Vertical MOS Transistor Nano-Wire Strain Induction
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Solution Overview
Problem
Current methods for forming vertical transistors face challenges in inducing strain in semiconductor nano-wires, which affects the drive current and short-channel effects, particularly in minimizing these issues for high-performance transistor designs.
Innovation Solution
The method involves forming a low-viscosity spacer around the nano-wire, followed by a local oxidation process to generate an oxide ring that encircles the nano-wire, creating tensile or compressive strain depending on the configuration, using a non-permeable layer to control oxygen penetration and enhance strain generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods are used to form vertical transistors, then the basic transistor structure is achieved, but strain induction in semiconductor nano-wires is insufficient, resulting in reduced drive current and increased short-channel effects
Solution Approach 1:
A sacrificial oxide layer is introduced as an intermediary material between the semiconductor nano-wire and the surrounding environment. This oxide layer serves as a mediator that, when removed, creates the necessary strain in the nano-wire channel. The oxide acts as a temporary structural element that facilitates strain induction without being part of the final transistor structure, resolving the contradiction between achieving sufficient strain and maintaining manufacturing simplicity.
Solution Approach 2:
The method changes the physical and chemical parameters of the nano-wire by introducing controlled oxidation and subsequent reduction processes. By adjusting oxidation conditions (time, temperature, oxygen exposure) and reduction conditions (hydrogen plasma parameters), the strain magnitude and distribution in the nano-wire can be precisely controlled. This parameter control enables sufficient strain induction while maintaining a manageable manufacturing process.
2Productivity
If strain is induced in the nano-wire to improve drive current, then transistor performance increases, but the manufacturing process complexity increases due to additional oxidation and reduction steps
Solution Approach 1:
The oxidation and reduction steps are merged into a single integrated process sequence that is incorporated within existing transistor fabrication flows. The sacrificial oxide formation is combined with other oxidation processes already present in the manufacturing sequence, and the reduction step is timed to coincide with other critical process windows. This merging reduces the net increase in process complexity while maintaining the strain induction benefit for improved drive current.
Solution Approach 2:
The sacrificial oxide layer is formed in advance during earlier processing steps before the nano-wire channel is fully defined. By preparing the oxidation environment beforehand and using the nano-wire itself as the reduction target in a subsequent step, the method eliminates the need for separate, dedicated strain induction equipment and process chambers, thereby reducing overall manufacturing complexity while achieving the desired drive current enhancement.
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 approach effectively generates significant tensile or compressive strain in the nano-wire, improving the drive current of vertical transistors and minimizing short-channel effects, with strain levels reaching up to 8G Pascal, thereby enhancing transistor performance.
Implementation Method 1
a local oxidation process to generate an oxide ring that encircles the nano-wire
Implementation Method 2
creating tensile or compressive strain depending on the configuration, using a non-permeable layer to control oxygen penetration and enhance strain generation
Data Source
AI summary
A vertical Metal-Oxide-Semiconductor (MOS) transistor includes a substrate and a nano-wire over the substrate. The nano-wire comprises a semiconductor material. An oxide ring extends from an outer sidewall of the nano-wire into the nano-wire, with a center portion of the nano-wire encircled by the oxide ring. The vertical MOS transistor further includes a gate dielectric encircling a portion of the nano-wire, a gate electrode encircling the gate dielectric, a first source/drain region underlying the gate electrode, and a second source/drain region overlying the gate electrode. The second source/drain region extends into the center portion of the nano-wire. Localized oxidation produces a local swelling in the structure that generates a tensile or compressive strain in the nano-wire.