Micromechanical Structure Trench Sealing via CMP Thinning
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Solution Overview
Problem
Existing methods for manufacturing micromechanical structures, such as MEMS functional layers, face limitations in controlling the gap distance between layers due to the thickness of oxide depositions, which is coupled to the width of trenches, making it difficult to achieve variable and narrower trench widths for applications like capacitive detection structures in sensors.
Innovation Solution
A method involving a vertically thin sealing layer with a special trench geometry, including an opening cup, allows for reliable sealing with less sealing material, enabling broader trenches to be filled and reducing gap distances between layers, using techniques like CMP for thinning and non-conformal deposition, and employing mask and polish stop layers for precise trench formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If oxide depositions are used to fill trenches and seal MEMS functional layers, then the trenches are sealed and layers are protected, but the oxide thickness is coupled to trench width, limiting the ability to achieve variable and narrower trench widths
Solution Approach 1:
The patent segments the trench filling process into two distinct phases: first filling narrow trenches with a initial oxide deposition to establish sealing, then widening trenches in a second step while maintaining the seal. This segmentation allows independent control of sealing requirements versus final trench geometry, enabling variable widths without compromising seal integrity.
Solution Approach 2:
The patent performs preliminary oxide deposition to create a sealing layer before final trench widening. The oxide is deposited early when trenches are narrower and easier to fill, establishing a seal that can then accommodate subsequent trench widening. This preliminary action decouples the sealing function from the final trench dimensions.
2Reliability
If thicker oxide depositions are used to ensure complete trench filling and sealing, then sealing reliability is improved, but gap distance between MEMS functional layers increases
Solution Approach 1:
The patent applies partial oxide deposition - depositing oxide only to the extent needed for sealing rather than completely filling trenches. The oxide thickness is controlled to be sufficient for sealing reliability but minimal for maintaining small gap distances. This partial action approach optimizes the trade-off between sealing reliability and gap distance.
3Length of stationary object
If minimum width trenches are used to reduce oxide thickness requirements, then gap distance is reduced, but manufacturing flexibility for variable width trenches is lost
Solution Approach 1:
The patent introduces dynamic control of trench width through a two-step process where trench width is first set to a minimum value for sealing, then dynamically adjusted to variable widths in a second widening step. This dynamic approach allows the system to adapt trench widths for different applications while maintaining reliable sealing throughout the process.
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 enables the reliable sealing of trenches of varying widths, reduces the oxide thickness to near zero, and allows for smaller gap distances between MEMS functional layers, improving the manufacturing flexibility and precision for micromechanical structures.
Implementation Method 1
a vertically thin sealing layer which is suitable in particular for layer depositions which have a restricted conformity
Implementation Method 2
a vertically thin sealing layer which is suitable in particular for layer depositions which have a restricted conformity
Implementation Method 3
the sealing point within the cup may be located below the upper side of the MEMS functional layer. This is used to thin back the sealing material after the layer deposition, for example, via a CMP process
Data Source
AI summary
A method for manufacturing a micromechanical structure and a micromechanical structure. The method includes: forming a first micromechanical functional layer; forming a plurality of trenches in the first micromechanical functional layer, which include an upper widened area at the upper side of the first micromechanical functional layer and a lower area of essentially constant width; depositing a sealing layer on the upper side of the first micromechanical functional layer to seal the plurality of trenches, a sealing point of the plurality of trenches being formed below the upper side of the first micromechanical functional layer and the first trenches being at least partially filled; thinning back the sealing layer by a predefined thickness; and forming a second micromechanical functional layer above the thinned-back sealing layer.