Tungsten Word Line Recess Etchant for Selective W/TiN Removal
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Solution Overview
Problem
Conventional wet-etch methods for tungsten and titanium nitride in 3D NAND fabrication face challenges such as low etch rates, long processing times, and damage to aluminum oxide layers, leading to inefficient use of NAND string channel length and on-current degradation.
Innovation Solution
Aqueous-based etchant compositions with controlled pH, comprising nitric acid and phosphoric acid as oxidizers, are used to selectively etch tungsten and titanium nitride with higher removal rates, ensuring compatibility with aluminum oxide layers and allowing for single wafer tool processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional wet-etch methods are used for tungsten and titanium nitride, then the etching process can be performed, but the etch rate is low and processing time is extremely long (over 1 hour)
Solution Approach 1:
The patent modifies the chemical composition parameters of the etching solution by incorporating specific oxidizers (nitric acid, phosphoric acid), fluorine-containing compounds, and organic solvents in optimized ratios. This chemical parameter optimization enables significantly higher etch rates for tungsten and titanium nitride while reducing processing time from over 1 hour to a practical range suitable for single wafer tool processing
Solution Approach 2:
The etching solution employs a composite chemical formulation combining multiple active ingredients (oxidizers, fluorine compounds, organic solvents) that work synergistically. The oxidizers activate the etching process, fluorine compounds enhance tungsten removal, and organic solvents control the reaction kinetics, achieving high etch rates for both tungsten and titanium nitride simultaneously
2Productivity
If conventional wet-etch chemicals are used to etch tungsten and titanium nitride, then the etching can proceed, but the aluminum oxide layer is damaged causing side wall recess and floating gate formation
Solution Approach 1:
The etching solution exhibits selective chemical reactivity toward different materials: it is highly aggressive toward tungsten and titanium nitride while being gentle on aluminum oxide. This local selectivity is achieved through the specific combination of oxidizers and fluorine compounds that preferentially attack W and TiN surfaces without significantly etching AlOx, preventing side wall recess and floating gate formation
Solution Approach 2:
The organic solvents in the etching solution act as intermediaries that moderate the chemical reactivity. They control the dissolution kinetics of the etched materials and provide a buffer that prevents excessive etching of the aluminum oxide protective layer while maintaining high etch rates for the target materials
3Manufacturing precision
If a thicker aluminum oxide etch-stop layer is used to achieve sufficient etch selectivity, then the etching stopping can be controlled, but the channel distance between select gate and first wordline increases, underutilizing the NAND string channel length
Solution Approach 1:
The patent changes the chemical parameters of the etching solution to achieve high selectivity ratios between tungsten/titanium nitride and aluminum oxide. This enhanced chemical selectivity allows the use of thinner aluminum oxide etch-stop layers (reducing channel distance) while maintaining precise etching stopping control, thereby optimizing the utilization of NAND string channel length
4Ease of manufacture
If dry etching methods are used to etch the bottom layer of W and TiN, then the process can be performed, but the dry-etching by product from the top layer remains in the trenches and restricts etching of the bottom layer
Solution Approach 1:
The patent replaces the dry etching process (physical/chemical vapor phase etching) with a wet etching process (liquid phase chemical etching). The liquid etchant can effectively penetrate and remove tungsten and titanium nitride from the bottom layer without leaving residual by-products in the trenches, achieving complete etching that dry methods cannot accomplish
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 etchant compositions provide faster processing times, higher tungsten etch rates compared to titanium nitride, and lower aluminum oxide etch rates, optimizing NAND string channel utilization and maintaining on-current performance.
Implementation Method 1
Aqueous-based etchant compositions with controlled pH, comprising nitric acid and phosphoric acid as oxidizers, are used to selectively etch tungsten and titanium nitride
Implementation Method 2
The etchant compositions provide faster processing times, higher tungsten etch rates compared to titanium nitride, and lower aluminum oxide etch rates
Data Source
AI summary
Described herein is an etching solution suitable for both tungsten-containing metals and TiN-containing materials, which comprises: water; and one or more than one oxidizers; and one or more than one of the components selected from the group consisting of: one or more fluorine-containing-etching compounds, one or more organic solvents, one or more chelating agents, one or more corrosion inhibitors and one or more surfactants.