P-Type Access Transistor Fabrication via Segmented RAD Structures
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Solution Overview
Problem
Conventional access devices in semiconductor circuitry face challenges in scaling down feature sizes, particularly in forming P-type doped gate transistors, as existing methods are not ideal for simultaneous formation with N-type doped transistors, and P-type workfunction materials do not integrate well with N+ doped materials.
Innovation Solution
The fabrication process involves forming periphery transistors using conventional MOSFET structures while using RAD or FinFET structures for access transistors, with P-type workfunction materials or P+ doped materials, allowing for the separate formation of access transistors with P-type doping, and integrating them into integrated circuit devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional MOSFET fabrication processes are used for simultaneous formation of periphery and access transistors, then N-type doping is achieved, but P-type doping capability is lost
Solution Approach 1:
The fabrication process is segmented into separate formation steps for periphery transistors and access transistors. Periphery transistors are formed first with N-type doping, then access transistors are formed separately with P-type doping capability, allowing each transistor type to have optimized doping without compromising the other
Solution Approach 2:
Different doping types (N-type for periphery, P-type for access) are applied to different spatial locations on the substrate. The process enables local customization of doping characteristics by forming access transistors in specific regions after periphery transistor formation, with each region receiving appropriate doping treatment
2Productivity
If feature sizes are reduced to scale down access devices, then device density increases, but conventional gate structures become inadequate
Solution Approach 1:
The gate structure transitions from conventional planar MOSFET gates to RAD gate structures that can dynamically adapt to smaller feature sizes. The RAD structure enables continuous scaling by adjusting the recess depth and gate dimensions, providing versatility across different technology nodes while maintaining high device density
Solution Approach 2:
The invention moves from two-dimensional planar gate structures to three-dimensional RAD gate structures with vertical recesses. This dimensional transition allows the gate to extend into the substrate vertically, increasing effective gate area and control without increasing lateral footprint, thereby enabling continued scaling at smaller feature sizes
3Adaptability or versatility
If P-type workfunction materials are used for access transistors, then P-type doping is achieved, but integration with N+ doped materials becomes difficult
Solution Approach 1:
The device structure is segmented into distinct periphery transistor regions with N+ doping and access transistor regions with P-type doping/workfunction materials. This spatial segmentation allows incompatible materials to coexist in the same integrated circuit without direct interaction, simplifying material integration while maintaining doping versatility
Solution Approach 2:
The fabrication process uses intermediary steps including spacer formation, selective etching, and separate doping processes that mediate between the N+ doped periphery transistors and P-type access transistors. These intermediary processes enable the transition between different doping types without requiring direct material compatibility, reducing overall integration complexity
Data Source
AI summary
Fabrication methods for gate transistors in integrated circuit devices enable the formation of recessed access device structures or FinFET structures having P-type workfunctions. The fabrication methods also provide for the formation of access transistor gates of an access device following formation of the periphery transistor gates. Access devices and systems including same are also disclosed.