Deep Trench Isolation Grid for RF Substrate Loss Reduction
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Solution Overview
Problem
Conventional semiconductor processes face challenges in integrating all elements of a front-end module (FEM) on a single chip due to substrate losses and non-linearities caused by parasitic coupling, particularly in RF switches, which degrade performance and require multi-chip modules.
Innovation Solution
A modified SiGe BiCMOS process with a grid of deep trench isolation regions and silicide blocking structures is used to isolate active and passive devices, reducing substrate losses and eliminating non-linearities by creating a high-resistivity path and preventing metal silicide formation over dummy active regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If all FEM elements are integrated on a single chip, then device complexity and system size are reduced, but substrate losses and parasitic coupling increase causing performance degradation
Solution Approach 1:
The semiconductor substrate is divided into multiple isolated regions by deep trench isolation structures. These trenches physically segment the substrate into separate isolation regions, preventing parasitic coupling between devices while maintaining single-chip integration. The segmentation creates electrical isolation without requiring multi-chip modules.
Solution Approach 2:
Deep trench isolation structures serve as intermediary elements between active devices and the substrate. These trenches filled with dielectric material act as mediators that block parasitic signal paths and reduce substrate losses, enabling high-performance integration of RF switches, LNAs, and power amplifiers on a single chip.
2Reliability
If deep trench isolation regions are formed, then substrate losses are reduced and isolation is improved, but manufacturing complexity increases
Solution Approach 1:
The formation of deep trench isolation regions is merged with the existing CMOS fabrication process sequence. The trenches are formed, filled with dielectric material, and planarized using standard CMP techniques that are already part of the manufacturing flow, thereby achieving improved isolation without significantly increasing overall process complexity.
Solution Approach 2:
The deep trench isolation structures are formed preliminarily before the final device fabrication steps. By preparing the isolated substrate regions in advance, subsequent device processing can proceed without interference, and the isolation structures are already in place to prevent parasitic coupling during final device assembly and testing.
3Reliability
If silicide blocking structures are formed over dummy active regions, then non-linearities are eliminated, but additional fabrication steps are required
Solution Approach 1:
Metal silicide formation is extracted or blocked specifically from dummy active regions while being maintained in actual device regions. Silicide blocking structures are selectively formed over dummy regions to prevent parasitic silicide formation that causes non-linearities, while allowing necessary silicide formation in active device areas for proper device operation.
Solution Approach 2:
Silicide blocking is applied locally only to dummy active regions rather than uniformly across the entire substrate. This localized approach eliminates non-linearities in isolation regions while preserving the electrical characteristics needed in active device regions, achieving linearity improvement with minimal additional process steps.
Data Source
AI summary
Methods and structures for improved isolation in a SiGe BiCMOS process or a CMOS process are provided. In one method, shallow trench isolation (STI) regions are formed in a first semiconductor region located over a semiconductor substrate. Dummy active regions of the first semiconductor region extend through the STI regions to an upper surface of the first semiconductor region. A grid of deep trench isolation (DTI) regions is also formed in the first semiconductor region, wherein the DTI regions extend entirely through the first semiconductor region. The grid of DTI regions includes a pattern that exhibits only T-shaped or Y-shaped intersections. The pattern defines a plurality of openings, wherein a dummy active region is located within each of the openings.