MEMS Gap Control Structures for Eutectic Bonding Precision
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Solution Overview
Problem
During the mass production of MEMS devices, it is challenging to maintain proper eutectic bonding and critical gaps between wafers, leading to inaccurate readings in devices like pressure sensors and other MEMS structures, as pressure control is difficult to maintain uniformly.
Innovation Solution
The implementation of a gap control structure on a silicon wafer, which includes a cavity and an oxide layer, bonded to another silicon wafer, with a eutectic bond to a third wafer, ensuring the maintenance of predetermined gaps through standoffs and a gap control structure that prevents gap narrowing during bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If eutectic bonding is performed during MEMS mass production, then productivity is improved, but manufacturing precision deteriorates due to inconsistent gap control
Solution Approach 1:
A gap control structure is introduced as an intermediary element between the first and second silicon wafers. This structure includes a cavity in the first wafer, an oxide layer coating the cavity walls, and a standoff extending into the cavity that contacts the second wafer during bonding. The intermediary structure physically defines and maintains the critical gap spacing, ensuring consistent gap control across all devices in mass production while enabling efficient eutectic bonding processes.
2Strength
If pressure is increased during eutectic bonding, then bonding strength is improved, but gap size control deteriorates due to gap narrowing
Solution Approach 1:
The gap control structure performs preliminary anti-action by pre-establishing the desired gap geometry before bonding occurs. The cavity and standoff are formed in advance with precise dimensions, creating a physical template that prevents gap narrowing during the bonding process. This allows high bonding pressure to be applied without compromising gap size, as the gap control structure resists compression and maintains the intended spacing throughout the bonding process.
Solution Approach 2:
The cavity and oxide layer are formed on the first silicon wafer before the eutectic bonding process. This preliminary preparation creates a pre-configured gap control structure that will define the gap geometry during subsequent bonding operations, ensuring that the critical gaps are established with high precision before the bonding pressure is applied.
3Measurement precision
If gap size is reduced to improve sensor accuracy, then measurement precision is improved, but reliability deteriorates due to inconsistent bonding
Solution Approach 1:
The gap control structure enables precise control of the gap parameter by physically defining the spacing through the cavity and standoff geometry. The oxide layer thickness, cavity dimensions, and standoff height are controlled parameters that directly determine the final gap size. By changing these geometric parameters, precise gap control is achieved, improving sensor accuracy while maintaining bonding reliability through consistent structural definition.
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 proper eutectic bonding and maintains critical gaps within MEMS devices, enhancing the accuracy and reliability of MEMS devices by controlling the gap size and preventing excessive bonding pressure.
Implementation Method 1
A first side of a second silicon wafer is bonded to the first side of the first silicon wafer
Implementation Method 2
A eutectic bond is bonding the second side of the second silicon wafer to a third silicon wafer
Data Source
AI summary
Provided herein is an apparatus including a cavity in a first side of a first silicon wafer, and an oxide layer on the first side and in the cavity. A first side of a second silicon wafer is bonded to the first side of the first silicon wafer. A gap control structure is on a second side of the second silicon wafer, and a MEMS structure in the second silicon wafer. A eutectic bond is bonding the second side of the second silicon wafer to a third silicon wafer. A lower cavity is between the second side of the silicon wafer and the third silicon wafer, wherein the gap control structure is outside of the lower cavity and the eutectic bond.