Microstructure Fabrication After HF Vapour Etching Residues
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Solution Overview
Problem
Existing HF vapour etching processes for silicon dioxide in microstructures and semiconductor devices leave behind undesirable residual layers, particularly due to unetched impurities like silicon, carbon, and ammonium salts, which form during the etching process and are difficult to remove.
Innovation Solution
A method involving the use of hydrogen fluoride (HF) vapour etching followed by sequential or concurrent treatments with hydrogen, oxygen, fluorine, or Xenon Difluoride (XeF2) vapour to react with and remove residual silicon, carbon, or ammonium salt impurities, utilizing a vacuum pumping system to evacuate by-products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If HF vapour etching is used to remove silicon dioxide sacrificial layer, then the sacrificial layer is effectively removed, but residual layers of silicon and other impurities remain on the microstructure surfaces
Solution Approach 1:
The patent converts the harmful residual silicon and impurity layers into removable volatile compounds by exposing them to fluorine-containing environments. The fluorine reacts with the residual silicon to form silicon tetrafluoride (SiF4) gas, which can be easily evacuated, thereby transforming the problematic residue into a beneficial removable gas phase product.
Solution Approach 2:
The patent changes the chemical environment parameters by introducing fluorine-containing gases or compounds after the HF vapour etching process. This parameter change enables the conversion of non-volatile residual silicon into volatile silicon fluorides, allowing for effective removal through vacuum evacuation or gas flow.
2Ease of manufacture
If doping materials are added to silicon dioxide layers, then step coverage and thermal properties are improved, but unetched impurity materials accumulate in the condensed fluid layer during HF vapour etching
Solution Approach 1:
The patent addresses the accumulation of doped impurities in the condensed fluid layer by introducing fluorine-containing species that react with these impurities. The fluorine converts the accumulated silicon and other impurity materials into volatile compounds that can be removed from the condensed fluid layer, preventing contamination and maintaining process effectiveness.
3Manufacturing precision
If multiple processing steps are added to remove residual layers, then surface cleanliness is improved, but process complexity and time increase
Solution Approach 1:
The patent merges the etching process with a residual layer removal function by introducing fluorine-containing gases during or after the HF vapour etching step. This combination allows both the silicon dioxide removal and the residual silicon/impurity removal to occur in a single integrated process sequence, reducing the total number of separate processing steps.
Solution Approach 2:
The fluorine-containing environment serves multiple functions: it continues the etching of remaining silicon dioxide while simultaneously reacting with residual silicon and impurity layers to form removable volatile compounds. This multi-functional approach eliminates the need for separate cleaning steps.
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
Significantly reduces the presence of residual layers, especially silicon-based residues, by exploiting differential etching rates and volatility of reaction products, ensuring cleaner microstructures and semiconductor devices.
Implementation Method 1
An HF vapour etch is a plasma-less chemical etch and is described by the reaction equations: SiO2(s) + 4HF(g) → SiF4(g) + 2H2O(g)
Implementation Method 2
Of all the compounds associated with the above described HF vapour etching process, water (H2O) has the lowest vapour pressure and therefore forms the basis of the condensed fluid layer 5
Implementation Method 3
reacting the silicon with a hydrogen gas to produce silane (SiH4)
Implementation Method 4
reacting the silicon with a fluorine gas to produce silicon tetrafluoride (SiF4)
Implementation Method 5
utilizing a vacuum pumping system to evacuate by-products
Data Source
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AI summary
There is provided a method of producing a microstructure that comprises employing a hydrogen fluoride (HF) vapour to etch a sacrificial layer of silicon dioxide (SiO2) and thereafter removing a residual layer formed when HF vapour etching the layer of silicon dioxide. The residual layer may comprise silicon, ammonium salt or carbon and various techniques are disclosed for removing such layers. These techniques may be applied concurrently, or sequentially, to the microstructure. The described methodologies therefore produce microstructures that exhibits reduced levels of residue when as compared to those techniques known in the art.