Gate Structure Nitrogen Barrier for Low Sheet Resistance
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Solution Overview
Problem
Conventional gate electrodes in high integration semiconductor devices face challenges with high sheet resistance due to nitrogen penetration from silicon nitride masks, which increases the resistance of refractory metal layers like tungsten, limiting their suitability for low resistance requirements.
Innovation Solution
A gate structure is developed with a polysilicon layer, a metal layer, a metal silicide nitride layer, and a silicon nitride mask, where the metal silicide nitride layer has a higher nitrogen concentration at its upper portion, and a nitrification prevention layer is used between the metal layer and the silicon nitride mask to prevent nitrogen diffusion, maintaining low sheet resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon nitride mask is formed on the tungsten layer, then the gate structure can be patterned, but nitrogen atoms penetrate into the tungsten layer and increase the sheet resistance
Solution Approach 1:
A titanium nitride layer is introduced as an intermediary between the silicon nitride mask and the tungsten layer. This intermediate layer acts as a barrier that prevents nitrogen atoms from penetrating into the tungsten layer while allowing the pattern transfer function to be performed. The titanium nitride layer thus mediates between the conflicting requirements of patternability and resistance control.
Solution Approach 2:
The gate electrode structure is segmented into multiple functional layers: the tungsten layer for low resistance, the titanium nitride layer for nitrogen barrier functionality, and the silicon nitride layer for masking. This segmentation allows each layer to perform its specific function optimally without interfering with the others, resolving the contradiction between patternability and resistance maintenance.
2Manufacturing precision
If ammonia gas is provided to control oxidation before forming the silicon nitride layer, then oxidation can be controlled, but nitrogen atoms from the ammonia gas penetrate into the tungsten layer and increase sheet resistance
Solution Approach 1:
The titanium nitride layer serves as an intermediary barrier that prevents nitrogen atoms from the ammonia gas during the oxidation control process from penetrating into the tungsten layer. This allows the oxidation control function to be performed while protecting the tungsten layer from nitrogen contamination.
Solution Approach 2:
The titanium nitride layer is formed preliminarily before the silicon nitride mask and ammonia gas treatment steps. This preliminary action establishes a protective barrier in advance that prevents nitrogen penetration during subsequent processing steps, allowing oxidation control to be performed safely.
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 solution effectively prevents nitrogen-induced resistance increases in the metal layer, enhancing the reliability and performance of semiconductor devices by maintaining low sheet resistance and thermal stability.
Implementation Method 1
a nitrification prevention layer is used between the metal layer and the silicon nitride mask to prevent nitrogen diffusion
Implementation Method 2
the metal silicide nitride layer has a higher nitrogen concentration at its upper portion
Data Source
AI summary
A gate structure can include a polysilicon layer, a metal layer on the polysilicon layer, a metal silicide nitride layer on the metal layer and a silicon nitride mask on the metal silicide nitride layer.