Low-Stress Silicon Oxide for Crack-Free MEMS Etching
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Solution Overview
Problem
Conventional methods for forming silicon oxide layers in MEMS fabrication result in high tensile stress, cracking, poor coverage, etch residue formation, and performance variations due to inadequate control over oxide deposition and etching processes, which damage mechanical structures and impair device functionality.
Innovation Solution
A method involving the decomposition of silicon precursor gases in a deposition chamber at a first temperature, followed by iterative deposition and annealing in an oxygen-rich environment at a higher temperature to achieve a highly conformal, low-stress silicon oxide layer that can be etched without residue, using techniques like LPCVD or PECVD, and subsequent HF vapor etching to remove any residue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional oxide deposition techniques (LTO, TEOS) are used to form silicon oxide layers, then the oxide can be deposited, but the oxide exhibits high tensile stress and cracks during deposition and high temperature processing
Solution Approach 1:
The patent changes the deposition temperature parameter from conventional low temperature (LTO) or standard temperature (TEOS) to a specific higher temperature range of 700-900°C. This parameter change transforms the oxide deposition process to produce layers with compressive or near-zero stress instead of high tensile stress, thereby preventing cracking during subsequent high temperature processing steps.
Solution Approach 2:
The patent employs oxygen plasma or ozone as strong oxidants during the deposition process to achieve complete oxidation of silicon and form high quality silicon oxide layers. This accelerated oxidation approach ensures thorough oxygen incorporation that reduces internal stress and prevents the formation of cracks, while also improving the uniformity and density of the deposited oxide layer.
2Area of stationary object
If conventional oxide deposition is used, then deposition can be achieved, but coverage of underlying surfaces is poor
Solution Approach 1:
The patent utilizes the higher deposition temperature (700-900°C) to enhance the mobility and reactivity of deposited species, enabling the oxide to conformally coat complex three-dimensional surfaces including vertical sidewalls and recessed areas. This temperature parameter change ensures uniform coverage across all surface geometries.
Solution Approach 2:
The use of oxygen plasma or ozone provides highly reactive oxygen species that rapidly and uniformly oxidize silicon surfaces, ensuring complete and conformal coverage even on complex three-dimensional structures with varying surface areas and geometries.
3Loss of substance
If conventional oxides are removed during MEMS formation, then oxide removal is achieved, but etch residue is produced on mechanical structures
Solution Approach 1:
The patent changes the oxide composition by depositing at 700-900°C in oxygen-rich environments, which produces silicon oxide layers with different chemical properties compared to conventional oxides. These modified oxide layers etch cleanly without leaving residue on the mechanical structures, as the high temperature deposition creates a more stoichiometric and uniform oxide composition.
Solution Approach 2:
The use of oxygen plasma or ozone during deposition ensures complete oxidation and removes carbon-containing contaminants that would otherwise form etch residues. This results in clean oxide layers that can be removed without leaving harmful residues on the MEMS mechanical structures.
4Productivity
If high temperature processing (800-1200°C) is applied to MEMS following oxide deposition, then processing can be completed, but oxide layers crack or damage MEMS structures
Solution Approach 1:
The patent changes the oxide stress state from highly tensile to compressive or near-zero by depositing at 700-900°C. This stress parameter change allows the oxide layer to withstand subsequent high temperature processing (800-1200°C) without cracking or damaging the delicate MEMS structures, as compressive stress prevents the formation of tensile cracks during thermal cycling.
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 produces silicon oxide layers with well-controlled stress, reduced contaminants, and uniform etching characteristics, preventing cracking and residue formation, thus enhancing the integrity and performance of MEMS devices.
Implementation Method 1
a silicon precursor gas is decomposed or oxidized in a deposition chamber containing a substrate at a first temperature
Implementation Method 2
a silicon precursor gas is decomposed or oxidized in a deposition chamber
Implementation Method 3
the deposition chamber is heated to a second temperature higher than the first temperature to anneal the silicon oxide layer
Implementation Method 4
subsequent HF vapor etching to remove any residue
Data Source
AI summary
A silicon oxide layer is formed by oxidation or decomposition of a silicon precursor gas in an oxygen-rich environment followed by annealing. The silicon oxide layer may be formed with slightly compressive stress to yield, following annealing, an oxide layer having very low stress. The silicon oxide layer thus formed is readily etched without resulting residue using HF-vapor.