Pulsed CVD Tungsten Deposition Without a Nucleation Layer
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Solution Overview
Problem
The deposition of low resistivity tungsten films with good step coverage is challenging in semiconductor fabrication, especially as devices shrink and become more complex, due to the need for nucleation layers which increase resistance and occupy more space in smaller features.
Innovation Solution
A method involving the deposition of a conformal boron layer on a substrate, followed by a pulsed chemical vapor deposition process with hydrogen and tungsten precursor pulses, eliminating the need for a nucleation layer and achieving low resistivity and good step coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tungsten nucleation layer is deposited on the substrate surface, then tungsten film deposition is enabled, but the film resistivity increases and the feature space is occupied
Solution Approach 1:
The invention extracts and eliminates the tungsten nucleation layer from the deposition process. By using a boron-containing reducing agent layer instead, the patent removes the harmful element (nucleation layer) that causes increased resistivity and space occupation, while still achieving successful tungsten film deposition through the pulsed CVD process
Solution Approach 2:
The invention changes the chemical composition parameter of the reducing agent layer from tungsten-based to boron-based. This parameter change allows the reducing agent to serve its function without introducing the harmful effects associated with tungsten nucleation layers, resulting in lower resistivity tungsten films
2Reliability
If a tungsten nucleation layer is deposited on the substrate surface, then tungsten film deposition is enabled, but the feature space is occupied by additional layers
Solution Approach 1:
The invention extracts and eliminates the tungsten nucleation layer from the deposition process. By using a boron-containing reducing agent layer instead, the patent removes the harmful element (nucleation layer) that causes increased resistivity and space occupation, while still achieving successful tungsten film deposition through the pulsed CVD process
Solution Approach 2:
The boron-containing reducing agent layer serves multiple functions: it acts as the reducing agent for tungsten deposition, provides conformal coverage on the substrate, and eliminates the need for a separate nucleation layer. This multi-functionality reduces the total number of layers and occupies less feature space
3Productivity
If continuous flow of tungsten precursor is used in CVD process, then deposition rate is high, but fluorine impurities increase in the film
Solution Approach 1:
The invention applies periodic pulsing to the tungsten precursor flow instead of continuous flow. The pulsed CVD process introduces the precursor in periodic bursts separated by intervals, which allows the reducing agent to react completely with the precursor during each pulse cycle. This periodic action maintains adequate deposition rate while significantly reducing fluorine impurity incorporation in the tungsten film
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 results in tungsten films with lower resistivity, larger grain size, and reduced fluorine impurities, improving step coverage and reducing the need for additional layers, thus enhancing semiconductor performance.
Implementation Method 1
The conformal boron layer is converted to a conformal tungsten layer by reacting with a reducing agent, such as hydrogen
Implementation Method 2
forming a layer including elemental boron (B) on the surface by thermal decomposition of a boron-containing reducing agent
Implementation Method 3
performing a pulsed chemical vapor deposition process to convert the layer including elemental boron to a tungsten layer
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 layer of boron (B) on a substrate. The substrate generally includes a feature to be filled with tungsten with the boron layer conformal to the topography of the substrate including the feature. The reducing agent layer is then exposed to a continuous flow of hydrogen and pulses of fluorine-containing tungsten precursor in a pulsed CVD process. The conformal boron layer is converted to a conformal tungsten layer.