Microstructure Sacrificial Layer Etching With Residue Removal
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Solution Overview
Problem
Existing methods for etching silicon dioxide sacrificial layers in microstructures and semiconductor devices using hydrogen fluoride (HF) vapour result in undesirable residual layers, particularly due to unetched impurities like silicon, carbon, and ammonium salts, which form residues that degrade the final product quality.
Innovation Solution
A method involving the use of HF vapour etching followed by sequential or concurrent removal of residual layers using gases like hydrogen, oxygen, fluorine, Xenon Difluoride (XeF2), or heating to convert these residues into volatile substances, which are then pumped out, thereby reducing residual layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HF vapour etching is used to remove silicon dioxide sacrificial layers, then the etching process is effective and widely used, but residual layers of unetched impurities (silicon, carbon, ammonium salts) form and degrade product quality
Solution Approach 1:
The patent segments the etching process into multiple distinct steps: (1) HF vapour etching to remove silicon dioxide, (2) oxidation step to convert residual impurities to volatile oxides, and (3) removal of the oxidized residues. This segmentation allows each step to be optimized independently, solving the contradiction between etching efficiency and residual layer quality.
Solution Approach 2:
The patent introduces an intermediary oxidation step using oxygen or oxygen-containing gases. This intermediary process converts the non-volatile impurity residues (silicon, carbon, ammonium salts) into volatile oxides that can be easily removed, thereby eliminating the residual layer problem while maintaining the effectiveness of the initial HF etching.
2Reliability
If doped silicon dioxide layers are used to improve step coverage and thermal properties, then layer performance is improved, but unetched impurity materials accumulate in the condensed fluid layer and form undesirable residues
Solution Approach 1:
The patent converts the harmful effect of doped impurities (which normally accumulate as residues) into a beneficial outcome by introducing an oxidation step. The impurities are transformed into volatile oxides that can be removed, turning the previously harmful residue-forming materials into easily removable byproducts.
Solution Approach 2:
The patent changes the chemical state of the impurity materials through oxidation. By introducing oxygen and controlling temperature parameters, the non-volatile impurities are converted into volatile oxides, fundamentally changing their removability and eliminating the residue problem while preserving the benefits of doped layers.
3Ease of manufacture
If conventional HF vapour etching is used, then the process is simple and widely applicable, but residual layers must be removed requiring additional process steps
Solution Approach 1:
The patent merges the etching and residue removal functions into a coordinated two-step process. The oxidation step is designed to work synergistically with the HF etching, where the oxidized residues are automatically removed in the same processing sequence, reducing the need for separate, additional 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
The method effectively minimizes residual layers, ensuring higher product reliability and quality by converting impurities into volatile forms that can be easily removed, addressing the issue of residues in 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 + 4HF → SiF4 + 2H2O
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
removing a residual layer formed when HF vapour etching the layer of silicon dioxide... converting impurities into volatile forms that can be easily removed
Implementation Method 4
heating to convert these residues into volatile substances, which are then pumped out
Data Source
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.