Tungsten Deposition Using a Boron Interlayer Without Nucleation
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Solution Overview
Problem
The deposition of low resistivity tungsten films with good step coverage is challenging, especially as devices shrink and more complex patterning schemes are used, due to issues with nucleation layers, resistivity, and stress in the films.
Innovation Solution
A method for forming tungsten bulk layers without a nucleation layer by depositing a conformal layer of elemental boron or boron and silicon on a substrate, followed by exposure to alternating pulses of a tungsten fluoride compound and hydrogen to form a tungsten bulk layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tungsten nucleation layer is deposited on the substrate surface, then tungsten bulk layer formation is facilitated, but the film resistivity increases and the feature size occupied increases
Solution Approach 1:
The patent extracts and removes the tungsten nucleation layer from the deposition process. By using a boron-containing reducing agent layer instead, the patent eliminates the intermediate tungsten nucleation layer that causes increased resistivity and occupies valuable space in scaled devices, while still achieving successful tungsten bulk layer formation
Solution Approach 2:
The patent introduces a boron-containing reducing agent layer as an intermediary substance between the substrate and tungsten bulk layer. This boron-based intermediary facilitates tungsten deposition through in-situ reduction of tungsten precursors, replacing the traditional tungsten nucleation layer and achieving lower resistivity films
2Reliability
If a tungsten nucleation layer is deposited, then tungsten bulk layer deposition is enabled, but the process complexity and number of deposition steps increase
Solution Approach 1:
The patent merges the functions of the nucleation layer and bulk layer deposition into a single integrated process. The boron-containing reducing agent layer serves dual purposes: it acts as both the nucleation substrate and the reducing agent for in-situ tungsten formation, eliminating the need for separate nucleation layer deposition and bulk layer deposition steps
Solution Approach 2:
The patent removes the tungsten nucleation layer deposition step from the process flow. By using a boron-based reducing agent layer that enables direct in-situ reduction, the patent simplifies the deposition sequence from multiple steps (nucleation layer + bulk layer) to a more streamlined process
3Manufacturing precision
If alternating pulses of tungsten fluoride compound and hydrogen are used, then low resistivity tungsten films are achieved, but the deposition process time increases
Solution Approach 1:
The patent employs periodic alternating pulses of tungsten fluoride compound and hydrogen to achieve low resistivity tungsten films. This pulsed deposition approach allows controlled reduction and film formation, optimizing electrical properties while managing deposition time through rhythmic gas phase switching
4Reliability
If the boron layer thickness is increased, then better coverage is achieved, but more boron remains in the final tungsten film increasing resistance
Solution Approach 1:
The patent optimizes the boron layer thickness parameter to achieve the right balance between coverage and contamination. By precisely controlling the boron layer thickness and composition, the patent ensures sufficient surface coverage for successful tungsten deposition while minimizing the amount of boron that would remain in the final film and increase resistance
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 method achieves tungsten films with lower resistivity and reduced B, Si, or B and Si concentration, along with large grain size and controlled grain orientation, while eliminating the need for a nucleation layer, which can increase resistance and occupy more space in smaller features.
Implementation Method 1
forming the layer comprising elemental boron (B) on the surface includes exposing the surface to a gas mixture comprising boron (B) and silicon (Si) wherein the B:Si ratio is between 1:1 and 6:1
Implementation Method 2
performing multiple cycles of exposing the substrate to alternating pulses of a tungsten fluoride compound and hydrogen (H2) to thereby form an elemental tungsten bulk layer on the surface
Implementation Method 3
performing multiple cycles of exposing the substrate to alternating pulses of a tungsten fluoride compound and hydrogen (H2)
Data Source
AI summary
Provided herein are methods of depositing tungsten (W) films without depositing a nucleation layer. In certain embodiments, the methods involve depositing a conformal reducing agent layer of boron (B) and/or silicon (Si) on a substrate. The substrate generally includes a feature to be filled with tungsten with the reducing agent layer conformal to the topography of the substrate including the feature. The reducing agent layer is then exposed to a fluorine-containing tungsten precursor, which is reduced by the reducing agent layer to form a layer of elemental tungsten. The conformal reducing agent layer is converted to a conformal tungsten layer.