Trench-Gate MOS Transistor Spacer Layout for Self-Aligned Doping
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Solution Overview
Problem
Existing methods for manufacturing MOS transistors with reduced cell pitch face challenges due to limited photolithography alignment control, leading to compromised electrical parameters and UIS performance.
Innovation Solution
A self-aligned contact approach is employed, utilizing symmetrical spacers to auto-align source, body, and enriched body regions with the gate electrode, eliminating the need for tight photolithography alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If photolithography alignment control is used to manufacture MOS transistors with reduced cell pitch, then device density increases, but alignment precision deteriorates leading to compromised electrical parameters and UIS performance
Solution Approach 1:
The patent employs self-aligned fabrication techniques where the source and body contact regions are automatically positioned relative to the gate trench through sequential doping steps. The first doping step creates source/body contacts, and the second doping step automatically defines the gate trench position based on the previously formed contacts, eliminating the need for external photolithography alignment and ensuring precise positioning regardless of cell pitch reduction
Solution Approach 2:
The patent performs preliminary doping actions to form source and body contact regions before defining the gate trench position. By pre-forming these contact regions with specific doping concentrations and patterns, the subsequent gate trench formation and final contact formation can proceed with automatic alignment, ensuring precise electrical parameters without relying on photolithography alignment control
2Reliability
If body-well doping is increased to improve UIS capability, then UIS performance improves, but threshold voltage control deteriorates requiring additional implant steps
Solution Approach 1:
The patent applies different doping concentrations to different regions of the semiconductor body. The body region receives a first doping concentration optimized for UIS performance, while the source region receives a second doping concentration optimized for threshold voltage control. This local differentiation of doping quality allows simultaneous optimization of both UIS capability and Vth control without requiring additional implant steps
Solution Approach 2:
The patent combines multiple doping functions into a unified doping strategy. The first doping step simultaneously establishes the body-well doping level for UIS performance and creates the basis for source contact formation. The second doping step then automatically positions and doses both source and body contacts in a single operation, merging what would traditionally require separate implant steps into an integrated process
3Ease of manufacture
If mask alignment is used for contact or enrichment formation, then manufacturing process simplifies, but current flow balance deteriorates due to asymmetrical doping distribution
Solution Approach 1:
The patent uses self-aligned doping techniques where the doping regions automatically position themselves relative to the gate trench and each other through the sequential doping process. The first doping step creates source/body contacts, and the second doping step automatically defines their final positions based on the gate trench geometry, ensuring symmetrical and balanced doping distribution without requiring external mask alignment
Solution Approach 2:
Instead of using mask alignment to define doping regions and then forming gates around them, the patent inverts the sequence by first forming the gate trench and then using it as the reference for automatic doping placement. This inversion ensures that the doping distribution is inherently symmetrical and balanced with respect to the gate center, eliminating current flow imbalance issues
4Area of stationary object
If cell pitch is reduced to decrease die size, then integration density increases, but photolithography capability becomes insufficient for tight alignment control
Solution Approach 1:
The patent employs self-aligned fabrication techniques where the source and body contact regions are automatically positioned relative to the gate trench through sequential doping steps. The first doping step creates source/body contacts, and the second doping step automatically defines the gate trench position based on the previously formed contacts, eliminating the need for external photolithography alignment and ensuring precise positioning regardless of cell pitch reduction
Solution Approach 2:
The patent transitions from planar photolithography alignment to a sequential vertical doping approach. By using multiple doping steps with different doping species and concentrations that automatically define each other's positions, the method achieves precise spatial control in the lateral dimension without relying on photolithography resolution, effectively adding a temporal/sequential dimension to the positioning process
Data Source
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AI summary
A MOS transistor (21) of vertical-conduction, trench-gate, type, including a first and a second spacer (34) adjacent to portions of a gate oxide (24, 26) of the trench-gate protruding from a semiconductor substrate (22), the first and second spacers (34) being specular to one another with respect to an axis of symmetry (H); enriched P+ regions (41) are formed by implanting dopant species within the body regions using the spacers (34) as implant masks. The formation of symmetrical spacers (34) makes it possible to form source, body and body-enriched regions that are auto-aligned with the gate electrode, overcoming the limitations of MOS transistors of the known type in which such regions are formed by means of photolithographic techniques (with a consequent risk of asymmetry).