Transistor Doped Region Formation by Lateral Epitaxy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In 3D integration of transistors, the formation of doped source and drain regions poses challenges such as increased access resistance due to undoped regions and the need for precise control of amorphization depth, especially at small feature sizes, and existing methods like SPER recrystallization are complex and incomplete.
Innovation Solution
A method involving the formation of doped regions by lateral epitaxy from an exposed edge, using a stack with insulating and semiconductor layers, and spacers of different materials to eliminate undoped regions and achieve full thickness doped regions without the need for an epitaxy seed, compatible with low temperature processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If SPER recrystallization method is used to activate dopants, then dopant activation is achieved at lower temperature, but undoped regions remain between channel and doped region increasing access resistance
Solution Approach 1:
The method performs preliminary removal of the amorphous semiconductor layer portion between the channel and doped region before final doping. This preliminary action eliminates the undoped region that would otherwise increase access resistance, while allowing dopant activation at lower temperatures through the subsequent epitaxial growth step.
Solution Approach 2:
The invention changes the processing approach from simple thermal annealing to a multi-step process involving amorphization, selective removal, and epitaxial regrowth. This parameter change in the processing method enables both low temperature operation and complete dopant activation without residual undoped regions.
2Temperature
If amorphization is performed to enable low temperature dopant activation, then processing temperature is reduced, but control of amorphization depth becomes critical and complex
Solution Approach 1:
The method extracts and removes the problematic amorphous layer portion between the channel and doped region. By taking out this intermediate amorphous layer, the invention eliminates the need for precise control of amorphization depth, as the amorphous layer is subsequently removed anyway and replaced by epitaxial growth.
Solution Approach 2:
The selective removal of the amorphous layer is performed as a preliminary action before final doping. This preliminary removal simplifies the overall process by eliminating the need for precise amorphization depth control, since the amorphous layer's exact depth becomes irrelevant when it is subsequently removed and replaced.
3Reliability
If conventional high temperature thermal annealing is used to activate dopants, then dopant activation is complete, but thermal budget is excessive for 3D integration
Solution Approach 1:
The invention utilizes phase transitions of the semiconductor material - specifically amorphization followed by epitaxial regrowth - to achieve dopant activation. This phase transition approach enables complete dopant activation at lower temperatures than conventional thermal annealing, reducing the thermal budget while maintaining effective doping.
Solution Approach 2:
The method replaces the conventional thermal mechanism (high temperature annealing) with a different physical mechanism involving amorphization and epitaxial regrowth. This substitution allows dopant activation to occur at lower temperatures through solid-phase transformations rather than thermal diffusion.
4Temperature
If SPER method is used for doping, then lower temperature processing is enabled, but the process becomes complex and recrystallization is generally not complete
Solution Approach 1:
The invention extracts and removes the problematic intermediate amorphous layer that causes complexity in the SPER method. By taking out this layer, the process becomes simpler and more reliable, as the removal step is straightforward and enables complete epitaxial regrowth without residual amorphous material.
Solution Approach 2:
The selective removal of the amorphous layer is performed as a preliminary action that simplifies subsequent processing. This preliminary step eliminates the complexity of trying to achieve complete recrystallization in place, replacing it with a simpler epitaxial growth process that naturally produces complete crystallization.
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 method reduces access resistance by eliminating undoped regions and simplifying the process, allowing for full thickness doped regions across the active layer, compatible with 3D integration and low temperature processing.
Implementation Method 1
a step of amorphising a portion of a semiconductor layer with an ion beam, with or without implanting dopants in the amorphous semiconductor layer
Implementation Method 2
these dopants are activated during solid phase recrystallisation of the amorphous semiconductor layer. The recrystallisation/activation step may be performed at a lower temperature
Implementation Method 3
forming the doped region by epitaxy from said exposed edge
Data Source
AI summary
A method for forming at least one doped region of a transistor includes providing a stack having an insulating layer, an active layer, and a gate pattern having a first lateral flank and removing a first portion of the active layer not overlaid by the gate pattern and extending down to the gate pattern, at the edge of a second portion of the active layer overlaid by the gate pattern, so as to expose an edge of the second portion. The edge extends substantially in a continuation of the lateral flank of the gate pattern. The method also includes forming a first spacer having an L shape and having a basal portion in contact with the insulating layer and a lateral portion in contact with the lateral flank; forming a second spacer on the first spacer; removing the basal portion of the first spacer by selective etching with respect to the second spacer, so as to expose the edge of the second portion; and forming the doped region by epitaxy from the exposed edge.