Oxidation Protection Layer for Hermetic MEMS Substrate Bonding
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Solution Overview
Problem
Existing bonding methods for MEMS substrates face challenges such as oxidation of bonding metallization surfaces, which leads to reduced adhesion and insulation due to oxide layer formation, making it difficult to achieve a stable and hermetic connection.
Innovation Solution
A method involving the application of a thin oxidation protection layer, typically made of noble metals like gold or platinum, which diffuses into the bonding material and forms a liquid phase to prevent oxidation, allowing for a mechanically stable intermetallic phase formation between substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wet cleaning is used to remove oxides from bonding surfaces, then cleaning effectiveness is improved, but MEMS structures stick together during drying
Solution Approach 1:
The patent applies preliminary action by performing oxidation protection before the bonding process. An oxidation protection layer is deposited on the bonding surfaces before bonding occurs, preventing oxide formation in advance. This eliminates the need for subsequent wet cleaning that would cause structures to stick together during drying.
Solution Approach 2:
The patent converts the harmful effect of oxidation into a beneficial protective mechanism. By intentionally introducing an oxidation protection layer (even if it contains some oxide-forming materials), the method prevents unwanted oxidation of the bonding metallization. The protection layer acts as a sacrificial barrier that protects the critical bonding surfaces.
2Object-generated harmful factors
If dry vapor or plasma cleaning is used for MEMS structures, then structure sticking is avoided, but bonding metallization is carried over by reducing reagent
Solution Approach 1:
The patent introduces an intermediary oxidation protection layer between the bonding metallization and the cleaning environment. This protection layer acts as a mediator that shields the sensitive bonding surfaces from both oxidation and the harmful effects of reducing reagents during dry cleaning processes. The intermediary layer can be selectively removed or allows controlled cleaning without compromising the bonding metallization.
3Ease of manufacture
If resists are dry stripped with oxygen plasma, then lacquer removal is achieved, but oxide layers form on bonding metallization reducing adhesion
Solution Approach 1:
The patent applies preliminary oxidation protection before the plasma etching and resist stripping processes. By depositing an oxidation protection layer beforehand, the bonding metallization is protected from oxide formation during subsequent plasma treatments. This preliminary protective action allows aggressive plasma cleaning to remove resists while preventing harmful oxide formation on bonding surfaces.
Solution Approach 2:
The oxidation protection layer serves as a cushioning barrier that absorbs the harmful effects of oxygen plasma exposure. This beforehand cushioning protects the bonding metallization from direct plasma oxidation, allowing the plasma process to proceed for effective resist removal without compromising bond adhesion.
4Object-affected harmful factors
If thick oxidation protection layer is used, then oxidation prevention is improved, but material cost and diffusion control become problematic
Solution Approach 1:
The patent applies partial action by using a thin oxidation protection layer instead of a thick one. The protection layer is deposited to minimal necessary thickness to provide adequate oxidation protection during bonding. This partial application reduces noble metal consumption while maintaining sufficient protective function, as complete oxidation prevention requires only a thin barrier layer.
Solution Approach 2:
The patent changes the parameter of protection layer thickness from thick to thin. By optimizing the thickness parameter of the oxidation protection layer, the method achieves adequate protection with minimal material consumption. The thin layer is sufficient to prevent oxidation during the bonding process while reducing costs and controlling diffusion behavior.
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 effectively prevents oxidation of the bonding metallization, ensuring a strong and hermetic connection by maintaining the bonding material's integrity and promoting the formation of a stable intermetallic phase like Cu3Sn, suitable for MEMS applications.
Implementation Method 1
the first oxidation protection layer is heated to a first temperature, at which a modified first bonding area forms in which the material of the first oxidation protection layer interdiffuses at least partially into the first bonding material
Implementation Method 2
Particularly favorable for bonding are those methods that take place via a liquid phase during the bonding process
Implementation Method 3
a typically 0.5 μm thin oxidation protection layer made of an oxidation-resistant material, such as gold, platinum, palladium, ruthenium, molybdenum, is applied above the bond material layer
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 1e
AI summary
The invention provides a method for joining two substrates, a corresponding arrangement of two substrates, and a corresponding substrate. The method comprises the steps of: providing a first substrate (S1) with a first front (V1) and a first back (R1) and a second substrate (S2) with a second front (V2) and a second back (R2); applying a first diffusion barrier layer (D1) to the first front (V1) and a second diffusion barrier layer (D2) to the second front (V2); applying a first bonding area with at least one first bonding material layer to the first diffusion barrier layer (D1) and a second bonding area with at least one second bonding material layer (B21, B22) to the second diffusion barrier layer (D2); and applying a first oxidation protection layer (O1) at least to the first bonding area.Heating at least the first substrate (S1) in a state separated from the second substrate (S2) to a first temperature at which the first oxidation protection layer (O1) diffuses at least partially into the first bonding region to form a modified first bonding region (B1'); subsequently bringing the first substrate (1a) and the second substrate (1b) together so that the first modified first bonding region (B1') and the second bonding region (B2) are opposite each other; and heating the first and second substrates (S1; S2) in the brought-together state to a second temperature at which at least one component of the first or second bonding region melts, and subsequently cooling to form a solid bonding region between the first substrate (S1) and the second substrate (S2).