SiN Selective Etch to SiO2 via Non-Plasma Dry Process
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Solution Overview
Problem
Current dry etching methods for 3D NAND devices face challenges in achieving selective isotropic etching of SiN versus SiO2, particularly in high-aspect-ratio apertures, where existing methods lack sufficient selectivity and control, leading to inefficiencies and impurity introduction.
Innovation Solution
The use of non-plasma dry thermal etching with fluorine-containing gases such as nitrosyl fluoride (FNO), trifluoroamine oxide (F3NO), and nitryl fluoride (FNO2) to selectively etch SiN or p-Si layers relative to SiO2 layers, allowing for controlled isotropic etching without plasma activation, thereby improving etch selectivity and reducing impurity introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wet etching process with H3PO4 is used to remove SiN, then SiN can be removed from HAR aperture, but liquid chemicals cannot reach the bottom of deep HAR trench due to surface tension effect
Solution Approach 1:
The patent replaces wet etching (liquid-based) with dry etching (gas-based) process. The dry etching process uses gaseous etchants that can diffuse into deep HAR trenches without being constrained by surface tension, enabling complete removal of SiN layers from the bottom of deep apertures while maintaining high selectivity to SiO2 layers.
Solution Approach 2:
The patent employs gaseous etchants delivered through controlled gas flow and pressure systems. The gas phase etching chemistry allows the etchant to penetrate deep into HAR trenches via diffusion and convection, overcoming the liquid delivery limitations imposed by surface tension while maintaining precise process control through gas flow parameters.
2Shape
If typical plasma dry etching is used, then anisotropic etch is achieved, but horizontal isotropic etching of SiN is required
Solution Approach 1:
The patent changes the fundamental parameters of the etching process by using thermal field-assisted dry etching instead of plasma-based dry etching. This parameter change transforms the etching mechanism from ion-driven anisotropic etching to thermally-driven isotropic etching, enabling horizontal etching of SiN while maintaining vertical profile control through field assistance.
Solution Approach 2:
The patent employs a composite approach combining thermal field assistance with dry gas etching chemistry. The thermal field (from heated susceptor or chamber walls) works synergistically with the gaseous etchant to achieve controlled isotropic etching of SiN, while the dry gas environment provides the necessary selectivity to SiO2 layers.
3Manufacturing precision
If non-plasma dry thermal etching with fluorine-containing gases is used, then high selectivity of SiN to SiO2 etch rates is achieved (10 to 3000), but process control must be maintained
Solution Approach 1:
The patent implements process monitoring and control mechanisms to manage the complex interactions between thermal fields and fluorine-containing gas chemistry. By monitoring etch rate, selectivity, and chamber conditions, the system maintains precise control over the etching process despite the complexity of thermal-field-assisted gas-phase reactions, ensuring consistent high selectivity results.
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 enables high selectivity ratios of SiN to SiO2 etch rates, ranging from 10 to 3000, facilitating efficient and controlled etching in 3D NAND device manufacturing, reducing process time, and minimizing impurity introduction, while maintaining the advantages of dry etching over wet etching.
Implementation Method 1
selectively etching SiN or p-Si materials versus SiO2 with a fluorine containing etching gas selected from the group consisting of nitrosyl fluoride (FNO), trifluoroamine oxide (F3NO), nitryl fluoride (FNO2) and combinations thereof
Implementation Method 2
non-plasma dry thermal etching process, with or without plasma activation of the fluorine containing etching gases
Data Source
AI summary
Methods for isotropic etching at least a portion of a silicon-containing layer on a sidewall of high-aspect-ratio (HAR) apertures formed on a substrate in a reaction chamber are disclosed. The HAR aperture formed by plasma etching a stack of alternating layers of a first silicon-containing layer and a second silicon-containing layer, the second silicon-containing layer is different from the first silicon-containing layer. The method comprising the steps of: a) introducing a fluorine containing etching gas selected from the group consisting of nitrosyl fluoride (FNO), trifluoroamine oxide (F3NO), nitryl fluoride (FNO2) and combinations thereof into the reaction chamber; and b) removing at least a portion of the second silicon-containing layers by selectively etching the second silicon-containing layers versus the first silicon-containing layers with the fluorine containing etching gas to produce recesses between the first silicon-containing layers on the sidewall of the HAR aperture. Alternatively, the disclosed etching processes are cyclic etching processes.