Multi-step Annealing for Dielectric Dopant Uniformity
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Solution Overview
Problem
Conventional nitridation processes for semiconductor devices result in non-uniform dopant distribution in gate dielectric layers, leading to increased leakage current and poor threshold voltage distribution in high voltage devices, especially for devices with gate sizes less than 100 nm, where silicon oxide is insufficient due to its low dielectric constant.
Innovation Solution
A multi-step annealing process involving a first annealing step with an inert gas at atmospheric pressure followed by a second annealing step with a gas mixture of inert gas and oxygen at low pressure, optimizing temperature and partial pressure ratios to achieve uniform dopant distribution and repair surface damage from plasma nitridation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If thermal nitridation process is used to dope nitrogen atoms into the dielectric layer, then the dielectric constant is increased, but the nitrogen dopants are not uniformly distributed in the dielectric layer
Solution Approach 1:
The patent divides the single nitridation process into multiple sequential annealing steps (first rapid thermal annealing, second rapid thermal annealing, and optional third annealing). Each step uses different gas compositions and temperature parameters to progressively improve dopant distribution uniformity while maintaining the dielectric constant enhancement.
Solution Approach 2:
The patent systematically changes process parameters including temperature (900-1100°C for first annealing, 1000-1200°C for second annealing), gas composition (inert gas atmosphere vs. oxygen-containing atmosphere), and pressure conditions across different annealing steps to optimize both dielectric constant and dopant distribution uniformity.
2Quantity of substance
If plasma nitridation process is used to dope nitrogen atoms into the dielectric layer, then the dielectric constant is increased, but the surface of the dielectric layer is destroyed resulting in direct-tunneling current
Solution Approach 1:
The patent converts the harmful surface damage caused by plasma nitridation into a beneficial process by applying subsequent rapid thermal annealing steps. These annealing steps repair the damaged dielectric surface, eliminate direct-tunneling current paths, and improve overall device reliability while preserving the nitrogen doping benefits.
Solution Approach 2:
The patent applies preliminary protective measures by using inert gas atmosphere during the first rapid thermal annealing step before oxygen exposure, which prevents further surface oxidation and damage while allowing nitrogen dopant redistribution. This preliminary protection prepares the surface for subsequent processing without additional harm.
3Device complexity
If conventional single-step annealing is used after dopant implantation, then the process is simple, but the dopant distribution in the channel region remains non-uniform affecting threshold voltage distribution
Solution Approach 1:
The patent segments the annealing process into multiple distinct steps with different gas atmospheres and temperature profiles. The first rapid thermal annealing in inert gas atmosphere specifically targets dopant redistribution in the channel region, while subsequent steps address other requirements, collectively improving threshold voltage distribution through controlled dopant uniformity.
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
The multi-step annealing process enhances dopant uniformity, improves dielectric layer performance by increasing the dielectric constant, and enhances the electrical characteristics of MOS transistors, including equivalent oxide thickness and threshold voltage, while being compatible with existing fabrication processes for scalable production.
Implementation Method 1
performing a first annealing process on a material layer with an inert gas at an atmosphere pressure after a plurality of dopants is doped into the material layer
Implementation Method 2
performing a second annealing process on the material layer with an gas mixture at a low pressure after the first annealing process is performed, wherein the gas mixture comprises the inert gas and an oxygen gas
Implementation Method 3
the gas mixture comprises the inert gas and an oxygen gas
Data Source
AI summary
A method of fabricating a dielectric layer is described. A substrate is provided, and a dielectric layer is formed over the substrate. The dielectric layer is performed with a nitridation process. The dielectric layer is performed with a first annealing process. A first gas used in the first annealing process includes inert gas and oxygen. The first gas has a first partial pressure ratio of inert gas to oxygen. The dielectric layer is performed with the second annealing process. A second gas used in the second annealing includes inert gas and oxygen. The second gas has a second partial pressure ratio of inert gas to oxygen, and the second partial pressure ratio is smaller than the first partial pressure ratio. At least one annealing temperature of the two annealing processes is equal to or greater than 950° C. The invention improves uniformity of nitrogen dopants distributed in dielectric layer.