Thermal Silicon Etch Using Fluorine Precursors
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Solution Overview
Problem
Conventional etching techniques face challenges in achieving uniform etching across high aspect ratio features in 3D NAND structures, with dry etches struggling to diffuse precursors effectively and wet etches causing deformation and pattern collapse, while maintaining selectivity and precision.
Innovation Solution
A dry etch process using a fluorine-containing precursor in a plasma-free environment at low substrate temperatures, allowing for uniform, isotropic etching of silicon and polysilicon with high selectivity relative to dielectrics, even in structures with aspect ratios greater than 50:1, by utilizing a substrate processing chamber that prevents plasma contact with the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wet etching is used to etch silicon, then etch selectivity is improved, but pattern collapse and deformation occur
Solution Approach 1:
The patent replaces wet chemical etching with a thermal field-based etching process using fluorine-containing precursors. The thermal energy activates the fluorine species to etch silicon selectively without the mechanical/chemical deformation caused by wet etchants, achieving both high selectivity and pattern integrity through field-based interaction rather than direct chemical contact.
Solution Approach 2:
The patent changes the fundamental etching parameters by using thermal activation at controlled temperatures (200-400°C) instead of room temperature wet chemistry. By controlling temperature, pressure, and fluorine precursor concentration, the process achieves selective silicon etching while maintaining dielectric integrity and avoiding pattern collapse.
2Length of moving object
If dry etching with local plasma is used to etch silicon, then trench penetration is improved, but substrate damage occurs due to electric arcs
Solution Approach 1:
The patent substitutes plasma-based physical sputtering with a thermal field-driven chemical etching process. Fluorine-containing precursors are thermally activated to produce reactive fluorine species that chemically etch silicon through the trench without requiring plasma discharge, eliminating electric arc damage while maintaining deep trench penetration capability.
Solution Approach 2:
The patent introduces fluorine-containing precursors as intermediary chemical species that mediate the etching process. These precursors are thermally activated to generate reactive fluorine atoms that selectively etch silicon through the trench structure, serving as a safe intermediary that avoids direct plasma-substrate contact and associated damage.
3Productivity
If conventional dry etching is used to etch high aspect ratio features, then etch rate is improved, but uniform etching profile is lost due to poor precursor diffusion
Solution Approach 1:
The patent changes the etching mechanism from plasma-driven physical sputtering to thermally-activated chemical etching. By controlling temperature (200-400°C), pressure, and precursor flow, the process achieves both high etch rates and uniform profiles in high aspect ratio features, as thermal diffusion of fluorine species penetrates more uniformly than plasma species.
Solution Approach 2:
The patent replaces plasma-based etching with thermal field-driven etching using fluorine precursors. The thermal energy enables uniform precursor diffusion throughout the trench structure, achieving consistent etching rates from top to bottom while maintaining high overall etch rates that conventional plasma methods cannot achieve in high aspect ratio features.
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 uniform etching profiles across vertical stacks, reducing feature size and maintaining structural integrity, with etch selectivity greater than 20:1 for silicon relative to dielectrics, and preventing deformation, thus improving the production of uniformly sized cells in 3D NAND devices.
Implementation Method 1
flowing a fluorine-containing precursor into a substrate processing region... removing silicon from the sidewalls of the trench
Data Source
AI summary
Exemplary methods for selectively removing silicon (e.g. polysilicon) from a patterned substrate may include flowing a fluorine-containing precursor into a substrate processing chamber to form plasma effluents. The plasma effluents may remove silicon (e.g. polysilicon, amorphous silicon or single crystal silicon) at significantly higher etch rates compared to exposed silicon oxide, silicon nitride or other dielectrics on the substrate. The methods rely on the temperature of the substrate in combination with some conductivity of the surface to catalyze the etch reaction rather than relying on a gas phase source of energy such as a plasma.