Nitrogen-Rich Silicon Nitride Capping Layer for MEMS
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Solution Overview
Problem
The miniaturization of semiconductor manufacturing processes leads to issues with hydrogen contamination in silicon nitride capping layers, causing pressure buildup in MEMS structures during thermal processing, which impairs their functionality.
Innovation Solution
A capping layer with a high carbon to hydrogen ratio, formulated as SiNxHy where x>1.33 and y>0, is deposited using high density plasma, reducing hydrogen outgassing and stabilizing N—H bonds, thereby minimizing pressure buildup at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If plasma-enhanced chemical vapor deposition is used to form silicon nitride capping layer, then the capping layer provides strength and hermeticity, but hydrogen contamination is incorporated causing pressure buildup during thermal processing
Solution Approach 1:
The patent changes the compositional parameters of the silicon nitride capping layer by controlling the nitrogen to hydrogen ratio. Specifically, it uses nitrogen-rich silicon nitride with composition SiNxHy where x>1.33 and y>0, optimizing the ratio to maximize nitrogen content while minimizing hydrogen. This parameter change transforms the material properties to reduce hydrogen outgassing during thermal processing while maintaining the required strength and hermeticity.
Solution Approach 2:
The patent employs a composite material approach by creating a nitrogen-rich silicon nitride compound with specific stoichiometry (SiNxHy where x>1.33). This composite composition combines the beneficial properties of silicon nitride (strength, hermeticity) while incorporating controlled amounts of nitrogen to suppress hydrogen outgassing. The optimized ratio of elements creates a material that simultaneously achieves mechanical integrity and thermal stability.
2Ease of manufacture
If thermal processing at elevated temperatures is applied, then further processing steps can be performed, but hydrogen releases from the capping layer causing vacuum compromise and pressure buildup
Solution Approach 1:
The patent applies preliminary action by pre-optimizing the capping layer composition before thermal processing. The nitrogen-rich silicon nitride is deposited with controlled hydrogen content and specific stoichiometry (x>1.33, y>0) in advance, creating a material that is inherently more resistant to hydrogen outgassing. This preliminary compositional preparation ensures that subsequent thermal processing can proceed without compromising vacuum integrity, as the pre-configured material structure suppresses hydrogen release.
3Ease of manufacture
If conventional silicon nitride deposition is used, then the process is simple and well-established, but the capping layer exhibits significant hydrogen contamination and outgassing
Solution Approach 1:
The patent modifies the deposition parameters by adjusting the plasma chemistry and process conditions to achieve nitrogen-rich silicon nitride with specific composition (SiNxHy where x>1.33, y>0). This parameter change in the deposition process transforms the material outcome from conventional hydrogen-rich silicon nitride to nitrogen-enriched silicon nitride with suppressed hydrogen content, reducing outgassing while maintaining process feasibility.
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 approach significantly reduces hydrogen outgassing during high-temperature processing, maintaining the performance of MEMS devices by limiting excess pressure in the cavity, with optimal results achieved when x=1.5 and y=0.5, resulting in reduced asymptotic outgassing levels.
Implementation Method 1
a silicon nitride capping layer with high carbon to hydrogen ratio is obtained when using a high density plasma in a plasma deposition tool
Implementation Method 2
the unavoidable incorporation of hydrogen in a silicon nitride layer, when typically grown from SiH4 and NH3 gas, is mainly incorporated in the form of N—H (covalent) bonds in this layer
Data Source
AI summary
Disclosed is a device comprising a substrate carrying a microscopic structure in a cavity capped by a capping layer including a material of formula SiNxHy, wherein x>1.33 and y>0. A method of forming such a device is also disclosed.