MOS Transistor Gate Insulator Nitridation for Leakage Reduction
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Solution Overview
Problem
Conventional MOS transistors face increased leakage currents due to the miniaturization of silicon oxide gate insulators, which limits their effectiveness in advanced technological processes, and existing methods struggle to form a silicon oxynitride interface layer below a certain thickness without compromising dielectric constant or requiring additional equipment and steps.
Innovation Solution
A method involving the formation of a high dielectric constant material like hafnium silicate with a thin silicon oxynitride interface layer, achieved by plasma nitridation at low temperatures followed by chemical deposition of the high-K material without intermediate anneal steps, allowing for a thinner interface layer and reduced manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of silicon oxide gate insulator is decreased to enable transistor miniaturization, then transistor size and operating speed are improved, but leakage currents between gate and substrate increase
Solution Approach 1:
The patent changes the material composition of the gate insulator by incorporating nitrogen atoms into silicon oxide to form silicon oxynitride. This parameter change in material composition increases the dielectric constant from 3.9 to 6-8, enabling the formation of a thicker effective gate insulator that reduces leakage current while maintaining the required gate-substrate capacitance for transistor operation.
2Reliability
If a silicon oxynitride interface layer is formed to increase dielectric constant, then leakage current is reduced, but the interface layer thickness cannot be reduced below a certain limit without compromising dielectric performance
Solution Approach 1:
The patent applies preliminary action by performing plasma nitridation at low temperature (below 400°C) to incorporate nitrogen atoms into the silicon oxide layer before forming the high-k dielectric layer. This preliminary nitrogen incorporation creates a silicon oxynitride interface layer with sufficient dielectric constant enhancement, allowing the layer to be kept extremely thin (below 1.2 nm) while still achieving the required electrical performance.
Solution Approach 2:
The patent changes the physical and chemical parameters of the interface layer by using low-temperature plasma nitridation to achieve high nitrogen concentration in a thin layer. This parameter change enables the formation of a ultra-thin silicon oxynitride layer that maintains high dielectric constant without requiring thicker layers for nitrogen stabilization.
3Stability of the object's composition
If conventional plasma nitridation followed by thermal anneal is used to stabilize nitrogen concentration, then nitrogen stability is improved, but manufacturing complexity and process time increase
Solution Approach 1:
The patent extracts the thermal anneal step from the conventional plasma nitridation process. By demonstrating that low-temperature plasma nitridation alone is sufficient to achieve stable nitrogen incorporation, the patent removes the unnecessary intermediate thermal anneal step, reducing manufacturing complexity and process time while maintaining nitrogen stability in the silicon oxynitride interface layer.
Solution Approach 2:
The patent applies self-service by allowing the plasma nitridation process itself to achieve nitrogen stabilization without requiring subsequent thermal annealing. The low-temperature plasma process inherently creates a stable nitrogen distribution in the silicon oxide layer, making the layer self-stabilizing and eliminating the need for additional process steps.
4Reliability
If high-k dielectric materials are used to further increase dielectric constant, then capacitance performance is improved, but manufacturing precision requirements increase for forming thin interface layers
Solution Approach 1:
The patent changes the manufacturing approach by using low-temperature plasma nitridation (below 400°C) instead of high-temperature processes. This parameter change in processing temperature enables precise control of the silicon oxynitride interface layer thickness at ultra-low values (below 1.2 nm) while maintaining adequate nitrogen concentration, thereby reducing manufacturing precision requirements compared to conventional high-temperature methods.
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 enables the formation of a silicon oxynitride interface layer with a thickness smaller than 1.2 nm and higher nitrogen atom concentration, improving dielectric constant performance and reducing manufacturing costs by eliminating unnecessary anneal steps, while maintaining interface quality.
Implementation Method 1
incorporating nitrogen atoms into the silicon oxide layer by plasma nitridation at a temperature lower than 200° C., to transform this layer into a silicon oxynitride layer
Implementation Method 2
The adsorption of nitrogen atoms followed by their diffusion into the silicon oxide transforms layer 13 into a silicon oxynitride layer 14
Implementation Method 3
coating the silicon oxynitride layer with a layer of a material of high dielectric constant, wherein steps b) and c) follow each other with no intermediate anneal step
Data Source
AI summary
A method for forming the gate insulator of a MOS transistor, including the steps of: a) forming a thin silicon oxide layer at the surface of a semiconductor substrate; b) incorporating nitrogen atoms into the silicon oxide layer by plasma nitridation at a temperature lower than 200° C., to transform this layer into a silicon oxynitride layer; and c) coating the silicon oxynitride layer with a layer of a material of high dielectric constant, wherein steps b) and c) follow each other with no intermediate anneal step.