Deep Trench Capacitor Isolation via Buried Plates
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Solution Overview
Problem
The scaling of DRAM cell structures is challenging due to inadequate storage capacitance and leakage issues in deep trench capacitors on SOI substrates, particularly with conventional diffusion doping processes becoming difficult at smaller dimensions and leading to unwanted implants and isolation problems.
Innovation Solution
The method involves forming deep trenches and isolation trenches in a SOI and doped poly layer, lining them with insulator material, and filling with conductive material to create deep trench capacitors with buried isolation plates that prevent leakage between capacitors, eliminating the need for doping within small trench openings and reducing unwanted implants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If deep trench capacitors are scaled to smaller dimensions, then manufacturing cost is reduced and integration level is increased, but storage capacitance becomes inadequate and leakage issues occur
Solution Approach 1:
The patent transitions from planar capacitor structures to three-dimensional deep trench capacitors, utilizing the vertical dimension to increase capacitance density. By etching deep trenches into the substrate and forming capacitor plates along the trench walls, the design achieves higher integration levels while maintaining adequate storage capacitance through increased surface area in the vertical direction.
Solution Approach 2:
The patent implements nested isolation structures where isolation trenches are positioned within or adjacent to the deep trench capacitor structures. This nesting approach allows isolation features to be integrated within the same vertical space, achieving both high integration and proper electrical isolation without sacrificing capacitance.
2Ease of manufacture
If conventional diffusion doping process is used through smaller deep trench openings, then dopant implantation becomes difficult and unwanted implants occur in the SOI layer
Solution Approach 1:
The patent performs dopant implantation into the substrate before forming the deep trench structures. By pre-doping the substrate, the need for subsequent implantation through narrow trench openings is eliminated, avoiding the difficulties and unwanted side effects of doping through small openings while still achieving the desired dopant distribution for capacitor formation.
Solution Approach 2:
The patent extracts the doping step from the trench formation sequence, performing it as a separate preliminary operation. This separation removes the constraint of having to dope through narrow openings, allowing doping to be performed under optimal conditions before the trench structures are created.
3Productivity
If deep trench spacing is reduced to increase density, then integration level is increased, but leakage between trenches occurs and isolation becomes problematic
Solution Approach 1:
The patent nests isolation trenches within or adjacent to the deep trench capacitor structures, allowing isolation features to occupy the same vertical space as the capacitors. This nested arrangement provides effective electrical isolation between adjacent capacitors even when the horizontal spacing is minimized, enabling higher integration levels without leakage problems.
Solution Approach 2:
The patent introduces isolation trenches as intermediary structures between adjacent deep trench capacitors. These isolation trenches act as electrical barriers that prevent leakage between neighboring capacitors, allowing the design to achieve high density while maintaining proper electrical isolation through the mediating isolation structures.
Data Source
AI summary
A structure and method is provided for fabricating isolated capacitors. The method includes simultaneously forming a plurality of deep trenches and one or more isolation trenches surrounding a group or array of the plurality of deep trenches through a SOI and doped poly layer, to an underlying insulator layer. The method further includes lining the plurality of deep trenches and one or more isolation trenches with an insulator material. The method further includes filling the plurality of deep trenches and one or more isolation trenches with a conductive material on the insulator material. The deep trenches form deep trench capacitors and the one or more isolation trenches form one or more isolation plates that isolate at least one group or array of the deep trench capacitors from another group or array of the deep trench capacitors.