Krypton Sputtering Tungsten Gate Stack Sheet Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As semiconductor integrated circuits continue to miniaturize, the conventional tungsten silicide gate structure's sheet resistance increases with decreasing feature sizes, making it difficult to manufacture at the 90 nm node and beyond, while sputtered tungsten's resistivity also becomes a problem at smaller gate lengths.
Innovation Solution
A gate stack structure using a tungsten nitride barrier layer overlain by a tungsten layer, where the tungsten layer is deposited by plasma sputtering with krypton as the sputter working gas, and the tungsten nitride is reactively sputtered using argon, to maintain low resistivity and reduce sheet resistance at smaller thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If tungsten silicide (WSix) is used for gate stacks at 90 nm node, then the structure can be manufactured with conventional processes, but the sheet resistance becomes too high (exceeds 6 ohms per square) to meet performance requirements
Solution Approach 1:
The patent changes the material composition parameters by transitioning from tungsten silicide to a tungsten nitride/tungsten composite structure, and further optimizes by using krypton sputtering to control tungsten layer density and resistivity. This material parameter change enables achieving below 6 ohms per square sheet resistance at 90 nm node while maintaining manufacturability
Solution Approach 2:
The patent employs a composite structure combining tungsten nitride barrier layer with tungsten via layer, where each material contributes different properties: tungsten nitride provides barrier functionality and tungsten provides low resistivity. This composite approach solves both the barrier requirement and the sheet resistance requirement simultaneously
2Ease of manufacture
If tungsten layer thickness is reduced to achieve lower aspect ratio, then manufacturing becomes easier, but the sheet resistance increases due to thinner conductive path
Solution Approach 1:
The patent changes the deposition process parameters by using krypton instead of argon as sputter gas, which alters the tungsten layer's microstructure, density, and electrical resistivity. This parameter change enables thinner tungsten layers to achieve lower sheet resistance than conventional thicker layers, breaking the traditional thickness-resistance tradeoff
Solution Approach 2:
The patent replicates the beneficial low-resistivity characteristics of bulk tungsten in thin-film form by optimizing the sputtering process, effectively copying the electrical properties of thick, low-resistance tungsten into thin-film structures that can be manufactured with low aspect ratios
3Device complexity
If conventional argon sputtering is used for tungsten deposition, then the process is simple and cost-effective, but the tungsten layer exhibits higher resistivity at thicknesses below 50 nm
Solution Approach 1:
The patent changes the sputter gas parameter from argon to krypton, which has different atomic mass and sputtering characteristics. This parameter change produces tungsten films with improved microstructure and lower resistivity, particularly effective for thin layers below 50 nm, while maintaining the overall simplicity of the sputtering process
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 maintains low resistivity and reduces sheet resistance at smaller thicknesses, particularly below 35 nm, enhancing the performance of gate stacks and integrated circuit structures with minimal modifications to existing processes and equipment.
Implementation Method 1
the tungsten layer is deposited by plasma sputtering using krypton as the sputter working gas
Implementation Method 2
the tungsten nitride is reactively sputtered using argon
Data Source
AI summary
A method of depositing a bilayer of tungsten over tungsten nitride by a plasma sputtering process in which krypton is used as the sputter working gas during the tungsten deposition. Argon may be used as the sputtering working gas during the reactive sputtering deposition of tungsten nitride. The beneficial effect of reduction of tungsten resistivity is increased when the thickness of the tungsten layer is less than 50 nm and further increased when less than 35 nm. The method may be used in forming a gate stack including a polysilicon layer over a gate oxide layer over a silicon gate region of a MOS transistor in which the tungsten nitride acts as a barrier. A plasma sputter chamber in which the invention may be practiced includes gas sources of krypton, argon, and nitrogen.