Ion Beam Charge Stripping for Trace Metal Contamination Control
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Solution Overview
Problem
High-energy ion implantation systems face challenges in filtering trace metal ions from desired higher-charged ions, leading to potential contamination in semiconductor wafers, which can impact device performance and are difficult to separate using existing downstream analyzing magnets, electrical filters, and velocity filters.
Innovation Solution
The system employs a charge stripper to convert lower-charge state ions to higher-charge state ions and a charge selector to remove trace metal ions, ensuring only the desired ions at the higher charge state are implanted, using a gas like sulfur hexafluoride for efficient electron stripping and an electromagnetic mass analyzer for selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If downstream analyzing magnets, electrical filters, and velocity filters are used to separate trace metal ions from desired higher-charged ions, then ion beam purity is improved, but the ability to separate ions with identical charge-to-mass ratios fails because trace metal ions and desired ions have the same charge-to-mass ratio
Solution Approach 1:
The patent changes the charge state parameter of the ion beam by passing it through a charge stripping apparatus that uses a gas medium (such as sulfur hexafluoride) to strip electrons from the ions. This transforms the charge-to-mass ratio of the desired ions, creating a difference that allows downstream filters to successfully separate trace metal ions from the desired ions, thereby resolving the separation difficulty while maintaining ion beam purity
2Productivity
If high-energy ion implantation is performed to achieve desired doping depth and concentration, then implantation effectiveness is improved, but trace metal contamination increases because trace metal ions are accelerated to high energies along with desired ions
Solution Approach 1:
The patent applies charge stripping and charge state selection before the acceleration stage. By converting the ion beam to a higher charge state and selecting the desired charge state before acceleration, the system ensures that only purified ions are subsequently accelerated to high energies. This preliminary purification action prevents trace metal contamination while maintaining implantation effectiveness
Solution Approach 2:
The charge stripping apparatus using a gas medium (such as sulfur hexafluoride) acts as an intermediary between the ion source and the acceleration stage. This intermediary process selectively modifies the charge state of the ion beam, enabling subsequent separation of trace metal ions and allowing high-energy implantation without contamination
3Productivity
If charge stripping is performed to convert lower-charge state ions to higher-charge state ions, then beam current at high energy is improved, but charge state distribution control becomes more difficult due to the time varying nature of RF acceleration fields and multiple acceleration gaps
Solution Approach 1:
The patent segments the acceleration process into distinct stages with the charge stripping apparatus positioned at a specific location within the RF linear accelerator. By placing the charge stripping section at a predetermined location, the system divides the complex RF acceleration process into manageable segments, allowing control of charge state transformation while maintaining overall beam current and energy delivery
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 trace metal contamination in semiconductor wafers by effectively separating and removing trace metal ions from the ion beam before implantation, improving the purity and performance of high-energy ion implants.
Implementation Method 1
A charge stripping apparatus is provided in the system and is configured to strip at least one electron from the first charge state ions along the beamline, thereby defining a stripped ion beam comprising second charge state ions and the trace metal ions.
Implementation Method 2
A charge selector is positioned downstream of the charge stripping apparatus, wherein the charge selector is configured to selectively pass only the desired ions at the second charge state therethrough.
Implementation Method 3
An accelerator is configured to accelerate the mass analyzed ion beam from a first energy to a second energy
Data Source
AI summary
A method for implanting high charge state ions into a workpiece while mitigating trace metal contamination includes generating desired ions at a first charge state from a desired species in an ion source, as well as generating trace metal ions of a contaminant species in a first ion beam. A charge-to-mass ratio of the desired ions and the trace metal ions is equal. The desired ions and trace metal ions are extracted from the ion source. At least one electron stripped from the desired ions to define a second ion beam of the desired ions at a second charge state and the trace metal ions. Only the desired ions from the second ion beam are selectively passed only through a charge selector to define a final ion beam of the desired ions at the second charge state and no trace metal ions, and the desired ions of the second charge state are implanted into a workpiece.