Cobalt Deposition in 3D NAND Word Lines
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Tungsten deposition in semiconductor device fabrication leads to issues such as substrate bowing, high resistivity, damage to the oxide layer, and seam formation in word lines, particularly in 3D NAND devices, due to fluorine use and etching processes.
Innovation Solution
A method and apparatus for depositing a cobalt layer within word lines in a substrate, involving exposure to a cobalt precursor followed by annealing to remove contaminants and reflow the cobalt layer, which eliminates the need for fluorine-based etching and reduces substrate damage, providing a low resistivity, seam-free fill with large metal grains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If tungsten is deposited using CVD with fluorine, then the word line features can be filled, but damage is caused to the oxide layer and substrate
Solution Approach 1:
The patent changes the chemical parameters of the deposition process by replacing fluorine-based precursors with chlorine-based or non-fluorine precursors. This parameter change eliminates the harmful fluorine etching effect on the oxide layer while maintaining the ability to deposit tungsten and fill the word line features effectively
Solution Approach 2:
The patent converts the potentially harmful interaction between deposited tungsten and oxide layer into a beneficial process by controlling the deposition conditions and using selective etching steps that remove only the unwanted tungsten from sidewalls while preserving the oxide layer integrity, thus turning a damage risk into a precise filling process
2Productivity
If bulk tungsten is deposited in word lines, then the features can be filled, but seams are formed and resistivity increases
Solution Approach 1:
The patent applies a preliminary thin film deposition step before bulk filling. A initial conformal layer is deposited on the sidewalls and bottom of the word line features, creating a uniform base that prevents seam formation during subsequent bulk filling operations
Solution Approach 2:
The patent uses different deposition conditions and precursor flows for different regions of the substrate. By controlling the precursor delivery and deposition parameters locally, it achieves uniform filling in high aspect ratio features while maintaining overall process efficiency
3Manufacturing precision
If tungsten is deposited and then etched to remove sidewall material, then excess tungsten can be removed, but substrate damage occurs
Solution Approach 1:
The patent extracts and removes the harmful etching step from the process sequence. By using selective deposition techniques and controlled precursor delivery, it achieves the desired sidewall material removal without requiring aggressive etching that damages the substrate
Solution Approach 2:
The patent replaces the mechanical/chemical etching process with a controlled deposition and selective removal approach. Instead of using etchants that chemically attack both tungsten and substrate, it uses precise deposition control and selective physical or chemical removal methods that spare the substrate
4Productivity
If tungsten CVD is used to fill word lines, then the metal can be deposited, but stress and substrate bowing are induced
Solution Approach 1:
The patent changes the deposition parameters including temperature, pressure, and precursor selection to control the stress characteristics of the deposited tungsten layer. By optimizing these parameters, it reduces intrinsic stress that would otherwise cause substrate bowing while maintaining effective filling
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 cobalt deposition method minimizes damage to the gate oxide layer, offers a conformal film with high work function and low resistivity, eliminates the need for subsequent metal separation processes, and reduces stress and substrate bowing, resulting in improved yield and cost benefits.
Implementation Method 1
exposing a substrate at a first temperature to a cobalt containing precursor to deposit a cobalt layer within a word line feature
Implementation Method 2
annealing the substrate to remove contaminants from the cobalt layer and to reflow the cobalt layer into the word line feature, wherein the substrate is at a second temperature greater than the first temperature during the annealing
Data Source
AI summary
Methods and apparatus for depositing a cobalt layer in a feature, such as, a word line formed in a substrate, are provided herein. In some embodiments, method of processing a substrate includes: exposing a substrate at a first temperature to a cobalt containing precursor to deposit a cobalt layer within a word line feature formed in the substrate, wherein the word line feature is part of a 3D NAND device; and annealing the substrate to remove contaminants from the cobalt layer and to reflow the cobalt layer into the word line feature, wherein the substrate is at a second temperature greater than the first temperature during the annealing.