MEMS Resonator Release Using Front-Side Trenches
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Solution Overview
Problem
Current methods for fabricating MEMS devices face challenges in achieving overlay accuracy better than 0.5 μm due to wafer warping and edge damage from grinding, and require complex backside photolithography and etching processes.
Innovation Solution
A method that involves providing a substrate with a material layer, etching trenches on one side, grinding the substrate to expose the trenches, and using them as etch holes to release a microelectromechanical element, thereby avoiding backside processes and improving fabrication simplicity and cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If backside photolithography and etch processes are used, then MEMS device fabrication can be completed, but overlay accuracy deteriorates due to wafer warping and edge damage from grinding
Solution Approach 1:
The patent inverts the conventional sequence by performing photolithography and trench etching on the front side of the wafer before thinning, rather than after. This reversal eliminates the need for backside processing, preventing wafer warping and edge damage that compromise overlay accuracy. The front-side processing ensures precise alignment while the subsequent thinning and release steps complete the MEMS fabrication without requiring complex backside photolithography.
Solution Approach 2:
The patent performs photolithography and trench etching as preliminary actions before wafer thinning. By defining the trenches and patterns on the front side while the wafer is still at its original thickness, the process ensures stable mechanical properties and precise overlay accuracy. The trenches are then used as etch holes after thinning, eliminating the need for subsequent backside photolithography and resolving the contradiction between manufacturing precision and process complexity.
2Manufacturing precision
If front side trench etching is performed before thinning, then overlay accuracy is improved, but the process requires additional steps to expose trenches through grinding
Solution Approach 1:
The patent merges multiple functions into the front-side trench etching step: defining the pattern, creating etch holes, and establishing alignment references. By performing photolithography and trench etching on the front side before thinning, the process combines pattern definition with the creation of release holes, eliminating the need for separate backside photolithography and etching steps. This integration maintains high overlay accuracy while improving overall fabrication efficiency.
Solution Approach 2:
The patent extracts the photolithography and trench definition steps from the backside processing sequence and relocates them to the front side. This extraction eliminates the problematic backside processing steps that cause wafer warping and edge damage, while the trenches created serve dual purposes: as pattern definitions and as etch holes for releasing the MEMS structure after thinning.
3Ease of manufacture
If polysilicon is used for the resonator, then fabrication is simplified, but mechanical properties and frequency stability deteriorate
Solution Approach 1:
The patent changes the material parameter from polysilicon to single crystalline silicon for the resonator structure. Single crystalline silicon provides superior mechanical properties and frequency stability compared to polysilicon, while the front-side processing approach enables this material change without complicating the fabrication process. The trench etching and release methodology remains compatible with single crystalline silicon, resolving the contradiction between ease of manufacture and reliability.
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 allows for the creation of MEMS devices with improved mechanical properties, reduced intrinsic losses, and integration of high-quality coils without additional process steps, enabling the packaging of single crystalline resonators with enhanced frequency stability and three-dimensional sensing capabilities.
Implementation Method 1
grinding the substrate from a second side of the substrate to expose the trench
Implementation Method 2
using the exposed trench as an etch hole for releasing a microelectromechanical element
Data Source
AI summary
A method of manufacturing an electronic device that comprises a microelectromechanical (MEMS) element, the method comprising the steps of: providing a material layer (34) on a first side of a substrate (32); providing a trench (40) in the material later (34); etching material from the trench (40) such as to also etch the substrate (32) from the first side of the substrate (32); grinding the substrate (32) from a second side of the substrate to expose the trench (40); and using the exposed trench (40) as an etch hole. The exposed trench (40) is used as an etch hole for releasing a portion of the material layer (34), for example a beam resonator (12), from the substrate (32). An input electrode (6), an output electrode (8), and a top electrode (10) are provided.