Trench Capacitor Polysilicon Bridge Doping for Lower ESR
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Solution Overview
Problem
Existing integrated circuit trench capacitors face challenges in reducing equivalent series resistance (ESR), which can be higher than desired due to limitations in the fabrication process, particularly in the formation of polysilicon bridges and contact regions.
Innovation Solution
The method involves etching trenches in a semiconductor layer, forming a trench dielectric layer, and depositing a doped polysilicon layer within the trenches, followed by patterning to create a polysilicon bridge. A blanket implant of a dopant is used to increase the doping level in the polysilicon bridge and contact regions, reducing ESR by enhancing conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication processes are used to form polysilicon bridges and contact regions, then the manufacturing process is simpler, but the equivalent series resistance (ESR) of the trench capacitor is higher than desired
Solution Approach 1:
The fabrication process is segmented into distinct stages: forming trenches with dielectric lining, depositing doped polysilicon within trenches, patterning to create polysilicon bridges, and performing blanket implant to create contact regions. This segmentation allows each step to be optimized independently for reducing ESR while maintaining process manageability.
Solution Approach 2:
The doped polysilicon layer is deposited within the trenches before the blanket implant step. This preliminary doping establishes a foundation of conductivity in the trench regions, and the subsequent blanket implant extends this doping to the contact regions and polysilicon bridges, cumulatively reducing ESR through staged doping actions.
2Reliability
If the doping level of the polysilicon layer is increased to reduce ESR, then the conductivity improves, but the fabrication process becomes more complex requiring additional implant steps
Solution Approach 1:
The blanket implant step merges multiple functions into a single process: it forms contact regions extending from the surface into the semiconductor layer, extends doping to the polysilicon bridges, and reinforces doping in the trench polysilicon. This consolidation achieves high conductivity throughout the capacitor structure without requiring separate implant steps for each region.
Solution Approach 2:
The doping concentration is varied through different stages: initial in-situ doping during polysilicon deposition establishes baseline conductivity, and the subsequent blanket implant increases the doping level to achieve the desired low ESR. This parameter change approach allows progressive optimization of conductivity without over-doping any single region.
3Manufacturing precision
If additional masks are used to precisely dope contact regions and polysilicon bridges, then the doping precision improves, but the fabrication cost increases
Solution Approach 1:
The blanket implant process exploits the self-alignment properties of the previously formed structures. The polysilicon bridges and contact regions are formed without requiring additional masks because the doping automatically concentrates in areas where polysilicon is present or where the implant geometry naturally directs dopant flow. This self-service approach achieves precise doping through process geometry rather than mask patterns.
Solution Approach 2:
The blanket implant serves multiple functions simultaneously: it forms contact regions, dopes polysilicon bridges, and reinforces trench polysilicon doping. This multi-functional approach eliminates the need for separate targeted implant steps that would require additional masks, reducing both process complexity and cost while achieving comprehensive doping coverage.
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 effectively lowers the ESR of trench capacitors to below 0.6Ω, reducing variation across wafers and improving the overall performance of the capacitors while eliminating the need for additional masks, thus reducing fabrication costs.
Implementation Method 1
The doping level of the polysilicon layer can be increased by increasing the flow rate of a precursor gas that includes the dopant
Implementation Method 2
A blanket implant of a dopant is used to increase the doping level in the polysilicon bridge and contact regions
Implementation Method 3
a doped polysilicon layer is deposited over the capacitor dielectric to fill the trenches
Data Source
AI summary
A method of fabricating an integrated circuit includes etching trenches in a first surface of a semiconductor layer. A trench dielectric layer is formed over the first surface and over bottoms and sidewalls of the trenches and a doped polysilicon layer is formed over the trench dielectric layer and within the trenches. The doped polysilicon layer is patterned to form a polysilicon bridge that connects to the polysilicon within the filled trenches and a blanket implant of a first dopant is directed to the polysilicon bridge and to the first surface. The blanket implant forms a contact region extending from the first surface into the semiconductor layer.