Tungsten Seed Layer for Copper TSV Diffusion and Stress Control
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Solution Overview
Problem
In semiconductor processing, particularly for Through Silicon Via (TSV) applications, challenges arise from the high cost and step coverage issues of tungsten-filled features, as well as the propensity of copper to diffuse into silicon oxide, leading to electrical resistance reduction and stress-induced substrate bowing.
Innovation Solution
A method involving the deposition of a tungsten seed layer and adhesion layer, followed by copper electroplating, where the tungsten layer acts as a diffusion barrier, seed layer, and stress buffer, utilizing materials like tungsten nitride, titanium nitride, and tantalum nitride to enhance adhesion and reduce CTE-induced stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conformal diffusion barrier layer is deposited on silicon surfaces followed by a conductive seed copper layer, then copper diffusion into silicon oxide is prevented, but the process cost increases and step coverage becomes problematic
Solution Approach 1:
The patent extracts the diffusion barrier function from a separate conformal layer and integrates it into the tungsten seed layer itself. The tungsten layer serves multiple functions: as a seed layer for copper electroplating and as a diffusion barrier preventing copper migration into silicon oxide, thereby eliminating the need for a separate barrier layer and reducing process complexity
Solution Approach 2:
The tungsten seed layer is designed to perform multiple functions simultaneously: it acts as an adhesive layer for copper electroplating, as a diffusion barrier against silicon oxide, and as a stress buffer. This multi-functionality reduces the total number of layers required and simplifies the overall process
2Ease of manufacture
If tungsten is used for filling TSV's, then certain processing challenges are avoided, but new challenges arise regarding adhesion and stress management
Solution Approach 1:
The patent employs a composite structure consisting of a tungsten seed layer combined with adhesion-promoting materials such as titanium nitride or tantalum nitride. This composite approach leverages the beneficial properties of each material: tungsten provides stress buffering and processing ease, while the nitride layers provide superior adhesion to both silicon and copper
Solution Approach 2:
The patent modifies the physical and chemical parameters of the seed layer interface by introducing intermediate adhesion layers with specific material properties. These layers have intermediate thermal expansion coefficients and surface energies that bridge the mismatch between tungsten and silicon, improving adhesion and stress distribution
3Productivity
If copper is used to fill TSV's, then electroplating efficiency is improved, but copper migration into surrounding materials becomes a problem
Solution Approach 1:
The tungsten seed layer acts as an intermediary barrier between the copper fill and the surrounding silicon oxide. It allows efficient copper electroplating to proceed while simultaneously blocking copper diffusion into the surrounding materials and reducing thermal expansion stress
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 reduces the need for costly barrier layers, minimizes excess tungsten and copper on the field region, and effectively fills TSVs with copper while maintaining low sheet resistance and ease of removal, thereby addressing the challenges of tungsten-filled features and copper migration.
Implementation Method 1
The tungsten layer serves as a diffusion barrier, a seed layer for copper electrofill and a means of reducing CTE-induced stresses between copper and silicon
Implementation Method 2
electroplating copper on the tungsten seed layer
Implementation Method 3
a means of reducing CTE-induced stresses between copper and silicon
Data Source
AI summary
Apparatus and methods for filling through silicon vias (TSV's) with copper having an intervening tungsten layer between the copper plug and the silicon are disclosed. Methods are useful for Damascene processing, with or without a TSV feature. The tungsten layer serves as a diffusion barrier, a seed layer for copper electrofill and a means of reducing CTE-induced stresses between copper and silicon. Adhesion of the tungsten layer to the silicon and of the copper layer to the tungsten is described.