Tungsten Feature Fill via Inside-Out Growth
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Solution Overview
Problem
Conventional methods for depositing tungsten into high aspect ratio features often result in the formation of seams and voids, leading to increased resistance, contamination, and degraded performance of integrated circuits due to pinch-off points and constrictions within the features.
Innovation Solution
A method involving conformal deposition of a first tungsten layer, followed by selective etching to remove tungsten from the feature sidewalls, allowing for the growth of tungsten from the interior, and subsequent selective deposition of a second tungsten layer without forming a nucleation layer, which can continue growth from the existing tungsten layer, reducing seam formation and improving fill efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CVD deposition is used to fill high aspect ratio features, then the feature filling process is simple and fast, but seams and voids form inside the features leading to high resistance and degraded performance
Solution Approach 1:
The deposition process is divided into multiple stages: initial conformal deposition to form a seed layer, selective etching to remove sidewall tungsten, and subsequent selective deposition to fill from the interior. This segmentation eliminates seams and voids by preventing pinch-off points while maintaining process control
Solution Approach 2:
A conformal seed layer is deposited first to prepare the feature interior for subsequent selective growth. This preliminary action ensures that tungsten grows from the interior rather than forming seams at sidewalls, preventing void formation before it occurs
2Manufacturing precision
If conformal deposition is used to fill features, then deposition is uniform, but grain boundary scattering increases resistance
Solution Approach 1:
Instead of allowing conformal deposition to proceed uniformly from all sidewalls (which creates grain boundaries), the method inverts the approach by selectively removing sidewall tungsten and allowing growth only from the feature interior. This produces larger grains with fewer boundaries, reducing scattering and improving electrical performance
3Manufacturing precision
If tungsten is deposited into high aspect ratio features, then feature fill is achieved, but under-layer materials have significant impact on resistance
Solution Approach 1:
The method extracts and removes the problematic under-layer materials (such as titanium nitride or titanium) from the feature interior through selective etching. By removing these high-resistance materials that would otherwise form the base layer, the final tungsten structure has lower resistance and is not constrained by the properties of underlying barrier layers
4Manufacturing precision
If selective etching is performed to remove sidewall tungsten, then seam formation is reduced, but the etching process becomes more complex
Solution Approach 1:
The selective etching process uses the tungsten itself as the target for removal, with the etch chemistry automatically selecting tungsten over the under-layer materials. This self-service approach eliminates seams without requiring complex multi-step etching sequences, as the process naturally stops when under-layer materials are exposed
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 enables void-free and seam-free filling of features with tungsten, reducing grain boundary scattering, improving electrical performance, and minimizing the impact of under-layer materials on resistance, while also simplifying the etching process for small features.
Implementation Method 1
Deposition of tungsten-containing materials using chemical vapor deposition (CVD) techniques
Implementation Method 2
the tungsten-containing materials are formed by the reduction of tungsten hexafluoride (WF6) with hydrogen (H2)
Data Source
AI summary
Described herein are methods of filling features with tungsten and related systems and apparatus. The methods include inside-out fill techniques as well as conformal deposition in features. Inside-out fill techniques can include selective deposition on etched tungsten layers in features. Conformal and non-conformal etch techniques can be used according to various implementations. The methods described herein can be used to fill vertical features, such as in tungsten vias, and horizontal features, such as vertical NAND (VNAND) word lines. Examples of applications include logic and memory contact fill, DRAM buried word line fill, vertically integrated memory gate/word line fill, and 3-D integration with through-silicon vias (TSVs).