Mixed-Species Buffer Film for Stress-Stable Ruthenium Metallization
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Solution Overview
Problem
Challenges arise in semiconductor device fabrication as copper metallization becomes difficult at sub-30 nm contact critical dimensions, leading to line bending and increased electrical resistance due to uneven stress during ruthenium deposition, especially in dual-damascene integration with varying trench sizes.
Innovation Solution
A buffer film with a coefficient of thermal expansion similar to the dielectric layer is introduced, using ruthenium-based compounds like ruthenium oxide or ruthenium-aluminum alloy, allowing for liner-less ruthenium deposition that matches the dielectric's thermal expansion, thereby reducing stress and preventing line bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ruthenium deposition is performed directly in dual-damascene integration with varying trench sizes, then metallization can be formed, but line bending occurs and electrical resistance increases due to uneven stress
Solution Approach 1:
A buffer film comprising a first material and a second material is introduced as an intermediary layer between the dielectric layer and the ruthenium metal material. The first material has a first coefficient of thermal expansion matching the dielectric layer, while the second material has a second coefficient of thermal expansion matching the ruthenium metal material. This gradient structure acts as a stress mediator that gradually transitions the thermal expansion properties, preventing sudden stress concentration and line bending at the interface.
Solution Approach 2:
The buffer film utilizes a gradual change in coefficient of thermal expansion parameters from the dielectric layer side to the metal material side. By selecting materials with intermediate CTE values and arranging them in a gradient sequence, the buffer film creates a continuous parameter transition that accommodates the mismatch between dielectric and metal thermal expansion coefficients, thereby reducing stress during thermal processing.
2Reliability
If additional liner layers are added to prevent line bending, then structural integrity improves, but device complexity increases
Solution Approach 1:
The buffer film combines multiple functional requirements into a single integrated structure. It simultaneously provides stress management through its gradient CTE design, adhesion between dielectric and metal layers, and serves as part of the metallization stack. This merging of functions into one layer reduces the total number of discrete layers needed compared to traditional approaches using separate liner and buffer layers.
Solution Approach 2:
The buffer film is constructed as a composite material system with at least two different materials having distinct coefficients of thermal expansion. This composite structure allows the buffer film to exhibit graded mechanical and thermal properties that bridge the gap between dielectric and metal materials, providing multi-functionality without requiring additional homogeneous layers.
3Reliability
If copper metallization is used at sub-30 nm dimensions, then electrical conductivity is high, but manufacturing difficulty increases and electrical resistance increases due to stress
Solution Approach 1:
The invention transitions from copper metallization to ruthenium metallization, changing the material parameter of choice. Ruthenium offers comparable or superior electrical conductivity at sub-30 nm dimensions while providing better mechanical stability and reduced stress effects. The buffer film further optimizes the interface properties to enable seamless ruthenium deposition, making the alternative material as manufacturable as copper.
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 mitigates line bending and maintains superior electrical properties by matching the thermal expansion of the dielectric layer, enabling seamless ruthenium deposition without the need for additional liners, thus improving structural integrity and reducing electrical resistance.
Implementation Method 1
A first coefficient of thermal expansion (CTE) α1 of the dielectric layer is larger than a second CTE α2 of the buffer film, which is larger than a third CTE α3 of the metal material
Implementation Method 2
a first physical vapor deposition (PVD) process is executed to form the buffer film including ruthenium oxide
Implementation Method 3
vaporizing a ruthenium metal source in a PVD chamber and introducing an oxygen gas into the PVD chamber
Implementation Method 4
a chemical vapor deposition (CVD) process is executed to form the metal material including ruthenium
Data Source
AI summary
A method of microfabrication is provided. The method includes providing a wafer including a dielectric layer having an opening formed in the dielectric layer. The opening includes a bottom and a sidewall. A buffer film is formed along the bottom and the sidewall of the opening. A metal material is formed over the buffer film to fill the opening. A first coefficient of thermal expansion (CTE) α1 of the dielectric layer is larger than a second CTE α2 of the buffer film, which is larger than a third CTE α3 of the metal material.