Projection Optics Calibration for Multi-Beam Image Distortion
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Solution Overview
Problem
Charged-particle multi-beam processing apparatuses face challenges in accurately controlling process parameters, leading to imaging defects such as spatial and angular distortion, which affect the precision of patterns written on targets.
Innovation Solution
A method is introduced to adjust the optical imaging system by determining and optimizing operating parameters of the projection optics, using calibration steps to correct image distortion through linear combinations of fingerprints representing changes in these parameters, thereby improving the control of beamlet landing positions and angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multi-beam charged particle processing apparatus is used to expose targets, then productivity is improved through parallel processing of multiple beamlets, but manufacturing precision deteriorates due to spatial and angular distortion in the beam field
Solution Approach 1:
The patent applies parameter changes by adjusting operating parameters of optical components in the projection optics system. Specifically, it determines optimized operating parameters that compensate for spatial and angular distortion, thereby correcting image distortion while maintaining the multi-beam parallel processing capability. This allows the system to achieve both high productivity and improved manufacturing precision.
2Productivity
If the projection optics system is used to image beamlets onto the target, then productivity is improved through simultaneous exposure of multiple pixels, but manufacturing precision deteriorates due to imaging defects such as spatial distortion
Solution Approach 1:
The patent implements feedback by determining image distortion characteristics of the beam field and using this information to calculate optimized operating parameters. The system measures or calculates distortion, then applies corrective parameter adjustments to the projection optics, creating a closed-loop feedback mechanism that continuously compensates for spatial distortion and maintains beamlet landing position accuracy.
Solution Approach 2:
The system changes operating parameters of the projection optics based on determined image distortion characteristics. By adjusting parameters such as lens currents or voltages, the system compensates for spatial distortion and angular distortion, thereby maintaining manufacturing precision while preserving the simultaneous exposure capability that enables high productivity.
3Ease of operation
If the projection optics system operates with fixed parameters, then ease of operation is maintained, but manufacturing precision deteriorates due to uncorrected image distortion
Solution Approach 1:
The patent applies preliminary action by determining optimized operating parameters in advance, before actual pattern exposure begins. The system calculates the distortion characteristics and determines the corrective parameters beforehand, then applies these pre-calculated settings to the projection optics. This allows the system to maintain ease of operation during actual use while achieving high manufacturing precision through pre-compensation for distortion.
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 significantly reduces imaging aberrations, enhancing the precision of patterns generated on the target by effectively managing spatial and angular distortions within the beam field.
Implementation Method 1
an electron gun (7), an extraction system (8) as well as a condenser lens system (9)
Implementation Method 2
The extraction system (8) accelerates the particles to a defined energy of typically several keV
Implementation Method 3
a condenser lens system (9)... The extraction system (8) accelerates the particles to a defined energy of typically several keV, e.g. 5 keV. By means of a condenser lens system (9), the particles emitted from the source (7) are formed into a wide, substantially telecentric particle beam (50)
Implementation Method 4
The PD system (4) is held at a specific position in the path of the lithography beam (lb), which thus irradiates the plurality of apertures and is split up into a number of beamlets... 'Switched off'-beamlets are deflected off their path (by very small angles) so they cannot reach the target
Implementation Method 5
a projection optics including at least one charged-particle-optical lens... The projection system (5) implements a demagnification of, for instance, 200:1 with two crossovers c1 and c2
Implementation Method 6
The charged-particle optical systems (3, 5) are realized using electrostatic and/or magnetic lenses
Implementation Method 7
The lithography beam (lb) then irradiates a PD system (4) which comprises a number of plates with a plurality of openings or apertures (24) (Fig. 2). The PD system (4) is held at a specific position in the path of the lithography beam (lb), which thus irradiates the plurality of apertures and is split up into a number of beamlets
Data Source
Figure 1
Figure 2
Figure 3A~3D
AI summary
The invention proposes adjusting the optical imaging system (5) of a charged-particle multibeam processing apparatus with regard to spatial and angular image distortion of the beam field, which describes the deviation of landing positions and landing angles of beamlets (60) from respective nominal values within the beam field. Starting from a determination of the image distortion, so-called fingerprints are determined, which represent the change of image distortion effected by a unit change of a respective operating parameter of a component (54) of the projection optics; then values of operating parameters are obtained which optimize a corrected distortion obtained from a superposition of the image distortion and a change of operating parameters that causes a variation of the image distortion, as expressed by a linear combination of said fingerprints. The optimizing values thus obtained are applied to the respective optical elements of the projection optics. The procedure may suitable be iterated until the distortion is suitably optimized.