Selective Doping in Semiconductor Trenches for Threshold Voltage Matching
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Solution Overview
Problem
Existing semiconductor technologies with a single polysilicon layer of specific conductivity cannot form diodes insulated from the substrate or realize a range of resistances on a small area, limiting flexibility in threshold voltage matching for NMOS and PMOS transistors and requiring additional implantations.
Innovation Solution
A method for fabricating semiconductor structures with selective dopant regions by forming trenches in a semiconductor substrate, using an auxiliary dopant source for drive-in doping within the trenches, and selectively introducing dopants of different conductivity types through implantation processes, avoiding the need for additional masks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single polysilicon layer with specific conductivity is used, then mask costs are reduced, but the ability to form diodes insulated from substrate and realize varied resistances is lost
Solution Approach 1:
The patent applies local quality by creating different conductivity regions within the same polysilicon layer through selective doping. By introducing dopant sources at specific locations (trench bottoms) and using drive-in diffusion, the polysilicon layer acquires locally different electrical properties, enabling formation of diodes, resistors, and threshold adjustment in different areas without adding mask layers.
Solution Approach 2:
The patent transitions from planar doping to three-dimensional doping by placing dopant sources at the bottom of trenches and using vertical drive-in diffusion. This dimensional change allows selective doping of underlying regions while the polysilicon layer remains undoped in other areas, achieving selective functionality without additional masks.
2Reliability
If additional implantation processes are used for threshold voltage matching, then transistor performance is improved, but process complexity increases
Solution Approach 1:
The patent merges the threshold adjustment function with the existing dopant source structures (trench bottoms). By placing dopant sources adjacent to or overlapping with transistor channels, the same diffusion process that creates selective regions also performs threshold voltage adjustment, eliminating the need for separate channel implantation steps.
Solution Approach 2:
The dopant sources serve multiple functions: they create selective doped regions for diodes and resistors, simultaneously perform threshold voltage adjustment for MOSFETs, and define channel regions. This multi-functionality reduces process complexity while maintaining transistor performance.
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
Enables the formation of diodes and resistors with varying breakdown voltages and conductivities without additional mask costs, enhancing the flexibility and performance of semiconductor structures, particularly in threshold voltage matching for transistors.
Implementation Method 1
parts of the semiconductor structure which lie within the trenches are doped by means of a drive-in
Implementation Method 2
selectively doped by an implantation process
Data Source
AI summary
A method for fabricating a semiconductor structure having selective dopant regions in a semiconductor substrate having trenches formed therein I disclosed. In one embodiment, by a dopant source of an auxiliary structure, parts of the semiconductor structure which lie within the trenches are doped by means of a drive-in. In one embodiment, the semiconductor structure is patterned in planar regions outside the trenches and selectively doped by an implantation process.