Sequential CVD Tungsten Deposition for Low Fluorine Films
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Solution Overview
Problem
Conventional tungsten deposition techniques face challenges in reducing fluorine concentration, stress, and resistance in tungsten films, particularly as devices shrink and feature sizes decrease, leading to issues like fluorine diffusion, high resistivity, and tensile stress that affect device performance and processing complexity.
Innovation Solution
The method involves depositing tungsten using a sequential CVD process with alternating pulses of hydrogen and tungsten-containing precursors, such as tungsten hexafluoride, at low pressure, and using fluorine-free precursors to minimize fluorine content and stress, while achieving high step coverage and low resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional CVD process is used to deposit tungsten bulk layer, then deposition speed is high, but fluorine concentration in the film increases
Solution Approach 1:
The patent divides the tungsten deposition process into two distinct stages: (1) nucleation layer deposition using simultaneous exposure to WF6 and H2, and (2) bulk layer deposition using sequential alternating pulses of WF6 and H2. This segmentation allows the nucleation stage to provide initial tungsten coverage while the bulk stage minimizes fluorine incorporation through pulsed exposure, thereby reducing overall fluorine concentration while maintaining deposition efficiency.
Solution Approach 2:
The patent employs periodic alternating pulses of tungsten hexafluoride (WF6) and hydrogen (H2) during bulk layer deposition. This periodic action allows controlled reaction cycles where tungsten is deposited during WF6 pulses while hydrogen pulses reduce fluorine incorporation. The cyclic nature of this process enables high deposition speed while systematically reducing fluorine concentration in the final film.
2Productivity
If conventional CVD process is used to deposit tungsten bulk layer, then deposition speed is high, but tensile stress increases
Solution Approach 1:
The patent segments the deposition process into nucleation and bulk stages with different process conditions. The nucleation layer is deposited first to establish a foundation, followed by bulk layer deposition using alternating pulses. This segmentation allows optimization of each stage: the nucleation layer provides adhesion while the pulsed bulk deposition controls stress accumulation, achieving high deposition speed with reduced tensile stress.
Solution Approach 2:
The patent changes process parameters between stages: the nucleation layer uses simultaneous exposure conditions while the bulk layer uses alternating pulse conditions. Additionally, the patent controls substrate temperature and pressure parameters during bulk deposition to optimize the balance between deposition rate and stress control, achieving high productivity with minimized tensile stress.
3Productivity
If conventional CVD process is used to deposit tungsten bulk layer, then deposition speed is high, but film resistivity increases
Solution Approach 1:
The alternating pulse process periodically introduces hydrogen between tungsten deposition pulses. This periodic hydrogen exposure reduces fluorine concentration and improves film crystallinity during bulk layer deposition, thereby reducing resistivity. The cyclic nature maintains high deposition speed while systematically improving electrical properties through controlled reduction reactions.
4Length of moving object
If thin tungsten films are deposited to accommodate smaller devices, then device scaling is achieved, but fluorine diffusion problems worsen
Solution Approach 1:
The patent changes the deposition parameters by using alternating pulses of WF6 and H2 instead of continuous exposure. This parameter change reduces fluorine concentration in thin films through controlled reaction cycles, minimizing fluorine diffusion even when film thickness is reduced for device scaling. The method maintains adequate tungsten coverage while suppressing harmful fluorine effects.
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 results in tungsten films with significantly reduced fluorine concentration, lower stress, and improved resistivity, enabling better device performance and processing ease, particularly in small features and complex structures like 3D NAND and vertical NAND structures.
Implementation Method 1
exposing a substrate in a chamber to alternating pulses of a reducing agent and a tungsten-containing precursor to deposit a tungsten nucleation layer on the substrate
Implementation Method 2
exposing the substrate to alternating pulses of hydrogen and a tungsten-containing precursor to deposit a bulk tungsten layer over the tungsten nucleation layer
Data Source
AI summary
Provided herein are methods of depositing bulk tungsten by sequential CVD pulses, such as by alternately pulsing tungsten hexafluoride and hydrogen gas in cycles of temporally separated pulses. Some methods include depositing a tungsten nucleation layer at low pressure followed by deposition of bulk tungsten by sequential CVD to form low stress tungsten films with low fluorine content. Methods described herein may also be performed in combination with non-sequential CVD deposition and fluorine-free tungsten deposition techniques.