Ion Source Co-Gas Mitigation for Fluorine Radical Damage
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Solution Overview
Problem
Ion sources in ion implanters used for semiconductor fabrication experience reduced lifetime due to the accumulation of corrosive fluorine radicals generated during the dissociation of fluorine-containing source gases, which react with refractory metals and cause degradation, leading to reduced ion current and increased particulates that affect semiconductor device yield.
Innovation Solution
Introducing a co-gas, such as hydrogen or krypton, into the ion source chamber with a fluorine-containing dopant gas to react with dissociated fluorine constituents, forming hydrogen fluoride molecules that are removed, thereby reducing damage to the ion source chamber and extending its lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fluorine-containing source gas (GeF4 or BF3) is used for ion implantation, then dopant implantation is achieved, but free fluorine radicals are generated that react with refractory metals and reduce ion source lifetime
Solution Approach 1:
The patent converts the harmful free fluorine radicals into beneficial hydrogen fluoride molecules by introducing hydrogen gas. The fluorine radicals that would otherwise attack and degrade the refractory metal components react with hydrogen to form HF molecules, which are then pumped away. This transforms a destructive chemical species into a removable byproduct, extending ion source lifetime while maintaining dopant implantation effectiveness.
2Temperature
If refractory metals (tungsten or molybdenum) are used to construct ion source chamber for structural integrity at elevated temperatures, then structural stability is maintained, but fluorine radicals react with these metals causing degradation and reducing ion source lifetime
Solution Approach 1:
The patent introduces hydrogen gas as an intermediary substance that mediates between the harmful fluorine radicals and the refractory metal components. The hydrogen acts as a sacrificial reactant, preferentially combining with fluorine radicals to form HF molecules before they can attack the tungsten or molybdenum structures. This protective intermediary mechanism allows the refractory metals to maintain their structural integrity at high temperatures without suffering fluorine-induced degradation.
3Strength
If tungsten hexafluoride or molybdenum fluoride molecules form through reaction of fluorine radicals with refractory metals, then these molecules decompose on hot surfaces and condense at cathode surface, but this accumulation increases cathode size and degrades electron emissions
Solution Approach 1:
The patent applies preliminary action by introducing hydrogen gas that proactively consumes fluorine radicals before they can react with refractory metals to form WF6 or MoF6 molecules. This preventive measure stops the formation of harmful fluoride molecules at the source, preventing their subsequent decomposition and condensation on the cathode surface. By acting in advance, the hydrogen eliminates the root cause of cathode degradation rather than addressing the symptoms.
4Reliability
If excess free fluorine radicals are present in the ion source chamber, then they etch chamber housing material and internal components, but this generates particulates that are transported to substrate and reduce semiconductor device yield
Solution Approach 1:
The patent converts the harmful free fluorine radicals that cause etching and particulate generation into beneficial hydrogen fluoride molecules through reaction with hydrogen gas. This chemical transformation eliminates the etching mechanism that creates damaging particulates, while the resulting HF molecules are easily removed by the pumping system. The conversion transforms a dual-harm scenario (structural damage plus particulate contamination) into a clean, removable byproduct.
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 method effectively reduces the accumulation of corrosive species, maintaining stable ion current and improving the longevity of the ion source by capturing free fluorine radicals and preventing etching, thus enhancing the productivity and yield of semiconductor devices.
Implementation Method 1
the co-gas reacts with dissociated and ionized fluorine constituents to reduce damage to the ion source chamber
Implementation Method 2
an ion source for outputting an ion beam... generate an ion beam by ionizing within the source chamber a source gas
Implementation Method 3
The dopant ions physically bombard the wafer, enter the surface and come to rest below the surface, at a depth related to their energy
Implementation Method 4
a beamline assembly including a mass analysis magnet for mass resolving the ion beam
Data Source
AI summary
An ion implantation system for improving performance and extending lifetime of an ion source is disclosed. A fluorine-containing dopant gas source is introduced into the ion chamber along with one or more co-gases. The one or more co-gases can include hydrogen or krypton. The co-gases mitigate the effects caused by free fluorine ions in the ion source chamber which lead to ion source failure.