiring more sophisticated correction methods.
Innovation Solution
The method involves identifying defective apertures and modifying the exposure levels of nearby image elements to minimize the impact on the global dose distribution by optimizing the dose values of correction elements, using a modified Lawson-Hanson NNLS algorithm to solve for the optimal dose changes within constraints, and implementing this correction in real-time during the exposure process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If defective apertures are present in the blanking aperture array, then the productivity of the exposure tool is maintained through parallel multi-beam processing, but the manufacturing precision of the exposed pattern deteriorates due to dose distribution errors
Solution Approach 1:
The system performs preliminary identification of defective apertures through test exposures and stores this defect information in a lookup table. Before actual pattern exposure, the control system uses this pre-acquired defect data to calculate and apply compensation values to adjacent image elements, ensuring that manufacturing precision is maintained without sacrificing the parallel processing productivity of the multi-beam system.
Solution Approach 2:
The system changes the dose parameter of image elements adjacent to defective apertures by applying compensation values. When a defective aperture is detected, the control system modifies the exposure dose parameters of neighboring image elements to compensate for the missing or erroneous dose, thereby maintaining the intended dose distribution and pattern quality while keeping the defective aperture operational in the parallel beam array.
2Device complexity
If existing correction methods are used for defective apertures near the DTC line, then the device complexity remains low, but the manufacturing precision deteriorates because these methods cannot effectively correct errors when the defective aperture is near or at the DTC line
Solution Approach 1:
The system implements a feedback mechanism where test exposure data from defective apertures is used to identify and characterize defects. This feedback information is then fed into the control system, which calculates compensation values and applies them to adjacent image elements. This closed-loop feedback approach enables effective correction of DTC line errors without adding physical hardware complexity, as the correction is achieved through software-based dose parameter adjustment.
3Manufacturing precision
If the exposure levels of correction elements are optimized to compensate for defective apertures, then the manufacturing precision of the exposed pattern is improved, but the complexity of the exposure process increases due to the need for identifying and correcting defective apertures
Solution Approach 1:
The system performs self-diagnosis by automatically identifying defective apertures through test exposures and autonomously calculating and applying compensation values without requiring external intervention or additional hardware. The control system serves itself by using the defect information from the aperture array to adjust the exposure parameters, thereby improving manufacturing precision while minimizing the increase in process complexity through automated self-correction.
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 effectively minimizes the error in the dose distribution by adjusting the exposure levels of correction elements, ensuring accurate pattern formation on the target surface, even with defective apertures, and can handle various types of aperture defects without additional hardware, enhancing the productivity and accuracy of the particle-beam exposure process.
Implementation Method 1
illuminating said pattern definition means by means of an illuminating wide beam, which traverses the pattern definition means through said apertures, thus forming a patterned beam consisting of a corresponding plurality of beamlets
Implementation Method 2
passing said patterned beam through a projection optical system, which forms an image of said patterned beam onto a target
Implementation Method 3
generating a relative movement between said target and the pattern definition means producing a movement of said pattern image on the target along a path over a region where a beam exposure is to be performed
Data Source
Figure 1~1A
Figure 2~3
Figure 4~5
AI summary
An exposure pattern is computed which is used for exposing a desired pattern on a target by means of a blanking aperture array in a particle-optical lithography apparatus which has a finite number of defects, said desired pattern being composed of a multitude of image elements within an image area on the target: A list of defective blanking apertures is provided, comprising information about the type of defect of the defective blanking apertures; from the desired pattern a nominal exposure pattern is calculated as a raster graphics over the image elements disregarding the defective blanking apertures; the "compromised" image elements (1105) are determined which are exposed by aperture images of defective blanking apertures; for each compromised element (1105), a set of neighboring image elements is selected as "correction elements" (1104); for each compromised element, corrected dose values are calculated for the correction elements, said corrected dose values minimizing an error functional of the deviation of the dose distribution including the defects from the nominal dose distribution, under the constraint that each of the corrected dose values falls within the allowed doses; and a corrected exposure pattern (1103) is generated by substituting the corrected dose values for the nominal dose values at the correction elements.