Ion Beam Current Inference at Optical Bend
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Solution Overview
Problem
Ion implantation systems face challenges in accurately controlling ion dosage due to variations in ion beam current measurements, particularly at the final bend in the optical element, leading to potential over- or under-dosing of semiconductor wafers.
Innovation Solution
The system employs both upstream and downstream ion beam current measurements to infer the beam current at the final optical bend, using a weighting function to adjust the workpiece scanning velocity and maintain dose uniformity, thereby controlling the exposure time and achieving a desired dopant density profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If only downstream ion beam current measurements are used, then the measurement is taken after the final optical bend, but the accuracy of dose control deteriorates due to neutralization effects and beam variations upstream of the bend
Solution Approach 1:
The patent divides the beam current measurement into two separate measurements: one upstream of the final optical bend and one downstream. By segmenting the measurement process, the system captures beam variations at different locations, allowing for more accurate inference of the actual beam current at the workpiece through computational mixing of the two measurements.
Solution Approach 2:
The patent introduces an intermediary computational model that mixes upstream and downstream measurements to infer the beam current at the final optical bend. This intermediary processing step acts as a mediator that combines information from both measurement locations to overcome the limitations of either measurement alone.
2Measurement precision
If beam current measurements are taken at multiple locations, then measurement accuracy improves, but system complexity increases due to additional measurement apparatus and computational processing
Solution Approach 1:
The patent makes the measurement system multi-functional by using both upstream and downstream measurement apparatus not only for their primary measurement purposes but also as inputs to a mixed inference algorithm. This universal approach allows the same measurement infrastructure to serve multiple functions: direct measurement and inferential measurement combined through computational mixing.
Solution Approach 2:
The patent changes the measurement parameters by taking measurements at two different locations (upstream and downstream of the final optical bend) rather than at a single location. This parameter change in measurement location, combined with computational mixing, enables accurate inference of beam current at the workpiece while utilizing existing measurement infrastructure.
3Manufacturing precision
If the workpiece scanning velocity is adjusted to compensate for beam current variations, then dose uniformity improves, but process control complexity increases
Solution Approach 1:
The patent implements a feedback control system where upstream and downstream beam current measurements are continuously monitored, mixed through an inference algorithm, and used to dynamically adjust the workpiece scanning velocity. This feedback loop ensures dose uniformity by automatically compensating for beam current variations in real-time during the ion implantation process.
Solution Approach 2:
The patent makes the scanning velocity dynamic rather than static. The workpiece scanning velocity is continuously adjusted based on the mixed inference of beam current from upstream and downstream measurements, allowing the system to adapt to real-time beam variations and maintain dose uniformity throughout the implantation process.
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 dose variation by accurately determining the ion beam current at the final optical bend, ensuring precise control of the ion implantation process and maintaining uniformity across the wafer, even in the presence of neutralization effects.
Implementation Method 1
an ion source configured to form an ion beam
Implementation Method 2
These ions are extracted from the source by an extraction system, typically a set of electrodes, which energize and direct the flow of ions from the source, forming an ion beam
Implementation Method 3
Desired ions are separated from the ion beam in a mass analysis device, typically a magnetic dipole performing mass dispersion or separation of the extracted ion beam
Implementation Method 4
A bending element, such as an energy filter, is positioned downstream of the mass analyzer, whereby the bending element is configured to alter a path of the ion beam
Implementation Method 5
a first measurement apparatus, for example, is positioned downstream of the bending element and configured to determine a first ion beam current of the ion beam
Data Source
AI summary
An ion implantation has an ion source and a mass analyzer configured to form and mass analyze an ion beam. A bending element is positioned downstream of the mass analyzer, and respective first and second measurement apparatuses are positioned downstream and upstream of the bending element and configured to determine a respective first and second ion beam current of the ion beam. A workpiece scanning apparatus scans the workpiece through the ion beam. A controller is configured to determine an implant current of the ion beam at the workpiece and to control the workpiece scanning apparatus to control a scan velocity of the workpiece based on the implant current. The determination of the implant current of the ion beam is based, at least in part, on the first ion beam current and second ion beam current.