Roughened Germanium Layer Penetrates Anti-Stiction Coating for Eutectic Bonding
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Solution Overview
Problem
The existing methods for bonding cap wafers to device wafers with anti-stiction coatings using aluminum germanium (AlGe) eutectic material often result in a poor bond, leading to structural weaknesses and potential separation of the cap wafer from the device wafer, known as 'cap wafer flyoff', which can cause device failure.
Innovation Solution
A method involving the formation of a roughened polycrystalline germanium surface on the cap wafer that penetrates the anti-stiction coating layer, allowing direct contact with the metal layer and enabling the formation of a uniform AlGe eutectic bond through heat and pressure application, thereby enhancing the bond strength and preventing cap wafer separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an anti-stiction coating is formed on the device wafer surface, then stiction prevention is improved, but AlGe eutectic bond strength deteriorates
Solution Approach 1:
A roughened germanium layer is formed on the cap wafer surface before bonding. This preliminary surface preparation enables the germanium to penetrate through the anti-stiction coating during bonding, creating direct contact with the metal layer for strong eutectic bonding while preserving the anti-stiction coating's protective function.
Solution Approach 2:
The roughened germanium layer acts as an intermediary that facilitates bonding through the anti-stiction coating. The germanium penetrates the coating to establish direct contact with the metal layer, enabling eutectic bond formation without removing or damaging the anti-stiction coating itself.
2Strength
If pressure is applied to bond the cap wafer to the device wafer, then bond formation is improved, but cap wafer flyoff increases
Solution Approach 1:
The surface morphology of the germanium layer is changed from smooth to roughened. This parameter change increases surface area and creates penetration points that allow the germanium to effectively penetrate the anti-stiction coating under bonding pressure, distributing stress and preventing cap wafer flyoff.
3Ease of manufacture
If a smooth germanium surface is used, then manufacturing simplicity is improved, but bond uniformity deteriorates
Solution Approach 1:
The germanium layer is deliberately roughened during the deposition process as a preliminary action. This roughened surface is then used for bonding, enabling uniform penetration through the anti-stiction coating and consistent eutectic bond formation across the entire bonding interface.
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 ensures a strong, hermetic seal and reduces the likelihood of cap wafer flyoff, improving the reliability and sensitivity of microelectromechanical systems (MEMS) devices by facilitating a uniform AlGe eutectic bond formation without compromising the anti-stiction coating.
Implementation Method 1
applying sufficient pressure to the second semiconductor substrate for at least a portion of the roughened germanium layer to penetrate the anti-stiction coating layer
Implementation Method 2
forming a mechanical bonding material between the first substrate and the second substrate. The forming of the mechanical bonding material includes applying heat to the roughened germanium layer and the metal layer
Implementation Method 3
forming a uniform AlGe eutectic bond through heat and pressure application
Implementation Method 4
The bonding material includes a metal of the metal layer and germanium of the germanium layer
Data Source
AI summary
A cap wafer bonded to a device wafer by a metal polysilicon germanium material to form a sealed chamber around a semiconductor device is provided. On the cap wafer, a stack of silicon (Si), polycrystalline silicon germanium (SiGe), and polycrystalline germanium (Ge) is formed. This stack of material layers is formed to intentionally have a roughened germanium surface. A metal structure is formed on a second wafer, having an anti-stiction coating layer on the surface of the metal structure. A metal silicon germanium bonding material is formed by placing the metal structure and germanium structure in contact and applying heat and pressure. The roughened germanium layer penetrates the anti-stiction coating layer upon application of the pressure. The germanium that penetrates to the metal is free of interfacial anti-stiction coating and allows for eutectic bond formation upon application of heat.