Tungsten Layer Grain Size Control in 3D NAND Memory
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Solution Overview
Problem
Existing manufacturing methods for three-dimensional NAND memory devices face challenges in producing low fluorine tungsten (LFW) with large grain size, low resistivity, and low fluorine concentration, which affects the control gate driving voltage, reliability, and threshold voltage distribution.
Innovation Solution
A manufacturing method involving nucleation and bulk formation of tungsten, using precursors that include tungsten halide, hydrogen, and a reducing agent, with controlled hydrogen flow and optional soak processes, to achieve a tungsten layer with large grain size and reduced fluorine content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional tungsten deposition methods are used, then the process is simple, but the tungsten layer has small grain size and high resistivity
Solution Approach 1:
The tungsten deposition process is segmented into multiple distinct stages: nucleation phase, soak phase, and bulk formation phase. Each phase serves a specific function - nucleation initiates grain formation, soak allows grain growth, and bulk formation deposits the majority of tungsten material. This segmentation enables precise control over grain size and resistivity by optimizing each phase independently.
Solution Approach 2:
The patent employs parameter changes by varying hydrogen flow rate (1000-20000 sccm), precursor concentrations, and deposition time across the different phases. By adjusting these parameters dynamically during the deposition process, the method achieves large grain size (70 nm or more) and low resistivity while maintaining process control.
2Reliability
If high fluorine concentration tungsten is used, then the deposition process is simpler, but fluorine damages high-k dielectric materials and floating gates
Solution Approach 1:
The patent uses parameter changes by controlling hydrogen flow rate (1000-20000 sccm) and precursor ratios to optimize the deposition environment. By adjusting these parameters, the process achieves low fluorine concentration in the tungsten layer while maintaining manufacturing feasibility through a systematic multi-phase approach.
Solution Approach 2:
The deposition process maintains continuous useful action through the sequential phases - nucleation continuously forms nuclei, soak continuously grows grains, and bulk formation continuously deposits tungsten. This continuous process ensures uniform low fluorine concentration throughout the tungsten layer while protecting sensitive structures.
3Manufacturing precision
If tungsten layer with large grain size is manufactured, then resistivity is reduced, but manufacturing precision becomes more difficult to control
Solution Approach 1:
The deposition process is segmented into nucleation, soak, and bulk formation phases, allowing independent optimization of each stage. This segmentation enables precise control over grain size (70 nm or more) and resistivity while maintaining threshold voltage distribution within acceptable ranges by controlling each phase's contribution.
Solution Approach 2:
The patent implements feedback control by monitoring and adjusting deposition parameters (hydrogen flow rate, precursor concentrations, temperature) during the multi-phase process. This feedback mechanism ensures that grain size and resistivity are controlled to achieve the desired performance while maintaining manufacturing precision.
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
The method effectively reduces the control gate driving voltage, minimizes damage to high-k dielectric materials and floating gates, narrows the threshold voltage distribution, and enhances the reliability of the memory device by achieving a tungsten layer with large grain size and low fluorine concentration.
Implementation Method 1
A nucleation precursor in the nucleation includes tungsten halide, hydrogen, and a reducing agent. A bulk precursor in the bulk formation includes tungsten halide, hydrogen, and a reducing agent.
Implementation Method 2
A tungsten layer is formed in the plurality of second openings, where the tungsten layer formed includes nucleation and bulk formation performed after the nucleation.
Data Source
AI summary
A manufacturing method of a memory device may be applied to a three-dimensional NAND memory device with high capacity and high performance. In a manufacturing process of the three-dimensional NAND memory device, a material of a control gate (word line) is tungsten. The forming method of a tungsten layer includes nucleation and bulk formation performed. In at least one of the nucleation and the bulk formation, hydrogen flow is between 1000 and 20000 sccm. At least one time of soak with nitrogen may also be performed after the nucleation. A tungsten grain size in the tungsten layer is 70 nm or more.