Nitrogen-Plasma Surface Treatment for Direct Bonding
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Solution Overview
Problem
Existing methods for direct bonding of silicon oxide or silicon surfaces often result in defective interfaces, particularly at low temperatures, due to the presence of defects such as bubbles and contamination, which are not adequately addressed by previous low-temperature bonding techniques.
Innovation Solution
A single surface treatment step using a nitrogen-based plasma generated by an inductively coupled plasma source, with a potential difference of less than 50V, is applied to form a superficial thin film of silicon oxynitride with a thickness of less than 5 nm, reducing defects and enhancing bonding interface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional plasma activation methods (oxygen or argon plasma with RIE/ICP) are used to activate silicon or silicon oxide surfaces for low-temperature bonding, then surface energy is increased and bonding capability is improved, but bonding interfaces present defects such as bubbles and contamination that are not adequately eliminated
Solution Approach 1:
The invention changes the chemical composition parameter of the plasma from conventional oxygen or argon to nitrogen-based plasma. This parameter change transforms the surface chemistry to create a nitrogen-containing surface layer that effectively eliminates defects like bubbles and contamination while maintaining high bonding capability at low temperatures.
Solution Approach 2:
The invention creates a composite surface structure by forming a nitrogen-containing surface layer on silicon or silicon oxide. This composite surface structure combines the properties of the base material with nitrogen-containing groups, resulting in a surface that is both highly reactive for bonding and free from typical plasma-induced defects.
2Strength
If high-temperature heat treatment (about 1000°C) is applied after bonding to enhance bonding energy, then bonding strength is improved, but the method becomes inadmissible for many applications requiring low-temperature processing
Solution Approach 1:
The invention changes the surface chemistry parameter through nitrogen-based plasma treatment, which creates a highly reactive nitrogen-containing surface layer. This chemical modification enables strong bonding at low temperatures by increasing surface energy and reactivity, eliminating the need for high-temperature heat treatment while maintaining or improving bonding strength.
3Object-affected harmful factors
If multiple surface treatment steps (plasma activation followed by RCA cleaning and drying) are used to prepare surfaces for bonding, then surface cleanliness is improved, but process complexity and time are increased
Solution Approach 1:
The invention merges multiple surface treatment functions into a single nitrogen-based plasma treatment step. This single step simultaneously achieves surface activation, cleaning, and defect elimination that previously required separate plasma activation, RCA cleaning, and drying steps, thereby reducing process complexity while maintaining or improving surface quality.
Solution Approach 2:
The nitrogen-based plasma treatment performs preliminary surface preparation by creating a nitrogen-containing surface layer that is inherently free from contamination. This preliminary action prevents the need for subsequent cleaning steps, as the plasma treatment itself eliminates bubbles and contamination while preparing the surface for bonding.
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 achieves a significantly reduced number of defects, potentially defect-free bonding interfaces, maintaining interface quality even after heat treatment up to 1300°C, with improved electron density and reduced surface and volume concentrations of -OH bonds.
Implementation Method 1
a single surface treatment step forming a superficial thin film of silicon oxynitride with a thickness of less than 5 nm, by means of a nitrogen-based plasma generated by an inductively coupled plasma source
Implementation Method 2
the nitride layer is formed by NH3 plasma enhanced chemical vapor deposition (PECVD)
Implementation Method 3
a nitrogen-based plasma generated by an inductively coupled plasma source
Data Source
AI summary
Two plates, each comprising a thin layer of silicon or silicon oxide at a surface thereof, are bonded by subjecting the thin layer of at least one of the plates to a surface treatment step forming a silicon oxynitride superficial thin film with a thickness of less than 5nm. The thin film is performed with a nitrogen-based plasma generated by an inductively coupled plasma source. Furthermore, a potential difference applied between the plasma and a substrate holder supporting said plate during the surface treatment step is less than 50 V, advantageously less than 15 V and preferably zero. This enables a defect-free bonding interface to be obtained irrespective of a temperature of any heat treatment carried out after a contacting step between the respective thin layers of the two plates.