Plasma-Generated HF for Oxide Removal
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Solution Overview
Problem
Conventional methods for removing native oxide layers from semiconductor and electronic components using hydrofluoric acid pose health and environmental risks due to the use of toxic chemicals and require exposure to ambient conditions, which can lead to oxide regrowth.
Innovation Solution
An electron beam is directed through a gas flow containing argon with trace concentrations of sulfur hexafluoride and water or ammonia, generating a plasma that produces low concentrations of gaseous HF, which effectively removes oxide layers without the hazards associated with aqueous HF solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aqueous hydrofluoric acid is used to remove oxide layers, then effective oxide removal is achieved, but serious health effects and environmental risks occur
Solution Approach 1:
The invention changes the physical state of HF from aqueous to gaseous form, and generates it in-situ within the plasma processing chamber. This parameter change allows HF to be delivered directly to the substrate surface in a controlled manner, achieving effective oxide removal while minimizing health and environmental risks associated with handling and storing aqueous HF solutions
Solution Approach 2:
The invention uses plasma as an intermediary medium to generate and deliver HF species to the substrate. Instead of directly applying aqueous HF, the plasma process uses reactive species in the plasma environment to produce HF in-situ, which then reacts with oxide layers. This intermediary approach provides precise control over HF delivery and eliminates the need for handling toxic aqueous solutions
2Reliability
If wet etching with HF is performed, then oxide layers are removed, but oxide regrowth occurs upon exposure to ambient conditions
Solution Approach 1:
The invention performs oxide removal as a preliminary action within the plasma processing chamber before the substrate is exposed to ambient conditions. By completing the oxide removal step in-situ under controlled plasma environment, the substrate surface is prepared and immediately protected, preventing oxide regrowth that would occur if the substrate were exposed to ambient air after wet etching
Solution Approach 2:
The plasma processing chamber provides an inert or controlled atmosphere environment that prevents oxide regrowth during and after the oxide removal process. The plasma environment maintains the substrate surface in a protected state, and the process can be integrated with subsequent processing steps without requiring exposure to ambient conditions, thereby preventing oxide regrowth
3Productivity
If large quantities of aqueous HF are used for industrial oxide removal, then effective processing is achieved, but toxic chemical waste is generated
Solution Approach 1:
The invention enables the system to generate its own HF species in-situ within the plasma chamber from precursor gases, eliminating the need for external HF supply and waste disposal infrastructure. The plasma process self-generates the necessary reactive species for oxide removal, and the byproducts can be more easily managed through standard plasma exhaust systems rather than requiring handling and disposal of toxic aqueous HF waste
Solution Approach 2:
The invention changes the delivery method of HF from liquid/aqueous form requiring large volumes and generating liquid waste to gaseous form generated in-situ from precursor gases. This parameter change transforms the waste stream from difficult-to-manage toxic liquid HF waste to gaseous byproducts that can be more easily treated and disposed of through standard plasma process exhaust systems
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 allows for in situ removal of native oxides with reduced health and environmental risks, producing a benign aluminum fluoride passivation layer that maintains surface integrity for applications like UV optical surfaces.
Implementation Method 1
An electron beam directed into the gas flow forms a plasma from the gas flow, with energy from the electron beam dissociating the F atoms from the precursor gas components
Implementation Method 2
which then produces HF from the hydrogen-containing precursor through hydrogen abstraction
Data Source
AI summary
Methods and apparatuses for the production of HF in an electron-beam generated plasma. A gas containing fluorine, hydrogen, and an inert gas such as argon, e.g., Ar/SF6/H2O or Ar/SF6/NH3 flows into a plasma treatment chamber to produce a low pressure gas in the chamber. An electron beam directed into the gas forms a plasma from the gas, with energy from the electron beam dissociating the F-containing molecules, which react with H-containing gas to produce HF in the plasma. Although the concentration of the gas phase HF in the plasma is a very small fraction of the total gas in the chamber, due to its highly reactive nature, the low concentration of HF produced by the method of the present invention is enough to modify the surfaces of materials, performing the same function as aqueous HF solutions to remove oxygen from an exposed material.