Deep Trench MIM Capacitor Layout to Prevent Shorting
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Solution Overview
Problem
Existing Metal-Insulator-Metal (MIM) capacitors in semiconductor integrated circuits face challenges in achieving sufficient capacitance and preventing electrical shorting due to limitations in their design and fabrication processes, particularly as geometry sizes decrease and functional density increases.
Innovation Solution
The formation of vertically extended MIM capacitors with increased conductor plate areas, using a deposition-etch-deposition-etch-deposition (DEDED) method and a cap layer to protect trench edges, along with separate patterning of bottom and top electrode layers with lateral offset to prevent shorting, enhances capacitance and reduces void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MIM capacitor fabrication processes are used, then manufacturing simplicity is maintained, but capacitance is insufficient and electrical shorting occurs
Solution Approach 1:
The capacitor fabrication is divided into multiple sequential deposition and etch cycles (DEDED process), with each cycle adding a specific layer or feature. This segmentation allows precise control over electrode thickness, insulator quality, and trench geometry, resolving the contradiction by trading process steps for improved capacitance and reliability
Solution Approach 2:
A cap layer is deposited over the trench opening before completing the trench formation. This preliminary action protects the trench edges from damage during subsequent processing steps, preventing electrical shorting and improving reliability without significantly increasing overall process complexity
2Productivity
If geometry size decreases to increase functional density, then more devices fit per chip area, but MIM capacitor performance deteriorates due to reduced surface area
Solution Approach 1:
The invention transitions from two-dimensional planar capacitor structures to three-dimensional vertical trench capacitors. By extending the capacitor structure vertically through deep trenches with conformally deposited electrodes and insulators, the surface area for capacitance is dramatically increased without occupying more chip area, thus maintaining high functional density while improving capacitor performance
Solution Approach 2:
The capacitor structure is nested within deep trenches that extend through multiple dielectric layers. The bottom electrode, insulator layer, and top electrode are nested concentrically within the trench walls, maximizing the use of available vertical space to achieve high capacitance in a compact footprint
3Reliability
If trench formation is extended deeper to increase capacitance, then capacitor performance improves, but void formation increases
Solution Approach 1:
The capacitor fabrication uses periodic cycles of deposition and etching (DEDED process) rather than continuous processing. Each cycle deposits a layer conformally on the trench walls, then etches back to expose the next layer. This periodic action ensures uniform layer thickness and complete coverage, preventing void formation even in deep trenches while maintaining high capacitance
Solution Approach 2:
The conformal deposition process provides inherent feedback control where each layer is deposited to a controlled thickness based on the previous layer's geometry. This self-regulating process ensures uniform electrode and insulator layers throughout the trench depth, preventing void formation and ensuring consistent capacitance
4Reliability
If electrode layers are patterned separately with lateral offset to prevent shorting, then electrical isolation is improved, but manufacturing complexity increases
Solution Approach 1:
The bottom and top electrode layers are patterned in separate, sequential steps with lateral offset between their positions. This segmentation of the patterning process creates built-in electrical isolation, preventing shorting while the offset geometry simplifies the alignment requirements compared to direct vertical alignment
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 increases capacitance, reduces void formation, and prevents electrical shorting, thereby improving the performance of MIM capacitors in semiconductor integrated circuits, particularly in CMOS image sensors, by effectively managing trench formation and electrode layer deposition.
Implementation Method 1
depositing a cap layer over the trench such that the cap layer overhangs edges of the trench
Implementation Method 2
conformally depositing a bottom electrode layer in the trench, conformally depositing an insulator layer over the bottom electrode layer, conformally depositing a top electrode layer over the insulator layer
Data Source
AI summary
Semiconductor structures and methods of forming the same are provided. A semiconductor structure of the present disclosure includes a contact feature disposed in a first dielectric layer, a first etch stop layer (ESL) over the contact feature and the first dielectric layer, a second dielectric layer over the first ESL, a second ESL over the second dielectric layer, a third dielectric layer over the second ESL, a third ESL over the third dielectric layer, a fourth dielectric layer over the third ESL, and a capacitor. The capacitor includes a bottom electrode layer continuously extending along a top surface of the fourth dielectric layer and vertically through the fourth dielectric layer, the third ESL, the third dielectric layer, the second ESL, the second dielectric layer, and the first ESL, an insulator layer disposed over the bottom electrode, and a top electrode layer disposed over the insulator layer.