Variable-Thickness Extraction Plate for Uniform Ribbon Ion Beams
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Solution Overview
Problem
Existing ion sources, particularly indirectly heated cathode (IHC) ion sources, face challenges in achieving uniformity of the ribbon ion beam, leading to uneven ion concentrations during semiconductor fabrication, which can be addressed by improving the extraction process.
Innovation Solution
An ion source with an extraction plate featuring a variable thickness, including protrusions on its interior or exterior surface, which increases the loss area for ions and electrons, thereby reducing plasma density and enhancing beam current uniformity across the width of the extracted ion beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional extraction plate with uniform thickness is used, then the structure is simple and easy to manufacture, but the beam current uniformity along the width direction deteriorates
Solution Approach 1:
The extraction plate is designed with variable thickness, featuring protrusions at specific locations (e.g., center or edges) that create localized differences in plasma loss area. This local variation in geometry allows different regions of the extraction aperture to have different plasma density characteristics, thereby improving beam current uniformity across the width direction without requiring complete structural redesign
Solution Approach 2:
The thickness parameter of the extraction plate is deliberately varied across different spatial locations rather than maintaining a constant value. By changing the geometric parameter (thickness) in specific regions, the plasma loss area is modified locally, which directly affects plasma density distribution and improves the uniformity of extracted beam current
2Manufacturing precision
If additional components such as quadrupole lenses are added to compensate for non-uniformity, then the beam current uniformity improves, but the system complexity and cost increase
Solution Approach 1:
The solution extracts the uniformity correction function from the beam line system and integrates it directly into the extraction plate structure. Instead of using separate compensating components downstream, the extraction plate itself is designed with variable thickness to pre-correct the plasma density distribution, thereby eliminating the need for additional quadrupole lenses or other beam shaping components
Solution Approach 2:
The extraction plate performs dual functions: it serves as the structural component for ion extraction and simultaneously acts as the plasma uniformity correction element. The variable thickness design enables the extraction plate to self-regulate plasma density distribution across the aperture, eliminating the need for external correction mechanisms and reducing overall system complexity
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
The solution significantly improves the uniformity of the beam current along the width direction by 20% to 50% by modifying the plasma density distribution through the use of a protrusion on the extraction plate, making it more uniform and suitable for existing ion sources.
Implementation Method 1
a plasma generator to generate a plasma within the chamber
Implementation Method 2
As current is passed through the filament, the filament emits thermionic electrons, which are accelerated toward the more positively charged cathode. These thermionic electrons serve to heat the cathode, in turn causing the cathode to emit electrons into the chamber
Data Source
AI summary
An ion source having an extraction plate with a variable thickness is disclosed. The extraction plate has a protrusion on its interior or exterior surface proximate the extraction aperture. The protrusion increases the thickness of the extraction aperture in certain regions. This increases the loss area in those regions, which serves as a sink for ions and electrons. In this way, the plasma density is decreased more significantly in the regions where the extraction aperture has a greater thickness. The shape of the protrusion may be modified to achieve the desired plasma uniformity. Thus, it may be possible to create an extracted ion beam having a more uniform ion density. In some tests, the uniformity of the beam current along the width direction was improved by between 20% and 50%.