Carbon Sacrificial Layer for Residue-Free Semiconductor Microphone Cavities
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Solution Overview
Problem
The existing methods for fabricating cavity structures in semiconductor devices, such as silicon microphones, face challenges with wet chemical etching, which involves costly and time-consuming processes, potential underetching, contamination, and environmental hazards due to the use of hazardous chemicals like hydrofluoric acid.
Innovation Solution
The use of a carbon layer as a sacrificial material deposited by chemical vapor deposition, which is subsequently removed through dry etching, eliminating the need for wet chemical etching and reducing environmental impact by converting carbon into gaseous reaction products like CO and CO2, allowing for residue-free cavity formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wet chemical etching is used to remove sacrificial layers like TEOS oxide, then the cavity structure can be formed, but the process becomes expensive, time-consuming, and leads to underetching and contamination
Solution Approach 1:
The patent uses a carbon sacrificial layer that is deliberately designed to be temporary and easily removable. The carbon layer serves its purpose during fabrication and is then completely removed through simple thermal treatment or plasma processing, leaving no residue. This disposable approach eliminates the need for complex wet chemical etching processes and multiple cleaning steps, directly resolving the contradiction between manufacturing precision and process complexity.
Solution Approach 2:
The patent changes the material parameter from traditional TEOS oxide to carbon, and changes the removal mechanism parameter from wet chemical etching to thermal decomposition or plasma oxidation. This parameter change transforms the removal process into a simpler, more controlled operation that avoids underetching and contamination while maintaining cavity structure quality, effectively resolving the technical contradiction.
2Manufacturing precision
If wet chemical etching is used to remove sacrificial layers, then cavity structures can be formed, but environmental hazards and equipment costs increase
Solution Approach 1:
The carbon sacrificial layer is designed as a temporary material that decomposes cleanly through thermal treatment or plasma oxidation. This removal process produces no harmful chemical waste and requires no special environmental controls, eliminating the environmental hazards associated with wet chemical etching while maintaining precise cavity structure formation.
Solution Approach 2:
The patent converts the potential harm of using a sacrificial material (which must be removed) into a benefit by choosing carbon as the sacrificial material. Carbon can be completely decomposed or oxidized without leaving harmful residues, turning what could be a contamination source into a clean removal process that benefits environmental safety while maintaining manufacturing precision.
3Manufacturing precision
If wet chemical etching is used, then sacrificial layers can be removed, but fluid exchange and drying steps increase process time
Solution Approach 1:
The carbon sacrificial layer is removed through thermal decomposition or plasma oxidation in a single step, completely eliminating the multi-step wet chemical etching process including fluid exchange and drying. This single-step removal maintains cavity structure cleanliness while dramatically reducing processing time, directly resolving the contradiction between manufacturing precision and loss of time.
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 method reduces defect density, minimizes contamination, and lowers production costs by enabling a batch process with high throughput, avoiding the need for expensive equipment and hazardous chemicals, while ensuring a clean and residue-free cavity structure.
Implementation Method 1
a carbon layer which is deposited by chemical vapor deposition (CVD)
Implementation Method 2
the carbon layer is removed by means of dry etching
Implementation Method 3
removed through dry etching using oxygen plasma
Data Source
AI summary
Embodiments show a method for fabricating a cavity structure, a semiconductor structure, a cavity structure for a semiconductor device and a semiconductor microphone fabricated by the same. In some embodiments the method for fabricating a cavity structure comprises providing a first layer, depositing a carbon layer on the first layer, covering at least partially the carbon layer with a second layer to define the cavity structure, removing by means of dry etching the carbon layer between the first and second layer so that the cavity structure is formed.