Embedded MEMS on SOI Substrate for IC Integration
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Solution Overview
Problem
The integration of micromechanical devices (MEMS) and integrated circuits (IC) on a single substrate is challenging due to compatibility issues with thermal processing steps, stress management, and complex backend integration, which affects the performance and sensitivity of both components.
Innovation Solution
A fully embedded micromechanical device is manufactured using a silicon on insulator (SOI) substrate with a monocrystalline silicon layer, buried oxide layer, and polysilicon barriers, allowing for interleaved fabrication steps that minimize stress and enable high integration density without damaging the substrate, using shallow and deep trench etching and epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MEMS-device is fabricated first, then MEMS structure is available, but the wafer surface must be planarized and the MEMS structure must withstand harsh semiconductor fabrication process conditions
Solution Approach 1:
The patent merges the fabrication processes of MEMS and IC devices into a unified sequence where IC devices are fabricated first on the silicon substrate, followed by MEMS device fabrication on top. This integration eliminates the need for separate planarization steps and allows both devices to share the same substrate and processing environment, reducing overall integration complexity.
Solution Approach 2:
The IC devices are fabricated in advance before MEMS device fabrication begins. This preliminary action ensures that the silicon substrate is already prepared with the necessary electronic components, and subsequent MEMS processing steps can proceed without requiring additional substrate preparation or planarization.
2Reliability
If IC device is fabricated first, then integrated circuit is available, but metallization must withstand high temperature annealing steps which are incompatible with IC metallization scheme
Solution Approach 1:
The patent segments the fabrication process into distinct temperature zones and sequences. IC devices are fabricated first at standard temperatures, then MEMS devices are fabricated at higher temperatures. This segmentation allows each device type to receive appropriate processing conditions without compromising the other, as the IC metallization is already formed and protected before high-temperature MEMS processing begins.
3Weight of moving object
If bulk micromechanics is used, then large mass is available for movable parts, but combination of different thermal processing steps is needed which conflicts with IC integration
Solution Approach 1:
The patent combines bulk micromechanics fabrication with IC fabrication in a unified process sequence. The silicon substrate serves as both the base for IC devices and the material source for bulk micromechanical structures. By integrating both fabrication approaches on the same substrate with a unified process flow, the patent eliminates the need for separate thermal processing sequences that would otherwise be required for standalone bulk micromechanics devices.
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 provides MEMS devices with mechanical properties similar to bulk micromechanics, integrated with IC devices on a single chip, offering improved performance and sensitivity without the need for additional chip processing, and reduces production costs by integrating MEMS and IC fabrication steps within standard CMOS processes.
Implementation Method 1
a monocrystalline silicon layer which is arranged on a buried silicon oxide layer is applied for manufacturing e.g. a movable component of the MEMS-device
Implementation Method 2
Often, the sensor uses electrostatic actuation and capacitive read-out for detecting a displacement of a movable component with respect to a static component
Implementation Method 3
capacitive read-out for detecting a displacement of a movable component with respect to a static component of the micromechanical device
Data Source
AI summary
A fully embedded micromechanical device and a system on chip is manufactured on an SOI-substrate. The micromechanical device comprises a moveable component having a laterally extending upper and lower surface and vertical side surfaces. The upper surface is adjacent to an upper gap which laterally extends over at least a part of the upper surface and results from the removal of a shallow trench insulation material. The lower surface is adjacent to a lower gap which laterally extends over at least a part of the lower surface and results from the removal of the buried silicon oxide layer. The side surfaces of the movable component are adjacent to side gaps which surround at least a part of the vertical side surfaces of the moveable component and result from the removal of a deep trench insulation material.